HANDICRAFT SF PI FS. 
 
 Cranl 
 tion G, 
 
 UNIVERSITY OF CALIFORNIA 
 
 AT LOS ANGELES 
 
 THE GIFT OF 
 
 MAY TREAT MORRISON 
 
 IN MEMORY OF 
 
 ALEXANDER F MORRISON 
 
 DAVID McKAY, Publisher, 1022 Market Street, Philadelphia.
 
 HANDICRAFT SERIES (continued}. 
 
 Glass Working by Heat and Abrasion. With 300 Engravings 
 
 and Diagrams. 
 
 Contents. Appliances used in Glass Blowing. Manipulating Glass Tubing. 
 Blowing Bulbs and Flasks. Jointing Tubes to Bulbs forming Thistle Funnels, 
 etc. Blowing and Etching Glass Fancy Articles ; Embossing and Gilding Flat 
 Surfaces. Utilising Broken Glass Apparatus ; Boring Holes in, and Riveting 
 Glass. Hand-working of Telescope Specula. Turning, Chipping, and Grinding 
 G ass. The Manufacture of Glass. 
 Building Model Boats. With 168 Engravings and Diagrams. 
 
 Contents.- Building Model Yachts. Rigging and Sailing Model Yachts. 
 Making and Fitting Simple Model Boats. Building a Model Atlantic Liner. 
 Vertical Engine for a Model Launch. Model Launch Engine with Reversing 
 Gear. Making a Show Case for a Model Boat. 
 Electric Bells, How to Make and Fit Them. With 162 En- 
 
 graving s and Diagrams. 
 
 Contents. The Electr c Current and the Laws that Govern it. Current 
 Conductors used in Electric-Bell Work. Wiring for Electric Bells. Elaborated 
 Systems of Wiring ; Burglar Alarms. Batteries for Electric Bells. The Con- 
 struction of Electric Bells, Pushes, and Switches. Indicators for Electric-Bell 
 Systems. 
 Bamboo Work. With 177 Engravings and Diagrams. 
 
 Contents. Bamboo : Its Sources and Uses. How to Work Bamboo. Bamboo 
 Tables. Bamboo Chairs and Seats. Bamboo Bedroom Furniture. Bamboo 
 Hall Racks and Stands. Bamboo Music Racks. Bamboo Cabinets and Book- 
 cases. Bambco Window Blinds. Miscellaneous Articles of Bamboo. Bamboo 
 Mail Cart. 
 Taxidermy. With 108 Engravings and Diagrams. 
 
 Contents. Skinning Birds. Stuffing and Mounting Birds. Skinning and 
 Stuffing Mammals. Mounting Animals' Horned Heads : Polishing and Mount- 
 ing Horns. Skinning, Stuffing, and Casting Kish. P. eserving, Cleaning, and 
 Dyeing Skins. Preserving Insects, and Birds' Eggs. Cases for Mounting 
 Specimens. 
 Tailoring;. With 180 Engravings and Diagrams. 
 
 Contents. Tailors' Requisites and Methods of Stitching. Simple Repairs 
 and Pressing. Relining, Repocketing, and Recollaring. How to Cut and 
 Make Trousers. How to Cut and Make Vests. Cutting and Making Lounge 
 and Reefer Jackets. Cutting and Making Morning and Frock Coats. 
 Photographic Cameras and Accessories. Comprising How TO 
 MAKE CAMERAS, DARK SLICES, SHUTTERS, and STANDS. With 160 
 Illustrations. 
 
 Contents. Photographic Lenses and How to Test them. Modern Half-plate 
 Cameras. Hand and Pocket Cameras. Ferrotype Cameras. Stereoscopic 
 Cameras. Enlarging Cameras. Dark Slides. Cinematograph Management. 
 Optical Lanterns. Comprising THE CONSTRUCTION AND MANAGEMENT 
 OF OPTICAL LANTERNS AND THE MAKING OF SLIDES. With 160 
 Illustrations. 
 
 Contents. Single Lanterns. Dissolving View lanterns. Illuminant for 
 Optical Lanterns. Optical Lantern Accessories. Conducting a Limelight 
 Lantern Exhibition. Experiments with Optical Lanterns. Painting Lantern 
 Slides. Photographic Lantern Slides. Mechanical Lantern Slides. Cinemato- 
 graph Management. 
 Engraving Metals. With Numerous Illustrations. 
 
 Contents. Introduction and Terms used. Engravers' Tools and their Uses. 
 Elementary Exercises in Engraving. Engraving Plate and Precious Metals. 
 Engraving Monograms. Transfer Processes of Engraving Metals. Engraving 
 Name Plates. Engraving Coffin Plates. Engraving Steel Plates. Chasing 
 and Embossing Metals. Etching Metals. 
 Basket Work. With 189 Illustrations. 
 
 Contents. Tools and Materials. Simple Baskets. Grocer's Square Baskets. 
 Round Baskets. Oval Baskets. Flat Fruit Baskets. Wicker Elbow Chairs. 
 Basket Bottle-casings. Doctors' and Chemists' Baskets. Fancy Basket Work. 
 Sussex Trug Basket. Miscellaneous Basket Work. Index 
 
 DAVID McKAY, Publisher, 1022 Market Street, Philadelphia.
 
 HANDICRAFT SERIES (continued}. 
 
 Bookbinding. With 125 Engravings and Diagrams. 
 
 Contents. Bookbinders' Appliances. Folding Printed Book Sheets. Beat- 
 ing and Sewing. Rounding, Backing, and Cover Cutting. Cutting Book Edges. 
 Covering Books. Cloth-bound Books, Pamphlets, etc. Account Books, 
 
 Contents. uookDinders Appliances, folding Printed Book sheets. Beat- 
 ing and Sewing. Rounding, Backing, and Cover Cutting. Cutting Book Edges. 
 Covering Books. Cloth-bound Books, Pamphlets, etc. Account Book 
 Ledgers, etc. Coloring, Sprinkling, and Marbling Book Edges. Marbling 
 Book Papers. Gilding Book Edges. Sprinkling and Tree Marbling Book 
 Covers. Lettering, Gilding, and Finishing Book Covers. Index. 
 
 Bent Iron Work. Including ELEMENTARY ART METAL WORK. With 
 269 Engravings and Diagrams. 
 
 Contents. Tools and Materials. Bending and Working Strip Iron. Simple 
 Exercises in Bent Iron. Floral Ornaments for Bent Iron Work. Candlesticks. 
 Hall Lanterns. Screens, Grilles, etc. Table Lamps. Suspended Lamps and 
 Flower Bowls. Photograph Frames. Newspaper Rack. Floor Lamps. 
 Miscellaneous Examples. Index. 
 Photography. With Numerous Engravings and Diagrams. 
 
 Contents Ihe Camera and its Accessories. The Studio and the Dark 
 Room. Plates. Exposure. Developing and Fixing Negatives. Intensifica- 
 tion and Reduction of Negatives. Portraiture and Picture Composition. 
 Flash-light Photography. Retouching Negatives. Processes of Printing from 
 Negative*. Mounting and Finishing Prints. Copying and Enlarging. Stereo- 
 scopic Photography. Ferrotype Photography. 
 
 Other Volumes in Preparation. 
 
 TECHNICAL INSTRUCTION. 
 
 Important New Series of Practical Volumes. Edited by PAUL 
 N. HASLUCK. With numerous Illustrations in the Text. 
 Each book contains about 1 60 pages, crown 8vo. Cloth, 
 $I.oo each, postpaid. 
 
 Practical Draughtsmen's Work. With 226 illustrations. 
 
 Contents. .-Drawing Boards. Paper and Mounting. Draughtsmen's Instru- 
 ments. Drawing Straight Lines. Drawing Circular Lines. Elliptical Curves. 
 Projection. Back Lining Drawings. Scale Drawings and Maps. Colouring 
 Drawings. Making a Drawing. Index. 
 Practical Gasfitting. With 120 Illustrations. 
 
 Contents. How Coal Gas is Made. Coal Gas from the Retort to the Gas 
 Holder. Gas Supply from Gas Holder to Meter. Laying the Gas Pipe in the 
 House. Gas Meters. Gas Burners. Incandescent Lights. Gas Fittings in 
 Workshops and Theatres. Gas Fittings for Festival Illuminations. Gas Fires 
 and Cooking Stoves. Index. 
 
 Practical Staircase Joinery. With 215 illustrations. 
 
 .Contents. Introduction : Explanation of Terms. Simple Form of Staircase 
 Housed String Stair : Measuring, Planning, and Setting Out. Two-flight 
 Staircase. Staircase with Winders at Bottom. Staircase with Winders at Top 
 and Bottom. Staircase with Half-space of Winders. Staircase over an Oblique 
 Plan. Staircase with Open or Cut Strings. Cut String Staircase with Brackets. 
 Open String Staircase with Bull nose Step. Geometrical Staircases. Winding 
 Staircases. Ships' Staircases. Index. 
 
 Practical Metal Plate Work. With 247 Illustrations. 
 
 Contents. Materials used in Metal Plate Work. Geometrical Construction 
 of Plane Figures. Geometrical Construction and Development of Solid 
 Figures. Tools and Appliances used in Metal Plate Work. Soldering and 
 Brazing. Tinning. Re-tinning and Galvanising. Examples of Practical 
 Metal Plate Work. Examples of Practical Pattern Drawing. Index. 
 
 Practical Graining and Marbling. With 79 illustrations. 
 
 Contents. Graining: Introduction, Tools, and Mechanical Aids. Graining 
 Grounds and Graining Colors. Oak Graining in Oil. Oak Graining in Spirit 
 and Water Colours. Pollard Oak and Knotted Oak Graining. Maple Graining 
 Mahogany and Pitch-pine Graining. Walnut Graining. Fancy Wood Grain- 
 ing. Furniture Graining. Imitating Woods by Staining. Imitating Inlaid 
 Woods. Marbling: Introduction, Tools, and Materials. Imitating Varieties 
 of Marble. Index. 
 
 Ready Shortly: Practical Plumbing Work. 
 
 Other New Volumes in Preparation. 
 DAVID McKAY, Publisher, 1022 Market Street, Philadelphia.
 
 " WORK" HANDBOOKS. 
 
 DYNAMOS AND ELECTRIC MOTORS
 
 THE 
 A.F. 
 MEMORIAL LIBRARY
 
 DYNAMOS AND ELECTRIC 
 MOTORS 
 
 HOW TO MAKE AND RUN THEM 
 
 WITH NUMEROUS ENGRAVINGS AND DIAGRAMS 
 
 EDITED BY 
 
 PAUL N. HASLUCK 
 
 
 EDITOR OF "WORK" AND "BUILDING WORLD," 
 AUTHOR OF " HAKDYBOOKS FOR HANDICRAFTS," ETC. ETC. 
 
 PHILADELPHIA 
 
 DAVID McKAY, PUBLISHER 
 
 1022, MARKET SJREET 
 1903
 
 PREFACE. 
 
 THIS Handbook contains, in a form convenient for 
 everyday use, a comprehensive digest of the informa- 
 tion on How to Make and Run Small Dynamos and 
 Electric Motors, scattered over ten thousand columns 
 of WORK, one of the weekly journals it is my fortune to 
 K edit and supplies concise information on the general 
 g= principles of the subjects on which it treats. 
 
 In preparing for publication in book form the mass 
 of relevant matter contained in the volumes of WORK, 
 C much that was tautological in character had to be re- 
 g jected. The remainder necessarily had to be arranged 
 anew, altered and largely re-written. From these 
 Z causes the contributions of many are so blended that 
 the writings of individuals cannot be distinguished for 
 acknowledgment. 
 
 Readers who may desire additional information re- 
 specting special details of the matters dealt with in 
 this Handbook, or instruction on kindred subjects, 
 should address a question to WORK, so that it may 
 be answered in the columns of that journal. 
 
 P. N. HASLUCK. 
 
 I.'t Belle Saw>.ioe, London. 
 
 434360
 
 CONTENTS. 
 
 CHAP. PAGfi 
 
 I. Introduction ...... 9 
 
 II. The Siemens Dynamo . . . .21 
 
 III. The Gramme Dynamo . . . .41 
 
 IV. The Manchester Dynamo .... 61 
 
 V. The Simplex Dynamo .... 66 
 
 VI. Calculating the Size and Amount of 
 
 Wire for Small Dynamos ... 76 
 VII. Ailments of Small Dynamo-Electric 
 
 Machines : their Causes and Cures . 89 
 VIII. Small Electric Motors without Castings . 98 
 IX. How to Determine the Direction of 
 
 Rotation of a Motor . . . .112 
 
 X. How to Make a Shuttle- Armature Motor 119 
 XI. Fifty- Watt Undertype Dynamo . .129 
 XII. Four-Hundred-and-Forty Watt Manchester 
 
 Type Dynamo . , 144
 
 LIST OF ILLUSTRATIONS. 
 
 ria. PA 
 
 1. Undertype Field Maguet 
 2. Overtype Field Magnet . 
 
 i-i 
 
 via. PAGE 
 36. Commutator Bearing, 
 showing Position of 
 
 3.-Single Coil Field Magnet 
 
 n 
 
 Brushes. 
 
 M 
 
 4,-Manchester Field Mag- 
 
 
 37. Brush Clamp . 
 
 80 
 
 net 
 
 ];> 
 
 38-40. Forms of Brushes 
 
 ::i 
 
 5. Gramme Field Magnet . 
 
 l.'I 
 
 41. Position of Brushes for 
 
 
 6. Plain Ring Armature . 
 7. Cogged Ring Armature . 
 
 15 
 
 is 
 
 Shuttle Armature 
 42. Siemens Type Dynamo 
 
 n 
 
 8. H-girder Armature. 
 
 u 
 
 complete 
 
 36 
 
 9. Double Shuttle Armature 
 
 is 
 
 43. Magnetising Field Mag- 
 
 
 10. LaminatedShuttle Arma- 
 
 
 nets .... 
 
 37 
 
 ture : Side Elevation . 
 
 16 
 
 44. Diagram of Series Con- 
 
 
 11. Centre Stampings for 
 
 
 nections . . . 
 
 39 
 
 Laminated Armature . 
 
 17 
 
 45. Diagram of Shunt Con- 
 
 
 12. End Stampings for 
 
 
 nections. . 
 
 M 
 
 Laminated Armature . 
 
 17 
 
 46. Gramme Dynamo com- 
 
 
 IS. End View of Shuttle 
 
 
 pleto .... 
 
 41 
 
 Armature 
 
 17 
 
 47. Iron Carcase of Gramme 
 
 
 14. Straight Pattern Binding- 
 
 
 Dynamo. 
 
 42 
 
 Post .... 
 
 is 
 
 48. Inner Face of Standard 
 
 
 15. Ball Pattern Binding- 
 
 
 with Bridge for Brush- 
 
 
 Post .... 
 
 is 
 
 Holders . 
 
 43 
 
 16, 17. Telegraph Pattern 
 
 
 49. Magnet Cores with 
 
 
 Binding-Posts 
 
 19 
 
 Flanges. 
 
 44 
 
 18. Flat Base Terminal . 
 
 19 
 
 50. Laminated Iron Punch- 
 
 
 19. Wing Nut Terminal 
 20. Nut and Piu Terminal . 
 
 20 
 
 211 
 
 ing for Armature . 
 51. Spider for Laminated 
 
 45 
 
 21. Wire Connector . 
 
 20 
 
 Armature 
 
 46 
 
 22. Outline of Siemens 
 
 
 52. Portion of Ring Armature 
 
 
 Dyuauio .... 
 
 21 
 
 ready for Winding 
 
 47 
 
 23, 24.-Forms of Field Mag- 
 
 
 53. Armature Spindle of 
 
 
 nets for Undertyt-e 
 
 
 Gramme Armature 
 
 48 
 
 Dynamos 
 
 22 
 
 54. Commutator for Ring 
 
 
 25.-Solid H-girder Armature, 
 
 
 Armature complete . 
 
 49 
 
 CommeuciUf; to Wind . 
 
 23 
 
 55. How to divide Com- 
 
 
 26. Spimllo Holder : End 
 
 
 mutator Ring . . 
 
 49 
 
 View .... 
 
 2-, 
 
 5f>. How to insulate Com- 
 
 
 27. -Section of Spindle Holder 
 2S.^Sectiou of Spindle Holder 
 and Commutator . 
 
 25 
 19 
 
 mutator Segments 
 57. Copper Connector for 
 Ends of Armature Coils 
 
 49 
 51 
 
 29. Laminated Iron Punch- 
 
 
 58.-Woo"den Shuttle for 
 
 
 ing for Armature . 
 
 M 
 
 winding Armatures 
 
 52 
 
 30. Iron Laminations Strung 
 
 
 59. Connection of Armature 
 
 
 on Spindle , . 
 
 M 
 
 Coils to Commutator . 
 
 M 
 
 31. Bearings for Armature : 
 
 
 60.-Rockerfor Brush-Holder 
 
 U 
 
 End View . 
 
 n 
 
 61 Brush-Holderaud Rocker 
 
 
 32. Bearings for Armature : 
 
 
 complete 
 
 56 
 
 Section .... 
 
 u 
 
 62. Clamp for Brushes . 
 
 56 
 
 33. Brass Ring for Com- 
 
 
 63. Winding Field Magnets 
 
 
 mutator. . . 
 
 29 
 
 of Gramme Dynamo . 
 
 57 
 
 34. Split-tube Commutator . 
 
 n 
 
 64. Connecting Fields in 
 
 
 35. Section of Complete 
 
 
 Series and in Shunt 
 
 58 
 
 Armature 
 
 30 
 
 65. Manchester Dyuaino 
 
 til
 
 LIST OF ILLUSTRATIONS. 
 
 HO. PAGE 
 
 66. Section of Manchester 
 Dynamo.showing wind- 
 ing of Field Magnet 
 Cores . . . 62 
 
 91. Magnet Core for Man- 
 chester Dynamo . . 63 
 68. Magnet Core with Fillets 
 
 to receive Flanges . 63 
 69. Magnet Core fitted with 
 
 Iron Flanges . . 63 
 70. Former for making Sim- 
 plex Armature Core . 67 
 71. Clamp for Armature Core 68 
 72. Method of winding Ring 
 
 Armature ... 68 
 73. Wooden Plug for Arma- 
 ture .... 69 
 74. Commutator of Simplex 
 
 Dynamo ... 70 
 75. Armature of Simplex 
 
 Dynamo complete . 71 
 76.-Pul Piece of ditto . . 72 
 77. Yoke for Magnet of ditto 72 
 78. Coil Flange ... 72 
 79. Bed-Plate of Simplex 
 
 Dynamo ... 73 
 80. Bearings of Armature . 73 
 81. Brush-Holder ... 74 
 82. Simplex Dynamo com- 
 plete .... 74 
 83. Section of Shuttle 
 
 Armature ... 85 
 84. Side View of ditto . . 85 
 85. Section of Cog - ring 
 
 Armature ... 86 
 86. Side View of ditto . . 87 
 87. Simple Electric Motor 
 
 complete I . . .98 
 88. Side Elevation of Field 
 
 Magnet and Block . 99 
 89. Plan of Field Magnet 
 
 and Block ... 100 
 90. Front Elevation of ditto. 101 
 91. Armature, showing f-in. 
 
 Limit .... 102 
 92. Shape of Brush . . 102 
 93. Face of Commutator . 102 
 94. Armature Shaft complete 103 
 95. End View of Brass Bear- 
 ing for Armature Shaft 104 
 96. End View of Miniature 
 Electric Motor with 
 Iron Yoke ... 106 
 97._Side Elevation of ditto . 106 
 98. Side Elevation of Small 
 Motor with Horse-shoe 
 Magnet and Wooden 
 Saddle .... 107, 
 99. End Elevation of ditto . 107 
 VOO. Plan of ditto . 108 
 
 FIO. PAflE 
 
 101. Bearing Brackets . . 108 
 102. Bobbin for Magnet Coils 109 
 103. Horse-shoe Magnet. . 110 
 104. Iron Armature . . . 110 
 105. Setting - out Contact 
 
 Breaker. . . .110 
 106. Fly - wheel Armature 
 
 and Contact Breaker . 110 
 107-110. Directions of Cur- 
 rents and Resultant 
 Magnetism in Bar 
 Magnets . . .113 
 111, 112. Series Motors . .114 
 113, 114. Shunt Motors . . 116 
 115, 116. Motors driven with 
 
 Two Batteries . . 117 
 117. Shuttle- Armature Motor 
 
 complete . . .119 
 118. Field Magnet Casting 
 for Shuttle - Armature 
 Motor .... 120 
 119. Armature Casting for 
 Shuttle-Armature Mo- 
 tor 121 
 
 120. Gun-metal Casting for 
 
 Armature Ends . . 121 
 121. Gun - metal Foot for 
 
 Motor . . . .122 
 122. Rocker for Brush - 
 
 Holders. . . .122 
 123. Castingfor Brush-Holder 123 
 124.-Casting for Milled Head 
 
 Screw .... 123 
 125. Brush-Holder complete. 124 
 126. Brass Screw with Milled 
 
 Head .... 124 
 127. Brush . . . .124 
 128. Commutator ... 125 
 129. Section of Motor, show- 
 ing winding ... 129 
 130,-Brush -Holders, Rocker, 
 
 and Brushes complete 128 
 131. Plan of Dynamo . . 132 
 132. Side View of ditto and 
 
 Motor .... 133 
 133. End View of ditto . . 136 
 13K Side View of Armature . 138 
 135.-End View of Armature . 138 
 136. Field Magnets showing 
 
 Method of Winding . 141 
 137. Position of Commutator. 142 
 138. Plan of Manchester Dy- 
 namo . . . . 14i 
 139. End View of ditto . . 147 
 140. Longitudinal Section of 
 
 ditto . . . .148 
 141. End View, showing me- 
 thod of winding Arm- 
 ature and Fields . . 151 
 142. Brush Gear . . 152
 
 DYNAMOS & ELECTRIC 
 MOTORS. 
 
 CHAPTER I. 
 
 INTRODUCTION. 
 
 SINCE the invention of the first dynamo in 1832, by 
 Pixii, the machine has passed through many phases of 
 evolution. It began under the name of a magneto- 
 electric machine, and continued to bear this name whilst 
 permanent steel magnets were employed in its con- 
 struction. It was then as truly a dynamo as any one 
 of its successors, because the permanent magnets only 
 acted as required when moved. It is not intended in 
 this Handbook to give a history of the machine, but 
 to show how to make small examples of those which are 
 now in general use for electric lighting purposes. These 
 may be arranged in classes named according to the 
 types of armatures, or of the field magnets used in 
 their construction. 
 
 Before describing either the dynamo or its action, it 
 would be as well to consider when and why the dynamo- 
 electric machine is used, instead of primary batteries, as 
 a means of generating electricity for lighting lamps, etc. 
 In the first place, the lighting of electric lamps by the 
 agency of primary batteries is only practicable under 
 somewhat restricted conditions. To get a sufficiently 
 high electro motive force it is necessary to have a 
 great number of cells connected in series, and big cells 
 are required to provide the current, or the battery will 
 soon run down. When a cell is required to give a current 
 of three amperes or more, it polarises very rapidly ; 
 hence to lower the resistance of the lamp circuit (as by
 
 io DYNAMOS AND ELECTRIC MOTORS. 
 
 placing the lamps in. parallel) 4s costly and inconvenient, 
 as a greater -demand ^fbr current is thus thrown on the 
 battery. . Then the costly, .dirty, and laborious job of 
 cleaning ] and tGcliarglhg the Tells- is enough to make 
 one wish for some better method of generating the 
 electric current. 
 
 Small electric lights, such as night-lights and occa- 
 sional lights of low candle power, may be fed with a small 
 two-cell chromic acid battery, or even a Fuller bichromate 
 battery. But when the area of lighting is extended, a 
 dynamo-electric machine is generally used. This is a 
 machine for converting mechanical energy into electric 
 energy. 
 
 There are many who believe that electricity actually 
 runs, or flows, from one end of a wire or conductor to 
 the other, in a certain direction, when the ends are 
 connected to a battery or dynamo. For instance, in 
 the case of a battery of primary cells, the current is 
 always spoken of as coming from the carbon terminal, 
 going through the external circuit, and returning to the 
 zinc. This, in point of fact, is misleading ; for the expres- 
 sion is quite conventional, and it might easily have been 
 expressed the other way, and would have made no 
 difference whatever to electrical formulae or laws. But 
 when electricity came to be studied and advance was 
 made in the science, it was mutually agreed to express 
 the phenomenon in this way. 
 
 In a similar manner it was agreed to call one end of 
 a magnet the north pole, and the other the south ; but 
 in this case we are brought face to face with a paradox. 
 It is this : either we have all along been giving our 
 magnet ends wrong names, or else Franklin, and many 
 others after him, have diligently been searching the 
 Arctic Seas for the North Pole when it is the south 
 all the time ; for like poles repel each other, unlike 
 poles attract Perhaps it has been noticed that many 
 writers are careful in calling the two ends of a magnet 
 the north-seeking and south-seeking poles respectively. 
 
 But as regards an electric current, this conventional
 
 INTRODUCTION. 1 1 
 
 way of expressing it must not be taken literally. 
 Electricity is not a liquid ; it does not flow through 
 a certain wire as water through a pipe. Although 
 water is a very useful substance to make use of as an 
 example when studying some of the phenomena of 
 electricity, yet electricity is unlike water in many ways 
 it can be said to work uphill; it is not influenced 
 by the force of gravity ; also, it can be said to act 
 two ways at once. 
 
 Whatever electricity may be, it is perfectly clear at 
 the present time that sources of electrical energy have 
 different effects upon different substances, copper, silver, 
 and other metals being very susceptible to this influence. 
 Hence, these metals are called the best conductors. 
 But glass, vulcanite, paraffin wax, and most com- 
 pound substances are considered, in one sense, bad 
 conductors some say non-conductors. 
 
 The actual time it takes a current of electricity to 
 traverse a given length of wire is often stated and 
 put down to be some fraction of a second ; but it must 
 on no account be understood from this that the current 
 flows from its source in one direction right round 
 the circuit and back again to that source ; but that 
 a "condition" is set up, when the circuit is closed, 
 both ways along the conductor or wire. 
 
 As far as we know, in an electric circuit nothing 
 can actually be said to flow from one end to the 
 other, but it is a "condition" set up throughout the 
 entire length ; and this length must form a complete 
 circuit or ring, the shape of which matters little. Also, 
 somewhere within this circuit, and forming part of it, 
 must be placed the means of setting up this "condition" 
 say, a battery or a dynamo. 
 
 The following outlines represent the field magnets of 
 some dynamos in general use : Undertype, Fig. 1 : 
 Two vertical cores of rectangular section joined to the 
 pole-pieces, cast with armature tunnel in lower part 
 Similar machines have cores of circular section. Over- 
 type, Fig. 2 : Two vertical cores of suitable section cast
 
 DYNAMOS AND ELECTRIC MOTORS. 
 
 with yoke at base, and the armature tunnel in upper 
 part. Coils may be wound separately, then slipped 
 over cores. Several modifications of this machine 
 have been designed. Some of these have round cores. 
 Single coil or simplex, Fig. 3 : One core of circular 
 section joined to suitable pole-pieces with the armature 
 tunnel at the side. In one form this machine has it? 
 single core spanning horizontally the two vertical pole- 
 pieces, with the armature tunnel in the upper part 
 Manchester, Fig. 4 : Two cores of circular section 
 bedded into two horizontal pole-pieces. Armature 
 tunnel in the central part of the machine between the 
 
 Fig. 1. Uudertype Field 
 Magnet. 
 
 Fig. 2. Overtype Field 
 Magnet. 
 
 two cores. Gramme , Fig. 5 : Four horizontal cores of 
 circular section bedding into massive pole-pieces in the 
 centre of the machine, and into vertical standards at 
 the sides ; armature tunnel in centre of the machine. 
 
 The field magnets of these machines are not made 
 up of steel permanently magnetised, but are constructed 
 of comparatively soft iron, containing residual mag- 
 netism, which, by dynamic energy imparted to the 
 armature, is induced to exert its influence on the arma- 
 ture coils, and create in them an electric current. This 
 current, or part of it, is then sent around the field 
 magnet coils, with the result that a stronger magnetism 
 is induced in the cores of the field magnets. Being 
 thus strengthened, they induce a higher electro-motive 
 force in the armature coils, and thus the full electric 
 power of the machine is worked up
 
 INTRODUCTION. 
 
 Now as to the way in which a current of electricity 
 is measured. The unit of current generally accepted 
 is the Ampbre. Some idea of its meaning may be 
 learned by comparison with other units of measure- 
 ment. For instance, in trades where the foot rule is 
 used, the foot and inch are units of measurement of 
 length. Where steam engines are used, we speak of 
 
 Fig. ,3. Single Coil or Sim- 
 plex Field Magnet. 
 
 Fig. 4. Manchester Field 
 Magnet. 
 
 pounds per square inch in estimating the pressure of 
 Bteam; and horse-power as a unit in estimating the 
 power of a steam engine. Where water is used as a 
 
 Fig. 5. Gramme Field Magnet. 
 
 motive power, we speak of its volume by cubic inches, 
 or gallons. In dealing with electrical measurements, 
 neither the foot rule nor the spring-pressure gauge can 
 be used, so electricians have had to invent a new set 
 of instruments, and new names for the units or divisions 
 marked on them. 
 
 The Ampere is defined as that current which is 
 obtained when an electro-motive force of one Volt 
 acts on a resistance of one Ohm. A volt is the unit 
 measure of electro-motive force roughly as given by the
 
 14 DYNAMOS AND ELECTRIC MOTORS. 
 
 current from one standard Daniell cell ; a better 
 standard is the Hibbert one-volt cell recently intro- 
 duced. An ohm is the unit of resistance. A 10-feet 
 length of '01 inch copper wire of 95 per cent, con- 
 ductivity has roughly one ohm resistance. If we 
 divide the total electro-motive force in volts by the 
 total resistance of the circuit in ohms, we obtain the 
 value or strength of the current in amperes. For 
 measuring amperes, an ampere-meter, or ammeter, is 
 used, and voltmeters are used for measuring the voltage or 
 potential difference between different points of a circuit. 
 
 The Watt is the electrical unit of power or activity. 
 Just as the rate at which an engine works is measured 
 by horse-power, so the rate of output of a dynamo is 
 measured in watts. Therefore to measure the output 
 of a dynamo in this way multiply the electro-motive 
 force at the terminals of the machine, in volts, by the 
 current in the external circuit, in amperes. Thus, watts 
 equal volts multiplied by amperes. Very nearly, 1 
 horse-power equals 746 watts. 
 
 An Ampere hour is a term frequently met with, and 
 means one ampere supplied or required for the space 
 of one hour, or the equivalent. Thus amperes multi- 
 plied by hours gives ampere hours. For instance, an 
 accumulator that is said to have a capacity of eighty 
 ampere hours, is one that might give a current of 1 
 ampere for eighty hours, 2 "amperes for forty hours, or 
 4 amperes for twenty hours and so on. 
 
 Armature is a name given to the iron keeper of a 
 permanent magnet. In dynamos it is applied to 
 that part which is rotated within the influence of 
 the field magnets. There are some exceptions, in 
 which the magnets are caused to revolve arid the 
 armature is stationary. Revolving armatures and fixed 
 field magnets have the merit of adding stability to the 
 machine and steadiness to its running and the output of 
 the current. Each inventor of a new dynamo appears 
 at first to have adopted a special form of armature; 
 henco we have almost as many forms of armature as there
 
 I NT ROD UC TION. 1 5 
 
 are inventors of machines. The armatures are generally 
 furnished with iron cores, around which insulated copper 
 wires are wound. Machines have been constructed with- 
 out iron cores, by Messrs. Siemens, Ferranti, Mordey 
 and Thompson. In some of those machines a looped 
 or zigzag band of copper has been attached to a brass 
 
 Fig. 6. Plain Ring 
 Armature. 
 
 Fig. 7. Cogged Ring or 
 Pacinotti Armature. 
 
 spider, mounted on a spindle, and forms the arma- 
 ture. By Lord Kelvin all armatures are divided into 
 four types : 
 
 Fig. 8. Shuttle 
 or H-girder Armature. 
 
 Fig. 9. Double Shuttle or 
 Walker Armature. 
 
 (1) Ring armatures, in which the coils are grouped 
 upon a ring whose principal axis of symmetry is also 
 its axis of rotation. 
 
 (2) Drum armatures, in which the coils are wound 
 longitudinally over the surface of a drum or cylinder. 
 
