GIFT OF J No. 1814 DESCRIPTION AND INSTRUCTIONS FOR CARE AND OPERATION OF FIRING MAGNETOS TYPES GA AND MA (TWO PLATES) MARCH 10, 1917 WASHINGTON GOVERNMENT PRINTING OFFICE 1917 No. 1814 DESCRIPTION AND INSTRUCTIONS FOR CARE AND OPERATION OF FIRING MAGNETOS TYPES GA AND MA (TWO PLATES) MARCH 10, 1917 WASHINGTON GOVERNMENT PRINTING OFFICE 1917 c. Wab Department, Office of the Chief of Ordnance, Washington, March 10, 1917* Tliia manual ia published for the information and government of the Regular Army and National Guard of the United States. By order of the Secretary of War: William Crozier, Brigadier General, Chief of Ordnance. 10067—17 C3 > 365263 Digitized by the Internet Archive in 2007 with funding from IVIicrosoft Corporation http://www.archive.org/details/careoperationOOunitrich DESCRIPTION AND INSTRUCTIONS FOR THE CARE AND OPERATION OF FIRING MAGNETOS. 1 . The firing magnetos described below have been developed to replace the firing pistol and battery used on seacoast gun carriages and the D. C. magneto used for firing mortars. MAGNETO TYPE GA, FOR GUNS. (Plate I.) 2. For gun firing, type GA'is used. This magneto is designed for firing one primer only, and is issued for all guns using separate ammunition. 3. The magnetos are numbered serially, the first 100 having a base differing slightly from those of higher number. Numbers 1 to 100 have two threaded lugs on the base through which the old-style firing cable with spiral armor passes. By means of a gasket, nut, and sleeve, the cable is made fast to the base. 4. Numbers 101 and following have a single entrance provided in the base for the twin conductor leaded and armored firing cable. 5. The principal parts of this magneto are: Case with base, firing lever, lever catch, lever spring, spring plunger and spring lever, lever shaft, gear segment, clutch-shaft pinion, clutch shaft, clutch- shaft bracket, clutch and spring, clutch-shaft gear, armature-shaft pinion, and magneto proper. The parts are named approximately in their order in the train from lever to magneto. 6. The firing magneto, complete, weighs 33 pounds. 7. The case is of bronze, and protects the interior from dust and excessive moisture. By means of a lug at the rear it is securely attached to the bracket provided on the sight standard. 8. The firing lever is heavily constructed to resist bending under excessive strain. It is held in the locked position by a catch, and when the lever is gripped preparatory to firing the catch is automati- cally released. The lever is returned to the locked position by the lever spring, assisted by the weight of the lever itself. It has been found that it is not necessary to raise the lever violently, as even a small and slow movement will fire a primer. The gear ratio is such that one complete revolution of the lever would give 48 revolutions of the armature. As the lever can be easily moved at the rate of one (5) T « c^ ^ c 6 turn in a second, it is seen that very high armature speeds may be obtained. When the lever is raised, the gear segment on the far end of the lever shaft turns the combination pinion and clutch. The latter, through the clutch sleeve, turns the clutch shaft and the large gear on the other end of this shaft meshing with the pinion on the armature shaft. The pinion on the clutch shaft is extended through the clutch shaft bearing and has on its inner end ratchet teeth. These are normally in mesh with the teeth on the clutch sleeve. The sleeve slides free on a flat section of the shaft, but must turn with it, and is held in mesh with the pinion by a spring. Thus, when the lever is raised, the armature is revolved, and when the lever stops the clutch teeth slide over each other, the spring allowing the sleeve to back off from engagement with the pinion clutch. The armature is thus allowed to revolve until its momentum is lost and sustain the current, 9. This magneto will deliver on open circuit about 45 volts at 2,000 r. p. m. Through an external resistance of 1 to 3 ohms, it will, at 2,000 r. p. m., generate about 0.8 ampere at 1 volt pressure. Small external resistances do not greatly affect the output and a primer can be fired with as much as 60 ohms resistance in the circuit. The armature and brush resistance is about 3 ohms. 10. The average current being about 0.8 ampere it will be ample to fire one primer. However, the capacity is in general not sufficient to fire in parallel, since about 0.4 ampere or more is necessary to fire a primer. As the resistance of the firing circuit is less than 1 ohm it is seen that while a large number of primers might be fired in series, only two could be fired in parallel, under favorable circumstances. The magneto should not therefore be expected to fire more than one primer except in series. 11. The magneto proper is made by the Sumter Telephone Manu- facturing Co., and is their type JR. The armature is wound with 530 to 540 turns of No. 21 wire (B. & S.) MAGNETO TYPE MA, FOR MORTARS. (Plate II.) 12. This magneto is quite similar in principle and construction to the type GA, the capacity being considerably greater, however. It is designed to fire four primers in parallel and for this purpose the current output must be at least 1.5 to 2.5 amperes. In the branches of a divided circuit the greater portion of the current flows in the branches of least resistance. It is therefore desirable to have as great an output of current as practicable in excess of the necessary requirement in order to insure that all branches have the necessary current. It is also very important that the resistance in all branches be kept as nearly the same as possible. 13. The characteristics of this magneto are as follows: The voltage on open circuit is about 50 at 4,000 r. p. m. Through an external resistance of 2 ohms at 4,000 r. p. m. the output is about 8 amperes at 16 volts, and at 1,000 r. p. m., through the same external resistance, the output is about 4.5 amperes at 9 volts. The armature and brush resistance is 0.4 ohm. 14. The gear ratios are such that one turn of the firing lever causes 30 turns of the armature. 15. It is expected that four primers will fire simultaneously with- out great effort. In experimental firing, the primers have been found to explode upon a very small and relatively slow movement of the handle. When difficulty is experienced in firing all primers simul- taneously, examination should be made to ascertain whether the branches of the divided circuit have approximately equal resistances. 16. The magneto, complete, weighs about 86 pounds. 17. The magneto proper is made by the Sumter Telephone Manu- facturing Co. and is designated by them as type AGD. 18. A wall bracket is provided in or near each mortar pit for mounting the magneto, which is there attached to the engineer cables. CARE OF MAGNETOS. ^ 19. The construction of the magneto complete is very simple, and but little attention is required to keep it in good condition. All nuts are of the crown type held by a split pin to avoid unscrewing by vibration. The studs for the six nuts at the base are pinned in position. 20. When the magneto is not in use for extended periods it should be removed from the carriage, mount, or emplacement, if practicable, advantage being taken of this opportunity to examine the interior before storing. 21. The only attention required is examination of the interior approximately twice during the year to prevent starting of rust and to allow oiling of gears and bearings. Openings in the case for this purpose have been omitted for the sake of greater protection. To examine the interior, remove the nuts at the comers and sides of the base. The base, with magneto which is held to it by the remainiag studs, can then be removed. There may be slight binding of the base on the studs so that it wiU be necessary to insert a thin tool between the base and the case in order to separate them. 22. The armature-shaft bearings are provided with grease pockets and these should be kept packed with waste soaked with light engine oil. 23. If difficulty is experienced in firing primers, it will probably be found that there is some irregularity in the firing circuit or magneto, and an examination should be made, rather than an attempt to over- come the difficulty by violent raising of the- lever. The lever should be raised with a moderately quick action aifd under proper conditions a relatively slow movement will fire the primer. The magnets should not be removed from the magneto frame unless absolutely necessary. To do so weakens the field and decreases the voltage. When the magnets are necessarily removed, they should be placed with the ends on pole pieces. COVER FOR^ FIRING MAGNETO. 