 (3) Pole armatures, having coils wound on separate 
 poles projecting radially from a disc or central hub. 
 
 (4) Disc armatures, in which the coils are flattened 
 against a disc.
 
 16 DYNAMOS AND ELECTRIC MOTORS. 
 
 Of these it is as well to say that early examples of the 
 first type were furnished by the machines of Gramme, 
 Schuckert, Giilcher, and Brush. Examples of the 
 second type are to be found in the Siemens (Alteneck), 
 Edison, Weston, and Elphinstone- Vincent machines. 
 Examples of the third type were to be seen in the 
 dynamos of Elmore and Lontin. There are but 
 few useful examples of the fourth type, except the 
 Desrosier. 
 
 When solid iron is employed for an armature core, 
 eddy currents are set up in the iron, and cause the 
 
 ~S j 
 
 
 m> 
 - 1 
 
 t 
 
 
 
 Fig. 10. Laminated Shuttle Armature. 
 
 armature to become hot. Iron armatures should there- 
 fore be built up of thin sheet-iron discs, or plates of hoop 
 iron, each layer of iron being magnetically insulated 
 from its neighbour by varnished paper or calico. The 
 armature coils should be of pure copper wire, well 
 insulated with silk or cotton, and the wires should be 
 as short and thick as is consistent with obtaining the 
 requisite electro-motive force without driving the 
 machine at an excessive speed. 
 
 Figs. 6 to 9 show the types of armatures in use for 
 small dynamos and electric motors. Fig. 6 shows a plain 
 ring armature. It is generally formed of rings or collars 
 of very thin sheet iron. These may be strung together 
 on gun -metal bolts, attached to the arms of brass spiders 
 as shown by the dotted lines, the armature spindle 
 going through the hole in the centre. The rings are 
 \Tound with several coils of wire, passing through
 
 fXTRODUCTIOff, 
 
 and over the rings. They can also be wound as a 
 drum by winding the coils over the rings only. The 
 drum armature may also be made of discs instead of 
 rings. Fig. 7 shows a cogged ring or Pacinotti armature. 
 This also is made of rings stamped from thin sheet 
 iron, which may be strung on bolts attached to brass 
 spiders. Small armatures are sometimes cast solid in 
 soft malleable iron. The cogs and spaces may vary from 
 
 Fig. 11. Centre Stamp- 
 ings for Laminated 
 Shuttle Armature, 
 
 Fig. 12. End Stampings for 
 Laminated Shuttle Arma- 
 ture. 
 
 Fig. 13. End View of Shuttle Armature. 
 
 six to sixteen, and the number of coils is determined 
 by the number of spaces between the cogs. Fig. 8 
 shows in section a shuttle or H-girder armature. In 
 small machines this is cast solid. It is also built up 
 of laminated stampings of sheet iron strung on a steel 
 spindle. One coil only can be wound on a shuttle 
 armature. Fig. 9 shows a double shuttle or Walker 
 armature, also built of sheet iron stampings. A coil 
 may be wound on each arm, making four coils in all, 
 or two coils may be wound crosswise. It is not a 
 good armature to wind, as the coils are apt to be of
 
 i8 DYNAMOS AND ELECTRIC MOTORS. 
 
 uneven length and resistance. Fig. 10 shows a laminated 
 shuttle armature of a somewhat improved form. The 
 stampings for the centre portion are of the ordinary 
 shuttle or H shape shown in Fig. 11, while the end stamp- 
 ings take the shape shown in Fig. 12. These are strung 
 on two bolts, and clamped together between two castings 
 shown in side elevation by Fig. 10, and in end elevation 
 by Fig. 13. The wire is wound over the central portion 
 or web, and through the spaces at the end, the shaft 
 Leing driven securely into the end castings. 
 
 Fig. 14. Straight Pattern Binding-Post. 
 
 Fig. 15. Ball Pattern Binding-Post. 
 
 Binding-Screws, etc. These are small clamps made 
 of brass, and cast or turned in various forms to suit 
 requirements. They are sometimes called " connectors " 
 and are used as convenient means of connecting one 
 part of an electric circuit with the rest of the circuit. 
 When made in the form of a pillar or post and fixed 
 by being screwed to a base, they are named " binding- 
 posts." When fixed to the two wires proceeding from 
 a generator of electricity so as to form the two poles of 
 the generator, they are named " terminals." The ac- 
 companying illustrations will show at a glance several 
 types of binding-screws. 
 
 Fig. 14 shows a binding-post as used for the terminal 
 poles of small dynamo machines. When used for this 
 purpose the post should be massive, the threads on the
 
 INTRODUCTION. 19 
 
 screws well cut, and the hole for the wire left large. 
 If these posts are nickel-plated, they enhance the ap- 
 pearance of the machine, and require less care to keep 
 them clean. Some makers taper the post from the base 
 upward, whilst others round off the tops. This is merely 
 
 Fig. 16. 
 
 Fig. 17. 
 
 Figs. 16 and 1 7. Telegraph Pattern Binding-Posts. 
 
 a matter of taste. The wires from the machine are 
 twined around the tang of the post and secured by a nut 
 beneath the base of the machine. Fig. 15 shows a ball 
 pattern binding-post used for a similar purpose. 
 
 Fig. 18. Flat Base Terminal. 
 
 Figs. 16 and 17 show two "telegraph pattern" binding- 
 posts. These are used for the terminals of telegraph in- 
 struments. When made large, they are useful terminals 
 for ammeters and similar instruments. Fig. 18 shows a 
 neat modification of the same terminal ; and Fig. 19 
 shows a similar terminal furnished with a wing nut. 
 This form of nut may be easily screwed and unscrewed
 
 20 DYNAMOS AND ELECTRIC MOTORS. 
 
 without the aid of pliers. It finds favour with 
 French workmen, and is used by them instead of the 
 milled head so commonly met with in binding-screws of 
 
 iff. 20. 
 Nut and Pin Terminal. 
 
 Fig. 21. Wire Connector. 
 
 English makers. Fig. 20 shows a simple nut and pin 
 terminal, as used to insert in the lead tops of carbons 
 used in Leclanche" batteries. Fig. 21 shows one form 
 of wire connector made from brass tube. Two holes 
 are drilled and tapped in the side of the tube to receive 
 two brass screws as shown in the sketch. These con- 
 nectors are useful when we wish to join a broken 
 wire or connect two wires together. Thick brass tube 
 should be used, or else a lug should be soldered to or 
 cast on the side to thicken it where the screw holes 
 have to be made, otherwise these will not contain 
 enough threads to allow of the screws being securely 
 tightened on the wires.
 
 CHAPTER IL 
 
 THE SIEMENS DYNAMO. 
 
 IN 1857, Dr. Werner Siemens invented the simple fo\m 
 of armature now known as the Siemens H girder, and 
 so called because its cross-section resembles the section 
 of an H iron girder. This is shown at Fig. 8, p. 15. As 
 this form of armature, together with the field magnets, 
 is easily made, wound, and set up, it has become a 
 general favourite. An outline of the machine in 
 
 Fig. 22. Outline of Siemens Dynamo. 
 
 general use is shown at Fig. 22, whilst Figs. 23 to 37 
 show in detail the forms of its several parts. The 
 diagram Fig. 22 shows the position of the parts com- 
 posing the skeleton, or carcase, of the machine ; A being 
 the armature ; M, M, the pole pieces ; c, c, the field 
 magnet cores ; and Y, the yoke to which the field 
 magnet cores are attached by bolts or screws. 
 
 The field magnets are often made to the form shown 
 at Fig. 23, or to that shown at Fig. 24, in various sizes, to 
 suit the other parts of the required machine, as shown
 
 22 DYNAMOS AND ELECTRIC MOTORS. 
 
 in the table on p. 24. They are cast in soft iron, and 
 are sent out annealed ready for use. A full set of 
 castings for a Siemens pattern machine of small size 
 can be obtained for about five shillings, and this will 
 make up a 5-candle power machine. The castings for a 
 machine of 120-candle power will cost about thirty-five 
 shillings. All castings received from vendors of these 
 things are in the rough as they come from the foundry, 
 unless otherwise ordered, and an additional price has to 
 be paid for the labour of shaping and fitting them ready 
 
 Fig. 23. Fig. 24. 
 
 Forms of Field Magnets for Undertype Dynamos. 
 
 for winding on the wire. Supposing, however, that the 
 castings are received in the rough, we will set about 
 preparing the field magnet castings. These should be 
 soft enough to file easily, or they are unsuited for our 
 purpose. 
 
 The first job will be to clean and true up the parts 
 that is, remove any rough ridges or lumps of iron 
 left on the edges of the armature tunnel. This may 
 be done in a lathe or by means of a half-round coarse 
 file. The two castings for the field magnets must be a 
 pair, and when stood side by side on a level bench, the 
 armature tunnel between them should be of regular
 
 THE SIEMENS DYNAMO. 23 
 
 form throughout, the cores of one height and size, and 
 parallel with each other when upright. If slight irregu- 
 larities appear on the sides of the tunnel, take them off 
 with the rounded face of the file. The corners of the 
 cores should also be filed round and smooth, to prevent 
 abrasion of the covering on the wire whilst these are being 
 wound. If the castings are shaped as shown at Fig. 23, 
 holes must be drilled and tapped in the top at a, 6, 
 to receive screwed studs to hold the yoke in its place on 
 the field-magnet cores. Holes about \ in. diam. must 
 also be drilled in the lugs at c, d, e, /, to receive screwed 
 studs or small bolts securing the armature bearings to 
 
 Fig. 25. Solid H-girder Armature commencing to wind. 
 
 the lugs. Two larger holes must also be drilled in tho 
 feet of the castings at g, h, to receive short coach screws 
 used for bolting the castings to their wood base. 
 
 The yoke to connect the field magnets, shown at Y 
 Fig. 22, is a rectangular piece of iron plate, and must 
 be bedded on the top of the field magnets' cores to hold 
 them in the position In the small Siemens machines 
 supplied by some makers this separate yoke is dis- 
 pensed with, as the top of one of the castings projects 
 sufficiently to bridge over the space between the two, 
 and thus forms the yoke. In the castings supplied by 
 others, also, the two projections have turned-up flanges, 
 as shown at Fig. 24, and these are bolted together. 
 The two field magnets must be connected in this or in 
 a similar way by an iron bridge, so as to form a horse- 
 shoe magnet, between the poles of which the armature 
 will revolve. 
 
 The armature of the solid H-girder form used in
 
 DYNAMOS AND ELECTRIC MOTORS. 
 
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 THE SIEMENS DYNAMO. 
 
 machines is shown at Fig. 25. It is a casting of 
 specially soft iron, and is supplied with the other 
 castings for the machine. The channel for the wire 
 should be true and smooth, and the ends of the web 
 should be rounded and smoothed to prevent abrasion 
 of the wire covering. The rounded faces of the cheeks 
 must also be free from lumps, and they must also be 
 true from end to end. The ends must "be filed or turned 
 true to form faces for the spindle-holders shown at Figs. 
 26 to 28. These are secured to the ends of the armature 
 by screwed studs, and holes must be drilled and tapped 
 to receive them. 
 
 Fig. 26. Fig. 27. Fig. 23. 
 
 Fig. 26. Spindle Holder : End View. Fig. 27. Section of 
 Spindle Holder. Fig. 28. Section of Spindle Holder 
 and Commutator. 
 
 In larger machines, the armature is built up of purch- 
 ings of sheet-iron shaped as shown at Fig. 11 (p. 17), or as 
 shown at Fig. 29. These stampings are sold at prices 
 ranging from 3s. b'd. to 10s. per gross, according to size. 
 The stampings are strung on a steel spindle, as shown 
 at Fig. 30, and secured at each end by nuts, so as to 
 pinch the whole series of plates between them. The 
 result is to form a channel for the wire, and faces 
 for the cheeks of the armature, similar to that of the 
 solid H-girder form. This laminated form lessens the 
 tendency of the armature to heat by generating cross 
 currents in itself whilst working. The laminations are 
 separated from each other by varnish or paper, and 
 these help to keep the armature cool. The spindle 
 should be long enough to pass through the end bearings. 
 
 The spindle-holders for the solid form of armature 
 are made o/ brass, either cast with a projecting boss,
 
 2 6 DYNAMOS AND ELECTRIC MOTORS. 
 
 or made up of a disc of brass with a piece of brass 
 tube fitted in the centre to give holding power on 
 the [spindles. The spindles should be of steel, turned 
 true and smooth, and fitted tightly in their respective 
 holders. The projecting bosses of these spindle-holders 
 running against the bearings prevent end shake of the 
 armature ; but when a laminated armature is employed, 
 the ends of the spindle may be turned down a little to 
 form a shoulder for this purpose. 
 
 The armature bearings for the smaller sizes of 
 machines, are cast in gun-metal to the form shown at 
 Figs. 31 and 32, or cut from sheet brass to the form shown 
 
 Fig. 29. Laminated Fig. 30. Iron Laminations 
 Iron Punching strung on Spindle to 
 
 for Shuttle form Shuttle 
 
 Armature. Armature. 
 
 at Fig. 36 (p. 30), aud are secured to the ends of the field 
 magnets by long bolts resting in the slots shown in the 
 lugs, Fig. 24. As the bolts run the whole length of the 
 sides of the machine, they then clamp the front and back 
 bearings together. The bearings for the other forms are 
 similarly made, but they are secured to the lugs of the 
 field magnets by screwed studs, or by small bolts passing 
 through holes drilled in the lugs. Whichever form of 
 bearing is employed, or however it may be secured to 
 the machine, the holes must be exactly in the centre of 
 the armature tunnel, so that the cheeks of the armature 
 may run no nearer to one side than to the other. 
 
 The field magnets may now be bolted together, 
 the bearings put on, and the running of the armature in 
 its tunnel tested. It should be centred so as to leave 
 about -^o of 'an inch of space between the cheeks of tlio 
 armature and the sides of the tunnel. A space the
 
 THE SIEMENS DYNAMO. 27 
 
 thickness of stout brown paper is enough, but if the 
 space is less than this, the cheeks may bind against 
 the sides of the tunnel. If excessive space is allowed, 
 part of the energy will be lost. If there appears to 
 be a danger of the armature touching the sides at any 
 particular part, mark the place, and ease it with a file. 
 A very effective way to test the running of the armature 
 is to paste a piece of paper over the cheeks, and then 
 revolve it in the tunnel. On taking it out carefully, 
 the abrasions on the paper will mark the prominent 
 parts, and these may then be eased. 
 
 This form of armature is wound with only one coil 
 of wire;; the commutator will be a " two-part commu- 
 tator " (see Fig. 33) that is, one divided into two sec- 
 tions, one for each end of the wire coil. These sections 
 must be insulated from each other, and must also be 
 insulated from the rest of the machine. The cheapest 
 and handiest insulating substance available is boxwood 
 well soaked in melted paraffin. Ebonite or vulcanised 
 fibre will also serve the purpose, but these are more 
 costly. Therefore get a chunk of boxwood out of 
 which can be turned a disc \\ in. in diameter and 
 about 1 in. thick. Turn this up true, with a hole bored 
 exactly in the centre to fit tightly when driven on one 
 of the spindles. Then get a piece of brass tube 1 inch 
 in length, that exactly fits over the boxwood, and force 
 it tightly on. The smallest sized machines take a com- 
 mutator I in. in diameter. 
 
 If now this brass-bound boxwood disc were forced on 
 the spindle as shown at Fig. 28, it might work loose in 
 time; so, to prevent it from slipping, turn down the 
 hub of the spindle-holder enough to get a good face 
 for the boxwood boss to fit against, then bore two J in. 
 holes in the holder, and fit them with two short brass 
 pins. When we have determined how the commutator 
 shall go on the spindle, two shallow holes may be 
 bored in the inside face of the boxwood disc to fit 
 those pins exactly, and so keep it from slipping. 
 The ring of brass must now be divided, and upon the
 
 2S Dl'XAMVS AND ELECTRIC MOTORS. 
 
 way this is done will depend all other parts being right 
 the proper working of the machine. If divided into 
 two equal sections, by sawing straight across the tube, 
 the current from the armature would be interrupted 
 abruptly, and sparks would be caused, which would 
 soon burn away the brass ring and also the brushes. 
 The saw-cut must therefore be made obliquely or 
 diagonally across the ring. 
 
 But here we must guard against making the division 
 as shown at A on the left in Fig. 34, for this would be too 
 oblique, and the interruptions would, in consequence, 
 
 Fig. 31. Fig. 32. 
 
 Bearings for Armature. Fig. 31. End View 
 Fig. 32. Section. 
 
 not take place at the proper time. To obtain the 
 proper direction for this saw-cut, turn the disc on 
 one end and draw a line diameterways across the centre, 
 and i in. on each side of this line draw two other 
 lines. Now scribe two lines on one side of the brass 
 exactly in a line with the two lines on the end. Turn 
 the disc over, and scribe two similar lines across the 
 opposite side. Now on both sides scribe a line across 
 the space between these two lines, from the right- 
 hand end of the top line to the left-hand end of the 
 bottom line. Next, drill and countersink two small 
 holes on each side of the line to receive two very 
 small brass screws, as shown at Fig. 34 (B), and put in 
 the screws, which must not touch the spindle when 
 driven well home. When this has been done, the ring 
 may be divided by sawing it through to the boxwood
 
 THE SIEMENS DYXAMO. 29 
 
 on both sides along the diagonal lines, using a hack-saw 
 for the purpose. 
 
 The saw-kerf should be widened a little, and cleaned 
 out well with a thin file, or it is apt to get choked 
 and bridged with fine particles of metal worn from the 
 
 Fig. 33. Brass Ring for Commutator. 
 
 brushes. The holes for the fixing-pins may now be 
 bored, and the commutator fixed in its place on the 
 spindle, having placed it so that the saw-cut in the 
 commutator ring shall be on the side of the coil 
 nearest the left-hand cheek of the armature. Two 
 
 Fig. 34. Commutator, showing Divided Brass Ring 
 and Screws. 
 
 small holes may now be drilled through the spindle- 
 holder (as shown at A, B, Fig. 26, p. 25). These are bushed 
 with ivory or some other non-conductor, and the ends of 
 the armature coil wire to come through these are securely 
 fastened to the commutator ring. 
 
 The brushes are long thin pieces of springy brass, 
 copper, or phosphor bronze fixed on each side of the 
 commutator to brush-blocks insulated from the rest of 
 the machine. Their duty is to pick up the impulses
 
 3 
 
 DYNAMOS AND ELECTRIC MOTORS. 
 
 of the interrupted armature current from the com- 
 mutator sections, and convey those impulses to the 
 field magnet coils and to the outer circuit. In the 
 machines of some makers the brushes are attached to 
 boxwood blocks fixed to the bearings of the armature 
 
 Fig. 35. Section of Complete Armature. 
 
 spindle (as shown at Fig. 36) ; in other machines they 
 are attached to brass pillars screwed into the wooden 
 base of the machine on each side of the commutator. 
 Probably, for small machines, wooden blocks as shown 
 at Fig. 36, with an adjustable brush -holder attached 
 
 Fig. 36. Commutator Bearing, showing Position of Brushes. 
 
 Fig. 37. Brush Clamp. 
 
 to each block, are the best. With the brushes fixed, as 
 they often are in small machines, their adjust- 
 ment becomes a tedious task. The brush-holder need 
 be only a small brass bracket with a set-screw, as 
 shown at Fig. 37. The brushes can then be shifted 
 to and fro, and adjusted at any angle required by 
 placing wedges of brass in the clamps above or below 
 the back ends of the brushes.
 
 THE SIEMENS DYNAMO. 31 
 
 A very good material for the brushes of small 
 machines is fine wire gauze cut into strips, and two or 
 three thicknesses soldered to the ends of stout brass 
 springs to ensure proper pressure on the commutator. 
 Three forms of brushes in general use are shown at Figs. 
 38, 39 and 40. That shown at Fig. 38 is merely a piece of 
 thin spring brass, shaped as shown, and fixed to a pillar 
 brush-holder. This is an objectionable form, as it 
 often gets out of order by wear, and cannot be replaced 
 or adjusted easily. Fig. 39 is an improvement on this 
 form. It is composed of thin sheet brass or hard 
 
 Fig. 38. 
 
 Fig. 39. Fig. 40. 
 
 Figs. 38 to 40. Forms of Commutator Brushes. 
 
 hammered copper cut to the form shown, with one end 
 slit into fingers to the length of 2 or 2| in., and a slot 
 cut in the other end to facilitate adjustment The 
 fingers soon wear away, and must then be replaced. The 
 brush shown in Fig. 40 consists of a piece of hard spring 
 brass, to one end of which is soldered a pad of copper 
 wire gauze. This bears on the commutator, and is 
 kept in contact with it by the strip of spring brass to 
 which it is soldered, the strip being curved as shown at 
 Fig. 36 for this purpose. This pad is most effective as 
 a brush ; it does not cut away the commutator like 
 spring brass and copper, and it is easily adjusted or 
 replaced if fixed in a brush-block with clamp, as shown 
 at Fig. 37. 
 
 The position of brushes for shuttle or H -girder arma- 
 tures is a matter of considerable importance. It does 
 not matter how the commutator is fixed to the shaft ; 
 that point is settled by the most convenient way of 
 holding the brushes. But the rule that must be observed
 
 32 DYNAMOS AND ELECTRIC MOTORS. 
 
 is that When the two cheeks of the armature are 
 electrically opposite the two pole-pieces of the field, 
 the brushes must rest on the insulating strips on the 
 commutator. 
 
 In Fig. 41 this position is shown by the brushes in 
 dotted lines ; but in practice the brushes are given a 
 slight " lead "that is, they are moved forward through 
 a small angle in the direction in which the commutator 
 moves. This brings the brushes on the insulating strips, 
 not when the cheeks of the armature exactly face the 
 pole-pieces, but just a little after they have passed the 
 centre line. 
 
 Fig. 41. rosition of Brushes for Shuttle Armature. 
 
 The brushes with this lead are shown in Fig. 41 in 
 full black lines, with a centre line showing the angle 
 through which they have been turned. The exact 
 amount of this lead can only be found when the 
 machine is at work, for some armatures require more 
 than others ; for instance, a rather hard solid shuttle 
 armature may require more lead than one built up of 
 separate punchings. The brushes should have just 
 enough lead for the machine to give its full current 
 without sparking. Just a trifle too much or too little 
 lead may easily bring about sparks, which not only 
 mean waste of power, but also eat away both brushes 
 and commutator, and should therefore be avoided.. 
 
 Before winding the armature, see that the channel is 
 free from lumps, and the ends of the web are smootlj
 
 THE SIEMENS DYNAMO. 33 
 
 Then cut a strip of silk large enough to envelop the web, 
 and coat this with good shellac varnish. Lay the silk 
 evenly to form a bed for the wire, and varnish the silk 
 and the channel, and when the varnish is dry proceed to 
 wind on the wire. This will be all the better for the 
 purpose in hand if it has been previously soaked in hot 
 melted paraffin. Commence winding as shown at Fig. 25, 
 p. 23, lay each coil evenly, as a reel of cotton is wound, 
 and wind close and tight, until the required amount of 
 wire has been wound on. The wire coil must not stand 
 above the cheeks of the armature. If a stray layer 
 stands up above the others, and threatens to knock 
 against the sides of the field magnet tunnel whilst being 
 revolved, it must be pressed into its place with a piece of 
 smooth wood. Then bring the two free ends to one end 
 of the armature, put on the spindle-holder (Fig. 26, p. 25), 
 bring the ends through the ivory-bushed holes A and B 
 made for this purpose, put on the commutator, and 
 solder the two ends of the coil to the two sections of 
 the commutator. Then put on the other spindle- 
 holder, and the armature is complete. Fig. 35, p. 30, 
 shows a section of the armature thus finished. It is 
 lettered as follows : w, web of armature ; E, spindle- 
 holders ; c, commutator ; s s, shaft or spindle ; and p, 
 driving pulley. 
 
 Whilst winding the wire on the armature or the field 
 magnets of a dynamo, great care must be exercised to 
 get each coil of wire close to its neighbour, and each 
 layer of wire regular and close to the layer beneath, for 
 on this will depend the full efficiency of the machine. 
 Slack and irregular winding will cause loss of power, 
 and this is specially observable in the winding of the 
 armature, where cross winding will not only prevent a 
 maximum number of coils being got in a given space, but 
 will also cause cross currents in the wires. Nevertheless, 
 whilst giving all attention to the tightness and snugness 
 of the winding, it is possible to be too zealous in this 
 direction, and fall into the more serious error of pulling 
 the wire so tightly over the iron ends of the armature as to
 
 34 DYNAMOS AND ELECTRIC MOTORS. 
 
 cause the iron to cut into the covering of the wire. One 
 such abrasion of the covering, however small, will render 
 the machine useless, as electrical contact will be made 
 through the iron of the machine as well as through its 
 wire coils. 
 
 Such accidents as these are of frequent occurrence, 
 and to detect them it is necessary to have a small 
 galvanometer, or current detector, and with it to test the 
 insulation of the covering as the winding proceeds. 
 Almost any price may be paid for a galvanometer, from 
 2s. 6d. up to 10, according to the value of material and 
 workmanship in the instrument ; but a plain and simply 
 constructed one, good enough for this purpose, can be 
 got for 10s., or perhaps less. To test the wire for com- 
 plete insulation whilst winding, connect a free end of 
 it to one stud of the galvanometer ; connect the other 
 stud to one terminal of a good battery (one cell of a 
 Bunsen or a bichromate will do very well), and attach a 
 length of copper wire to the other terminal of the 
 battery. With the end of this wire touch the bare iron 
 of any part of the armature (or of the field magnets 
 whilst winding them). If the needle of the galva- 
 nometer is deflected, it may be taken for granted 
 that the wire covering is abraded, and each coil must 
 be unwound until the faulty place is discovered. 
 Such faults are best repaired with a thread of un- 
 spun silk or soft darning-cotton, soaked in melted 
 paraffin and wound around the abraded spot. If the 
 galvanometer needle does not move at all when the 
 iron is touched with the battery wire, we may be fairly 
 certain that the coil is insulated from the iron of the 
 field magnet core, or of the armature, as the case may be. 
 
 Greater care is needed in winding a laminated arma- 
 ture than in one having a solid core, since the edges of 
 the end plates are liable to cut through the protecting 
 coat of silk and covering of the wire if this is pulled too 
 tightly over the edges. Some little difficulty also will be 
 experienced in getting the coils of wire to lie close to the 
 spindle whilst winding them on one side. This may be
 
 THE SIEMENS DYNAMO. 35 
 
 overcome by tying each coil back with a short piece of tape, 
 until the curvature of the spindle has been passed In 
 winding a laminated H-girder armatumfora Manchester 
 field, the coils may be prevented from slipping at the 
 ends by bending forward two of the laminated plates at 
 each end, so as to form two flanges, against which the 
 coils can rest as against the sides of the end slot in a 
 solid armature. As there are no spindle-holders through 
 which to pass the ends of the coil we have to fasten 
 them direct to the sections of the commutator, to the 
 inside edgea of which they should be secured by solder. 
 It will also be advisable to tie the ends down to 
 the spindle with a few turns of tape, to prevent the 
 outer coil from shaking loose in working. 
 
 Before winding the field magnet cores, it will be neces- 
 sary to prepare them for the wire by wrapping around 
 them a layer of silk ribbon well soaked in melted paraffin, 
 applied to the iron warm, and then made quite smooth. 
 The wire should also be prepared for winding by first 
 dividing the allotted quantity into two equal parts, 
 making these into hanks or coils large enough to go loosely 
 over a two-gallon stoneware jar, and then well soaking 
 them in melted paraffin. The wire for the dynamos 
 specified in the table on p. 24 may be divided by 
 measurement, if it is found inconvenient to divide it by 
 weight, if we remember that No. 22 S.W.G. d.c.c. copper 
 wire measures 125 yards in the Ib. The wire may be 
 wound on by hand if the worker is unprovided with 
 suitable apparatus, but it can be wound more regularly, 
 smoother, and tighter in a lathe, or by means of a special 
 winder, which can be easily and cheaply made up for 
 the purpose from a few scraps of wood, a few bolts, and 
 a winch-handle. Centre the field magnet casting in the 
 lathe, and when it runs true, proceed to wind on the 
 wire. 
 
 If the hank of wire has been placed over a glazed 
 stoneware bottle filled with water, the coils will slip off 
 easily as the wire is wound on the casting. Commence at 
 the channel or bottom end of the core ; wind some seven
 
 3 6 DYNAMOS AND ELECTRIC MOTORS. 
 
 or eight inches of the wire on a pencil to form a close 
 spiral, to be stretched out after winding to form 
 connections. Lay this close to the bottom end, take 
 one turn around the casting, and secure the spiral 
 to this turn with a piece of strong twine. Wind 
 on the coils evenly side by side, and when within two 
 inches of the end, lay in two four-inch lengths of tape 
 under the last few coils on the outside of the core, 
 leaving the ends hanging. Before winding back with 
 
 Fig. 42. Siemens-type Dynamo complete. 
 
 the next layer, bring the ends down over the first 
 layer, and thus secure the last few coils of the first 
 layer from slipping away under the pressure of the 
 next. If the ends of each layer are thus bound, 
 there will be no danger of the top layer sinking in 
 between the coils of that beneath it. 
 
 When all the wire has been wound on, tie the 
 free end to one of the coils, or to the core, with a 
 piece of stout twine. Serve the other field magnet 
 core in a similar manner, testing each layer for insula- 
 tion as the work proceeds ; then coat the outer wires 
 with a layer of sealing-wax varnish, and set them aside 
 to dry. As the cores of some forms of field magnets
 
 THE SIEMENS 
 
 37 
 
 are unprovided with flanges, this method of taping 
 just described will be found very convenient in pre- 
 venting slipping of the end coils; but flanges are 
 preferable where these can be introduced, as they 
 not only prevent slipping but also protect the coils 
 from possible injury. 
 
 The various parts having been prepared, they must 
 
 Fig. 43. Magnetising Field Magnets. 
 
 now be fitted together. It is well known that a straight 
 bar magnet has two opposite poles one at each end. 
 One of these is called the north pole of the magnet, 
 its opposite being the south pole. If now we bend the 
 bar in the shape of a horse-shoe, the two poles are 
 brought near each other, but they still preserve 
 their characteristic opposite polarities. 
 
 If we wind an insulated copper wire around a straight 
 bar of steel or of iron as in the left half of Fig. 43, and send 
 an electric current in the direction of the arrow, through 
 the wire, we shall find that the lower end N of the 
 
 434360
 
 -^ 
 
 38 DYNAMOS AND ELECTRIC MOTORS. 
 
 iron or steel bar has assumed a north magnetic polarity, 
 and at the same time its opposite end s has a south 
 magnetic polarity. If an iron bar be bent into the 
 shape of a horse-shoe with the wire on, it will 
 then resemble the two field magnets of Fig. 43, 
 with space between the legs in which the armature 
 may revolve. The two field magnets are wanted, 
 with a north pole on one side of the armature 
 and a south pole on the other side. As both of 
 the cores have been wound from the bottom or 
 channel end, it follows that if we send a current 
 through each separately in the same direction in which 
 they are wound, the two bottom cheeks would be 
 both north poles, and if we connected the finishing end 
 of one coil of wire with the commencing end of the 
 other, we should realise the same result ; but if we 
 connect together the two finish ends of the coils, as 
 shown at Fig. 43, and send a current from the left- 
 hand end to the right, it will enter at N, traverse 
 the coils in the direction shown by the arrow, leave 
 at s, cross over to the right-hand core, and traverse 
 its coils in the opposite direction, thus producing a 
 south pole at the bottom and a north pole at the top. 
 
 Connect one or two quart Bunsen or bichromate 
 cells to the coils, taking care to join the carbon of 
 the battery with N on the left, and the zinc of the 
 battery with s on the right. As the current in a 
 battery may be supposed to start from the zinc and 
 move through the liquid towards the other element, 
 we can by this means always ensure sending a current 
 in the right direction. When thus magnetised, the 
 field magnets may be connected together and the 
 machine fitted together. 
 
 The field magnets are fastened securely together by 
 the yoke at the top, but to ensure proper rigidity and 
 stability to the machine, they must also be firmly 
 secured to a thick, well-seasoned board of oak, teak, 
 walnut, or mahogany by short coach screws passing 
 through the lower outstanding flanges. This board
 
 THE SIEMENS DYNAMO. 39 
 
 may be trimmed at the edges, planed, and polished, 
 to ensure a finished appearance. The complete machine 
 is illustrated at Fig. 42, p. 36. 
 
 From the simplicity of its design, this type of 
 machine lends itself readily to illustrate how the wires 
 of a dynamo should be connected. Figs. 44 and 45 
 show two distinct methods of connecting the wires. The 
 
 Fig. 44. Diagram of Series 
 Connections. 
 
 Fig. 45. Diagram of Shunt 
 Connections. 
 
 method shown by the full lines at Fig. 44 is called con- 
 necting as a series machine that is, the field magnets, 
 the armature, and the outer circuit may be regarded as 
 three cells of a battery, and the whole connected up 
 one after the other in one circuit. No current can 
 pass through the field magnet coils until the outer 
 circuit is completed. When one end of the field 
 magnet wires is connected to the brush A, and the 
 other end to the brush B, as shown by dotted lines in 
 the diagram Fig, 44, the machine will be short-
 
 40 DYNAMOS AND ELECTRIC MOTORS. 
 
 circuited. But if we break one of the wires at c, 
 and take it to a binding-screw, then take the piece 
 hanging to B, and connect that to another binding- 
 screw as shown by the full lines, the two screws will 
 form the two poles of the machine, to which the 
 wires from the outer or working circuit must be 
 attached. This method of connecting the wires is only 
 suitable in special cases, as for working arc lamps. 
 
 Fig. 45 shows a method of connecting the machine 
 in shunt that is, only part of the current generated 
 in the machine passes through the coils of the field 
 magnets. The ends of the coils are then connected 
 with the two brushes, and these are both connected 
 with the binding-screws which form the terminal poles 
 of the machine. The circuit is now divided, part of 
 the current going through the work in the outer 
 circuit, and part going through the field magnet coils. 
 This is the method of connecting occasionally adopted 
 in dynamos intended for running incandescent electric 
 lamps, because the electro motive force generated is, 
 within certain limits, kept constant. Compound wind- 
 ing, a combination of the series and shunt, is, however, 
 better suited to this purpose. The letter references in 
 this Fig. correspond to those in Fig. 44.
 
 CHAPTER III 
 
 THE GRAMME DYNAMO. 
 
 IN 1871 a French electrician named Gramme in- 
 vented a dynamo in which he used as the armature a 
 ring of soft iron wires with insulated copper wire wound 
 
 Fig. 46. Gramme Dynamo Complete. 
 
 in sections over it. Although he was not the first to 
 use a ring armature made of iron, he was able to patent 
 this modification, which gave birth to the form of 
 armature since modified and altered in many different 
 ways, but still known as the Gramme ring. The 
 patent expired in 1884. 
 
 The many modifications of Gramme's iron ring, 
 including the Gramme ring itself, must, however, be 
 regarded as developments of a discovery made in 1860 
 by Dr. Antonio Pacinotti, Professor at the University of
 
 42 DYNAMOS AND ELECTRIC MOTORS. 
 
 Pisa, who found that he could make a most efficient 
 dynamo by employing as an armature an iron wheel 
 with sixteen cogs, and winding between the cogs 
 sixteen coils of insulated copper wire. Here, then, 
 was the first ring armature. 
 
 Some idea of the general appearance of a Gramme 
 dynamo will be gathered from Fig. 46, which represents 
 a small Gramme machine complete. 
 
 The carcase of the Gramme dynamo differs in form 
 
 Fig 1 . 47. Iron Carcase of Gramme Dynamo. 
 
 and structure from that of others. A general idea of 
 it is given in Fig. 47, where s, s, represent the iron 
 standards or supports ; c, c, c, c, the field magnet cores 
 without flanges ; and M, M, the pole pieces between which 
 the armature revolves. Soft iron castings can be cheaply 
 obtained, and as probably they will be received rough as 
 they come from the foundry, they must be put into shape 
 and fitted for use by the dynamo maker himself. The 
 first thing to be considered and taken in hand will be 
 the standards, one of which is shown at Fig. 48, fitted 
 with a bridge for the brush -holders. It will be seen, on 
 referring to Fig. 47, that each standard has two project- 
 ing lugs, one on each side. The uses of these are : in
 
 THE GRAMME DYNAMO. 43 
 
 one standard to hold the bolts which support the bridge 
 of the brush-holders, and in the other standard to hold 
 the terminals of the machine. The bridge for the brush- 
 rocker bearing may be one of the iron castings sent with 
 the carcase. This must be mounted on the face-plate 
 of a lathe, the boss bored to allow the spindle to pass 
 through, and turned on the outside to hold the rocker of 
 the brush-holder. In Fig. 48, the holes F, F, above and 
 below the bridge (marked R) are for the bolts of the 
 field magnet cores to pass through. It is essential that 
 
 Fig. 48. Inner Face of Standard with Bridge for 
 Brush-Holders. 
 
 the flanged ends of the cores should be in perfect 
 magnetic contact with the iron of the standards, so it 
 will be advisable to surface the rough iron within the 
 diameter of the core flanges shown in Fig. 49, to form 
 bearing surfaces for the bright ends of the turned core 
 flanges. The other standard must now be treated in a 
 similar manner, but in this the holes in the lugs will be 
 plugged with ebonite, to hold the terminals. Holes 
 must be bored in the feet of the standards, to receive 
 bolts for fastening the machine to a bench or to the floor. 
 The cross-shaped slots in each standard are intended to
 
 44 DYNAMOS AND ELECTRIC MOTORS. 
 
 hold the brass bearings, which are fitted into the lower 
 portion of the slot, and held in position by small 
 wedges. 
 
 The field magnet cores (Fig. 49) are best cast in 
 one with the cheeks, or pole pieces, and the flanges, 
 and with a wrought-iron bolt embedded at each end of 
 the casting with the threaded part projecting as shown. 
 Perfect contact is then ensured between all the parts, 
 and this is important in order to maintain magnetic 
 continuity between the pole pieces and the standards 
 which form their yokes. The outside faces of the 
 flanges should be turned true and bright, to ensure a 
 clean surface contact. Both cores with their pole pieces 
 
 Fig. 49. Magnet Core with Flanges and Pole Pieces. 
 
 may now be fitted to the standards, the ends of the 
 projecting pins screwed and fitted with nuts, and the 
 cheeks made to hang in line with each other. Then 
 bolt the cores and standards up tight, mark by small 
 nicks with a file on flanges and standard the positions 
 of each piece, and drill on each side of the core through 
 each flange |-in holes into the standards to the depth 
 of i in. Iron pins fitted in these holes and fixed in the 
 flanges, will form a guide in fitting the parts together 
 after the cores are wound with wire, and ensure that 
 the cores shall be placed in their right position. 
 
 The armatures of small Gramme machines are not 
 now made of iron wire, as in the original machines. 
 They are now built up of rings of sheet-iron, shaped 
 as shown at Fig. 50, with a number of cogs on the 
 periphery of each ring. It will thus be seen that the
 
 THE GRAMME DYNAMO. 45 
 
 armature is practically a Pacinotti ring armature. The 
 number of cogs and intermediary spaces are arranged on 
 each machine to suit the designer, and may be any even 
 number, such as ten, twelve, fourteen, sixteen, and so on. 
 In the small machine shown, the number is ten, and 
 the laminations range in thickness from fourteen to 
 twenty-five to the inch. The method of building 
 up is as follows : small holes are drilled through 
 alternate cogs of each lamination, as shown at Fig. 50. 
 
 Fig. 50. Laminated Iron Punching for Ring Armature. 
 
 These holes may be \ in. or f in. in diameter, but they 
 must exactly coincide with each other through the whole 
 number of plates, as they have to admit rods on which 
 the laminated plates are strung. The rods should be 
 of a material of high electrical resistance, to avoid 
 eddy currents in the armature when at work Both 
 ends of each rod may be threaded, and fitted with 
 suitable hexagonal nuts. Ebonite bushes and washers 
 should be placed between the nuts and the armature 
 spiders and plates. 
 
 The plates may next be coated with good tough
 
 4 6 
 
 DYNAMOS AND ELECTRIC MOTORS. 
 
 varnish, such as Japan or Brunswick black, and set aside 
 until the varnish is dry and firm. They are then strung 
 on the rods, and all bolted securely together to form 
 one continuous wide ring. This ring must now be 
 mounted on a support, which in turn has to be fixed to 
 the spindle, whilst space must be left between them for 
 winding the coils of wire. This support, or spider, may be 
 of brass or of gun-metal, and is generally sold with the 
 other castings. One with five spokes, to suit a ten-cogged 
 
 Fig. 51. Spider for Laminated Ring Armature. 
 
 armature, is shown at Fig. 51. Each arm must have a 
 hole drilled in it as shown, to fit the ends of the rods 
 running through the armature plates. The hole in the 
 centre must also be bored true to fit the spindle, and a 
 key- way cut as shown. When bolting these spiders to the 
 armature, care should be taken to tighten all the nuts 
 gradually, and so bring the plates and spiders together 
 without straining the threads. This done, the surplus 
 thread should be cut off, the ends of the rods 
 rounded, and each nut secured with a touch of soft 
 solder. 
 
 In preparing the armature each space between the
 
 THE GRAMME DYNAMO. 47 
 
 cogs will be filled with a coil of wire, wound by 
 passing one end of it through the space between 
 the arms of the supporting spider and around the 
 combined thickness of the laminations, as shown at 
 Fig. 52. As the space inside is slightly less than that 
 between the cogs there is a danger of the inner part of 
 one coil encroaching on the wire space of its neighbour. 
 To prevent this, wooden guides may be employed, fixed 
 between the cogs on the outside, and secured to other 
 wooden guides inside the armature by suitable screws 
 
 Fig. 52. Portion of Ring Armature ready for Winding. 
 
 passing through the ends, as shown at Fig. 52, and 
 also in section at A B, A B, Fig. 50. These effectually 
 prevent slipping of the wire coils whilst the wire is being 
 wound on, and can be moved from one space to another 
 as the work proceeds. 
 
 Before ; preparing the spindle for the armature, 
 it will be advisable to fit the bearings in their 
 places in the standards. These should be fitted in the 
 lower part of the crosses in the standards; the 
 cross-slit receives an iron plate, fixed in with 
 wedges, to hold the bearings down, and the 
 upper part of the cross forms a space for the 
 lubricator. The stem of this lubricator is screwed to fit 
 a hole in the wedge-plate, and the oil is conducted
 
 48 DYNAMOS AND ELECTRIC MOTORS. 
 
 through a hole in the upper half of the bearings, which 
 are turned true, and fixed securely. 
 
 The spindle should be made of mild steel, of a size 
 and length suitable to the machine in hand, and turned 
 to the shape shown at Fig. 53. The left-hand end from 
 A to B will run in the left-hand bearing of the machine, 
 shown at Fig. 46 (p. 41), and carry the driving-pulley. 
 The two shoulders at B and c are for the bearing and the 
 boss of the armature spider respectively : At D and E 
 holes must be drilled through the shaft and fitted with 
 pins, which project and fit the key-ways left in the 
 spiders, and thus prevent the armature from turning 
 round on the spindle. The space between E and the 
 screwed part at s will be occupied by the commutator ; 
 
 Fi. 53. Armature Spindle of Gramme Armature. 
 
 the remainder of the spindle will run in the right-hand 
 bearing, Fig. 46. 
 
 A hexagonal nut must be fitted on the thread at s 
 to bring the commutator and the spiders of the arma- 
 ture in close contact with each other. The spindle 
 being prepared, next mount the armature on it, put the 
 spindle into its place, and spin it round to see that 
 every part runs true, as now will be the time to make 
 any alteration required. This done, with a half-inch 
 square file trim off any roughness which may appear 
 on or between the armature cogs, so as to make the 
 whole smooth. If the cogs do not properly clear the 
 pole-pieces, the projecting parts may be trimmed off in 
 a lathe. The spaces between the cogs should now be 
 coated with varnish and the armature set aside to dry, 
 preparatory to being wound with wire. 
 
 The commutator is furnished with several seg- 
 ments, corresponding in number with the coils on the
 
 THE GRAMME DYNAMO. 
 
 49 
 
 armature. Fig. 54 gives a general idea of its appear- 
 ance when finished, whilst Figs. 55 and 56 show how it 
 is constructed. In the centre of a piece of well- 
 seasoned boxwood, large enough to turn out a solid hub 
 
 Fig. 54. Commutator for Ring Armature complete. 
 
 of not less than 2 in. in length and 3 in. in diameter, 
 bore a hole to fit the armature spindle. On this 
 cylinder of boxwood mount the bars of the commu- 
 tator, as shown in Fig. 54. It would be possible to 
 
 Fig. 55. How to divide 
 Commutator Ring. 
 
 Fig. 56. How to insulate 
 Commutator Segments. 
 
 cut out these bars one by one from a sheet of hard 
 brass, and fit each to the outside of the cylinder ; but 
 the commutators of small dynamos may be built up by 
 a more convenient and accurate method. Procure a 
 piece of gun-metal tube, with sides quite \ in. thick, 
 and of a diameter large enough to fit over the box-wood 
 hub, after a light boring cut ha? been taken through the
 
 50 DYNAMOS AND ELECTRIC MOTORS. 
 
 inside to render it smooth. Cut off a piece of the tube 
 long enough to cover the hub, and fit it tightly on. 
 Now divide the ring into as many equal-sized sections 
 as there are cogs on the armature. If there are ten 
 cogs have ten sections, if fourteen cogs have fourteen 
 sections, but each section must be equal, so as to form a 
 series of equal-sized bars all round the hub. The 
 division lines should be deeply marked with a sharp steel 
 scriber, and then nicked with a hack-saw, as shown at 
 Fig. 55. Next drill a small hole through each end of 
 each section and into the hub beneath ; countersink the 
 mouth of each hole, and drive a short brass screw into 
 each, as shown in Fig. 55. This done all round, with 
 a saw separate each section from its neighbour, and 
 allow the saw to enter the boxwood hub to the depth of 
 nearly \ in., to form a hold for the insulating substance 
 to be placed between each section. The insulating sub- 
 stance may be either vulcanised fibre or asbestos mill- 
 board. Procure some sheet fibre or millboard, a trifle 
 thicker than the saw-cut divisions, and from it cut slips 
 large enough to fill the cuts exactly, as shown by the 
 thick black lines at Fig. 56. 
 
 Slightly ease the screws of each section, wedge the 
 prepared insulating strips firmly into each saw-cut, then 
 tighten the screws again, and so pinch each strip tightly 
 on each side between the edges of the sections. When 
 this is done, mount the hub in a lathe, and true up all 
 rough projecting parts with a sharp tool, or with a rough 
 file at first and then with a smoother file. 
 
 Each segment of the commutator will have to be 
 connected to the ends of two coils of wire, and the best 
 means of making a connection is in the following 
 manner : Choose either end of the commutator to go 
 next the armature, and in the extreme end of each section 
 drill a -^ in. hole, and tap each hole to receive a 
 screw. Next take a length of No. 12 S.W.G. hard copper 
 wire, and cut it up into two-inch lengths. Flatten one end 
 of each length as shown at Fig. 57, and screw the other 
 ends to go into the tapped holes made to receive them.
 
 THE GRAMME DYNAMO. 51 
 
 Tin the screwed ends of each connector with solder, 
 and as they arc done screw them into their places, 
 giving each a touch with the soldering-bit to make the 
 solder run, and fix the connector firmly in its place. 
 
 A disc of vulcanised fibre, slightly larger in diameter 
 than the commutator, should now be turned out 
 of a piece of |-in. sheet fibre. This must be placed 
 between the end of the commutator and the arms of the 
 armature spider, to ensure the complete insulation of 
 the one from the other when they are tightened up 
 on the spindle. 
 
 Before winding the wire on the armature, calculate 
 how much will be needed for all the coils, and divide 
 this quantity equally among them, to ensure each coil 
 
 Fig. 57. Copper Connector for Ends of Armature Coils. 
 
 having the same resistance. A table at the end of this 
 chapter gives particulars suitable to each size of arma- 
 ture. In this table only three sizes are specified : 
 namely, Nos. 16, 20, and 22 s.w.G. By remembering that 
 No. 1C cotton-covered copper wire runs about 25 yards 
 in the lb., No. 20 runs 80 yards in the lb., and No. 22 
 runs 120 yards in the lb., we can easily calculate the 
 length of wire for eacli coil by multiplying the number 
 of yards per lb. by the number of Ibs. to be used, and 
 dividing this by the number of coils to be placed on the 
 armature. For instance, supposing we have to use 4 Ibs. 
 of No. 20 S.W.G. on an armature with 10 divisions : 4 X 80 
 = 320 ; and this, divided by 10 (the number of divisions), 
 will give 32 yards to each division. Measure off the 
 length for each coil, and roll the wire up into hanks, con- 
 taining one coil in each hank. Place each hank in a 
 vessel containing hot melted paraffin, and let it soak 
 for several minutes, then hang it up to drain dry. 
 
 Next make a shuttle of tough hard wood, to
 
 S 2 DVXAMOS AND ELECTRIC MOTORS. 
 
 the shape shown at Fig. 58. This shuttle may be 
 9 in. in length, and of a width suitable to the size 
 of the spaces through which it has to pass ; the gaps 
 in the ends must also be cut large enough to take 
 the whole coil of wire, and this Avill vary with the 
 size of the armature to be wound. The shuttle for the 
 smallest on the list (on page 59) should measure 9 in. 
 X 1 in. X i in., and should have gaps | in. deep by jj in. 
 in width. All edges must be rounded and made quite 
 smooth, to prevent chafing of the cotton or silk cover- 
 ing whilst winding the coil. This shuttle must now be 
 neatly wound with one of the coils of wire, and then 
 we are ready for transferring it to the armature. 
 
 Fig. 58. Wooden Shuttle for winding Armatures. 
 
 This is a two-handed job, and it is necessary to have 
 a helper whilst doing it. The armature ring may be held. 
 on a low trestle between the winder and his assistant. 
 Examine the edges of the spaces between the cogs and 
 inside the ring, to detect any rough places likely to 
 abrade the wire covering. If any of these appear, do not 
 file them down for in so doing the dried coat of shellac 
 varnish would be injured but cover them with short 
 pieces of broad tape, stuck on after being well soaked in 
 hot paraffin wax. 
 
 Begin winding on the left-hand side of one of the 
 spaces, next to an arm of the spider. Wrap a few turns 
 of the outside end of the wire around the arm of the 
 spider, just to hold it in its place, pass the shuttle to the 
 assistant over the armature, and get him to pass it back 
 through the ring ; lay the coil up close to the left-hand 
 cog, and draw it moderately tight ; then pass the shuttle 
 over again to the assistant, who will return it through as 
 before (see Fig. 52). Thus proceed, laying each coil close
 
 THE GRAMME DryA.\ro. 53 
 
 against the one preceding it, until the space between 
 the two cogs has been covered by one layer. Then 
 wind back from right to left until this layer has been 
 closely and regularly ^covered with another layer. If 
 using large wire, such as No. 20 or No. 16, there will be 
 a tendency on the part of each coil to bulge in the 
 centre of the space. This bulging must be kept down 
 from the start by gently tapping the bulging part 
 (whilst tightening the coil) with a small wooden 
 mallet, or by placing a piece of wood on the wire, 
 and striking the wood with a hammer. The wire 
 must be kept level and compact in the outside 
 space, but in the inside this may be disregarded. 
 Whilst winding the coil test it frequently for insulation, 
 and make good each fault before going on further, 
 for leakage here will destroy the efficiency of the 
 machine. When the first coil has been wound, leaving 
 the wire ending on the side of the space opposite to 
 that where it commenced, and with enough projecting 
 to reach the commutator, fasten down the wire and coat 
 the outside of the coil with some quick-drying varnish. 
 Remove the guiding pieces of wood (shown in Fig. 52, 
 p. 47), and coat the inside coils with varnish in a similar 
 manner. This will help to fix the wire in its proper 
 position, and also secure better insulation of one coil 
 from its neighbour. The whole wire should now receive 
 one or two coats of varnish, the commencing end of each 
 coil being also painted with a distinctive colour to 
 facilitate its recognition when connecting the ends to 
 the commutator bars. 
 
 When the varnish is dry and hard, the armature may 
 be mounted on the spindle. The commutator must 
 be forced on tight in its place, and fixed close to the 
 fibre washer by screwing up the nuts on the threaded 
 end of the spindle. It is well to have two nuts, one 
 to lock the other and prevent the parts from shaking 
 loose. The coils may now be connected to the com- 
 mutator bars by soldering the commencing end of 
 one coil and the finishing end of its neighbour to it*
 
 54 DYNAMOS AND ELECTRIC MOTORS. 
 
 connector, as shown at Fig. 59. It will be found con- 
 venient to bare the ends of the wires and clean them, 
 then to twist the end of one coil round the commence- 
 ment of another, so as to form a clip on each side of the 
 connector, and then to tin this twisted part with the 
 soldering-bit before soldering to the connector. 
 
 When a small armature is tightly wound with a 
 coil of fine wire covered with some two or three coats 
 of varnish, the whole should hold well together. But 
 there is always a danger of disruption, owing to the 
 
 "Fig. 59. Connection of Armature Coils to Commutator. 
 
 immense centrifugal stress, when whirled round at from 
 2,000 to 3,000 revolutions per minute, and a wire thrown 
 out would entail disastrous consequences when the 
 coils revolve close to the pole-pieces. It will be well, 
 therefore, to bind the middle of the armature coils with 
 several coils of tarred tape, so as to form a hoop, and 
 to wind tightly over this a length of No. 24 s.w.o. 
 phosphor-bronze wire, laid evenly side by side, for a 
 distance of about a ^ in. in width. The ends of the 
 wire must be twisted together and soldered, using resin 
 only as a flux ; and it will also be advisable to solder
 
 THE GRAMME DYNAMO. 55 
 
 the whole layer of wires together here and there, where 
 they pass over the cogs of the armature. 
 
 The brush-holders and brushes for this type of 
 machine are not fixed to the bearings or to the pillars, 
 as is done in the small Siemens machine ; they are 
 made in the form of a rocker, pivoted on a bridge 
 attached to one of the standards, as shown at Fig. 48 
 (p. 43), and are therefore free to be moved round the 
 commutator as desired. The rocker is often an iron 
 casting, shaped as shown at Fig. 60. The large hole 
 in the centre is turned to fit loosely on the boss of 
 the bridge shown at Fig. 48. A hole is drilled and 
 
 c 
 Fig. 60. Rocker for Brush-Holder. 
 
 tapped in the crown, as shown at c, Fig. 60, to receive 
 a set-screw which is used to fix the rocker in any 
 required position. Two in. holes, B, B, are drilled 
 through the rocker, these holes are plugged with ebonite, 
 and through each plug a \ in. hole is drilled to receive 
 the screwed ends of the brass spindles, s, s, which carry 
 the brush clamps, c, Fig. 61. The spindles may be made 
 of | in. brass rod, and the outer ends should come 
 within \ in. of the inner edge of the commutator. 
 The inner ends must be turned down to go through 
 the ebonite plugs in the rocker, and screwed to take 
 a hexagonal nut on each side of the rocker, as shown 
 at A, A, Fig. 61. These nuts must be insulated from 
 the rocker by washers of ebonite or of vulcanised fibre. 
 The opposite ends of the spindles must be fitted with 
 two more hexagonal nuts to hold the brush clamps ; 
 these are of gun metal, shaped as shown in Fig. G2. The
 
 56 Dm AMOS AND ELECTRIC MOTORS. 
 
 upper part of this clamp is formed to receive the brushes, 
 which are made of strips of hard brass, copper gauze, 
 phosphor bronze, or whatever material may be chosen. 
 The strips are held by a brass plate placed on top of 
 them, and secured by the thumb-screw d. Holes are 
 bored in the lower part, as shown at e, e, for the spindle 
 to pass through. The clamp being thus free to move 
 around the spindle, together with the movement of the 
 
 Fig. 62. Clamp for holding 
 Brushes. 
 
 Fig. 61. Brush-holder 
 and Rocker complete. 
 
 rocker, allows the brushes to be adjusted to any re- 
 quired angle. A small brass staple soldered to the 
 inside of each clamp receives the end of a spiral spring 
 threaded on the spindle, and this ensures due pressure 
 of the brushes on the commutator, whilst it also keeps 
 the clamp in its proper position at the end of the spindle. 
 In adjusting the .brushes it is found advisable to move 
 the rocker by means of an insulated handle made of 
 ebonite or vulcanite, as shown at one end in Fig. 61. The 
 handle may be attached by screwing it on a short stud
 
 THE GRAMME DVXA.MO. 
 
 57 
 
 fixed in the end of the rocker. A similar handle may be 
 fixed at the other end if desired. 
 
 In the field magnets of a Gramme machine the wire 
 will be wound in four separate coils, so it will be ad- 
 visable to divide the total quantity of wire to be used 
 into four equal parts, and to treat each part as recom- 
 mended in the case of the wire for the armature. 
 
 Fig. 63. Winding Field Ma^nete of Gramme Dynamo. 
 
 After each coil of wire has been soaked in paraffin- 
 wax, it should be wound on a stout wooden bobbin, 
 as it will run off more easily from a bobbin than 
 from a hank. The method of winding so as to secure 
 a north pole piece above the armature and a south pole 
 piece below the armature is shown at Fig. 63. 
 
 Mount the core to be wound in a lathe geared 
 to slow speed. Twist one end of the wire A round the 
 core, cross it over the pole piece, take one turn round
 
 58 DYNAMOS AND ELECTRIC MOTORS. 
 
 its own core, and tie this turn with a short piece of 
 twine. Then proceed to wind on the wire evenly and 
 regularly, with the coils close side by side, from the 
 pole piece on the right to the end of the core at the 
 left, to and fro, until all the wire has been wound on ; 
 then tie the last coils together tightly with a piece of 
 narrow tape to prevent them from springing loose when 
 the end E is free. Next unfasten A from the right-hand 
 
 Fig. 64. Connecting Fields in Series and in Shunt. 
 
 core, and commence winding on the next coil, beginning 
 at B and winding from left to right, observing the same 
 precautions as in the first coil, finishing off the opposite 
 end at H. Next, wind the cores for the lower pole piece, 
 commencing each at c and D respectively, and finishing 
 off at F and i. If the fields are to be connected in 
 series, the two ends E and F will now be led to the two 
 terminal binding-screws, and the two ends H and i to 
 the two brushes ; whilst A will be coupled to B, and 
 c to D by screw connectors, as shown by full lines in 
 Fig. 64. If the fields are to be connected in shunt, the 
 two ends E and F will be connected together to form
 
 THE GRAMME DYNAMO. 
 
 59 
 
 a continuous coil from H to I. These two ends only will 
 be connected to the brushes, and from the brashes two 
 short pieces of wire will go to each terminal The dotted 
 lines in Fig. 64 show this more clearly. When the two 
 finishing ends of the left-hand coils are connected to the 
 two terminals A, A, and the two finishing ends of the right- 
 hand coils are connected to the brushes B, B, the circuit 
 can only be completed through the external circuit in 
 series with the coils and joining the terminals. But 
 when the two ends of the left-hand coils are coupled 
 direct, as shown at c, and the brushes are connected 
 with the terminals, as shown by the dotted lines, the 
 current is shunted through the coils, and when the 
 machine is running the cores are always magnetised. 
 The cores must be charged with initial magnetism, 
 given by a battery sending a current through the coils, 
 as explained on page 38. 
 
 The dimensions of the various parts have cot been 
 mentioned in the general instructions which are applic- 
 able to several sizes of machines. All parts are, how- 
 ever, made proportionate to the size of the castings, and 
 the vendor of these will also supply the various parts in 
 the rough at a less cost than would be incurred by 
 making patterns and having the parts cast to order. The 
 following list of Gramme machines gives the dimen- 
 sions of various parts and the output to be obtained. 
 
 TABLE OF GRAMME DYNAMOS. 
 
 
 
 ArXSfr,. 
 
 Double cotton 
 
 Wire on 
 Armature, 
 
 A'-v-,<. p^r 
 Minute. 
 
 Power Dneloped. 
 
 
 
 Miil/nett. 
 
 
 
 
 
 Diam. Depth. 
 
 Lbs. 
 
 .wo 
 
 Ux. 
 
 S.WO 
 
 
 C.P. 
 
 Aros. 
 
 Vita 
 
 UX2 
 
 3 X 2 
 
 6 
 
 22 
 
 5 
 
 22 
 
 2,500 
 
 30 
 
 3 
 
 40 
 
 2X3J 
 
 4g X 2^ 
 
 10 
 
 22 
 
 4 
 
 20 
 
 2,000 
 
 65 
 
 5 
 
 50 
 
 3X6 
 
 0X6 
 
 20 
 
 20 
 
 4 
 
 16 
 
 1,500 
 
 150 
 
 10 
 
 55 
 
 4X7 
 
 7 X 10 
 
 90 
 
 16 
 
 12 
 
 16 
 
 1,200 
 
 450 
 
 90 
 
 55 
 
 The various parts of the machine may now be 
 assembled. The field magnet coils should have two 
 or three coats of varnish to cement the wire together,
 
 6o 
 
 DYNAMOS AND ELECTRIC MOTORS. 
 
 and to give the whole a finished appearance. In ad- 
 justing the brushes, move the rocker until by actual 
 trial the best position is found. This position is indi- 
 cated when with a full current at the terminals there is 
 very little noise at the brushes, and little or no sparking 
 where the brushes touch the bars of the commutator. 
 
 Machine No. 1 has a solid cogged armature ; all the 
 others are built up of cogged laminated plates. The 
 armature of No. 4 has two strands of No. 16, used 
 side by side to carry the current in the armature coils. 
 
 The following table will help in determining the 
 horse-power needed to drive Gramme dynamos : 
 
 A T os. 
 
 Watts. 
 
 C.P. 
 
 H.P. Required. 
 
 1 
 
 120 
 
 30 
 
 I to I 
 
 2 
 
 250 
 
 65 
 
 ito 
 
 3 
 
 550 
 
 140 
 
 1 
 
 4 
 
 1,650 
 
 430 
 
 2*
 
 CHAPTER IV. 
 
 THE MANCHESTER DYNAMO. 
 
 THE Manchester dynamo shown at Fig. 65 (introduced by 
 Messrs. Mather and Platt, of Salford, Manchester) 
 
 Fig. 63. Manchester Dynamo complete. 
 
 now claims our attention. In point of simplicity in 
 construction and in usefulness it is superior to the 
 Siemens and Gramme machines already described.
 
 63 DYNAMOS AND ELECTRIC MOTORS. 
 
 The carcase of a Manchester dynamo may be 
 made up from four castings. These consist of the bed- 
 plate and bottom pole piece in one casting, and the 
 top pole piece and yoke also in one casting, and the two 
 cores. The whole arrangement is shown in section at 
 Fig. G6, where A represents the top pole piece. B 
 the lower pole piece, and c, c, the two cores. From 
 this illustration it will be seen that the two cores form 
 pillars to support the upper pole piece and yoke. 
 The cores should have threaded pins of wrought-iron 
 
 Fig. 66. Section of Manchester Dynamo, showing 
 winding of Field Magnet Cores. 
 
 cast in each end. These pins pass through holes drilled 
 in the top yoke and the bottom bed-plate, and the cores 
 are securely fastened to those parts by nuts fitted to the 
 screwed pins. 
 
 The cores and pole pieces of all dynamos should be 
 made of the best soft iron, the cores being fitted with 
 flanges. These flange ends, together with a corresponding 
 round area on the yoke and bed-plate, should be turned 
 bright and fitted close together. This is done before 
 the cores are wound with wire, so it will be much easier 
 to wind them thus made up in the form of bobbins ; the 
 wire will be protected from injury whilst bolting the 
 parts of the machine together, and tne magnetic con- 
 nection between the cores and pole pieces will be 
 good.
 
 THE MANCHESTER DYNAMO. 63 
 
 When .cores are not thus flanged] it frequently 
 happens that whilst bolting the parts together the iron 
 of the upper pole piece or yoke is forced into electric 
 connection with some of the coils of wire, and this alone 
 is the cause of some failures with this class of machine. 
 The difference in magnetic intensity of the field is often 
 most marked when cores are thus carefully brought into 
 cloae connection with the pole pieces. As the efficiency 
 of the machine depends largely upon its field magnets, 
 this point should not be neglected. : 
 
 Figs. 67, 68, and 69 show how the flanges may be 
 put on ; Fig. 67 shows the core as in general use ; and 
 Fig. 68 the same core with a light fillet cut in a lathe, 
 
 Fig. 67. Fig. 68. Fig. 69. 
 
 Fig. 67. Magnet Core for Manchester Dynamo. 
 
 Fig. 68. Core with Fillets to receive Flanges. 
 
 Fig. 69. Core Fitted with Iron Flanges. 
 
 on each end. This core must fit the hole in a wrought- 
 iron collar or washer when the collar is hot, and when 
 cold the collar will be firmly fixed. Fig. 69 shows the 
 collars shrunk on the core and turned up bright. The 
 field magnet cores may be wound with wire in the same 
 manner as those of the Gramme machine ; that is, so as 
 to make the top a north pole and the bottom a south 
 pole, as described in Chapter III., where the method of 
 connecting the ends is also given. 
 
 The ring or the H-girder forms of either solid or 
 laminated armatures may be easily adapted to the Man- 
 chester field. In some of these machines Pacinotti cogged 
 armatures are employed ; in some others the Gramme 
 ring. For small armatures the H form is convenient, and 
 will be most efficient when built up of laminated plates, as 
 shown at Fig. 10 (p. 16). When armatures of the Gramme 
 or Pacinotti type are used, it will be necessary to build
 
 6 4 
 
 DYNAMOS AND ELECTRIC MOTORS. 
 
 up the commutator as described in the last chapter for a 
 Gramme machine, because we must have a commutator 
 with several sections to receive the ends of the armature 
 coils. But when the H -girder form of armature is 
 chosen, we must also select the two-part commutator 
 used in the Siemens machine, and illustrated at Figs. 
 33, 34, 35 (pages 29 and 30). 
 
 The massive and broad cast-iron bed-plate carries 
 the bearings on each side of the pole pieces, and these 
 are set wide enough apart to admit a long armature 
 spindle. We have therefore room enough for a rocker 
 arrangement and adjustable brush-holders such as those 
 shown at Figs. GO, 61, 62 (pages 55 and 5G). The rocker 
 works on a gun-metal sleeve fixed to the inside of one 
 of the brackets. The brushes are best made of copper 
 wire gauze soldered to thin strips of sheet copper. Con- 
 nections between them and the wires should be made 
 as directed for the Gramme machine. 
 
 The instructions for winding the armature and all 
 other necessary particulars in the chapters on the 
 Siemens and Gramme machines apply equally to 
 a machine with field magnets of the Manchester type, 
 and, indeed, to all others. 
 
 The following table gives particulars of Manchestei 
 dynamos of various sizes. 
 
 LIST OF MANCHESTER TYPE DYNAMOS. 
 
 Size 
 of Cores. 
 Inches. 
 
 Armature. 
 Inches. 
 
 Wire on 
 F.M.'s. 
 
 Wire on 
 Armature. 
 
 Output obtainable. 
 
 Revs, j 
 per j 
 Min. ; 
 
 Diam.Lgtb 
 
 Diara.Lgth. 
 
 Lbs. 
 
 s.w.o. 
 
 Lbs. 
 
 s.w.a. 
 
 Volts. 
 
 Amps. 
 
 C.P. 
 
 
 ix 4 
 
 3iX 2 
 
 6 
 
 22 
 
 U 
 
 22 
 
 40 
 
 3 
 
 30 
 
 2.500 1 
 
 2* X 6|- 
 
 4iX2 
 
 10 
 
 22 
 
 4 
 
 20 
 
 50 
 
 5 
 
 65 
 
 2,000- 
 
 3 X7i 
 
 6X6 
 
 20 
 
 20 
 
 4 
 
 16 
 
 50 
 
 10 
 
 125 
 
 1,500' 
 
 4 X 10 
 
 7X7 
 
 90 
 
 16 
 
 12 
 
 16 
 
 50 
 
 30 
 
 400 
 
 1,200- 
 
 All the above machines are intended to have* 
 laminated cogged ring armatures. That the last i*
 
 THE MANCHESTER DYNAMO. 65 
 
 to be wound with two strands of No. 16 wire run side 
 by side, and wound on together. This is found more 
 convenient for winding than a coarser wire, and the 
 effects obtained are equally good. After winding on two 
 strands in this way, the ends should be bared, twisted 
 together, and soldered, before fastening them to the 
 commutator bars. Large machines are furnished with 
 Gramme armatures, often wound with forty or more coils 
 of wire. The small machines have fewer coils on 
 their armatures. Some large machines have also 
 compound wound field magnets that is, the cores are 
 wound with two sizes of wire, the smaller connected 
 in shunt with the armature, the larger being in series 
 with the armature winding and outer circuit. In the 
 small machines above described, the field magnet coils 
 should be connected in shunt with the armature. In 
 making arrangements for connecting the machine with 
 the outer circuit, it will be advisable to mount a slab 
 of polished mahogany or other hard wood on the top of 
 the dynamo, as shown in section at D, Fig. 66, and screw 
 the terminals into the wooden slab as shown.
 
 66 
 
 CHAPTER V. 
 
 THE SIMPLEX DYNAMO. 
 
 Tui3 chapter will describe the construction of a small 
 dynamo, or motor, made almost entirely of wrought- 
 iron forgings, which can be obtained from any smith or 
 made by the dynamo maker himself. 
 
 This machine generates a current of 5 amperes at a 
 pressure of 10 volts; and is about capable of lighting 
 two 8 candle-power lamps when used as a dynamo, 
 and, being shunt-wound, is also suitable for charging 
 storage batteries. When used as a motor, running at 
 about 2,500 revolutions per minute, its power will be 
 about 1*5 h.-p. The current required will be about 
 5 amperes at 15 volts. 
 
 To drive this machine about i horse-power would 
 be required. An engine to develop this horse-power 
 would have the following dimensions : Cylinder, 2 in. 
 bore, 2 in. stroke ; revolutions of fly wheel, 200 per 
 minute ; boiler about 18 in. by 9 in. ; pressure, 20 Ibs. 
 on square inch. 
 
 The armature is of the old Gramme ring type, 
 constructed of soft iron wires over-wound with 
 insulated copper wires. About l Ib. of No. 20 to 
 24 S.W.G. iron wire will be required, and also a circular 
 wooden mandrel, or former, of shape and dimensions 
 shown in Fig. 70. This former should be turned from 
 hard wood, with one of the flanges or cheeks removable, 
 so that the iron ring when completed may be slipped 
 off ; for the same purpose the former should be covered 
 with a layer of smooth paper, the edges of which 
 may be held in place with sealing-wax. To wind 
 on the iron wire, the former should either be mounted 
 between the centres of a lathe, or a pin should be driven
 
 THE SIMPLEX DYNAMO. 67 
 
 into the centre of each end, and the former mounted 
 between two wooden supports, as shown in Fig. 70. 
 The wire should be wound upon the former in even 
 layers, with a coat of shellac varnish between every two 
 layers, until the outside diameter of the ring is 2| in.; 
 the thickness of the core will then be about f in. 
 The whole surface of the armature should be coated 
 with shellac varnish, and the armature and former 
 placed in a hot oven until the shellac melts and binds 
 the iron wires together. When cool, the removable 
 cheek may be unscrewed, and the armature should 
 then slip off the former easily. The armature should 
 then be insulated by entirely covering it with silk tape, 
 
 Fig. 70. Mandrel or Former for making Core of Arma- 
 ture of Simplex Dynamo. 
 
 the edges of which must overlap, and the surface then 
 coated with shellac varnish. When dry, the winding of 
 the armature may be proceeded with. It is not essential 
 for the iron wire of the armature coil to be in one 
 continuous hank or coil ; the core may be built up of a 
 number of hanks, provided that the length of wire con- 
 tained in each is considerable, and that each added 
 piece is properly joined to the wire last wound. To 
 join the wires, twist the ends together, coil the joint 
 upon the layers of wire previously wound, and coat 
 with shellac varnish. When this is hard, file the joint 
 down level with a smooth file, again varnish, and pro- 
 ceed with the winding. 
 
 The armature is completely overwound with three 
 layers of No. 20 s.w.o. double cotton-covered copper 
 wire divided into twenty sections or coils, each section
 
 68 DYNAMOS AND ELECTRIC MOTORS. 
 
 having twenty-four turns of wire, the whole weigh- 
 ing about f Ib. Before proceeding to wind on the 
 wire, the armature should be firmly fixed to a bench 
 or table by passing a strip of hard wood through the 
 interior and fastening the strip to the bench by screw- 
 ing in the manner shown in Fig. 71. For the purpose 
 
 Fig. 71. Clamp for Armature Core. 
 
 of facilitating the winding and also to keep the arma- 
 ture properly balanced, it is best to divide the 
 armature with a pair of compasses into a number ot 
 equal parts, and to treat each part separately. Thus, if 
 the armature is divided into four parts, five sections 
 will be allotted to each part, and the coils can be 
 arranged so as to fill the spaces allotted to them. A 
 sufficient length of wire to reach twenty-four times 
 around the armature, with about one foot over for con- 
 nections, etc., having been cut off, one end is fastened to 
 the hardwood strip, as shown in Fig. 71, and the wire is 
 
 Fig. 72. Method of winding Ring Armature. 
 
 then carried over the top of the armature and threaded 
 through the inside, and pulled tight. This is repeated 
 three times ; the last inside turn rests upon the two 
 wires previously wound, as represented at A, Fig. 72. The
 
 THE SIMPLEX DYKAMO. 69 
 
 wire is thus wound alternately upon the interior surface 
 of the armature and upon the preceding turns until 
 eight turns have been completed, when the wire is tem- 
 porarily fastened to the hardwood strip until the next 
 layer is commenced. 
 
 The second section is commenced and ended in 
 the same way, and the winding proceeds thus until 
 about five or six sections have been wound upon the 
 armature. The outside wire should be beaten down flat 
 with a small wooden mallet, and the wires on the inside 
 surface should be pressed with a wooden rod for the 
 same purpose. A coat of shellac varnish should then 
 be applied to the wires, and when this becomes hard 
 the second layer is proceeded with in exactly the 
 same way as the first layer, with the exception that 
 
 Fig. 73. Wooden Plug for Armature. 
 
 the wires on the inner surface of the armature are 
 arranged between those already wound, as repre- 
 sented in Fig. 72, where the white circles show the 
 first layer, and the black circles the second layer. 
 When this second layer is completed, the first layer 
 on the second portion of the armature may be com- 
 menced, and when two layers have been wound upon 
 half of the armature, the third layer may be wound 
 on in exactly the same way as the first layer. 
 
 After this third layer is completed, the ends of the 
 sections may be permanently coupled up by cleaning, 
 twisting, and soldering the adjacent ends of the sec- 
 tions together, the finishing end of one section being 
 connected to the commencing end of the next section, as 
 shown at B, Fig. 72. The whole armature should then 
 be coated with shellac varnish. A hardwood plug
 
 jo DYNAMOS AND ELECTRIC MOTORS. 
 
 (Fig. 73) is next made, through this a spindle of \ in. 
 steel is driven tight, and the plug is then driven tight 
 into the armature. The armature should now revolve 
 truly upon the spindle, and to prevent the wires from 
 bulging out when the armature is revolving use binding- 
 wires consisting of two bands each of twelve strands 
 of No. 36 S.W.G. copper or brass wire wound upon two 
 -in. strips of thin mica or paper and soldered together 
 so as to form solid bands. When these are completed 
 the armature may be connected to the commutator. 
 
 The commutator consists of a brass washer, 2 in. is 
 diam. and about % in. thick, with twenty countersunk 
 holes drilled at equal distances apart, and fastened 
 against a hardwood disc with twenty brass screws | ia 
 
 Fig. 74. Commutator of Simplex Dynamo. 
 
 long, as shown in Fig. 74. A hole should be drilled 
 through this disc to fit tight on the shaft. After 
 being screwed to the disc the washer is sawn into 
 twenty segments, which, being divided, are insulated 
 from each other though fastened to the hardwood 
 disc. Each of the twenty separate armature sections 
 is composed of twenty-four turns in three layers, 
 each having one commencing end and one finishing end 
 so there will be a total of forty ends in the whole 
 armature. These are cleaned, and the commencing 
 end of each coil is twisted to the finishing end of the 
 adjacent coil all round the armature. The separate 
 windings will thus form a continuous spiral, and twenty 
 ends will be left. These ends are soldered one to each 
 of the twenty brass screws holding the commutator 
 segments. The ends of the wires are soldered to the 
 ends of the screws, which project through the disc 
 as shown in Fig. 74. The disc should then be driven
 
 THE SIMPLEX DYNAMO. 71 
 
 over the spindle and screwed to the centre plug. A 
 layer of string over the screws completes the arma- 
 ture, which is thus represented in Fig. 75. 
 
 The field magnet is of wrought iron, of shape and 
 dimensions shown, and consists of the two pole pieces 
 (Fig. 76) and the yoke (Fig. 77). Two coil flanges will 
 also be required. The two pole pieces are fitted so 
 that the armature revolves in the space between 
 with a clearance of about -^ in. They are fixed to 
 the yoke by means of two -^ in. screws or rivets. The 
 coil flanges are of hard wood, zinc, or sheet brass, and 
 are slipped over the magnet core and held in place by 
 the wire. Before fixing the pole pieces, the magnet 
 should be wound with about 3 Ibs. of No. 22 s.w.o. 
 
 Fig. 75. Armature of Simplex Dynamo complete. 
 
 single cotton-covered copper wire. The yoke is first 
 covered with a layer of paper, and the wire is then 
 wound upon it in even layers, until the entire space is 
 filled, when a coat of shellac varnish is applied to the 
 wire, and the pole pieces and bed-plate are fixed per- 
 manently to the magnet by suitable screws. 
 
 Cast iron may be used for the field magnet, but as 
 it has a lower permeability than wrought iron the 
 sectional area must be increased. Therefore make the 
 cast-iron field magnet 1 J in. instead of | in. in thickness. 
 Wire of the same thickness (22 s.w.o.) may be used as 
 with thewrought-iron core, but more of it will be required. 
 
 The bed-plate is also of wrought iron, and is shown 
 in Fig. 79. Through it are drilled three -^ in. counter- 
 sunk holes for wood screws, four -^ in. tapped holes for 
 holding down the bearings, and three ^ in. clearance
 
 72 DYNAMOS AND ELECTRIC MOTORS. 
 
 holes for fixing the bed-plate to the magnet. The bed- 
 plate is fixed to the yoke by means of two T s in. screws 
 or rivets, which also fix the lower pole piece, and by 
 
 Fig. 76. Pole Piece of Simplex Dynamo. 
 
 a third screw underneath the yoke, as shown in Fig. 77. 
 The bearings (Fig. 80) are made of brass, and each 
 
 Fig. 77. Simplex Dynamo Yoke for Magnet. 
 
 consists of an upright piece drilled with a \ in. hole to 
 carry the armature and spindle, and a base-plate 
 
 Fig. 78. Coil Flange. 
 
 soldered to the upright piece and fixed to the bed- 
 plate by two fV in. screws. One of the bearings is also 
 drilled with a small hole in the upright piece fof 
 fixing the brush-holder, as shown in Fig. 80.
 
 THE SIMPLEX DYNAMO. 
 
 73 
 
 The brush-holder (Fig. 81) is made of sheet brass, 
 bout \ in. thick, drilled with a i-in. hole in centre, and 
 two holes at each end to take wood screws, which secure 
 
 Fig. 79. Bud-Plate of Simplex Dynamo. 
 
 small pieces of ebonite or boxwood. These serve to insu- 
 late and carry the brushes, which are made of thin sheet 
 brass or copper at one end drilled with two small holes, 
 for taking round-headed brass screws, one of which 
 fixes the brush to the insulating block while the othei 
 
 Fig, 80. Bearings of Armature. 
 
 fixes to the brush the flexible connecting wire from the 
 terminal. The screws holding the brushes must not 
 be in metallic contact with the brush-holder itself. 
 A small slot is also made as shown in the brush- 
 holders, so that the brushes may be moved through a 
 small arc until the correct position is found on the 
 commutator. Then the brush-holder is fixed by a small 
 screw, as shown in Fig. 82, which represents the com- 
 plete machine. 
 
 The terminals can be of almost any of the well-known 
 types, as Figs. 14 to 20 (pp. 18 to 20), and may either be
 
 74 DYNAMOS AND ELECTRIC MOTORS. 
 
 fixed upon a hardwood board placed upon the magnets, 
 as shown in Fig. 82, or upon a board carrying the whole 
 machine. In either case the wires from the magnet, 
 coil, and brushes are connected, as shown in Fig. 82. 
 
 Fig. 81. Brush-Holder. 
 
 The pulley may be of brass, from \\ in. to 2 in. in 
 diameter, about 1 in. on the face, and fixed to the 
 spindle either by a screw or a key. The belt should be 
 of leather, about 1 in. in width, and not more than \ in. 
 
 Fig. 82. Simplex Dynamo complete. 
 
 thick. The machine may be finished by giving it a 
 coat of paint and then varnishing. 
 
 To start the dynamo, run the armature at from 
 2,500 to 3,000 revolutions per minute, and if the machine 
 is properly constructed it will excite itself after the 
 fields have been initially magnetised by the current
 
 THE SIMPLEX DYNAMO. 75 
 
 from a small battery. If the machine is wanted to 
 run as a motor, about seven or eight chromic acid cells 
 or accumulator cells will be required. It is immaterial 
 which is the north or south pole of the magnet. The 
 commencing end of the field-magnet coil must be con- 
 nected to one brush, and its finishing end to the other 
 brush. 
 
 Below are given dimensions of a shunt-wound 
 dynamo for lighting four 10-candle-power lamps, at a 
 pressure of 15 volts, this being also suitable for charging 
 six accumulator cells if the latter are required. The 
 current will be 10 amperes, and the speed 2,500 revolu- 
 tions per minute. Armature, 2 in. wide, 3 in. diameter, 
 core | in. thick, constructed of annealed iron wires, and 
 wound with two layers of No. 16 B.W.G. double cotton- 
 covered copper wire, divided into twenty sections, 
 each in two layers, with eight turns per layer total 
 turns of wire on armature, 320. Diameter of spindle, 
 | in. ; outside diameter of commutator disc, 3 in. ; 
 inside diameter, If in. ; thickness of segments, in. 
 Field magnet of rectangular wrought iron 2| in. wide by 
 \\ in. thick. Length of field coil, 4 in. ; thickness of 
 pole piece, about \ in. Flanges of bobbin, about \ in. 
 thick. Bobbin wound with about 11 Ib. No. 18 S.W.G. 
 single cotton-covered copper wire. With an engine 
 running at 300 revolutions per min., and a flywheel of 
 18 in. diameter, a pulley about 2i in. diameter by \\ in. 
 wide would be required on the armature spindle to get 
 2,500 revolutions.
 
 CHAPTER VI. 
 
 CALCULATING THE SIZE AND AMOUNT OF M IEB FOB 
 SMALL DYNAMOS. 
 
 WE commence with the armature, because all other 
 parts are subordinated to it. When a loop of copper 
 wire is placed between the poles of a magnet in such 
 a manner as to vary the lines of magnetism supposed 
 to be passing through it, an electro-motive force is set 
 up in the loop. This principle governs all dynamo- 
 electric machines. The loop of wire, multiplied many 
 times and wound over a core of iron, is named the 
 armature, and the magnet corresponds to the field of 
 the machine. 
 
 Amongst other things, the length of wire on the 
 armature determines the voltage ; and in small machines 
 the safe carrying capacity of this wire determines the 
 current obtainable. The size and form of an armature 
 are determined by the desired output of the machine. 
 ' . The armatures most in use may be classed under 
 one of three types viz., the shuttle, the ring, and the 
 drum. These three types admit of several variations. 
 In the shuttle type, one coil of wire is wound in the 
 channel between the two cheeks, and the two ends of 
 the coil are attached to two halves of a commutator ring. 
 In the ring type, some six, eight, or more wire coils each 
 of the same length are wound in sections over the ring, 
 the ends of each coil being brought out and soldered to 
 as many bars on the commutator as there are coils on 
 the armature, the finishing end of one coil and the 
 commencing end of the next being soldered to one bar. 
 In the drum type the coils of wire are wound in sections 
 altogether over the armature, not through the ring, as 
 in the ring form, but the coils we connected in the 
 same manner.
 
 CALCULATING WIRE FOR SMALL DYNAMOS. 77 
 
 The shuttle form of armature is most easily wound 
 and connected, but its use is confined to small machines. 
 This specially applies to solid shuttle armatures, as 
 these soon get so hot as to reduce the output of the 
 machine and endanger the insulation of the wire. 
 When the shuttle is laminated that is, built up of thin 
 iron plates this tendency is considerably modified. It 
 is the type of armature usually employed in model 
 dynamos, with fields of the simple horseshoe or Siemens 
 type (See Chap. II.). 
 
 The ring-type of armature is preferable to the 
 shuttle for larger dynamos, but is very difficult to 
 wind when small, since the space through which to 
 pass the spool carrying the wire becomes more and 
 more contracted with each layer and section of wire 
 wound. It is generally used in dynamos with fields of 
 the Gramme, Manchester, Brush, Kapp, and Simplex 
 types. 
 
 The drum type of armature is more easily wound 
 than the ring, since all the wire is wound over the arma- 
 ture outside in sections ; but it is difficult to connect, as 
 the winder is apt to lose sight of the exact order in 
 which the ends of wire are to be connected. If each 
 coil is marked with a different tint or colour of cotton or 
 silk thread, this trouble will be much mitigated. 
 
 The voltage obtainable from a shuttle dynamo is 
 roughly determined by the length of insulated copper 
 wire coiled on its armature. The diameter of the wire 
 governs the length that can be got on an armature of 
 a given size. In model dynamos, each yard of active 
 wire on the armature will give about 1 volt (all 
 other conditions being favourable) when moving at a 
 circumferential velocity of 1,250 ft. per minute. This 
 last statement requires some explanation to make it 
 clear. Active wire is that portion of each coil of 
 wire which is employed in cutting through the lines 
 of magnetic force given out by the field-magnets. On 
 a drum armature, all the wire except the parts of the 
 coils over the ends of the drum is active wire. The
 
 DYNAMOS AND ELECTRIC MOTORS. 
 
 dead wire on a drum or a shuttle armature should not 
 exceed one-third of the total length employed ; but 
 for this efficiency the length of the armature must not 
 be less than three times its diameter. In a ring arma- 
 ture, the relative quantities of dead and active wire 
 will depend upon the thickness of the ring. 
 
 The circumferential velocity of the wire coils may 
 be taken to be the same as that of the periphery of 
 the armature on which they are wound. As the 
 circumference of a ring or drum is 3'14 times its 
 diameter, multiply the diameter of the armature in 
 inches by 314 to ascertain its circumference in inches. 
 This done, find how many times it will have to turn to 
 cover a foot length, and multiply this number by 1,250 
 to find how many revolutions the armature must make 
 in a minute to produce one volt from each active yard 
 of wire in its coils. It will thus be seen that the 
 voltage is conditional on the speed of the armature ; it 
 is also conditional upon the strength of the magnetic 
 rield, which must be at its maximum to get the best 
 result. The following table gives particulars of the 
 weight, resistance, carrying capacity, etc., of copper 
 wire in sizes on the Birmingham Wire Gauge. 
 
 PROPERTIES OF B.W.G. COPPER WIRES. 
 
 * 
 
 
 
 r 
 
 8 fe 
 
 I 
 
 Is 
 
 K 
 
 4 
 
 || 
 
 Approximate 
 Yards to Ib. 
 
 || 
 
 6, 
 | 
 
 I 
 
 II 
 
 * 
 
 * H 
 
 
 ** 
 
 6> 
 
 !* 
 
 fj 
 
 8 
 
 165 
 
 Bare 
 
 4-05 
 
 Silk 
 
 4 
 
 Cotton'.Sllk 
 
 4 \ 5 
 
 CuU'. 
 
 5 
 
 00475 
 
 2564-1 
 
 40 
 
 10 
 
 134 
 
 6-14 
 
 6 
 
 5'8 7 
 
 6 
 
 0109 
 
 1666-6 
 
 28 
 
 12 
 
 109 
 
 9-28 
 
 9 
 
 8'8 9 
 
 8 
 
 0249 
 
 1098-9 
 
 18 
 
 14 
 
 083 
 
 16 
 
 157 
 
 15-5 
 
 11 
 
 10 
 
 0741 
 
 666-6 
 
 10 
 
 16 
 
 065 
 
 26 
 
 25'5 
 
 24 
 
 14 
 
 13 
 
 1971 
 
 400 
 
 6 
 
 18 
 
 049 
 
 47-9 
 
 47 
 
 45 
 
 19 
 
 16 
 
 6629 
 
 2127 
 
 3 
 
 20 
 
 035 
 
 85 
 
 83 
 
 80 
 
 25 
 
 23 
 
 2-095 
 
 120-4 
 
 2 
 
 22 
 
 028 131 
 
 129 
 
 120 
 
 29 
 
 27 
 
 4-976 
 
 77'5 
 
 1-5 
 
 24 
 
 022 1 176-4 
 
 173 
 
 162 
 
 34 
 
 30 
 
 9-009 
 
 57-8 
 
 1
 
 CALCULATING WIRE FOR SMALL DYNAMOS. 70 
 
 Carrying capacity in amperes is calculated at about 
 2,000 amperes per square inch. The safe carrying 
 capacity of the wire is the maximum current it will 
 carry without heating to such an extent as to affect 
 the insulation seriously. In a series shuttle dynamo, 
 the current in the outer circuit passes- through armature 
 coils and field-magnet coils ; therefore the wire on the 
 latter should be of a diameter about equal to that on 
 the former. The accompanying tables will serve as a 
 guide to selecting suitable wire 'for the armature and 
 field-magnet coils. The following table deals with 
 wires on the Standard Wire Gauge. 
 
 PROPERTIES OF S.W.Q. COPPER WIRES. 
 
 
 
 
 WEIGHT 
 
 RESISTANCE 
 
 No. OF TURNS 
 
 CURRENT IN 
 
 
 
 
 IN LB. 
 
 IN OHMS. 
 
 PER INCH. 
 
 AMPERES. 
 
 
 
 tl 
 
 4 
 
 
 ^ 
 
 
 
 
 
 ft 
 
 11 
 
 If 
 
 It 
 tt 
 
 |l 
 
 si 
 
 
 
 | 
 
 I 
 
 1 
 
 
 
 
 it 
 
 |s 
 
 {? 
 i.i 
 
 & 
 
 I 1 
 
 CO $i 
 
 1 
 
 1 
 
 
 
 I 
 
 A 
 
 B 
 
 C 
 
 51 
 
 51 
 
 ft 
 
 22 
 
 028 
 
 0006 
 
 7 
 
 12 
 
 4078 
 
 71-8 
 
 24 
 
 28 
 
 26 
 
 6 
 
 9 
 
 T2 
 
 20 
 
 036 
 
 ooio 
 
 12 
 
 21 
 
 24'11 
 
 43-4 
 
 20 
 
 2G 
 
 23 
 
 1 
 
 1*5 
 
 2 
 
 19 
 
 18 
 
 '040 
 '048 
 
 0012 
 0018 
 
 15 
 21 
 
 26 
 
 37 
 
 19-9835-2 
 13'88 24'4 
 
 18 
 16 
 
 23 
 
 20 
 
 20 
 17 
 
 1-2 
 1-8 
 
 1-8 
 27 
 
 2'4 
 3-6 
 
 17 
 
 056 
 
 0024 
 
 28 
 
 50 
 
 10-2 
 
 17'9 
 
 14 
 
 17 
 
 15 
 
 2'4 
 
 3'6 
 
 4'8 
 
 1G 
 
 064 
 
 0032 
 
 37 
 
 66 
 
 7'6 
 
 13-6 
 
 12-8 
 
 15 
 
 14 
 
 3'2 
 
 4'8 
 
 6'4 
 
 15 
 
 072 
 
 0040 
 
 47 
 
 83 
 
 6-11 
 
 10-7 
 
 11-5 
 
 13 
 
 12 
 
 4 
 
 6 
 
 8 
 
 14 
 
 '080 
 
 0050 
 
 57 
 
 102 
 
 5' 
 
 8'8 
 
 10-5 
 
 11 
 
 10 
 
 5 
 
 7'5 
 
 10 
 
 13 
 
 092 
 
 0066 
 
 76 
 
 135 
 
 378 
 
 6-6 
 
 9'5 
 
 10 
 
 9 
 
 6'6 
 
 9'9 
 
 13-2 
 
 12 
 
 104 
 
 0085 
 
 98 
 
 173 
 
 2-95 
 
 5-2 
 
 8-5 
 
 9 
 
 8 
 
 8'5 
 
 1275 
 
 17 
 
 11 
 
 116 
 
 0105 
 
 122 215 
 
 2-36 
 
 4'2 
 
 7-5 
 
 7 
 
 6 
 
 10-5 
 
 1575 
 
 21 
 
 10 
 
 128 
 
 0128 
 
 148 262 
 
 1'95 
 
 3'4 
 
 7 
 
 6 
 
 8 
 
 12-8 
 
 19-2 
 
 25'6 
 
 9 
 
 144 
 
 0162 
 
 188 332 
 
 1'55 
 
 27 
 
 6 
 
 5 
 
 5 
 
 16'2 
 
 24'3 
 
 32-4 
 
 8 
 
 160 
 
 0201 
 
 245 409 
 
 1-26 
 
 2'2 
 
 57 
 
 4 
 
 4 
 
 20'1 
 
 30'15 
 
 40-2 
 
 The resistances given above are for 100 per cent 
 conductivity copper at a temperature of about 65 F.
 
 8o DYNAMOS AND ELECTRIC MOTORS. 
 
 Under the heading "No. of turns per inch" will be seen 
 three divisions A, B, and c. Of these B and c refer 
 to wires which, in the small sizes, have special thin 
 coverings of silk and cotton respectively. Under A the 
 insulation is reckoned at the rate of 12 mils = ^TQ ^ n - ^ 
 double cotton in sizes below No. 16. Above this size 
 the average covering is about 14 mils, varying from 10 
 to 20 mils, however. 
 
 The output of a dynamo that is, its electrical 
 power is generally calculated in watts. This is ob- 
 tained by multiplying the total voltage by the amperes. 
 But as this method of stating a dynamo's output admits 
 of uncertain interpretation, it is best to specify the volts 
 and amperes separately. 
 
 In a series machine the field magnet coils are con- 
 nected in series with the outer circuit. The magnetism 
 in the fields, therefore, varies inversely as the resistance 
 of the circuit, being less when the resistance is high 
 than when it is low. In a shunt-wound machine the 
 field magnet coils are connected in a shunt with the 
 outer circuit. There are, therefore, two paths open to 
 the armature current : one through the field magnet 
 coils, and the other through the outer circuit. The 
 resistance in the outer circuit being lower than that 
 of the field magnet coils, more current goes by way of 
 the outer circuit than goes round the coils, but when the 
 resistance of the outer circuit is increased, more 
 current goes by way of the coils, and this raises the 
 magnetic intensity of the fields. The effect of this is to 
 raise the voltage of the current, and enable it to over- 
 come the extra resistance. In a compound-wound 
 machine the field magnet coils are partly of thick wire 
 connected in series with the armature and outer circuit, 
 while a small wire of high resistance is connected in 
 shunt. This form of machine may be made to give 
 almost a constant potential difference at the ter- 
 minals. 
 
 Each style of winding has its own peculiar advan- 
 tages, adapting it to the kind of work to be done by the
 
 CALCULATING WIRE FOR SMALL DYNAMOS. 81 
 
 machine. A shunt-wound dynamo becomes self-regu- 
 lating to a certain extent ; for as the lamps are switched 
 off the resistance in the outer or lamp circuit becomes 
 greater, and more current is shunted through the field 
 coils, thereby generating a higher voltage to overcome 
 the increased resistance, while a compound-wound 
 dynamo is self-regulating to a still greater extent. 
 
 A rough rule for shunt-wound machines with about 
 90 per cent, efficiency is as follows : Let the resistance 
 of the armature be represented by 1, that of the outer 
 circuit by 20, then that of the field magnet circuit should 
 be 400 that is to say, the outer circuit should have a 
 resistance twenty times that of the armature, and the 
 field magnet circuit should have a resistance four hundred 
 times that of the armature. In a series machine, the 
 field magnet coils should have a resistance about two- 
 thirds that of the armature coil. In a compound machine, 
 the resistance of the series coils should be the same as 
 that of the armature. In small machines these propor- 
 tions have to be considerably modified. In a 300-watt 
 machine to give 6 amperes at 50 volts the field magnet 
 resistance may be reduced to 200 instead of 400, and 
 this proportionate resistance rapidly diminishes with 
 each small reduction in the size of the machine, until 
 the smallest workable dynamo will only admit of the 
 resistance of the field magnet coils being some twelve or 
 fifteen times that of the armature coil. It is almost 
 impossible to determine exactly the output of such 
 small machines ; for apart from the variations from 
 theoretical rules, others are likely to crop up through 
 differences in the qualities of iron employed, hardness 
 of wire, irregular or loose winding, insulation, connec- 
 tions, size, form and make of commutator, and quality, 
 position, and pressure of brushes, etc. 
 
 Properly designed castings for the carcase 'of the 
 dynamo usually have ample space allowed for winding 
 sufficient wire to suit the electrical output of the 
 machine. If the carcase of the machine has to be forged 
 or cast, and the rings or punchings for the armature
 
 82 DYNAMOS AND ELECTRIC MOTORS. 
 
 made to order, proper space must be allowed for the 
 wire. By referring to the tables given on pages 78 and 
 79, the spa< e likely to be occupied by the wire will be 
 found under the heading " No. of turns per inch " that 
 is, so many turns of wire of a given gauge will lie side 
 by side in 1 in. of space. The channel in a shuttle 
 armature must be large enough to take the required 
 wire without bulging beyond the cheeks. The space 
 between the outer edge of the ring or drum armature 
 and the sides of the tunnel in which it is to work 
 should be sufficient to leave ^a i n - between the wire and 
 the sides after three layers of the wire have been wound 
 on. One layer is theoretically the best, but three layers 
 are admissible. 
 
 The length of the field magnet cores may be about 
 three or three and a half times their diameter, and 
 provision should be made to admit of enough wire to 
 increase the diameter of the core from two and a half to 
 three times. The space to be occupied by the wire may 
 be ascertained by estimating its length and weight or 
 length Tper pound, noting how many turns to the inch 
 it will run. Estimate the probable diameter of the 
 wound core, and find the mean between this and the 
 bare core, then multiply this by the factor 3'14, and so 
 ascertain the number of turns and the space likely to be 
 occupied by the wire. Heavy yokes and pole pieces 
 are always admissible, because dynamos work best when 
 the iron in them is in excess of that needed to maintain 
 magnetic saturation. It is also advisable to have a 
 larger carcase than will be actually needed to furnish 
 the required output, since machines may always be safely 
 worked to light fewer lamps than they were designed 
 for ; but it is not safe to work them at a higher speed 
 to procure a larger output. 
 
 Before the plan for winding the armature can be drawn 
 up, the resistance of the outer circuit namely, the work 
 to be done by the machine must first be ascertained. 
 If this resistance is too low, a shunt machine will fail 
 to supply the required current, and a series machine
 
 CALCULATING WIRE FOR SMALL DYNAMOS. 83 
 
 will burn its coils. If too high, no current will be 
 obtained from a series machine, and that from a shunt 
 machine will be diminished. In large machines, care- 
 fully wound, an efficiency of 1 volt per foot of effective 
 wire on the armature moving at a circumferential 
 velocity of 1,250 feet per minute has been attained, but, 
 as has been stated, 1 volt per yard is what may be 
 expected from small machines. Although the voltage of 
 a machine may be increased by increasing the speed of 
 its armature, it is not always safe to do so, because an 
 increased voltage will send more current round the field 
 magnet coils, and this may dangerously heat them. In a 
 series machine, all the current passing through the outer 
 circuit also traverses the field magnet coils. In a com- 
 pound machine, the bulk of all its current passes 
 through the series coils and only a fraction of it through 
 the shunt coils. In a shunt machine, only a fraction of 
 the current passes through the field magnet coils. Con- 
 sequently, the fields of the series machine are not 
 magnetised when the outer circuit is open, and the 
 fields of the shunt machine are then" most highly 
 magnetised. When a machine is run at a higher speed, 
 the brushes should be given a more forward lead, to 
 compensate for increased distortion of the field. 
 
 The wires for dynamos may be protected by using 
 indiarubber or gutta-percha dissolved either in benzole 
 or in naphtha. This solution will make an elastic 
 insulating varnish, but it is liable to injury from oil, 
 which renders the varnish soft and sticky. Shellac 
 varnish is one of the best for the purpose. This is 
 made by digesting shellac in methylated spirit, kept in 
 a stoppered glass jar in a warm place for twelve hours. 
 Green or red sealing-wax digested in warm methylated 
 spirit is also used as an insulating varnish. 
 
 Few persons can get the calculated amount of wire 
 on an armature, although a full allowance has been 
 made for slack winding. To take an armature in 
 one hand and let the wire run through the fingers of the 
 other, drawing it more or less tight, winding as one
 
 84 DYNAMOS AND ELECTRIC MOTORS. 
 
 would wind up a ball of string, sometimes working 
 evenly, sometimes not, will not do. To wind an arma- 
 ture properly, especially if of either the drum or ring 
 type, is work for two people. Even a shuttle armature 
 should not be attempted by one person unless he is an 
 experienced winder ; and even then he will wish he had 
 three hands. 
 
 After the wire has been properly paraffin-waxed and 
 drained, it should be wound on as tight as possible, 
 without, of course, breaking it. Any wire that is not 
 perfectly straight, or is in the least respect faulty should 
 be driven well into place by means of a small wooden 
 hammer or by a small wooden stick, neatly squared and 
 smoothed at the end, and used as a punch. Every wire 
 should be made to go as .near to its neighbour as possible. 
 It will be seen that winding an armature properly is no 
 light work. 
 
 Cheap wire is very bad, for two reasons one is 
 that the wire itself has a comparatively low percentage 
 of copper, and wire should not be used that has less than 
 97 per cent, as it gives the armature a needlessly high 
 resistance. The other is that cheap wire has bad, 
 thick cotton for its covering, and consequently occupies 
 space wastefully. Another source of trouble is thick, 
 clumsy taping. There should be just enough to ensure 
 perfect insulation, and no more. Bad taping takes up a 
 lot of room, and space is precious to a winder of 
 armatures. Remember this, and do not be .afraid of 
 using the wooden hammer. 
 
 In treating the subject of calculating the length of 
 wire for armatures, two types only will be taken viz., 
 the Siemens H-girder, or shuttle armature (Figs. 83 and 
 84) and the cog-ring armature (Figs. 85 and 86), as un- 
 doubtedly they are the best types of armatures for small- 
 sized dynamos ; the former for the very small sizes, and 
 the latter for somewhat larger ones. They are also the 
 easiest kinds to wind and correct, and are therefore very 
 suitable for amateur workers. 
 
 As an illustration, it would be best to take a sample
 
 CALCULATING WIRE FOR SMALL DYNAMOS. 85 
 
 armature, fix upon a certain gauge of wire, and follow up 
 the working to get at the weight and length of wire 
 required ; by this means the reader will have an 
 example at hand to work from in cases of armatures of 
 other sizes. 
 
 The first example will be a laminated shuttle arma- 
 ture, 2 in. long, l in. in diameter (Figs. 83 and 84), 
 
 {.- ,*_. 
 
 Fig. 83. Section of Shuttle Armature. 
 
 having the web flush with the ends. An armature of this 
 size would probably have wire spaces I in. wide, and by 
 
 Fig. 84. Side View of Shuttle Armature. 
 
 making the segment of the circular area form a rectangle 
 of equal area, as shown by the dotted lines in Fig. 83, the 
 wire space would be in. deep, leaving f in. for the 
 thickness of the web. In calculating shuttle armatures 
 the shaft need not be taken into consideration, as it does 
 not affect the amount of wire that will go into the 
 channels, though it makes the winding at the ends 
 irregular, which cannot be helped ; the slight extra
 
 86 DYNAMOS AND ELECTRIC MOTORS. 
 
 length required through this irregularity can in practice 
 be neglected. 
 
 The next operation will be to make a sketch of the 
 side of the armature, as in Fig. 84, where the full line 
 will represent the last coils of wire ; then by setting 
 in. off at each end, the longest coil is obtained as a 
 rectangle. (See the dotted lines in Fig. 84.) The next 
 thing to find is the mean length of all the turns. This 
 will be the shortest turn, added to the longest turn, 
 divided by 2. The shortest length is one of the turns in 
 the first layer, and will be, of course, rather more than 
 (2 X 2i) + (2 x I) = 52 ; the longest length will be 
 the length of the sides of the rectangle in dotted lines 
 
 Fig. 85. Section of Cog-ring Armature. 
 
 (Fig. 84), which was shown to represent the longest 
 coil ; then the longest turn will be (2 X 3J) + (2 X li) 
 = 9 1 ; so the mean length of all the coils will be 
 5J + 9J -*-2 = 7f in. 
 
 For this example, No. 20 S.W.G. cotton-covered wire 
 will be taken to wind the armature. Upon looking in 
 the tables (p. "78), it will be found that this wire can be 
 coiled twenty- three coils to the^ linear inch. Should 
 there be no tables at hand, take a spare piece of wire of 
 the gauge to be used, and coil it round neatly on any- 
 thing smooth, and count how many coils go to an inch. 
 As the wire space is | in. wide, and in. deep, it can be 
 assumed that twenty coils, eleven layers deep, can be got 
 into the space ; this will make 220 coils in all. Now it 
 has been found that the average, or mean coil of all the 
 coils is 7| in. long ; therefore the total length of wire 
 will be 220 X 7| = 1,705 in., or 47 yds., 1 ft, 
 1 in. say 47 yds. No. 20 S.W.G. cotton-covered
 
 CALCULATING WIRE FOR SMALL DYNAMOS. 87 
 
 wire goes 80 yds. to the pound, so the amount 
 of wire for this armature would be 7 yds. over 
 \ lb., or say J Ib. Of course, it will be observed that 
 ehould the armature be solid, with the web set 
 back from the ends, much less wire can be got on, also 
 the winding would be neater and more compact if the 
 shaft did not run through the web. 
 
 For the other example a laminated cog-ring arma- 
 ture will be taken, 5 in. in diameter, 3 in. deep, having 
 twelve cogs ; wire spaces f in. wide and | in. deep, with 
 
 ~VT 
 
 Fig. 86. Side View of Cog-ring Armature. 
 
 the core of the armature | in. thick at the wire spaces 
 and in. thick at the cogs. (See Figs. 85 and 86.) This 
 armature it is proposed to wind with No. 12 S.W.G. cotton- 
 covered wire. The mode of operation is very similar to 
 the example above, one whole coil being calculated first. 
 A section of the armature core through a wire space 
 must be drawn as in Fig. 85 ; then setting off the f in., 
 the depth of the wire space all round, the longest mean 
 coil is found as a rectangle, as shown by dotted lines. 
 
 Proceeding as before, the mean length of all the 
 coils is found ; thus the shortest (2 X 3) + (2 X f ) 
 = 6 i in. ; and the longest (.2 X 3J) + (2 X U) = 9* ; 
 then the mean coil will be 8| in. long. The wire
 
 88 DYNAMOS AND ELECTRIC MOTORS. 
 
 tables (p. 78) show that eight coils of No. 12 S.W.G. 
 cotton-covered wire go to the linear inch ; so in 
 the space f in. X f in. there will be room for five 
 coils, three layers deep, which will make fifteen coils in 
 all. As the mean coil is 8J in. long, the total length will 
 be 15 X 8 = 123| i n - ; but as there are twelve separate 
 coils on the armature the total length of wire for the 
 whole armature will be 123f X 12 = say 41 yds. No. 12 
 S.W.G. cotton-covered wire runs 8'8 yds. to the pound ; 
 so between 4J Ib. and 4J Ib. will be enough. 
 
 A simple way to determine the mean length of the 
 coil is to add together any two adjacent sides of the 
 rectangles forming the longest and shortest coils. 
 Taking the first example (p. 85), shortest coil = 
 (2 X 2 in.) + (2 X f in.) j longest coil = (2 X 3 in.) 
 + (2 X If in.) ; mean coil = half the sum of these. 
 Now, the shortest coil may be written : 2 (2J in. + | in.). 
 Similarly, the longest coil = 2 (3J in. + If in.) : and 
 combining the two, and talking half the sum for the 
 mean coil, we get 
 
 ${(2j in. + f in.) + (3j in. + If in.)} 
 
 * 
 
 which is equal to mean coil ; and by cancelling the 
 multiplier and divisor of fraction, we have left, 2J in. + 
 | in. + 3J in. + If in. = mean = 6 in -f 1^ in = 7J in.; 
 and in the second example, 3 in. + f in. -f- 3f in. 
 + li in. = mean = 6| in. + 1J in. = 8| in.
 
 CHAPTER VII. 
 
 AILMENTS OF SMALL DYNAMO-ELECTRIC MACHINES, THEIR 
 CAUSES AND CUHES. 
 
 To localise the faults common to dynamos, we [shall 
 require a battery of three or four cells of a strong 
 and constant type, a galvanometer or current detector, 
 such as those used by electric-bell fitters, and a mag- 
 netised needle or a pocket compass. To repair the 
 faults we shall need a soldering-iron, some soft solder, 
 and some resin to solder faulty joints ; a pair of stout 
 pliers, a screwdriver, small spanners to fit the nuts 
 on the machine, and some soft cotton or tape, or both, 
 well soaked in melted paraffin wax. 
 
 The best battery for the purpose is the single fluid 
 bichromate battery that is, a battery composed of jars 
 or wide-mouthed bottles of glass or stoneware, each 
 holding a pint. Each jar contains a plate of amal- 
 gamated zinc between two plates of carbon, and is 
 charged with a liquid composed of 3 ozs. bichromate of 
 potash dissolved in a pint of water, and 3 ozs. of 
 sulphuric acid. This liquid must be allowed to cool 
 before the zinc plate is placed in it. 
 
 The zinc plate in one cell must be connected to the 
 carbon plate in the next cell by a stout copper wire, say 
 No. 16 s.w.a, and all the cells must be thus con- 
 nected so as to leave one zinc plate free at one end of 
 the row, and one carbon plate free at the other end of 
 the row. About 2 ft. of No. 18 or No. 20 S.W.G. wire, 
 attached to these end plates by suitable binding-screws, 
 will serve to connect the battery with the galvanometer 
 and the machine. A steel darning-needle, magnetised 
 by rubbing it on a permanent magnet, and suspended by 
 a piece of cotton to hang horizontally, witt- serve as a
 
 QO DYNAMOS AND ELECTRIC MOTORS. 
 
 substitute for a pocket compass. With this apparatus 
 the following faults may be localised. 
 
 If the cores of the magnets are not magnetised, no 
 current will be generated in the armature coil. If one 
 of the field magnet coils of an overtype or undertype 
 machine is wound in the wrong direction, both pole 
 pieces may have a like magnetism, and the same negative 
 result will be obtained. One pole piece must have 
 an opposite polarity to the other. The compass needle 
 being held near the pole pieces of an ordinary two-pole 
 machine, one of them should attract the north pole 
 of the needle, and the other repel it. The machine 
 should be tested in this way whilst the armature is at 
 rest, and also when it is running. If the coils are 
 wrongly connected, there may be a similar result. If 
 the compass needle does not indicate any magnetism, 
 or only a feeble magnetism, it may be assumed that the 
 pole pieces are not magnetised. 
 
 The whole of the armature current in a series machine, 
 and a portion of it in a shunt machine, will be em- 
 ployed in maintaining the magnetism of the field ; we 
 must be careful so to convey it through the field-magnet 
 coils as to retain the polarity of the cores induced 
 initially by the battery current. 
 
 A series-wound dynamo employed in depositing 
 metals from their solutions, or in charging accumu- 
 lators, is liable to have its poles reversed by a back 
 current from the plating-vat or the accumulator cells. 
 For this reason series dynamos are not suitable for 
 such work. The polarity of the core is also reversed 
 when current is sent through its coils from a battery, or 
 another dynamo, to run the machine as an electric motor. 
 Compound-wound machines are also liable to a reversal 
 of their magnetism from a similar cause, owing to a 
 high reverse current passing through the series coils. A 
 shunt-wound machine can only be reversed by such 
 means when its field-magnet coils are wrongly con- 
 nected to a battery ; therefore, a shunt-wound machine 
 should always be used for charging accumulators and
 
 AILMENTS OF SMALL DYNAMO MACHINES, gi 
 
 for electro-depositing work. This altered polarity of 
 the field-magnets may be detected by the compass 
 needle being held to them, and the original magnetism 
 can be restored by the means adopted at first for 
 magnetising the cores. 
 
 Magnetism neutralised, which may also be named 
 short-circuiting the magnetic poles, occurs when the 
 poles are bridged by a mass of iron, as when an under- 
 type field is bolted direct to an iron bed-plate, or an over- 
 type field is bridged by an iron plate secured to the pole 
 pieces. When an air space is left between the polar 
 extremities of a horseshoe magnet, the magnetic lines 
 of force may be supposed to stretch across from one 
 pole piece to the other, and are then in a position 
 to pass through the armature coils. But when a 
 piece of iron bridges these polar extremities, the greater 
 number of the magnetic lines pass by way of this 
 bridge, and so are diverted through the armature from 
 their useful path, and, as there are, therefore, few 
 or no lines of force passing through the armature, 
 there will be a very faint current from the machine, 
 or none at all. 
 
 The field-magnets have been short-circuited by 
 placing a guard of thick iron over the armature gap 
 The guard over the armature space of an overtype 
 dynamo should be of zinc or gun-metal ; and if it is 
 necessary to have a metal bed-plate for an undertype 
 dynamo, brackets of gun-metal or of zinc should be 
 interposed between the magnet poles and the iron of 
 the bed-plate. 
 
 If the machine does not give a current or the desired 
 effect, though the magnetic properties of the field have 
 been tested as directed and found perfect, leakage or 
 short-circuiting of the coils may be suspected. To detect 
 this we must employ a battery and galvanometer, as 
 before explained. Leakage most frequently takes place 
 between the wire of the coils and the iron of the field 
 magnets or the armature. Perhaps ^the rough corners 
 on the castings have not been made smooth. Perhaps
 
 92 DYNAMOS AND ELECTRIC MOTORS. 
 
 the iron has not been coated with a sufficiently thick 
 layer of varnish, paraffined tape, or calico ; or the wire 
 has been pulled tight over these rough or unprotected 
 parts, and the insulation has been cut through, thus 
 bringing bare copper into contact with bare iron. As a 
 consequence, the current takes a short cut by way of 
 the iron instead of going through all the coil of wire, 
 and the result is seen in a diminished output from the 
 machine. 
 
 - The following is a rough-and-ready means fre- 
 quently adopted for discovering this fault. Disconnect 
 the ends of the field magnet coils from their terminals, 
 and connect one end of the coils to one terminal of the 
 battery. Then take a long exploring wire and connect 
 to the opposite terminal of the battery, and with the 
 free end of this] scrape the iron-work and metal- work of 
 the machine at several points. If any bare part of the 
 wire coil is touching the bare iron of the machine, a 
 bright spark will be seen to flash from the part of the 
 machine touched with the exploring wire. By discon- 
 necting the two coils from each other and testing each 
 separately, the faulty one may be discovered. The 
 armature coils may be tested in a similar manner in 
 fact, they must be tested for leakage as well as those of 
 the fields. It is advisable, however, in both cases to 
 place the galvanometer in circuit by connecting the bat- 
 tery to it, and then to connect the exploring wire to the 
 galvanometer. If the needle moves, it shows that there 
 is a leakage, however small or large this may be, but the 
 rough test will only reveal a bad leakage. 
 
 Leakage of another form may occur between adjacent 
 turns or layers of wire in the same coil, and is due to the 
 stripping off of the insulation, from some such cause as 
 hammering the coils to get them in their proper places, 
 or from pulling them too tight. If a machine is over- 
 driven, or if a series machine is short-circuited, the 
 insulating covering may get burnt off, and thus the 
 coils become short-circuited. 
 
 This fault can only be discovered by means of the
 
 AILMENTS OF SMALT. DYNAMO MACHINES. 93 
 
 galvanometer in circuit with the battery. Each coil 
 must be placed in circuit separately, the deflections of the 
 galvanometer needle noted, and these compared. Equal 
 lengths of wire should have equal resistances, and this 
 should be indicated by equal deflections of the galvano- 
 meter needle. If the needle swings over much farther 
 when one coil is in circuit than when a similar coil of the 
 same length is tested, we may expect that coil to be 
 short-circuited somewhere, because it offers a less resist- 
 ance than the perfect coil. Each coil of the armature 
 should be unsoldered from the commutator bars and 
 tested separately in comparison with the others. All 
 faulty coils must be unwound and the fault repaired by 
 winding paraffined cotton or tape over the bare spot. 
 
 Leakage sometimes occurs between the commutator 
 bars and the spindle, or between the sections of the com- 
 mutator itself, or between the brush-holders and other 
 parts of the machine. Any of these leakages may be 
 detected by the galvanometer and one or more cells of 
 the battery. The commutator bars may be accidentally 
 placed in contact with the spindle by using long screws. 
 To detect this fault, attach one battery wire to the 
 spindle and the other to the galvanometer, then 
 touch each bar with the free wire from the galvano- 
 meter and watch the indications of the needle. If 
 the needle moves when a bar is touched, that bar is 
 in contact with the spindle. Any faulty screw must 
 be withdrawn, and a shorter one used. If the bars are 
 accidentally connected by metal dust, or by expansion of 
 the sections whilst heated, this fault may be detected by 
 placing one wire from the battery on one bar and the 
 wire from the galvanometer on the next bar. The coils 
 must be disconnected from the bars whilst this is being 
 done. Sometimes the brush-holders are not insulated 
 from the machine. This fault may be detected by 
 testing each separately with the body of the machine 
 in circuit, and then testing the two together. If all 
 is right, no current should pass between them and the 
 machine or between the two holders when the brushes
 
 94 DYNAMOS AND ELECTRIC MOTORS. 
 
 are off, and they are disconnected from the outer circuit. 
 Perfect insulation at these points is of the greatest 
 importance. 
 
 A machine tested at all points indicated above and 
 found all right, or the detected faults put right, and yet 
 that will not give satisfaction, may have a fault in the 
 brushes. All brushes, in any type of machine, should be 
 held in suitable brush-holders fixed to an insulated 
 rocker, or in insulated sleeves attached to such a rocker. 
 Fixed brushes on standards, or on blocks attached to the 
 machine, give much trouble, since they can only be ad- 
 justed by the exercise of much time and patience, and even 
 then cannot be trusted to remain right for any length of 
 time. The most inexpensive and efficient material for 
 brushes in small dynamos is copper gauze, cut into strips 
 of suitable width and length, and formed into pads by 
 soldering the strips together at the ends to go in the 
 brush-holders. As these pads have very little elasticity 
 in them, it is advisable to back them with a strip of spring 
 steel, German silver, or brass, so as to ensure enough 
 pressure to keep them in good contact with the commu- 
 tator. Machines frequently fail because of having hard 
 brass brushes, which press unevenly on the commutator, 
 or get thrown out of contact when the machine is driven 
 at a high speed. Pads of copper gauze bear and wear 
 more evenly than springs of hard brass. 
 
 When these pads are fixed to a rocker, they may be 
 easily adjusted to any position. The theoretically right 
 position for the brushes is for their ends to bear on the 
 commutator bars opposite the centre of the open spaces 
 between the field magnets. The position practically 
 right is always in advance of this, because the armature 
 current distorts the lines of force in the magnetic field. 
 This forward position or lead of the brushes must be 
 found by experiment, because it varies with the type and 
 speed of every machine. As a rule, the highest speed 
 demands the most forward lead. If the machine is con- 
 nected to the thick coil of a suitable ammeter when 
 driven at the required speed, and the brushes are
 
 AILMENTS OF SMALL DYNAMO MACHINES. 95 
 
 moved until the best effects are noted by the deflec- 
 tion of the needle, this will be the best position for the 
 brushes. 
 
 Sparking at the Brushes. The machine may run all 
 right, and give a fairly good current for a short time, 
 but there may be much sparking at the brushes, burn- 
 ing them away and burning pits in the commutator. 
 This shows defective construction or bad adjustment 
 of the brushes. The likely faults in construction 
 are : Coils of a varying length and resistance on the 
 armature, insufficient resistance in the field magnet 
 coils, or leakage between the armature coils and 
 the carcase of the machine. This last defect may be 
 found by examining the armature coils. Perhaps these 
 touch the iron occasionally, and rub off the insulating 
 coating. This may be due to too much end-shake of the 
 armature spindle, to a worn bearing, or to a loose 
 bearing allowing the armature to wobble. 
 
 A small washer on the spindle will correct too much 
 end-play, tightening the nuts will remedy a loose 
 bearing, but a worn bearing must be bushed with 
 brass to cure side-shake. If leakage occurs, the worn 
 spot should be coated with varnish worked in well 
 between the folds of the wire. Sparking may indicate 
 that too much work is being thrown on the machine. 
 Sparking due to bad adjustment of the brushes can 
 be cured by altering their lead, as described in the 
 previous section (p. 94). 
 
 Broken Armature Wire. Such a wire can be 
 mended as follows : If it is outside the winding, bare 
 and clean the' two ends, twist and solder them together, 
 then paint the joint over with either Brunswick black or 
 red sealing-wax varnish. If it is in the winding, bare 
 and bevel the two ends, tin the bevels, and sweat the 
 joint together ; then work up to as near the size of 
 the wire itself as possible, relap the joint with silk, 
 and dip it in melted paraffin wax, or paint it over 
 with Brunswick black. 
 
 Sunning Hot. Some of the best designed and
 
 96 DYNAMOS AND ELECTRIC MOTORS. 
 
 constructed machines will get too warm after a day's run 
 on heavy work. The passage of an electric current through 
 the wire coils will always warm them more or less, and 
 much of this rise of temperature is unavoidable. When 
 the temperature rises considerably, as when the field 
 magnet coils feel quite hot if touched by the hand, there 
 is always a serious loss in heating the wires, because 
 hot wires offer more resistance to the current than cool 
 wires. The main cause of this excessive heating is an 
 employment of wires too small to carry the current 
 properly ; or, in other words, the machine is required 
 to do more work than it is properly capable of. The 
 remedy here is clear enough. But sometimes the heating 
 of a machine is due to defective construction, or it may 
 be due to leakage. Solid iron armatures, and laminated 
 armatures which are not insulated, may get unbearably 
 hot in a short time, because of cross or eddy currents 
 circulating in the mass of iron from end to end of 
 the armature. 
 
 When the laminations are separated from each other 
 by an insulating substance (even a thin coat of varnish 
 is sufficient), these currents are broken up, and cannot 
 travel from end to end. Machines with solid iron 
 armatures, or with badly-insulated laminations, will 
 get hot enough to melt the soft solder connections at 
 the commutator and distort the commutator sections. 
 In series and compound machines leakage across the 
 brushes will also heat the coils injuriously. Short- 
 circuiting a series machine may seriously damage it, 
 by charring the insulating covering of the wires. 
 
 These are the most common ailments of small 
 dynamos. Others there are, but it will often be found 
 that these are due only to faulty workmanship or to 
 wear and tear. 
 
 It may be useful here to say a few words as to the 
 possibility of receiving shocks from dynamos. There 
 cannot be any serious shock to a person handling a 
 dynamo giving a current of low voltage. Neither can a 
 person receive a shock merely by touching the machine
 
 AILMENTS OF SMALL DYNAMO MACHINES. 97 
 
 with one hand, provided the machine as a whole is 
 insulated from the ground, because the body does not then 
 form a link in a closed electrical circuit. It is unsafe 
 to meddle with large dynamos, or with any part of an 
 electric light circuit in a large installation, even to 
 touching it with one hand only, unless you are 
 thoroughly acquainted with it, because of the uncer- 
 tainty of knowing when the mere act of touching may 
 complete a circuit. 
 
 The general attention which a dynamo requires is 
 similar to that needed by all high-speed machines. Keep 
 all bearings and wearing parts clean and properly oiled. 
 See that the driving-belt is wide enough to take a good 
 grip on the pulley, and thus maintain a good speed with- 
 out undue tightness. It must also be remembered that, 
 in addition to the bearings, the commutator and brushes 
 are the wearing parts of the machine. The brushes must 
 be adjusted to the proper angle, as before explained. 
 Sparking wears away brushes and commutator very 
 fast, and thus will demand frequent adjustment of the 
 brushes to keep them bearing on the best part of the 
 commutator. When the brushes have cut grooves in 
 the commutator it is necessary to re-true the furrowed 
 part, and sometimes to put in a new segment.
 
 CHAPTER VIII. 
 
 SMALL ELECTRIC MOTORS WITHOUT CASTINGS. 
 
 THE little model shown at Fig. 87, if made according 
 to the following instructions, requires no castings and 
 no lathe for its successful construction. It is also 
 
 Fig. 87. Simple Electric Motor complete. 
 
 within the reach of the younger readers of this book 
 who have an idea of using a few tools, and will 
 exercise a little ingenuity and patience. The motor, 
 when complete and judiciously painted with such 
 simple colours as red sealing-wax varnish and Bruns- 
 wick black, looks very presentable, to say nothing of 
 its use in illustrating the laws of electro-magnetism. 
 
 For the field magnet get a piece of f in. round 
 wrought iron 4 in. long, as soft as possible, and bend 
 it into the form of a horse-shoe, with the ends } in. 
 apart on the inaide ; go over it with a file to take tha
 
 ELECTRIC MOTORS WITHOUT CASTINGS. 99 
 
 roughness off, and then file up the two ends true and 
 square one with the other. Cut a long strip of paper 
 i-in.-wide newspaper will do and paste it well, 
 and wind it round the horse-shoe until there are about 
 three thicknesses on all over, except within i in. 
 from the ends ; paste the outside of the paper all 
 over, and go over it with the fingers to get it even ; 
 when this is dry give it a coat of Brunswick black. 
 Thin magnet does not require any bobbins, so we 
 
 Fig. 88. Side Elevation of Field Magnet and Block. 
 
 can go straight on winding it with some No. 28 S.W.G. 
 silk-covered copper wire. Begin just short of the 
 edge of the paper cover, with a half hitch, leaving 
 the end about 6 in. long ; wind the wire on close and 
 even until reaching the other end, just within the edge 
 of the paper; then, still winding the same way, go 
 back over the first coils, but be careful that the wire 
 does not slip, and that the second row does not sink 
 between the first. 
 
 After going back about \ in. or so, fix the end 
 by giving two or three turns on the opposite leg of 
 the magnet or by any other way that may be con- 
 venient, and give the whole magnet another coat of
 
 ioo DYNAMOS AND ELECTRIC MOTORS. 
 
 Brunswick black; let this get dry (it does not take 
 long), and go ahead again, always applying a fresh coat 
 of varnish when an end is reached. By taking care in 
 turning, and repeating the coats of Brunswick black, 
 all danger of slipping will be avoided. 
 
 The wire coils will not lie close together on the out- 
 side of the bent part of the iron core. Keep them close 
 
 Fig. 89. Plan of Field Magnet and Block. 
 
 on the inside, however, and make them radiate nicely 
 for the sake of appearance ; winding round the bent 
 part in this way will not interfere with the working. 
 
 When the winding has been continued till the 
 coils laid measure about | in. in diameter all over, 
 finish off at the opposite end from which you began 
 by tying a piece of thread close up to the finish, 
 leaving another 6-in. length of wire. Wind the 
 thread in different directions, and fasten it off with a 
 knot. See that the ends of the iron core are flat 
 and bright. (See Figs. 88, 89, and 90.) 
 
 For the armature take a small piece of soft 
 wrought iron, Ifi in. long, \ in. thick, or a little
 
 ELECTRIC MOTORS WITHOUT CASTINGS. 101 
 
 thicker, and f in. wide ; file it smooth all over, and 
 take off all sharp edges. Get a short strip of paper, 
 f in. wide, and paste it Touri,d the exact middle of the 
 iron until there are thwfe'-'Ot four thicknesses on. 
 Give the paper a coat of Brunswick Wack. and let 
 it dry. 
 
 Now begin to wind the armature, using No. 36 s.w.o 
 silk-covered copper wire. Take great care in winding 
 
 Fig. 90. Front Elevation of Field Magnet and Clock. 
 
 the armature, turning backwards and forwards as with 
 the field magnet, giving each layer a coat of Bruns- 
 wick black, and wind on as much wire as the armature 
 will accommodate. The more neatly the work is done 
 the more wire will be got on, and the better will be 
 the results ; finish off in the middle, and leave tags 
 at each end about 2 in. long. See that the coils are 
 not more than in. across in front, or the magnet will 
 rub them. Fig. 91 (p. 102) will show what is meant. 
 While winding the armature, it may be tried in different 
 positions against the magnet, to see that the coils are 
 quite clear of other parts, for if they do not touch 
 while the armature is against the magnet, it may be 
 assumed that they will be all right afterwards.
 
 loz DYNAMOS AND ELECTRIC MOTORS. 
 
 The brushes are simply two thin copper strips, 3 in. 
 long and ^ in. wide, bent to the required shape, with 
 a piece' trf silk-covered, 'coppe? wire about 6 in. long 
 soldered to each, and each' liaving a small hole drilled 
 
 Fig. 91. Armature, showing |-in. Limit. 
 
 at one end to take a small wood screw, as shown in 
 Fig. 92. 
 
 The commutator should be in two parts, arranged 
 BO that the brushes work on one face, and not on 
 
 Fig. 92. Shape of 
 Brush. 
 
 Fig. 93. Face of 
 Commutator. 
 
 the rim. This plan has been adopted ^ as the motor is 
 designed to be made without using a lathe, and to 
 true up a round surface is next to impossible without 
 a lathe. 
 
 For the body of the commutator take a cylindrical 
 piece of hird wood not less than f in. diameter, and
 
 ELECTRIC MOTORS WITHOUT CASTINGS. 103 
 
 cut off in. of it quite square. A piece of an old 
 round ruler does very well indeed ; true up both flat 
 faces, and carefully drill a hole through the exact 
 centre large enough to fit tightly on a thick knitting- 
 needle, 2 in. of which will make a very good steel 
 shaft. 
 
 From sheet copper cut a disc of the same size as 
 the wooden body, and fasten it on the wood with 
 four small wood screws, and counter-sink them as 
 
 Fig. 94. Armature Shaft complete. 
 
 shown in Fig. 93. Cut the copper right through the 
 centre with a file, and saw down through the wood for 
 about \ in ; the thickness of a small saw-cut will be 
 quite wide enough for the slits. 
 
 Having gone so far, take off the two pieces of copper, 
 mark them so that they can be put on again in the 
 same positions, and cut a notch in the middle of each 
 as in Fig. 93, to prevent any chance of contact with the 
 shaft ; screw them on again, and glue into each side of 
 the slot two little pieces of boxwood or bone, so that 
 they stand just above the copper. Then file up 
 the whole face, bone strips, and screw-heads to a true 
 and even smooth face, square with the shaft-hole. 
 
 Make the yoke for the armature from sheet brasa 
 about ^ in. thick. Cut a piece about If in. long and 
 J in. wide, and bend it as shown to the right in Fig. 94, so
 
 104 DYNAMOS AND ELECTRIC MOTORS. 
 
 that it will touch the ends of the armature and enclose 
 the coils. It may perhaps be necessary to cut it a 
 little longer than If in. ; all depends on how much 
 wire has been wound on the armature. 
 
 In the centre of this yoke drill a hole to fit the 
 bit of knitting-needle which forms the shaft ; then 
 carefully adjust the yoke on the armature so that the 
 hole for the shaft comes exactly in the centre of the 
 armature and coils ; fasten both together with twine to 
 prevent any chance of shifting, and solder the two 
 ends of the yoke to the two ends of the armature. 
 
 Now place the steel shaft through the hole in the 
 yoke, see that it is perfectly perpendicular to the 
 
 Fig. 95. End View of Brass Bearing for Armature Shaft. 
 
 face of the armature, and solder it in, taking care not 
 to drop any hot solder upon the armature coils. As 
 there will not be much chance of truing up afterwards, 
 try to get everything square when fixing in the shaft. 
 
 The shaft bearings are four pieces of brass cut from 
 the same piece as the yoke, or from sheet brass a little 
 thicker ; two measure about 1 in. by T \ in., and two 
 about in. by -^ in. They are each drilled, as shown 
 in Figs. 94 and 95, to take four small wood screws and 
 the shaft. The best way to drill the shaft-hole, shown 
 in the centre of Fig. 95, is to fix both pairs of brasses 
 to any spare piece of wood side by side, just in the 
 position they will occupy on the frame, only close to- 
 gether, and carefully drill right through both at once, 
 square and true. Before taking them off mark them 
 all, to ensure getting them back in their places when 
 they are to be fixed. 
 
 The [stand and blocks can be made of any kind of 
 hard wood preferred. Their form does not matter much, 
 so long as the one at the top of the field magnet is made 
 as shown in Figs. 88, 89, and 90. 
 
 The block for the bearings and shaft can be a simple
 
 ELECTRIC MOTORS WITHOUT CASTINGS. 105 
 
 cube ; only both blocks must be of such a height as to 
 bring the centre line of the shaft on a level with the centre 
 line of the field magnet ends. The blocks can be glued 
 on the stand after their positions have been determined, 
 or fastened by screws through the bottom of the stand, 
 or they may be fixed in both ways. Four little binding- 
 screws will be wanted for the stand, as in Fig. 87 (p. 98), 
 which is a sketch of the model in its simplest form 
 complete, but not drawn to scale. 
 
 When fixing, the commutator, with its copper face 
 outwards, can be slipped on the shaft right up to the 
 yoke, the slits being parallel with the length of the 
 armature. A little strong glue dropped on each side, 
 between the yoke and the wooden back of the com- 
 mutator, will hold them together quite tight enough, 
 especially if the shaft-hole is not large. 
 
 Now bring out the ends of the coil, one to each side 
 of the yoke ; cut them just long enough to reach the 
 edge of the copper face of the commutator, but not to 
 press against the yoke ; bare the ends, and solder one to 
 each segment of the rim, taking care that no solder runs 
 on up the copper face. 
 
 Cut a small disc of stout lead A, solder this 
 on the end of the shaft in such a place that it balances 
 the armature, commutator, etc., and put it on true to 
 prevent any wobbling. This little disc has two uses : 
 it makes the model run easier by means of its balancing 
 power, and it helps the armature over the two dead 
 points. 
 
 The magnet may now be screwed tight on its seat, 
 silk ribbon having been previously wound round the coils 
 to prevent the wood cutting them. The brass bearings 
 can then be put on the other block in their proper places, 
 the one farthest from the magnets being flush with the 
 side of the block, so that a little brass washer can work 
 against it. This washer must be soldered on the shaft 
 as shown at B in Fig. 94, where A is a lead disc, c o 
 the bearings, D the brush, E the commutator, v the 
 yoke, and a the armature.
 
 io6 
 
 DYNAMOS AND ELECTRIC MOTORS. 
 
 Put on the shaft, and fasten up the bearings. 
 Slack the button of the field magnet, and adjust 
 it so that the armature will run freely, as near as 
 possible to the end of the magnet without any chance of 
 touching. Fasten on the brushes, one on each side of the 
 shaft, and between the bearings ; mind they touch 
 nothing but the wood. Set the armature opposite the 
 ends of the magnet, and bend the brushes so that they 
 each press gently on the commutator. The dotted lines 
 
 Fig. 96. End Elevation. Fig. 97. Side Elevation. 
 
 Figs. 96 and 97. Miniature Electric Motor with Iron Yoke. 
 
 in Figs. 93 and 94 (pp. 102 and 103), show a position for 
 the brushes, but their best place will be found after 
 the model has been set going. 
 
 Now bring the ends of the wires from the brushes to 
 the two first binding-screws, and the two ends of the 
 field magnet coil to the other two. Let us number the 
 four binding-screws from 1 to 4, Nos. 1 and 2 being con* 
 nected to the two fore ends of the field magnets, and 
 Nos. 3 and 4 to the two brushes. By connecting 
 one pole of a battery to Nos. 1 and 3, and the 
 other pole to Nos. 2 and 4, the armature and fields 
 will be in parallel. In other words, if it were a 
 dynamo, with a lamp where the battery is in the 
 circuit, it would be said to be a shunt machine. 
 If now, with a short length of spare wire, Nos. 2 
 and 3 be joined, and one pole of the battery con- 
 nected to No. 1, and the other to No. 4, the armature 
 and fields will be in series. Also by connecting Nos. 1
 
 ELECTRIC MOTORS WITHOUT CASTINGS. 107 
 
 and 4 with a spare piece of wire, and the battery to 
 Nos. 2 and 3, they will still be in series, but the current, 
 not the motor, will be reversed that is, if you have not 
 turned the battery round, or placed the pole that was in 
 No. 1 into No. 2, and the same the other side. Another 
 way is to connect one cell to Nos. 1 and 2, and another 
 cell to Nos. 3 and 4, then reverse the current in either 
 Nos. 1 and 2, or Nos. 3 and 4, and the motor will be 
 reversed. 
 
 Anyone who follows the foregoing instructions with 
 a little care may have a small model electric motor at a 
 
 U 
 
 Fig. 98. Side Elevation. 
 
 Fig. 99. End Elevation. 
 
 Fijjs. 98 and 99. Small Motor, with Horse-shoe Magnet 
 and Wooden Saddle. 
 
 merely nominal cost, the only expense being the copper 
 wire, four small binding-screws, and some small wood 
 screws ; almost any kind of close-grained wood can be 
 used for the stand. All the rest of the stuff, such as the 
 iron, odd bits of copper, brass, etc., might be got from 
 an old scrap-heap. 
 
 Two other small motors are shown in Figs. 96 to 106. 
 A fair-sized motor of this type, with a fly-wheel about 
 lj in. in diameter, will be found very handy to revolve 
 small Geissler tubes, or to work small models. In the 
 motor here described, the balance-wheel of a small round 
 American clock was used for a fly-wheel, which is about 
 f in. in diameter. The drawings are all in proportion, 
 so that a scale can be made, which will serve to work 
 from.
 
 io8 DYNAMOS AND ELECTRIC MOTORS. 
 
 Figs. 96 and 97 (p. 106), show an end and side eleva- 
 tion of the motor, with a small angle iron for a yoke, into 
 which the magnet cores are either screwed or bolted. 
 This method, of course, is the neatest, and will look the 
 best ; but as it necessitates the use of a few extra tools, 
 nothing more will be mentioned about it, the drawings 
 speaking for themselves. The simpler form, shown 
 complete by Figs. 98, 99, and 100, will be followed ; 
 here a piece cf round bent iron serves for a magnet, held 
 in its place by a small wooden saddle and a button. 
 In fact, the whole motor given in these three figures 
 can be made from a few scraps of iron, brass, and wood. 
 
 Fig. 100. Plan of Small 
 Motor. 
 
 Fig. 101. Bearing 
 Brackets. 
 
 A piece of soft iron wire, \ in. in diameter, will make 
 the magnet, bent to the form and proportions given in 
 Fig. 103 (p. 110). Two little brown-paper bobbins, with 
 very thin wooden ends, will be required, as in Fig. 102 ; 
 fill these with No. 26 s.w.o. or No. 28 S.W.G. silk- 
 covered copper wire. It does not matter at which end 
 of the bobbins the wire ends come out as long as they 
 are connected one with the other. 
 
 To connect the coils of the magnet, one end it 
 matters not which will have to go direct to one of the 
 binding-screws, and be clamped under it, while the 
 other end has to be clamped under the foot of the back 
 bearing bracket. The wire from the other binding-screw 
 goes to the foot of the break spring (see Figs. 98 to 100). 
 
 Having made a little stand of polished or varnished
 
 ELECTRIC MOTORS WITHOUT CASTINGS. 109 
 
 wood, fix a small block at one end and clamp in the 
 magnet and bobbins by means of a wood screw and a 
 wooden button. Figs. 98 and 100 show this part of the 
 fitting. The bearing brackets (Fig. 101) are cut out of 
 sheet brass. The back one, between the bobbins of the 
 magnet, has a small hole drilled half through it; the other 
 carries a small screw with a hole drilled at its end ; the 
 two form point bearings for the fly-wheel spindle. These 
 brackets should be fastened to the stand, so that the cross 
 armature may revolve as close as possible to the poles 
 of the electro- magnet without touching it (see Figs. 98 
 
 Fig. 102. Bobbin for Magnet Coila. 
 
 to 100). Two small binding-screws are fixed to the 
 side of the stand (see Figs. 98 to 100) ; one end of the 
 coil on the bobbins is fixed under one binding-screw, 
 and the other end of the coil is fixed under the back 
 bracket bearing. 
 
 The most delicate part of this model is the contact 
 spring, and as the machine is so small the pressure of 
 this spring must be very slight indeed, although making 
 good contact when required. One of the best methods 
 of making this spring is to take a length of No. 24 s.w.G. 
 or No. 22 S.W.G. silk-covered copper wire and bare about 
 i in. at one end ; beat this out with a hammer, almost 
 as thin as copper foil, cut the tip square, coil up the rest 
 of the wire to form a spiral, and slip it loosely over a 
 small wooden peg in the stand (see Figs. 98 to 100), 
 fixing the bottom of the spring to the stand by means of 
 a small spot of glue. The little flattened tip must be 
 bent with a pair of pliers, so that it will just touch the 
 tips of the teeth on the contact breaker, leaving them 
 free whenever the arms of the armature are exactly 
 opposite the poles of the magnet. The other end of this 
 contact spring goes under the other binding-screw. All
 
 no DYNAMOS AND ELECTRIC MOTORS. 
 
 ends of wire are, of course, scraped clean and bright just 
 before being clamped under binding-screws, etc. 
 
 The small armature is made of soft wrought iron, 
 about T \ in. thick, and must be cut to the shape shown 
 in Fig. 104. File and trim it up true, and drill a hole 
 
 Fig. 103. Horse-shoe 
 Magnet. 
 
 u 
 
 Fig. 104. Iron 
 Armature. 
 
 through its centre to take the spindle or shaft. Tin 
 the tips of the arms on one side ; then, with a small 
 copper bit, solder the tips to the rim of the balance- 
 wheel. 
 
 The contact breaker for this size of motor should 
 
 Fig. 105. Setting-out 
 Contact Breaker. 
 
 Fig. 10G. Fly-wheel Arma- 
 ture and Contact Breaker. 
 
 be about \ in. in diameter when finished. It is made 
 from sheet brass, T* in. thick. Fig. 105 shoAvs the 
 method of setting out the four teeth, which can be cut 
 with a small file. A hole must be carefully drilled 
 through the centre and the contact breaker soldered to 
 the shaft of the fly-wheel, as shown in Fig. 106, on the 
 side opposite to the armature. After trimming all up, 
 this completes the fly-wheel. 
 
 It is not necessary to describe how to make such 
 small binding-screws as will be required; dealers sell 
 them for about ld. each.
 
 ELECTRIC MOTORS WITHOUT CASTINGS, in 
 
 The model works by the current entering at one 
 binding-screw, going round the coils of wire and 
 making the core a magnet, which then attracts its 
 armature. At the moment the armature is opposite 
 the poles, the current is broken by the spring leaving a 
 tooth on the contact breaker ; the core immediately 
 ceases to be magnetic, and allows the armature to 
 proceed by the impetus given to the fly-wheel it is 
 fastened to till the spring touches the next tooth, and 
 so on. 
 
 A small dry cell will be the most convenient for 
 driving the little model. One pole of the cell must be 
 connected to one binding-screw, and the other pole to the 
 other binding-screw. A small switch can be added to 
 cut ofl the current and stop the motor ; otherwise, one 
 wire must be 1 disconnected from one of the binding- 
 screws. 
 
 A half -pint bichromate cell also will drive the little 
 motor well, and for one charge from six to eight 
 hours' work can be taken from it, either at odd times 
 or at one run 
 
 When the model is complete, for appearance 
 sake it should be neatly painted with red sealing- 
 wax varnish, black paint, or Brunswick black. 
 Sealing-wax varnish is used so much for electrical 
 models, etc., on account of its insulating properties, 
 which are far above ordinary oil paints. The coils need 
 not be painted ; and unless special wire is bought, the 
 silk on it will be green. Keeping all brass bright 
 and showing the coils of green silk-covered wire will 
 give a very pretty appearance to the model, which 
 when made very small, is a taking little novelty.
 
 XI2 
 
 CHAPTER IX. 
 
 HOW TO DETERMINE THE DIRECTION OF ROTATION O? 
 A MOTOR. 
 
 IN dealing with some of the principles on which electric 
 motors act, we will take as an example the Siemens H. 
 girder type. This form of motor has been chosen partly 
 because of its simplicity of construction, partly as it is 
 such a favourite form for small motors. In this chapter 
 an endeavour will be made to make the principles clear 
 by illustrating some of the laws that govern this type 
 of machine, without in any way going into the subject 
 of construction. 
 
 The principal law to understand is that governing 
 what happens when a length of covered copper wire is 
 wound round a bar of soft iron, and an electric current 
 is passed through the wire. It is, of course, well known 
 that the iron becomes a magnet, and remains a magnet 
 as long as the current flows ; but there are other laws of 
 great importance to be considered. 
 
 Take a small bar of iron, as N s in Fig. 107 ; hold the 
 end N in your left hand, and wind a length of covered 
 copper wire upon the iron, beginning from your left 
 hand and proceeding towards the other end, describing 
 circles with your right hand in the same direction as 
 the hands of a clock turn that is, away from you on 
 top of the iron, and towards you underneath. If you 
 now pass an electric current through the wire coil, from 
 the left-hand end to the right-hand end, as shown by 
 the arrows that is, if you connect the carbon plate 
 of an active battery to the left hand, and the zinc plate 
 to the right the left-hand end of the iron becomes the 
 north pole of a magnet, and the end that is at your 
 right hand becomes the south pole.
 
 DIRECTION OF ROTATION OF A MOTOR. 113 
 
 Now take the iron bar, but wind it in the reverse 
 way that is, as you wind on the wire describe circles 
 with your right hand in a direction contrary to that 
 taken by the hands of a clock, as in Fig. 108 that is, 
 pass the wire from you when going under the iron, aud 
 bring it towards you when coming over the top. Then 
 send the current, as before, in at the left-hand end and 
 out at the right, as shown by the arrows, and the poles 
 
 sr/y / / 
 
 |H 
 
 Fig. 109. 
 
 \ 
 
 Nl\\\\\k 
 jj V V v V v ' 
 
 Fig. 110. 
 
 Figs. 107 to 110. Directions of Currents and Resultant 
 Magnetism in Bar Magnets. 
 
 will be reversed that is, the north pole will be towards 
 the right hand, N, and the south pole to the left, s. 
 
 Fig. 109 is wound in the same direction as Fig. 107, 
 but the current flows, as shown by the arrows, from the 
 right hand to the left ; this will cause the poles to be 
 reversed. Fig. 110 is wound in the same direction as 
 Fig. 108 ; but by reversing the direction of the current, 
 as shown by the arrows, the poles again become reversed, 
 as occurred in the other case. This is what happens in 
 a shuttle armature when the brushes cross the insulating 
 strips of the commutator : the direction of magnetism 
 set up in the armature by the armature current is 
 reversed by the current being reversed. 
 
 A very good way to master this rule is to get a piece 
 of wood, and mark one end "S" and the other end 
 " N." Then get a piece of string; on one end tie a label, 
 ft
 
 ii4 DYNAMOS AND ELECTRIC MOTORS. 
 
 marked " +," or positive, on the other end tie another 
 label marked " ," or negative. With the stick and the 
 string practise the foregoing rule. 
 
 The next law to be understood is (a) if poles of the 
 same kind are brought near each other, they will repel 
 one another ; (6) if two different poles are brought to- 
 gether, they will attract one another that is, north to 
 
 Fig. 111. Tl'l'l Fig. 112. 
 
 Figs. Ill and 112. Series Motors. 
 
 north, repulsion ; south to south, repulsion ; but north to 
 south, attraction. 
 
 In the diagrams of motors (Figs. Ill to 116), the 
 commutators and brushes have been left out in order 
 to simplify the drawings. It must be understood that 
 at the moment the two poles of the armature are 
 opposite the two poles of the field magnet, the two 
 brushes are resting upon the insulating strips of the 
 commutator ; immediately after that, as the armature 
 rotates, the direction of the current is changed through 
 the armature and its poles reversed. Though this is 
 not the exact fact in practice, in this case we may 
 assume it to be so. 
 
 In a motor of the Siemens type driven in series, the 
 current passes either first round the magnets, then
 
 DIRECTION OF ROTATION OF A MOTOR. 115 
 
 through the armature, and back to the batter y, as in 
 Fig. Ill, or in the reverse direction, first through the 
 armature, then the magnets, and back to the battery, 
 as in Fig. 112. It may appear curious, but whichever 
 way a current is sent through a series motor, as shown, 
 it will rotate the same way. 
 
 Let us follow the winding in Fig. Ill, starting 
 from the battery. We will suppose that the direction of 
 the current is as shown by the arrows. The first magnet 
 core to be reached is the left-hand one ; this, it will be 
 observed, is wound as the iron bar in Figs. 108 and 110, 
 and if the foregoing law has been understood, it will 
 be seen that a south pole is left behind the winder. 
 Crossing over to the other core, the winding is done 
 as shown in Fig. 108, and this produces a north pole 
 at N. After this the current goes to one brush, then 
 through the commutator (these are not shown), and into 
 the armature, wound in the same way as the bar in 
 Fig. 109, which produces a north pole to the right and a 
 south pole to the left. After this, the current again goes 
 through the commutator, through the other brush, and 
 so returns to the battery. 
 
 The position of the armature as shown in Fig. 
 Ill is a little beyond the horizontal, so that the 
 brushes are in contact with the commutator, and the 
 current will flow through the whole machine. Now 
 study what happens. The south pole of the armature 
 is against or near the south pole of the magnet, and 
 the north pole of the armature is near the north pole 
 of the magnet. This means mutual repulsion, so the 
 armature takes the motion indicated by the curved 
 arrow above it, which, by the way, shows the direction 
 of motion in all the diagrams. Influenced by repulsion, 
 this motion continues until the south pole of the arma- 
 ture nears the north pole of the magnet ; then, as they 
 are of different poles, they will attract each other until 
 the south pole of the armature has arrived exactly 
 opposite the north pole of the magnet. At that moment 
 the insulating strips cross the brushes and change the
 
 n6 DYNAMOS AND ELECTRIC MOTORS. 
 
 poles of the armature, and what was formerly the south 
 pole in the armature now becomes its north pole, and 
 like poles are again together and mutual repulsion is 
 set up, causing a repetition of the same series of motions 
 as has just been described. 
 
 If the battery current is now reversed, as shown in 
 Fig. 112 (p. 114), and the winding is followed out, it will 
 be found that every pole has been changed, so that again 
 we have like poles to like, and the motion becomes the 
 
 Fig. 113. Fig. 114. 
 
 Fig. 113 and 114. Shunt Motors. 
 
 same as in Fig. 111. This means that if a motor is 
 driven in series, it will turn in the same direction, 
 whichever way the current goes. 
 
 When a motor is driven as a shunt machine, the current 
 from the battery is divided part being shunted to the 
 magnets and part to the armature. After the divided 
 current has passed through the machine, it again unites 
 in one wire and returns to the battery. By following 
 the windings and the direction of the current in Fig. 113, 
 it will be seen that the left-hand limb s is the same 
 as s in Fig. Ill (p. 114), and that it is a south pole; 
 the other must, of course, be a north pole, as the two
 
 DIRECTION OF ROTATION OF A MOTOR. 117 
 
 limbs of the magnet are always wound so as to give 
 opposite poles. Now follow out that branch of the 
 current which passes through the armature ; this will 
 enter on the left-hand side and be wound with a coil 
 going in the direction shown in Fig. 109 (p. 113); this 
 will give a north pole to the left, and a south pole to 
 the right. The current then goes through the commu- 
 tator, etc., after which it joins the current round the 
 magnet, and so returns to the battery. 
 
 In this case it will be seen that we have unlike poles 
 
 Fig. 115. Fig. 116. 
 
 Figs. 115 and 116. Motors driven with Two Batteries. 
 
 near each other ; these exert mutual attraction, and the 
 armature rotates in the direction opposite to that shown 
 in both Figs. Ill and 112 (p. 114). 
 
 Now study what happens when the shunted part of 
 the current is reversed through the armature, and the 
 part of the current through the magnets is left as it was. 
 Fig. 114 will show this. We have like poles together, 
 exerting mutual repulsion, and the motion of the arma- 
 ture is reversed, turning in the same direction as shown 
 in Figs. Ill and 112. We should also get a reversal by 
 reversing the current round the magnet whilst keeping
 
 nS DYNAMOS AND ELECTRIC MOTORS. 
 
 the current in the armature in the same direction as in 
 Fig. 113 (p. 114). 
 
 For further study, suppose that the motor is driven 
 with two batteries, one to excite the magnets and the 
 other to excite the armature, as in Figs. 115 and 116. 
 If now the windings and the direction of the current 
 are followed out as in all the other cases, the direction 
 in which the armature will move will be seen readily. 
 Here, as was the case with the shunt motor, if the current 
 is reversed in either the magnet or the armature, the 
 direction in which the motor turns will be reversed. 
 
 Note that all the diagrams, from Fig. Ill to Fig. 116, 
 are wound the same way ; this has been done to show 
 some of the different ways that one motor can be driven, 
 by making different combinations with the current. But 
 too much space would be required to show all com- 
 binations of winding and all combinations of current 
 possible. As there are many more combinations than 
 those shown, the reader will find it useful to sketch out 
 a few skeleton diagrams, and put the windings and the 
 currents in various ways different from these, and work 
 out the motions himself. 
 
 As an example, supposing you have just bought the 
 castings of a small model girder-motor, and that you 
 wish to make it turn the reverse way to Figs. 1 11 and 112 
 (p. 114), when driven in series. Wind the magnet as in 
 Figs. Ill and 112, but wind the armature as in Figs. 110 
 and 113 ; or, on the other hand, wind the armature as it 
 is in Figs. Ill and 112, but reverse the twist in the 
 magnet. Then you will have a motor that, when driven 
 in series, will turn in the reverse direction to that shown 
 in Figs. Ill and- 112. All this is very simple when 
 once the law of winding a simple bar of iron has been 
 mastered, and it is remembered that two like poles repel, 
 and two unlike poles attract each other. 
 
 Finally, it must be said that it is always best to drive 
 a motor with the current it was intended to take, and if 
 it is desired to try experiments of this sort, rig up a 
 motor specially for the purpose.
 
 CHAPTER X. 
 
 HOW TO MAKE A SHUTTLE-AKMATURE MOTOR. 
 
 THE small electro-motor shown in the accompanying 
 illustration (Fig. 117) is suited to the requirements of 
 those who have access to a lathe for turning certain 
 parts. It is a machine that will look very well indeed 
 
 Fig. 117. Shuttle- Armature Motor Complete. 
 
 if good workmanship is shown in the fitting and 
 finishing of the various parts. But some careful fitting 
 is required to make it run well. When properly 
 made, it will drive a small polishing or dental lathe, or 
 a small fretwork machine, or a small drilling-machine, 
 or even a light sewing-machine, with a battery power of 
 some three or four quart chromic acid cells, or the 
 equivalent electrical energy from any other source. 
 
 The set of castings required consists of two malleable 
 iron field magnet cores and bridges, as shown at Fig. 118, 
 each measuring 4 in. in length by 2J in. in width ; one 
 malleable iron casting (Fig. 119) for the armature,
 
 120 DYNAMOS AND ELECTRIC MOTORS. 
 
 measuring Z\ in. in length by If in. in diameter ; two 
 gun-metal castings, 1| in. in diameter (Fig. 120), for ends 
 of the armature ; two brass castings of four-legged 
 spiders for the bearings of the spindle ; one brass casting 
 of a pulley, l\ in. diameter by T 9 ^ in. thick ; one brass 
 casting of a collar, 1 in. diameter by in. thick ; two 
 brass end-pieces, 2^ in. by f in. (Fig. 121), to form feet 
 for the field magnets ; one brass casting for a brush 
 rocker, 2 in. in length (Fig. 122) ; two brass castings 
 
 Fig. 118. Field Magnet Casting for Shuttle-Armature 
 Motor. 
 
 of brush-holders (Fig. 123) ; two brass castings of set 
 screws (Fig. 124) ; castings for the brass nuts, brass tube 
 for commutator, and a strip of phosphor bronze for the 
 brushes. These having been obtained, we will set about 
 fitting and finishing the various parts and putting them 
 together. 
 
 The field magnet castings, if rough, will require 
 to be filed to make them fit and have a presentable 
 appearance. All lumps should first be filed down with 
 a flat bastard file. The channel for the armature must 
 next be smoothed with a half-round file, care being taken 
 not to do more than smooth the casting. The corners 
 of the cores should be rounded off, to prevent them 
 from cutting into the insulating cover of the wire aa 
 this is being wound o*n. The outsides may now be 
 smoothed and the ends trued, to make the whole fit well
 
 A SHUTTLE- ARMATURE MOTOR. isi 
 
 together. The top casting for the field magnet is usually 
 a little thicker than the under one. The under field 
 magnet casting will have the two brass feet or holding- 
 down pieces, shown at Fig. 121, fitted under each end, 
 and must therefore have two hoies drilled at each end. 
 These receive two small screws, which pass through the 
 
 Fig. 119. Armature Casting for Shuttle-Armature Motor. 
 
 brass feet and the lower casting into the top casting, as 
 shown in Fig. 129 (p. 126). Small holes for set screws, 
 to hold the feet of the spiders, must also be drilled and 
 tapped in the corners of the armature channel, as shown 
 
 Fig. 120. Gun-Metal Casting for Armature Ends. 
 
 at Fig. 129 ; these are fitted with round-headed brass 
 screws. Thus prepared, the castings may have a coat 
 of Japan black and be set aside to dry. 
 
 The armature is of the Siemens H-girder type, in one 
 casting of malleable soft iron. This must be filed smooth 
 and true at the ends, and the channel must be made 
 smooth with a file. The gun-metal end-pieces shown at
 
 122 DYNAMOS AND ELECTRIC MOTORS. 
 
 Fig. 120 will be fitted to the ends of the armature, to 
 hold the steel spindles. These are made from two 2-in. 
 lengths of -in. steel rod, turned true and smooth down 
 to -j 8 ,,- in. diam. Turn the end-pieces smooth, drill a 
 T \ in. hole through the boss of each, and drive one end 
 of each spindle into each boss. 
 
 The end-pieces will be secured to the ends of the 
 
 
 
 Fig. 121. Gun-Metal Foot for Motor. 
 
 armature, after being fitted true to it, by small brass 
 screws ; holes must therefore be drilled through the end- 
 pieces and into the armature, which is tapped to receive 
 the screws. In one of the end-pieces drill two extra holes 
 for the ends of the armature coil to come through, and 
 bush these holes with small tubes of ivory or bone. When 
 
 Fig. 122. Rocker for Brush-Holders. 
 
 the ends are fitted on, mount the armature in a lathe, 
 and true it by turning away just enough to take off the 
 rough skin. This done, mark all the screws and screw- 
 holes to correspond, so that they can be identified when 
 the machine is being put together. Take off the ends, 
 and dress the web and channel with shellac or good 
 sealing-wax varnish, then set aside to dry, ready for 
 winding. 
 
 Brass castings as shown at Fig. 117 fulfil the 
 double purpose of clamps to hold the field magnets
 
 A SHUTTLE- ARMATURE MOTOR. 123 
 
 together and of bearings for the armature spindles. 
 These must now be drilled to fit the spindles, with 
 holes in each foot to receive the holding studs, and 
 with small oil holes for each bearing ; then they must be 
 filed smooth and neatly polished. The projecting boss 
 of one of these bearings must be turned to form a 
 bearing for the brush rocker (Fig. 122), which will fit on 
 
 Tig. 123. Casting for Brush-Holder. 
 
 like a sleeve. The insides of the spider legs and bodies 
 should also be turned smooth. 
 
 The casting for the brush rocker is shown at Fig. 122. 
 The hole in the centre must be bored to fit the boss on 
 the bearing above-mentioned ; and a hole must be 
 drilled and tapped in the edge of the rocker to receive a 
 set screw for fixing the rocker in any required position. 
 
 Fig. 124. Casting for Milled Head Screw. 
 
 Two rough brass castings, as shown at Fig. 123, must be 
 turned and filed to the form shown at Fig. 125 (p. 124), to 
 form brush-holders, and these are held in holes, B B, drilled 
 through the ends of the rocker (Fig 122). The holes in 
 the ends of the rocker are drilled T \ in. in diameter, 
 and bushed with vulcanite or asbestos board, with a 
 collar of the same on each side, to insulate the brush- 
 holder from the rocker. A fairly good bush can be 
 cut from a piece of rubber tube, with two collars of thin 
 cloth to come between the shoulder of the brush -holder 
 and the rocker on one side, and the nut and the rocker 
 011 the other ; but indiarubber is liable to be destroyed
 
 124 DYNAMOS AND ELECTRIC MOTORS. 
 
 by oil. In Fig. 125 the part B is first turned to in. 
 diameter, and a thread chased on it to receive a brass 
 nut. The plain part to the left of the chased thread 
 must be drilled transversely with a -j^-in. hole, c, to 
 receive the conducting wire, and this hole is met with 
 another, E, drilled from the end, and tapped to receive a 
 binding-screw with a milled head, as shown at Fig. 126. 
 
 Fig. 125. Brush -Holder Fig. 126. Screw with 
 
 complete. Milled Head. 
 
 The other end of the brush- holder, D, is turned parallel, 
 a slot gV in. wide is cut up to the shoulder A, one side of 
 the holder is filed flat, and a ^ in. hole is drilled through 
 both jaws ; the hole in one jaw is tapped to receive a 
 brass screw, which passes freely through the other jaw. 
 
 The brushes are strips of phosphor bronze foil, 
 2 in. by ^ in., cut to the form shown at Fig. 127. Six 
 
 Fig. 127. Brush. 
 
 of these strips soldered together at one end form a pad. 
 A slot, \ in. by i in., is cut through the middle to 
 receive the adjusting and tightening screw. There is a 
 brush-holder (Fig. 125) at each end of the rocker, and in 
 the jaws of this the brush is held. 
 
 A two-part commutator, made of a brass ferrule split 
 into two equal parts, will be required. On this form of 
 armature there is only one coil, the two ends of which 
 are connected to the two parts of the commutator. The 
 brass tube which will be suitable for the castings has an 
 internal diameter of \\ in. This is fitted on a boxwood 
 boss \ in. in width, bored with a hole which exactly
 
 A SHUTTLE- ARMATURE MOTOR. 125 
 
 fits the spindle at that end of the armature with 
 the bushed holes in it. The ferrule is now to be 
 scribed into two equal parts, and on each side of the 
 dividing lines scribe two more lines, so as to have the 
 three lines on each side i in. apart. Through the centre 
 of each of the two side lines drill small holes into the 
 boxwood to receive brass screws, as shown in Fig. 128. 
 
 Countersink the mouths of these eight holes, and 
 screw in the screws tight; then cut the ferrule into 
 two equal parts with an oblique cut, as shown 
 at Fig. 128. This is best done with a hack-saw, 
 so as to make a clean cut through the brass and into 
 the boxwood_beneath it. The boss, with its split ferrule, 
 
 Fig. 128. Commutator. 
 
 is now pressed on the spindle with the inner ends of the 
 oblique cuts adjusted so as to coincide with the wire 
 holes in the armature ends. 
 
 Winding the armature is a simple matter. Measure 
 off 60 ft. of No. 20 S.W.G. double cotton-covered copper 
 wire, roll it into a hank, and soak it for a quarter of 
 an hour in melted paraffin wax, then hang it up to drain 
 and cool. When cool, take the armature in the left 
 hand, and the wire in the right. Place the commencing 
 end of the coil with 2 in. left projecting at the loft side 
 of the channel, and hold it down with the left thumb 
 whilst the wire is wound closely around the web of the 
 armature in close regular turns, side by side, to the right 
 side of the channel, then back again with the same care 
 and regularity, until all the wire has been wound on in 
 regular and even layers. Then twist the two ends to- 
 gether to keep the coil from unwinding. Test each 
 layer for insulation as it is wound on, and test the 
 whole coil again when complete.
 
 126 DYNAMOS AND ELECTRIC MOTORS. 
 
 The end-pieces may now be put on, then the ends of 
 the armature coil may be brought out through the 
 bushed holes in the casting and connected to the 
 commutator. Each end of the wire should be soldered 
 to the inner edge of one of the commutator pieces, along 
 which they may lie to a length of in. The coil may 
 now be given a coat of sealing-wax varnish and then set 
 aside to dry. 
 
 The field magnets must be so wound as to cause the 
 pole above the armature to assume a magnetism of 
 opposite polarity to that of the pole below the armature. 
 It matters but little whether a north pole is at the 
 
 Fig. 129. Section of Motor showing Winding. 
 
 top and a south pole at the bottom, or a south pole at 
 the top and a north pole at the bottom, but they must 
 not be both north poles or both south poles. The cores 
 on the two sides of the arch must be wound in opposite 
 directions. Thus, if we wind the left-hand core of the 
 top magnet from left to right overhanded, we must wind 
 the right-hand core from left to right underhanded. 
 In commencing to wind the lower cores from the left- 
 hand side, we must wind the left-hand core overhanded 
 and the right-hand core underhanded. This ensures a 
 south polarity to the lower pole, as shown in Fig. 129, 
 if the current is sent through the wires in the direction 
 shown by the arrows. 
 
 Wind each core regularly with three layers of No. 20
 
 A SHUTTLE-ARMATURE MOTOR. 127 
 
 S.W.G. double cotton- covered copper wire, and test each 
 layer for insulation. When the last turn on each 
 core has been reached, cut off the wire so as to leave 
 6 in. more than is needed to make the turn ; pass 
 this in under the turn of wire so as to form a kind 
 of half-hitch, and draw it tight to prevent the wire 
 from unwinding ; then give the whole a dressing of 
 sealing-wax varnish to secure each coil in its place, 
 and to give the whole a finished appearance. 
 
 When the machine is being put together, the coils 
 must be connected as here described, and shown 
 at Fig. 129. The finishing end of the first coil at A 
 must be bared of the cotton covering and cleaned ; 
 so also must the commencing end of the second coil 
 on the next core at B. Dip both cleaned ends into 
 some soldering fluid, tin them with a hot soldering-bit, 
 twist the tinned ends together with a pair of pliers, then 
 give them a final touch with the soldering-bit to fuse the 
 solder and unite them. Each end must be thus treated 
 and connected, namely, A to B, c to D, and E to F. The 
 two ends c D may be passed down holes made in the 
 base of the motor, and connected beneath. The two 
 free ends above the upper pole will then go, one to one of 
 the brushes, and the other to one of the terminal binding- 
 screws on the base, if the coils are to be connected in 
 series with the armature ; or both will be connected to 
 the brushes if the coils are to be connected in parallel 
 with the coil on the armature, so as to make a shunt 
 motor. 
 
 When fitting the parts together, the field magnets 
 may be fitted first, the ends of the coils soldered and 
 tucked in out of sight, the screws holding the two cores 
 inserted and screwed tight, and the brass feet screwed 
 on. Next, fit the already turned and polished spider- 
 bearing to the end opposite to that on which the com- 
 mutator is fixed. Then put in the armature, slip the 
 other bearing on its spindle, and screw this bearing in 
 its place. Now turn the armature round by hand, 
 and see that it runs truly in the tunnel, not touching
 
 128 DYNAMOS AND ELECTRIC MOTORS. 
 
 anywhere, but equidistant from the sides at all parts. 
 The back pulley (see Fig. 117, p. 119) should now be 
 fitted on the spindle, and tightened on it by means 
 of a small set screw passing through the boss on the 
 outside. The rocker may next be fitted on, and se- 
 cured to the outside of the bearing by a small set 
 screw. One of the brushes will have its free end bearing 
 on the top of the commutator, and the other brush will 
 press lightly against the under-side of the commutator. 
 
 The brushes B, brush-holders H, and rocker R. complete, 
 are shown in Fig. 130. The exact position of the brushes 
 
 Fig. 130. Brush-Holders, Rocker, and Brushes complete. 
 
 will be determined by the direction of rotation of the arma- 
 ture, the commutator running away from the brushes. The 
 correct angle to set these must be found by experiment. 
 The rocker can easily be moved until the best effect has 
 been obtained, then fixed in this position by the set 
 screw. The collar is now slipped on the spindle, the 
 armature brought forward until it runs free in its proper 
 position, and the collar tightened to prevent undue end 
 shake of the spindle in its bearings. A little end play 
 or shake is always admissible, but side shake, due to 
 loose fitting in the bearings, must never be allowed. 
 The motor may now be mounted on a base made 
 of oak, teak, or mahogany, and furnished with brass 
 terminals to the wire coils, as shown at Fig. 117 (p. 119). 
 The insulation of the wires on the field and armature 
 may be tested in the manner described in Chapter VII.
 
 I2 9 
 
 CHAPTER XI 
 
 UKTY-WATT UNDEETYPE DYNAMO AND MOTOR. 
 
 The following figures show a dynamo which will cither 
 light three 10-volt 5-candle-power lamps, or work well 
 as a motor when supplied with current from a battery. 
 The illustrations are all to a scale of one-half full 
 size, and dimensions may be measured from them. 
 Assuming that the castings and other materials are 
 leady, it will be convenient to consider the work of 
 construction in three divisions first, mechanical con- 
 struction ; second, insulation ; third, winding on the 
 wire and connecting up. 
 
 Commence with fitting up the brackets and armature ; 
 the holes for the shaft must be drilled on the bearings 
 A, A, Figs. 131 and 132 (pp. 132 and 133); at each end of 
 the boss, punch a centre in the middle of the round part of 
 the top of the bearing. The hole should be drilled rather 
 less than in. diameter, a little way in from one end 
 first, then reverse the bearing, and drill up a little from 
 the other end, reverse again, and so on until the holes 
 meet at about the middle. The oil cups B, B, Fig. 132, 
 can be ditlled as shown, the hole at the bottom, about 
 ^a in. diameter, being drilled through into the bearing- 
 hole to allow oil to pass. Drilled thus, the holes for 
 the bearing will be found to be somewhat rough and 
 perhaps not exactly in line ; this will be remedied by 
 a reamer or rose-bit passed carefully through. Use 
 a little oil as lubricant, and work from one end only. 
 If the drilling has been carefully done with a drill about 
 s 1 ^ in. less than the finished size the hole will be reamed 
 quite smooth. Care must be taken not to spoil the 
 bearing surfaces when handling the castings for other 
 operations. 
 I
 
 130 DYNAMOS AND ELECTRIC MOTORS. 
 
 The bore of the field-magnet casting, Figs. 133 
 and 136, if well cast will be very nearly a true circle ; it 
 should be cleaned out with a file to remove any lumps 
 or irregularities. To take a cut through with a boring 
 bar on the lathe makes the best job, but good results may 
 be obtained without this if a good casting is secured. 
 To get the bearings in alignment a dummy armature 
 and shaft must now be made. Get a piece of iron or 
 steel rod just the length of the armature shaft and of 
 a convenient diameter, such as f in., and on this mount 
 tightly a piece of hard wood, about If in. diameter, of 
 the length the armature core will be, and in the same 
 position. Turn the wood to fit tightly in the bore of 
 field-magnet, and turn the rod also at each end to fit 
 the bearings. Place the dummy tight in the bore, 
 slip the bearing castings on the spindle, and fit the 
 end lugs D, Fig. 132, to bed flat on the sides of the 
 field-magnet ; if they are much out, the castings may be 
 hammered until they are somewhere near right, and the 
 final adjustment effected with the file. A little red 
 ochre mixed with oil and smeared on the magnet will 
 show where the lugs touch. It is important that these 
 brackets should bed properly, or they will not be in 
 line when screwed in place, and the shaft will run stiffly. 
 
 The holes for the screws E, Figs. 132 and 133, may be 
 drilled in the bearing castings ; then slip the bearings on 
 the dummy shaft and mark the field-magnet by drawing 
 the point of a scriber round the holes in the castings. 
 Some chalk rubbed on the magnet where the bearings 
 come will assist to show the line. Tapping holes for 
 ^-in. screws may be drilled about | in. deep in the 
 centres of the marked circles. Mark off holes in the 
 field magnet feet for the holding-down screws, the posi- 
 tions being taken from the drawing (see F, Fig. 131). The 
 diameter of the holes may be about ^ in., chamfered 
 to suit the wood screws intended to be used. 
 
 The armature, Figs. 134 and 135, is now to be made ; 
 its shaft is of steel 7f in. long ; if made from rod that is 
 quite straight and true, the diameter can be / in., so
 
 UNDERTYPE DYNAMO AND MOTOR. 131 
 
 that the central portion need not be turned; but it 
 is better to have the diameter f in., and take a lighl 
 cut all along, reducing to & in. diameter. At th 
 pulley end a length of \\ in. has to be turned down to 
 form the bearing, and at the commutator end a length of 
 1\ in. These necks should be left a little large, so that 
 they can be fitted in after the core discs H, Fig. 135 
 (p. 138), are tightened up in place, the screwing up of the 
 clamping nuts J having a tendency to bend the shaft. 
 The screwed portions for the clamping nuts are cut as 
 shown, for about \ in. at each end ; a screw with about 
 twenty threads to the inch is necessary, and is best cut 
 on a screw-cutting lathe ; but if this is not available, the 
 thread may be started with stock and dies and finished 
 with a comb chaser. 
 
 About 120 core discs, about ^ in. thick, must now be 
 prepared. The central holes must pass over the shaft 
 easily ; any burrs must be filed off, for if not flat the 
 screwing-up of the nuts will cause uneven parts to 
 bend the shaft. In the middle of the core is the circular 
 groove K, Fig. 134, \ in. long, to take the binding cord. 
 To make this, a few discs should be reduced in diameter 
 and put on the shaft when half the other discs are on. 
 It is a difficult job to turn out this groove on the lathe 
 if left till the core is complete. Before threading the 
 discs on the shaft one side of each should be painted 
 with a thin coat of enamel or Brunswick black and left 
 to dry. The clamping nuts J, Fig. 134 (p. 138), are 
 circular pieces of brass f in. diameter, with a hole in 
 the centre drilled and tapped T 5 ^ in. to fit the screwed 
 shaft. The side of the nut which is to go next to the 
 discs should be faced up true on a screw mandrel, and 
 the outside corner rounded off as shown in the drawing. 
 Two parallel flats are filed on the edge (see Fig. 135, 
 p. 138) to take a spanner. 
 
 Put the core discs on the shaft, the painted sides all 
 facing one way; see that the core is in the right 
 position lengthways on the shaft, and that the channel 
 L, Fig. 135, for the insulated wire is straight; then
 
 132 DYNAMOS AND ELECTRIC MOTORS. 
 
 screw up the nuts as tight as possible, leaving the flats 
 flush with the channel ; a little oil between the face of 
 the nut and end disc assists. Test the shaft between 
 
 centres, and, if required, straighten it ; then turn 
 down the necks to fit the bearings. When a good fit is 
 attained, place the armature in the field magnet and fix 
 the brackets in place. The armature should be central 
 in the bore and should spin freely with the fingers ; if 
 stiff, ease the shaft bearings until it runs freely and yet
 
 UXDERTYPE DYNAMO AND MOTOR. 133 
 
 without shake. An end movement of about -^ in. is ad- 
 visable. The armature core should coincide lengthways 
 with the field magnet ; should it project from one side 
 
 more than the other, the magnet will try to pull it into 
 a central position. In doing this it pulls against a bear- 
 ing, which will have a tendency to get hot. Any of the 
 core plates that project can be levelled down with a file. 
 The commutator consists of a piece of brass tube M,
 
 134 DYXAUOS AXD ELECTRIC MOTORS. 
 
 Fig. 134, fixed on a wooden bush and carried on the arma- 
 ture shaft. The brass tube is divided into two equal 
 segments by saw-cuts nearly parallel to the axis of the 
 shaft, one portion being connected to one end of the 
 armature wire and the other portion to the other. It is 
 essential that the two portions must not be in metallic 
 communication except through the armature wire, and 
 the segments must not be in metallic communication 
 with the shaft. The commutator may be a piece of seam- 
 less drawn tube, and should be a little over 1 in. outside 
 diameter and f in. long. The thickness may be about 
 i in., so as to allow for truing the surface from time to 
 time as it becomes worn by the brushes. The hardwood 
 insulating bush o, Fig. 134, will be | in. long. Through 
 its centre drill the hole for the armature shaft, using the 
 same drill as for the bearings, and ream it out to fit 
 tightly on the shaft. It is best to use a mandrel to turn 
 the bush on, and when this has been done the tube should 
 be fixed with cement and left to set. The bush must pro- 
 ject I in . at the end nearest the bearing. Mark off centres 
 for two holes in the tube at diametrically opposite points 
 for the screws which are to hold the commutator 
 segments to the bush. These holes may be J in. diam. 
 countersunk into the tube, so that the screw-heads will 
 come nearly flush, just leaving enough projecting to quite 
 fill the hole up when the outside of the tube has been 
 turned true. These screws should be of brass, and must 
 fit tightly, or when turning up the commutator they 
 will come loose. It is very important to have these 
 screws short, so as not to touch the shaft, as there 
 must be no metallic connection between the tube and 
 the shaft. 
 
 Mark on the tube two diametrically opposite lines 
 running from one end to the other midway between the 
 ecrews just put in. These lines are to locate the posi- 
 tions for the cuts p, Fig. 132 (p. 133), which separate the 
 tube into equal parts. These cuts are sawn about -^ in. 
 wide, and aslant, as shown in Fig. 128 (p. 125) ; this 
 causes the brushes to pass from one segment to the other
 
 UNDERTYPE DYNAMO AND MOTOR. 135 
 
 gradually, and lessens the sparking and wear. The 
 amount of slant is not important ; a deviation of about 
 iV in. each side of the centre line will do. Saw down to 
 the bush and slightly into it, so as to separate the seg- 
 ments completely ; see that the slot is perfectly clear of 
 cuttings ; and to keep the segments apart and prevent 
 dust from getting into the slot, insert a thin strip of 
 wood or mica. A little cement or shellac varnish will 
 keep it in place. In each brass segment, at the end next 
 to the armature core, saw a nick just large enough to 
 allow the ends of the armature wire to go in and fit 
 tightly. The complete commutator may now be gently 
 driven on the shaft, the slots being in line with the round 
 part of the core, as shown by Fig. 137 (p. 142) that is, at 
 right angles to the centre of channel L, Fig. 135 (p. 138). 
 
 The oil-guard K, Fig. 133, can be of brass, and is 
 driven tight on the shaft after the commutator is in 
 place. The oil-guards for the pulley ends can be tapped 
 to fit the screwed part of the shaft, or made to fit the 
 plain part, and can be put in place after the armature 
 is wound. 
 
 To fit up the brush gear, Figs. 131, 132, and 133, com- 
 mence with the rocker T, Fig. 132 (p. 132). This allows 
 the brushes to be moved round the commutator in order 
 to find the position which gives best results when working. 
 Bore a hole about in. in diameter in the boss u to fit 
 on to the boss on the bracket, so that the arm is straight 
 and square with the hole. Put the rocker on a mandrel 
 and face each side of the boss. Now put the bearing 
 bracket on a mandrel, and turn down the projecting 
 boss to fit the hole in the rocker. The small boss at 
 the side of the rocker is to take a set-screw, as shown 
 in Fig. 132 ; this screw should fit in the thread. A 
 piece of hard wood is required for the crosspiece to 
 carry the brush-pins (see v, Fig. 131). This should be 
 filed up about \\ in. by in. by \ in. thick ; the angle 
 to receive it must be filed out square to the hole in boss, 
 so that when the crosspiece is fixed in, the pins will 
 come parallel to the shaft. Mark the exact centre of
 
 136 
 
 DYNAMOS AND ELECTRIC MOTORS 
 
 the crosspiece, and drill a hole to clear a countersunk 
 screw \ in. diameter. Now place the crosspiece in posi- 
 tion in the angle of the rocker arm, so that it projects 
 equally at each side, and with a scriber mark off on the 
 
 Fig. 133. End View of Dynamo. 
 
 brass the position of the hole ; drill and tap it to fit the 
 screw. The crosspiece can now be fixed in place. At 
 | in. on each side of the middle, mark centres for the 
 brush-pins, on the centre line of the crosspiece, and drill 
 and tap two holes & in diameter. 
 
 The brush-holders w, Fig. 131 (p. 132), must be 
 finished next. The castings should be filed all over, and 
 the ends squared. Mark the centre at one end of the
 
 UNDERTYPR DYNAMO AND MOTOR. 137 
 
 circular part of the casting, and drill a -&-in. hole through 
 it. The slots for the brushes can be cut from one end 
 with a saw, as shown dotted in Fig. 131. They should be 
 ^ in. long fully -^ in. wide, and parallel with the holes 
 already drilled. Drill and tap the bosses for -in. diameter 
 clamping screws, as shown. These bosses may be 
 turned by putting a small mandrel in the screw-holes 
 before they are tapped and holding the mandrel in a 
 chuck. To make the pins, if straight ^~in. brass rods 
 are chosen to fit the holes in the brush-holders they will 
 only need to be polished. Screw one end of each pin for 
 a length of ^ in., and at the other end drill a small 
 hole through the diameter. In this hole place a pin tc, 
 prevent the brush-holder from being forced off by the 
 spring. The pins can now be screwed tightly in place 
 in the cross-arm. Make two hexagonal nuts to screw 
 on the threaded part which projects through the cross- 
 arm ; these are to clamp the flexible wires x, Fig. 132, 
 which carry current to the terminals. For adjusting 
 the tension on the springs, two collars, as shown, are 
 required. They may be made from |-in. brass rods, 
 drilled to fit the pins, and each should be fitted with 
 a set-screw to fix it in the required position. A small 
 hole is drilled in the face at one side of each collar to 
 take one end of the spring, and a similar hole should 
 be drilled at the end in each brush-holder to take the 
 other end of the spring. The spiral springs are made 
 of hard brass wire, about No. 24 S.W.G. ; one is coiled 
 left-handed, and the other right-handed. 
 
 The terminal blocks Y, Fig. 133, are filed all over 
 and polished, and holes are drilled and countersunk to 
 take wood screws, which hold the blocks down on the 
 terminal- board. A hole is drilled and tapped in each 
 block at the end next the commutator to take J-in. 
 cheese-head screws, which clamp the field-wires and 
 brush-wires (see Fig. 131). Holes are drilled through 
 the upright blocks to receive the outer-circuit wires 
 which are held by set-screws put in from the top. 
 
 The terminal-board z, Figs. 132 and 133, can be
 
 138 DYNAMOS AND ELECTRIC MOTORS. 
 
 made from a piece of mahogany about \\ in. by 
 2 in. by f in. thick, and polished or varnished according 
 to taste. Holes are drilled in it to take two ^e-in. 
 countersunk screws, which fix the board to the field 
 magnet. The holes in the magnet should be drilled and 
 
 Fig. 134. Armature (Side View). 
 
 tapped last, and marked off for position from the 
 terminal-board. 
 
 The driving pulley (shown in Figs. 132 and 133) may 
 be made suitable for either a flat or a round belt, and of 
 dimensions to suit the manner of driving. If the 
 dynamo is to be driven from a foot lathe or hand wheel, 
 a pulley about 1 in. diameter over all is a convenient 
 
 Fig. 135. Armature (End View). 
 
 size, with a V groove to take round belt of ^ in. 
 diameter. The width of the pulley should be about 
 f in., and it can be bored with a tapering hole to fit a 
 taper shaft, or hole and shaft can be made parallel, and 
 a set-screw put in the boss will hold them together. The 
 fit should be good ; and when the armature has been put 
 between centres and the pulley finally turned true in 
 its place, the mechanical construction is finished. 
 
 To proceed with the insulation. Take the armature 
 out and the bearings off. Examine the field magnet
 
 UNDER TYPE DYNAMO AND MOTOR. 139 
 
 where the wire is to be wound, and with a file smooth 
 off all corners, any rough places, and all sharp edges and 
 points likley to cut through the insulation. Wrap two 
 layers of thick brown paper round each core, sticking 
 them on with shellac varnish. Cut out four rectangular 
 cardboard cheeks or flanges Q, Figs. 132 and 133, to 
 fit the cores ; the wire will extend about f in. from the 
 core, so the cheeks must be made to suit ; they can be 
 sprung on the cores if a slanting cut is made across one 
 side and a piece of paper is pasted over the cut to keep 
 it together when the cheeks have been pushed to their 
 places at the ends of the core. Carefully look over 
 the insulation and see that it is sound everywhere, so 
 that the wire cannot come into contact with the iron 
 at any point. Then brush a thick coat of shellac over the 
 paper wrapping and cheeks, and leave them until quite 
 dry. 
 
 The armature must be treated in a similar way. 
 Smooth all projecting points, edges, and corners along 
 the channel where the wire is to be wound ; then with a 
 single layer of thick brown paper cover the channel, the 
 ends of the core, and the shaft to the oil-guard at the 
 pulley end and to the commutator at the other end. 
 Leave the paper projecting a little beyond the edges of 
 the channel, so as to be sure that the insulation comes up 
 to the edges ; it can be trimmed down after the wire is 
 wound on. The edges at the ends of the channel can 
 have an extra thickness of paper put on over the first 
 covering, as the covering on the wire is liable to be 
 cut through at these points. Examine the insulation ; 
 if all right, give it a thick coat of shellac and leave to 
 dry. 
 
 To wind the field-magnet requires about 2 Ibs. of 
 No. 22 S.W.G. single cotton-covered copper wire, which 
 may be wound, layer by layer, by hand, in the direction 
 shown in Fig. 136, keeping it as even as possible with 
 a moderate tension. The number of layers is not 
 important, and the winding may be finished either 
 at the top or bottom. It does net matter greatly
 
 140 DYNAMOS AND ELECTRIC MOTORS. 
 
 if the number of layers on each core is not quite the 
 same ; try to put about 1 Ib. of wire on each core ; 
 but it is essential for the winding to be in the 
 direction shown in Fig. 136, and kept so throughout. 
 As each layer is finished it should be brushed all over 
 with sufficient shellac varnish to give the surface a 
 good coat. The commencing ends of the wire B and A, 
 Fig. 136, which reach from the core outwards, should 
 be wrapped round with thin paper along the part 
 which is buried in the end of the coil, and varnished 
 with shellac to make sure that the current goes straight 
 to the innermost layer and does not leak away to the 
 other layers. The current must go through the wire 
 from end to end without making a short cut across at 
 any point. If a bare or frayed place is found while 
 winding, cover it with some thin paper. The most 
 convenient way to wind the coils is to fix a strip of 
 wood to the top of the magnet by the terminal-board 
 screws, and then to fasten the wood to a face-plate 
 fixed on the lathe, bringing each core in turn to 
 the centre. If the weight of the overhanging core is 
 counterbalanced, the magnet will be rotated more 
 conveniently ; turn the face-plate round with the 
 left hand, guiding on the wire with the right hand, 
 assisted by the left where the wire requires passing 
 between the cores. The magnet may be made with a 
 joint through the top to allow of winding the coils in 
 the lathe, if the joint is made to be in close contact all 
 over the surface. The extra trouble taken to wind 
 the coils as described is nothing compared with extra 
 work needful to construct the joint and magnet in one 
 piece in the way mentioned. Completely wind one core 
 first to the full depth of the cheeks, and then pro- 
 ceed with the other, joining the ends to make the 
 final connections. Cover the last layer with two or 
 three coats of shellac varnish. 
 
 To wind the armature requires about J Ib. of No. 20 
 S.W.G. double cotton- covered copper wire. Put the 
 armature in the lathe between centres, with the com-
 
 UNDERTYPE DYNAMO AND MOTOR. 141 
 
 mutator to the right hand. Commence from the right- 
 hand end and lay the wire from there, along the channel 
 to the left-hand end, then across the end and under- 
 neath along the channel to the right-hand end, across 
 the channel for one layer, then back again for second 
 layer. Get on as much wire as possible, and continue 
 winding until the channel is quite full 
 
 Fig. 136. Field Magnets, showing Method of Winding. 
 
 Each layer" of wire should have a coat of shellac 
 varnish. If found more convenient, the portion of the 
 channel on one side of the shaft may be filled up first 
 and then that on the other side. Having commenced to 
 wind the wire round the core in a certain direction, this 
 direction must be maintained right through, as is shown 
 by Fig. 25 (p. 23). It is easy to reverse the direction of 
 the winding when passing from one side of the shaft to 
 the other, and care must be taken to avoid this mistake.
 
 142 DYXAMOS AND ELECTRIC MOTORS. 
 
 The wire being all wound, bind it tightly with 
 strong thin cord wrapped round the centre groove of 
 the core K, Fig. 134, prepared to receive it. This makes 
 an even binding about \ in. long, and it prevents the 
 wires swaying outwards owing to centrifugal force 
 when the armature is rotating. The beginning and 
 the finishing ends of the wire on the armature must 
 now be connected to the commutator. One end goes 
 to each segment, and both must be soldered into the 
 nicks made for them ; it is well also to bind some cord 
 round these wires to keep them in place. When all is 
 finished, give the wire and binding cord a thick coat 
 of shellac. 
 
 The commutator can now be finally trued up in the 
 lathe, taking a very light cut, to remove any surplus solder 
 
 Fig. 137. Position of Commutator on Armature. 
 
 and to make it run quite true. Put a disc of thin card 
 between the pulley-end oil -guard and the armature wire, 
 to prevent any chance of damaging the insulation. 
 
 The dynamo can now be finally put together. The 
 field- wires are connected up to the terminal blocks as 
 shown in Figs. 132, 133, and 134, and also joined to- 
 gether in the centre as shown in Fig. 136. This last joint 
 should be twisted and soldered to make good contact. 
 Connect the brush-holder pins by flexible copper wires to 
 the terminal blocks, so that the rocker may be easily 
 moved. These flexible wires are made by coiling some 
 No. 20 S.W.G. insulated wire on a rod T \ in. diameter, 
 just as spiral springs are made ; enough of the wire at 
 each end is stripped of its covering to make contact with 
 the clamping screws.
 
 UNDERTYPE DYNAMO AND MOTOR. 143 
 
 The brushes may be made of sheet copper or of copper 
 wire ; they should be flexible, to make good contact 
 with the commutator and brush-holders. A good 
 brush may be made from copper wire, about No. 24 
 S.W.G. ; fix one end in a vice, take hold of the other end 
 with a pair of pliers and give a fair pull, to stretch the 
 wire a little and straighten it. Cut off sufficient pieces, 
 each 2 in. long, to make two brushes each J in. wide, and 
 at one end solder the wires together. It is a good plan 
 to curve the brush where it touches the commutator, 
 so that there is a surface of contact about J in. broad all 
 along the brush. 
 
 The dynamo is now complete, but, to commence 
 with, its field magnet requires exciting ; afterwards it will 
 always excite itself. The direction for running is that of 
 the hands of a clock, when the observer looks at the side 
 of the pulley as if looking at a clock face. Rotate the 
 armature in this direction at a high speed ; if it sud- 
 denly works stiffly and sparks appear at the brushes, it 
 has started itself all right, and the field magnet will not 
 require any further assistance ; but if this does not 
 occur, and the dynamo fails to light a 10-volt lamp, an 
 electric battery will be required to give the field magnet 
 the necessary start. Put a piece of paper between one 
 of the brushes and the commutator to prevent the 
 current going through the armature. Now, looking from 
 the commutator end, connect the positive wire of a 
 strong battery to the right-hand terminal, and the nega- 
 tive wire to the left-hand terminal. While the batteiy 
 is thus connected, gently tap the iron of the field magnet 
 with a hammer for half a minute ; disconnect the battery, 
 remove the paper from under the brush, and on driving 
 the armature again the machine should work all right. 
 The output of this dynamo, with 3,000 revolutions per 
 minute, is about 10 volts at 5 amperes ; but it will give 
 higher electro-motive forces up to about 20 volts with 
 less current if run at higher speeds. The dynamo can 
 be painted to suit taste.
 
 144 
 
 CHAPTER XH. 
 
 440- WATT MANCHESTER TYPE DYNAMO. 
 
 THE dynamo described in this chapter is of the Man- 
 chester type, shunt wound, and designed for an output 
 of 440 watts viz. 8 amperes at 55 volts when run- 
 ning at 1,800 revolutions per minute. Figs. 138 and 
 139 (pp. 145 and 147) show a plan and an end view of 
 the machine complete. 
 
 The field magnet castings can be bought with the 
 armature tunnel bored out, 5^ in. diameter, and the 
 field magnet cores fitted. The base of each pedestal is 
 turned, making the centring of the armature in the 
 tunnel much easier than when a flat-bottomed pedestal 
 is used. The field magnet cores, 2f in. diameter and 
 5j in. long, are wound with 11 Ib. of No. 20 S.W.G. 
 cotton-covered wire 5^ Ib. being wound on each core. 
 The direction of the winding is shown in Fig. 141 
 (p. 151), producing a north pole at the top and a south 
 pole at the bottom. 
 
 The field-magnet bobbin ends may be fixed by 
 turning a shoulder on each end and shrinking on these 
 shoulders circular plates of iron ^ in. in thickness. 
 But if unable to turn these shoulders, the bobbin end.s 
 may be made of either sheet brass, sheet vulcanite ^ in. 
 thick, or thin hard wood. To make wood ends, procure 
 eight sheets, each in. thick, by 6 in. square, of any 
 close-grained hard fretworking wood, such as pear, 
 holly, walnut. Glue pairs of the sheets together 
 face to face, with the grain of one running at right 
 angles to the grain of the other, and cramp them 
 in a flat press for twenty-four hours, thus making four 
 sheets | in. thick. Then screw the four sheets together 
 at their corners, mount them on the face-plate of a 
 lathe, and in the centre bore a hole to fit the magnet
 
 MANCHESTER TYPE DYNAMO. 145 
 
 cores tightly. Turn the outside to make a disc 5 in. 
 diameter, and thus make the bobbin ends. 
 
 The cores of the field magnet are drilled at each end, 
 and tapped in. A stud 3 in. long is screwed into one 
 end, and in the other end place a hexagon-headed bolt 
 3 in. long. Centre the end of the stud and the bolt 
 head, and place the core between the lathe centres to 
 see that it runs fairly true. Then paint the core with 
 Brunswick black, and, while wet, push the bobbin ends 
 on and paint them on the inside and round the joint. 
 The ends of the cores must be left clean and bright, 
 
 Fig. 138. Plan of Manchester Dynamo. 
 
 otherwise they will make a bad joint with the pole- 
 pieces, and so lower the efficiency of the dynamo. 
 
 Winding the wire direct on the core would tend to 
 force off the bobbin ends. Pieces of wood i in. thick 
 and 5 in. square, with holes in the centre to pass over 
 both the stud and the bolt, and pressed against the ends 
 of the cores by two i-in. nuts, will prevent this. The 
 wire can be wound on evenly by hand in the lathe, using 
 a very slow speed. It should previously be coiled, and 
 placed so that it may run freely ; and can then be run 
 through the hand without causing kinks. An empty
 
 146 DYNAMOS AND ELECTRIC MOTORS. 
 
 bobbin held in the palm of the hand, for the wire to 
 run over, will avoid making the fingers sore. 
 
 A coat of shellac varnish should be given each layer, 
 and allowed to dry ; then wind back, and so continue 
 until all the wire is wound on. When both cores are 
 wound, put them in a warm place for a few hours to 
 dry and harden. 
 
 The armature is 5 in. diameter and 4 in. wide, and 
 is built up of 150 soft iron cog-ring stampings, having 
 ten channels 1 in. wide and in. deep. An easy 
 method of insulating the laminations is to cut 150 sheets 
 of tissue paper 6 in. square, and with shellac varnish 
 paste a sheet on each stamping. Then thread the 
 stampings together with five brass rods J in. diameter 
 and 5 in. long, screwed each end for f in. Put washers 
 on the brass rods to equal the thickness of the bosses on 
 the spider arms, and screw up the end nuts until the 
 armature is 4 in. wide, using the calipers to ascertain 
 that the end faces are parallel. 
 
 Fig. 140 (p. 149) shows a section through the spiders. 
 The outside is comparatively flat, and the inside has a 
 central boss and also smaller bosses near the end of 
 each arm. A circle 4j in. diameter ought to bisect each 
 boss on the end of the five arms. In the centre of each 
 boss drill a J-in. hole to receive the ends of the brass 
 rods. If the rods do not enter their respective holes, the 
 spider arms may be bent by light blows with a hammer. 
 
 When the spiders are bolted on the armature, run it 
 between the lathe centres, and adjust centre dots placed 
 in the spiders till the whole runs true. Having marked 
 the position of the spiders, take them off and bore a 
 |-in. hole in the central boss of each. Decide which 
 one is going to be placed at Jthe commutator end, and 
 in it file a keyway J in. wide and T % in. deep ; this 
 should be under one of the arms, so as to weaken the 
 spider least. 
 
 The steel spindle is shown at Fig. 140 (p. 149) ; it ia 
 14| in. long, its collar being Ij in. by J in. The central 
 portion is \ in. diameter by 7| in. long, the journals being
 
 MANCHESTER TYPE DYNAMO. 147 
 
 Q in. diameter by 2 in. long. The keyway must bo cut 
 at the commutator end in. deep and J in. wide for a 
 length of 3 in. A keyway -^ in. wide and deep must 
 also be cut at the pulley end. 
 
 The bearings are of cast iron, and their bases have 
 the same radius as that of the armature tunnel, the 
 bearing steps being turned and the tunnel bored at the 
 same operation. The web of the bearing stands out- 
 wards when in position. Bore each bearing to take the 
 shaft, and, at the inner side of the bearing at the com- 
 mutator end, turn a shoulder Ij in. diameter and in. 
 
 nrn 
 
 rim. 
 
 Fig. 139. End View of Dynamo. 
 
 wude to take the brush rocker. In the top of each 
 bearing drill and tap an -in. gas-thread hole for a 
 lubricator. Mount the bearings together on a mandrel, 
 and turn up their bases. They are fixed with |-in. bolts. 
 The height for the bearings may be found by trying 
 the armature when it is mounted on the shaft, to see 
 that the air space is equal above and below. 
 
 The cast-iron driving pulley is 2 in. diameter by 
 ij in. across the face. It should be bored to f in., 
 and fastened to the shaft with a key ^ in. wide. The 
 depth of the slot in the pulley should be J in. This 
 key must have a head, so that it can be drawn when 
 required. 
 
 File or turn three grooves f in. wide and <fa in. deep 
 round the armature stampings, to take binding wire, as 
 explained on p. 54, one groove in the centre and the
 
 148 DYNAMOS AND ELECTRIC MOTORS. 
 
 other two 1 in. from each end of the armature. 
 Sinking the binding wire into the iron core allows a 
 margin for wear in the bearings, and gives a small air 
 space, thus tending to make the machine more efficient. 
 
 Carefully remove all sharp corners from the armature, 
 as if the stampings cut the insulation of the wire the 
 whole coil has to be unwound, the insulation repaired, 
 and finally the coil rewound, which may take hours 
 to complete. The whole of the armature should 
 now have a coating of shellac varnish. When an 
 assistant is to help wind the armature, the shaft 
 and spiders are removed ; it is then laid on a trestle 
 and held firmly down by a strip of wood passed 
 through the core. For a single-handed job, fasten it 
 down to a table, as shown on p. 68, so that it will thus 
 be possible to work at it sideways, and get at each end. 
 
 Before winding the wire the channels must be covered 
 with paraffin-soaked tape, one layer being sufficient ; as a 
 further protection, an extra strip of narrow tape may be 
 put across each of the corners. 
 
 The wire, consisting of 5 Ib. of No. 17 S.W.G. double- 
 cotton-covered, must be divided into ten equal lengths. 
 To do this, fix two empty cotton-reels at a distance of 
 45 ft. apart ; then fasten one end of the coil to one reel, 
 and wind the wire backwards and forwards round each 
 reel until the whole coil is unwound. The wire so 
 wound should consist of ten lengths, but if there is any 
 short or over, measure it and shift the reels apart so 
 that all the wire is used in ten turns round the two 
 reels. Then cut the wires where they pass round the 
 reels, and produce ten equal lengths. By placing the 
 reels at half the distance apart and cutting at one end 
 only, the same result is to be obtained. Each length 
 must be loosely coiled, soaked in melted paraffin wax, 
 and allowed to drain and harden. Proceed to wind one 
 of these coils on a wooden shuttle, 24 in. long, l in. wide, 
 and \ in. thick, the ends being hollowed out like a 
 butcher's tray (see Fig. 58, p. 62). Cut from hard wood 
 ten pieces, $ in. square and 1| in. long, with a J-in hole
 
 MANCHESTER TYPE DYNAMO. 149 
 
 drilled f in. from the end of each piece, and secure them 
 to the ends of the brass rods, as shown at A, in Fig. 141 
 (p. 151), to take the place of the spider arms. The enda 
 of the coils are kept in position by these, and the wire 
 is prevented from getting under the spider arms when 
 they are being placed on to the ends of the armature. 
 
 When the armature is in position for winding, 
 take the shuttle of wire, cut the insulation off the end 
 for a distance of 1 in. or so, and secure it to the bench 
 by a screw. Wind the wire into the channel by bring- 
 ing the shuttle over the armature, and passing it back 
 through it, starting at the left-hand side (when looking 
 at the commutator end), winding to the right and then 
 
 Fig. 140. Longitudinal Section of Dynamo. 
 
 back again to the left, and so on till all the wire on the 
 shuttle is wound on the armature, finishing at the 
 risht-hand side. Beat the wire regular by a small 
 wooden mallet, or by a piece of wood struck with a 
 hammer. The bulging of the wire on the inside is apt 
 to be overlooked, but must be watched for carefully ; 
 otherwise, when pushing the shaft through the armature, 
 it may damage the insulation. A galvanometer should 
 be used, if possible, for testing the latter. 
 
 When this coil is completely wound, 3 in. being left 
 to connect to the commutator as a temporary protec- 
 tion to the wire, wrap a band of calico round the coil, 
 securing it with thread ; then proceed to wind the other 
 coils similarly. The commencing end of one coil must 
 be soldered to the finishing end of the next, one end of
 
 150 DYNAMOS AND ELECTRIC MOTORS. 
 
 the soldered wires being made into an eye, and secured 
 to a commutator strip by means of a brass headed 
 screw. Another method of fastening the ends of the 
 armature coils is to solder both the wires to a short 
 length of brass rod screwed vertically into the end of 
 the commutator strip (see Fig. 54). 
 
 When all the coils are wound, take the armature 
 off the bench, lay it on one end, remove the five pieces 
 of wood, and put the spider on quickly and carefully, 
 all corners on the spiders having been well rounded. 
 Next turn the armature the other end up ; place the 
 second spider on the shaft, and put the latter through the 
 armature and through the first spider ; then remove the 
 remaining pieces of wood. Put the spider on its place, 
 and screw up the nuts until both the spiders ara well 
 home ; then secure the nuts with soft solder. 
 
 The commutator and the spider must be separated 
 by a vulcanite washer, 2j in. diameter and in. or ^ in. 
 thick, as shown in Fig. 140 (p. 149). The binding-wire 
 can now be wound round the armature coils, using 
 No. 26 B.W.G., and securing each band with solder where 
 it crosses the iron. Insulate the bands from the arma- 
 ture coils by strips of tape, asbestos, or mica. 
 
 The casting for the commutator is a parallel brass 
 cylinder, 2 in. outside diameter, 1| in. wide, and J in. 
 thick. This has to be mounted on a cylindrical block 
 of insulating material, and, vulcanised fibre, ebonite, or 
 lignum-vitse are specially suitable. Boxwood is, however, 
 more likely to be used. Turn a piece 2; in. long, and of 
 a diameter that will allow it to be driven into the com- 
 mutator casting ; take care to have the grain running 
 across the piece diameter ways, or it will split when 
 pushing the commutator on the shaft. Cut from one 
 end a length f in. (see A B, in Fig. 140), while the wood 
 is in the lathe, with the two parted surfaces quite flat. 
 Divide the commutator casting round the outside face 
 into twenty equal divisions by lines parallel to tLe axis. 
 Ten of these lines taken alternately will show where the 
 saw-cuts may be, the other ten where the holding-down
 
 MANCHESTER TYPE DYNAMO. 151 
 
 screws must be placed. In each strip, on the latter 
 line, three holes must be drilled, that on the extreme 
 left, being T \ in. tapping ; the next ^ in. away, and the 
 third, on the extreme right, being both countersunk for 
 a Hn. brass screw. When all the holes are drilled and 
 tapped, file away all burrs and lumps from the inside of 
 the casting, observing that the button-headed screws, 
 which are fitted to the T Vin. tapped holes, do not project 
 inside the cylinder when screwed down to the head. 
 
 Warm the casting while melting some glue, which 
 should be thin, so as to have a close joint. Then drive 
 in the short piece of boxwood, parted face first, until 
 flush with the end of the brass cylinder ; put a little 
 
 Fig. lil. End View showing: Method of Winding 
 Armature and Fields. 
 
 glue on the parted face of the other piece, and drive it 
 into the open end with a mallet, so that the grain of the 
 two pieces is at right angles when they meet in the centre 
 of the brass casting. Directly the wood is driven home 
 place the whole endways between the jaws of the vice, 
 and keep it under pressure for some hours. If the 
 grain were uniform across the cylinder, some screws 
 fastening the commutator strips would be apt to strip ; 
 but with the grain at right angles one screw is sure to 
 hold. 
 
 When the glued joint is set quite hard, screw all the 
 brass holding-down screws into their respective holes; 
 then with a hack saw cut through the casting along the
 
 152 DYNAMOS AND ELECTRIC MOTORS. 
 
 lines already drawn, taking care not to saw deeper 
 than -fa in. into the boxwood. 
 
 When all the strips are sawn apart, lift each alternate 
 one, singly, and clean away all brass filings, etc. ; then 
 put strips of mica in the saw cuts, and jam them tight, 
 by screwing the commutator strip home, but be careful 
 not to put too great a strain on the brass screws. 
 
 The boxwood projects at the end carrying the button- 
 headed screws, so that the commutator may be held 
 in a chuck when boring the central hole. Bore this 
 hole | in., taking care not to get it too large, and work- 
 ing by calipers, as it is impossible to try it in place. 
 Hand pressure is sufficient to force the commutator into 
 
 Pig. 142. Brash Gear. 
 
 place. The commutator must be driven by a vulcanite 
 or ebonite key, fitted into the existing keyway in the 
 shaft, but which need go no more than \ in. into the 
 boxwood. When the commutator is mounted on the 
 shaft, turn it up in the lathe, using a fine-pointed tool, 
 and taking a very light cut ; then finish up with fine 
 glass-paper, not emery-cloth. 
 
 The brush rocker and brush gear are shown at 
 Fig. 139 (p. 147), with the rocker fitted to the bearing, 
 together with one brush and brush-holder. The brass 
 rods to carry the holders are \ in. in diameter by l in. 
 long, turned down to f in. for another \\ in., and 
 screwed for in. at the small end. Fig. 140 (p. 149) 
 shows a half section of the brush rocker, with a vulcan- 
 ised fibre bush and washers at each end. 
 
 Fig. 142A is a section showing an easy method of
 
 MANCHESTER TYPE DYNAMO. 153 
 
 regulating the pressure of the brushes upon the com- 
 mutator by means of the piece of thin spring steel. 
 The width at the lower end of this piece of steel in 
 exactly that of the space between the cheeks of the 
 brush-holder, therefore, when the strip of steel is secured 
 to the ^brass supporting rod by the small steel screw, 
 there is no side-play in the brush-holder. The other 
 end of the steel strip is J in. wide and 3| in. long, with 
 a nut soldered to it, and has a ^ in. thumb-screw. The 
 spring, shown in plan at B, is about 4j in. long, over all. 
 
 The brushes are held off the commutator by means 
 of the steel tongue shown in position at A, and also in 
 detail at c. 
 
 The end of this tongue, which is bent round at right 
 angles, must be secured to the holder by a T Vin. screw, 
 the other end having a Q -shaped hole, so that when the 
 brush is off the commutator this hole drops over the 
 head of the cheese-head screw, which must have half its 
 head partly filed down to receive it. To release the 
 brush the tongue must be lifted with the finger off the 
 screw-head. The larger steel spring, through which 
 this tongue passes, then presses the brush on the com- 
 mutator with a pressure that can be adjusted by means 
 of the thumb-screw at the end of the spring. A piece 
 of sheet steel as wide as the brush is fixed so that the 
 thumb-screw presses against it, and a similar piece is 
 placed on the top of the brush, extending from the 
 brush-holder to the toe of the brush. 
 
 When the machine is ready for trial, secure it 
 to the floor, and connect it by a If-in. belt to the 
 driving-power. Looking at the commutator end of the 
 armature, it must run clockwise, with the brushes 
 diametrically opposite, and pointing in the direction of 
 rotation. Connect the end of the last coil of the left- 
 hand field magnet to the left-hand brush, and the last or 
 outside coil end of the right-hand field magnet to the 
 right-hand brush, the two ends of the bottom layers of 
 each field-magnet coil being joined together. Next 
 connect the positive pole of a set of four Leclanchtf or
 
 154 DYNAMOS AND ELECTRIC MOTORS. 
 
 three bichromate cells to the left hand brush, and the 
 negative pole to the right-hand brush. One of these 
 wires must be cut with clean ends, so that they can, 
 when brought in contact, complete the circuit. 
 
 Hold the two ends of this wire in the hand, and 
 run the machine at about 1,800 revolutions per minute ; 
 then, when fully under way, touch the two ends of the 
 wires together. If the batteries are in good condition, 
 they ought to be strong enough to start the magnetism 
 in the field magnets. If the dynamo begins to excite, 
 the first thing that will be noticed is that the tone 
 given out by the revolving armature will change from a 
 whirr to a low humming sound ; sparks also will be 
 observed at the brushes. Directly the machine starts to 
 excite, disconnect the battery circuit, and keep the 
 machine running for a few minutes. Then stop and 
 connect a 50-volt 16-candle-power or 8-candle-power 
 lamp to the brush-holders by two wires of any con- 
 venient length. Run the machine again, and the lamp 
 ought to light up when running at 1,800 revolutions per 
 minute. If the machine will not excite the first time, 
 cross the leads from the field magnets to the brushes, so 
 that the right-hand brush is connected with the left- 
 hand coil and the left-hand brush with the right-hand 
 coil ; then run the machine again, and if unsuccessful, 
 try six, then eight, batteries in series to excite the 
 field magnets; if still unsuccessful, there is a broken 
 wire, or the insulation has given way in the armature. 
 This must be discovered and repaired. Then connect up 
 six more lamps of 16 candle-power each, one by one as 
 the machine is running, and if the brushes start spark- 
 ing, bring them slowly forward, by means of the rocker, 
 in the direction of rotation until the sparking ceases. 
 The power required to drive the machine, when under 
 full load, will be about brake horse-power. 
 
 Not until the machine works properly should the 
 finishing touches be put on.
 
 INDEX. 
 
 Ailments of Small Dynamos, 89 
 Ampere, Meaning of, 13 
 
 hour, Meaning of, 14 
 
 Armature, Meaning of, 14, 76 
 
 , Cogged King or Pacinotti, 17 
 
 , , Winding, 146 
 
 , Double Shuttle or Walker, 17 
 
 , Drum, 76 
 
 for 50-watt Undertype Dynamo, 
 
 130 
 , Fixing to Bench for Winding, 
 
 
 
 , Gramme, Building up, 44 
 
 , Preparing for Winding. 
 
 47 
 
 , Insulating, 67 
 
 , Manchester, 63, 146 
 
 , , Winding, 148 
 
 , Method of Winding, 84, 148 
 
 for Model Electro-motor, 100, 
 
 lOt, 110 
 
 of Motor, Preparing, 121 
 
 , Winding, 125 
 
 , King, 76 
 
 , Shuttle, 17, 18, 77 
 
 .Siemens H-girder, 21, 25 
 
 , , Testing, 27 
 
 , , Winding, 33 
 
 of Simplex Dynamo, 66 
 
 , Speed of, 83 
 
 Armatures, Classes ot, 15, 76 
 
 Armatures, Laminated, 18, 25 
 
 , Ring, When Used, 77 
 
 Attraction and Repulsion of PoK.-s, 
 
 114 
 
 B 
 
 Batteries for Night Lights, etc., 10 
 
 , Primary, for Lighting, 9 
 
 Battery for Driving Model Motor, 
 111 
 
 for Localising Faults in Dy- 
 namos, 89 
 
 Bearings of Simplex Armature, 72 
 
 of Manchester Dynamo, 147 
 
 Bed-plate of Simplex Dynamo, 71 
 
 of Undertype Dynamc, 91 
 
 Belt of Simplex Dynamo, 74 
 Binding Posts, IS 
 
 Screws, 18, 110 
 
 Wires, Use of, 70 
 
 Bobbin Ends of Field Magnets, 144 
 Broken Wires, Joining, 20 
 Brushes, 50-watt Uudertype Dy- 
 namo, 135, 143 
 
 of Manchester Dynamos, 153 
 
 of Model Electro-motor, 102 
 
 , Position of, 94 
 
 of Shuttle Armature Motor, 
 
 128 
 
 of Siemens Dynamo, 29, 31 
 
 of Simplex Dynamo, 73 
 
 .Sparking at the, 95 
 
 Brush-holder of Gramme Dynamo,
 
 '56 
 
 DYNAMOS AND ELECTRIC MOTORS. 
 
 Brush-holder of Motor, 124 
 
 of Siemens Dynamo, 30 
 
 of Simplex Dynamo, 73 
 
 Calculating Wire required for 
 
 Armature, 51 
 Care of Dynam js, 97 
 Castings, Cost of, 22 
 
 of Gramme Dynamo, 42 
 
 , Rough, Trueing-up, 22 
 
 for Shuttle-Armature Motor, 
 
 120 
 
 Clamp for Armature Core, 68 
 
 for Holding Brushes, 56 
 
 Classification of Dynamos, 9 
 Commutator of Crypto Dynamo, 
 134 
 
 , Firing to Shaft, 31 
 
 of Gramme Dynamo, 49 
 of Manchester Dynamo, 150 
 
 of Model Electro Motor, 102, 
 
 124 
 
 of Siemens Dynamo, 27 
 
 of Simplex Dynamo, 70 
 
 Compass, Substitute for, 89 
 
 Compound Winding, 40, 65 
 
 Connecting Wires of Dynamos, 39, 
 153 
 
 Connections, Accidental, 93 
 
 Connectors, 18 
 
 Contact Breaker, 110 
 
 Spring, 109 
 
 Cost of Dynamo Castings, 22 
 
 Current from Dynamo, How Calcu- 
 lated, 80 
 
 , How Determined, 76, 
 
 79 
 
 Currents, Directions of in Bar 
 Magnets, 113 
 
 Discs, Preparing, 131 
 
 Driving Pulley of Crypto Dynamo, 
 
 138 
 Dummy Armature and Shaft, Use 
 
 of, 130 
 Dynamo for Charging Accumula 
 
 tors, 90 
 
 , Definition of, 10 
 
 for Electro-depositing, 90 
 
 , 50-watt Undertype, 129 
 
 Gramme, 41 
 
 , Invention of, 9 
 
 for Lighting Pour 10-c.-p 
 
 Lamps, 75 
 
 to Light Two 8-c.-p. Lamps, 66 
 
 , Manchester, 144 
 
 , Model, Type of Armature ton 
 
 77 
 
 , Siemens, 21 
 
 , Simplex, 66 
 
 Dynamos, Classification of, 9 
 
 Electric Current, Explanation of 
 
 10 
 Electrical Energy, Effects of, 11 
 
 Measurements, 13 
 
 Electro Motor (See Motor) 
 Engine to Develop i Horse-power 
 
 66 
 Experimenting with Motors, 118 
 
 Faults in Dynamos, Localising, 89 
 
 in Winding, 31 
 
 Field Magnets. Castings of. 1?,0, 130, 
 141
 
 INDRX. 
 
 '57 
 
 Field Magnets, Compound- Wound, 
 
 65 
 of 50-watt Undertype 
 
 Dynamo, 139 
 of Gramme Dynamo, 12, 
 
 44,57 
 
 , Length of Cores of, 82 
 
 , of Manchester Dynamo, 
 
 12,63 
 
 of Model Motors, 98 
 
 , Overtype, 11 
 
 of Siemens Dynamo, 22 
 
 of Simplex Dynamo, 12, 71 
 
 , Types of, 11 
 
 , Winding, 35, 57, 126, 139, 
 
 144, 145 
 
 " , Undertype, 11, 139 
 
 Fifty-Watt Undertype Dynamo and 
 
 Motor, 129 
 
 Finishing Simpler Dynamo, 74 
 Former for Winding Armature of 
 
 Simplex Dynamo, 66 
 
 Galvanometer, Cost of, 34 
 
 , Use of, 34, 93, 149 
 
 Gramme Dynamo, 41 
 
 , Dimensions and Output 
 
 of, 59 
 
 , Horse-power to Drive, CO 
 
 Guard over Armature Gap, 91 
 
 Handle for Moving Rocker, 56 
 Heating, Excessive, 95 
 Horse-power to Drive Gramme Dy 
 
 Insulating Armature, 67 
 
 Brushes of Simple* Dyt 
 
 73 
 
 nsulating Commutator Segments, 
 27,50 
 
 Varnishes, 83 
 usulation, Defective, 93 
 
 oining Wires, 67 
 
 laminated Armatures, 18, 25 
 Laws Governing Electro-motors. IIS 
 Lead of Brushes, 32, 83 
 
 .kage, Discovering, 92 
 in Dynamos, 91 
 
 ghting, Electric (See Batteries and 
 
 Dynamos) 
 Lubricator for Gramme Dynamo, 47 
 
 Magnetism Neutralised, 91 
 
 , Want of, 90 
 
 Magnets, Poles of, 10, 37, 112 
 Manchester Dynamo, 61, 144 
 Dimensions and Outputs 
 
 of, 64 
 
 , Winding, 35 
 
 Measurements, Electrical, 13 
 
 to Drive Small Lathe, 119 
 
 Driven with Two Batteries, 118 
 
 Motor, 50-watt Undertype, 129 
 Model, made without Castings, 
 
 H 
 
 , Shuttle Armature, 119 
 , Small, with Horseshoe Magnet 
 
 and Wooden Saddle, 107 
 Mounting Motor, 128 
 
 Ohm, Meaning of, 14 
 Oil Guards for 50-watt Undertypy 
 Dynamo, 135
 
 158 
 
 DYNAMOS AND ELECTRIC MOTORS. 
 
 Kacinotti, 41 
 
 Armature, 17 
 
 Piiii, 9 
 
 Plug, Wooden, for Armature of 
 
 Simplex Dynamo, 70 
 Polarity, 38 
 
 , Detecting Alteration of, 91 
 
 Poles of Magnets, 10, 37, 112 
 Primary Batteries for Lighting, 9 
 
 Repairing Faults in Dynamos, Tools 
 
 for, 89 
 
 Faulty Wire, 93 
 
 Rocker for Gramme Dynamo, 55 
 
 for Manchester Dynamo, 152 
 
 Rotation of a Motor, Direction of, 
 
 112 
 Running 50-watt Undcrtype Dy- 
 
 namo, 143 
 
 Hot, 95 
 
 Manchester Dynamo, 151 
 
 Safe Carrying Capacity of Wire, 79 
 Screws, Faulty, Replacing, 93 
 Series Connections, 39 
 
 Motors, Direction of Current 
 
 in, 114 
 
 and Shunt Dynamos, Differ- 
 ences between, 80, 83 
 
 Shocks from Dynamos, 96 
 Short Circuiting, 40, 91 
 Shuut Connections, 40 
 
 Motors, Direction of Current 
 
 in 117 
 
 Wound Dynamos, Rules for, 
 81 
 
 Shuttle- Armature Motor, 119 
 
 or H-girder Armature, 17 
 
 for Winding Armatures, 52 
 
 Siemens Dynamo, 21 
 
 Dynamos, Table of Sizes, 
 
 Wires, Outputs, etc., 24 
 Simplex Dynamo, 66 
 Dynamo running as a Motor, 
 
 75 
 Starting Simpler Dynamo, 74 
 
 Taping, 36, 84 
 
 Terminals of Dynamos, 19, 30, 74 
 
 Testing for Insulation, 34, 149 
 
 Shaft, 132 
 
 Tools for Repairing Dynamos, 89 
 
 Varnish for Dynamos, 36, 46, 53, 14 >' 
 
 Volt, Meaning of, 13 
 
 Voltage, How Determined, 76, 78 
 
 Obtainable from Small Dyua 
 
 mos, 77, 83 
 
 Watt, Meaning of, 14 
 Watts, How Determined, 80 
 Winding Armatures of Motors, 101, 
 
 125 
 
 Field Magnet, 139 
 
 50-watt Undertype Armature, 
 
 140 
 
 , Detecting Faults in, 34 
 
 Dynamo Armatures, 33, 31, 51. 
 
 52, 66, 84, 140, 148 
 
 Field Magnets of Motors, 126 
 
 , General Hints on, 33 
 
 Gramma Armature, 51, 52
 
 INDEX. 
 
 159 
 
 Win-ling Gramme Field Maguets, 
 
 57 
 
 Manchester Armature, 148 
 
 Field Magnets, 144, 145 
 
 Siemens Armature, 33 
 
 Simple* Armature, 66 
 
 Of Sories Motors, 115 
 
 Wire, Armature, Broken, 95 
 
 for Armature, Calculating, 51 
 
 , Cheap, Disadvantages of, 81 
 
 , Circumferential Velocity of, 
 
 78 
 . Copper, Properties of. 78 
 
 Wire, Dead and Active, 77 
 
 , Joining, 67 
 
 for Laminated Cog-ring Arma- 
 ture, Calculating Length of, 87 
 
 , Preparing, for Winding, 35,84, 
 
 148 
 
 , Protecting, 83 
 
 , Safe Carrying Capacity of, 79 
 
 for Shuttle Armature, Calcu- 
 lating Length of, 85 
 
 for Small Dynamos, Calcu- 
 lating, 76 
 
 Wooden Slab for Dynamo, 38
 
 FEINTED BY 
 
 CASSELL AND COMPANY, LIMITED, LA BELLE SADVAtt! 
 LONDON, E.C.
 
 CONTAINING 
 
 FACTS, FORMULA TABLES AND QUESTIONS 
 
 ON POWER, ITS GENERATION, TRANSMISSION AND MEASUREMENT; 
 HEAT, FUEL AND STEAM; THE STEAM-BOILER AKp ACCESSORIES; 
 STEAM-ENGINES AND THEIR PARTS ; THE STEAM-ENGINE IN- 
 DICATOR ; GAS AND GASOLINE ENGINES ; MATERIALS, 
 THEIR PROPERTIES AND STRENGTH: 
 
 TOGETHER WITH A 
 
 DISCUSSION OF THE FUNDAMENTAL EXPERIMENTS IN 
 
 ELECTRICITY, 
 
 AND AN EXPLANATION OF 
 
 >YNAMOS, MOTORS, BATTERIES, SWITCHBOARDS, TELE- 
 PHONES, BELLS, ANNUNCIATORS, ALARMS, ETC., 
 
 AND ALSO 
 
 RULES FOR CALCULATING SIZES OF WIRES. 
 
 BY 
 
 STEPHEN ROPER, ENGINEER, 
 
 AUTHOR OP 
 
 ' Roper's Catechism of High-Pressure or Non-Condensing Steam-Engines," 
 ''Roper's Hand- Book of the Locomotive," " Roper's Hand-Book of 
 Land and Marine Engines," " Roper's Hand-Book of Modern 
 Steam-Fire Engines," "Young Engineer's Own Book," 
 "Use and Abuse of the Fleam-Boiler," "Ques- 
 tions and Answers for F\gineers," etc. 
 
 FIFTEENTH EDITION. 
 
 REVISED AND GREATLY ENLARGED BY 
 
 EDWIN B. KELLER, M. E., 
 
 AND 
 
 CLAYTON W. PIKE, B. S., 
 
 Ex-President of ttte Electrical Section of the Franklin Institute, 
 
 PHILADELPHIA : 
 DAVID McKAY, 
 
 1022 MARKET STREET. 
 1903.
 
 MAR *H u* 
 
 APR 2 0199 
 16 
 
 OCT 6 1 
 
 ft. L 
 
 LOS ANGELES 
 LFRRARV
 
 0856 
 
 Books 
 
 [remen. 
 
 TK 
 
 9911 
 
 H27d 
 
 EDITION. 
 
 ENGINEERS 
 
 IS. 
 
 nd Elcctric- 
 
 ..... $2.00 
 i Engineers 
 
 ..... 2.00 
 Engines, . 3.50 
 im Boiler, 2.00 
 sr, .. 2.00 
 
 ..... 2.50 
 
 Engineers 
 ..... 2.00 
 
 Roper's Hand-Book of Modern Steam Fire Engines, . 
 
 DAVE) MCKAY, Publisher, 
 
 1022 Market Street, Philadelphia, Pa.
 
 Soi 
 
 Li,