24. A cotton duck cover is provided with each magneto for pro- tection against the weather when not in use. TESTING LAMP. 25. There is provided a testing lamp for testing out the gun-firing circuit and magneto. It consists of a low-voltage incandescent lamp attached to a dummy primer. When this dummy is inserted in the vent, the firing circuit is closed in the usual manner. Upon operating the magneto the lamp will glow. If the circuit is in good condition the lamp will glow brightly, but the capacity is such that a current which will even produce a duU-red glow will fire a primer. List of parts of firing magneto, their piece marks, number, and location. TYPE GA. Piece Num- mark. i ber. P67Q. P66G. P67P. P67L. P67S. P67T. P67X. P61H. P67A. P67J.. P67K. P67C. P67F. P66K. P80E. P66H. P80F. P66C. P66E. P80D. P66N. P61F. P67N. P67G. P66F. P67H. P67E. P66D. P67Y. P67B. P61G. Name of part. Base (for use with flexible conduit) . Base (for use with armored cable) . . Bushings Case Clutch Clutch sleeve Clutch-shaft bracket . Gaskets, coupling. . . Gear Intermediate shaft. . Key. Location. ...do Key, Woodruff No. 1 Lever Lever catch Lever-catch pin Lever-catch spring Lever-return spring Lever shaft , Lever stop Magneto, Sumter JR, or equal . Nameplate Nuts, coupling Nuts, crown do do do Pinion Pins, dowel Pins do. Plunger pin . Rivets, countersunk. Screws, filister head. do. Segment , Sleeves, conduit. Split pin. do. Bottom of case. Do. For base P67Q. Slips on magneto bracket. On intermediate shaft. Do. Secured to armature yoke. On conduit sleeves. On intermediate shaft. In clutch-shaft bracket. Intermediate shaft. Lever shaft. Armature shaft. On end of lever shaft. On lever. Lever catch to lever. Riveted to lever catch. Around spring plunger. In bearings in case. Riveted to lever catoh. Secured to base of case. On front of case. Screw on bosses on base. For studs P67M;. On clutch end of intermediate shaft. On end of lever shaft. On gear end of intermediate shaft. On end of armature shaft. In bottom of case for base. For studs P67M;. For studs P66P. Connects spring plunger and spring lever. For fastening spring to lever catch. For fastening clutch shaft bracket. For nameplate. On intermediate shaft. In coupling nuts. For plunger pin. For lever-catch pin. List of parts of firing magneto, their piece marks, number, and location — Continued. TYPE GA— Continued. Piece mark. Num- ber. Name of part. Location. P61G Split pin .. . For nut P67H. For nut P67G. P67U Spring clutch .... On intermediate shaft P66A Spring lever . Do. P66B . Soring nlunger Between spring lever and lug on case. Fasten base to case. P67M Studs P66P ..do . .. . To hold magneto to base. On lever-catch pin. On intermediate shaft. P66J Washer P67W.... Washer, clutch P67D Washer Do. TYPE MA. P74B 1 1 4 1 Base .. . Bolted to bottom of case. P74A Case Slips on magneto bracket. On intermediate shaft. P76R Clutch P76K Clutch sleeve Do. P76L Clutch spring > Do. T97P Conductor terminal Attaches to terminal end bracket. T97Q P76M do Dowel pins Intermediate gear Do. In bottom of case for base. On intermediate shaft. P76F Intermediate shaft In terminal end and pinion end bracket P75A Lever bearings. On lever shaft. P75E Lever catch On lever. P75G Lever-catch pin Lever catch to lever. P75F Lever-catch spring . Riveted to lever catch. P75B Lever shaft In bearings in case. P75P Lever stop ... Riveted to lever catch. P73E P73C Magneto, Sumter AGD, or equal Magneto cable Bolted to base. From plug to terminals. Connects to plug box. On armature shaft. Do. P73D Magneto-cable plug P76N P76P Magneto pinion Magneto-pinion key P73A P74G P74E P76G P75C P76H P73F P76E Nameplate Nuts, crown do do do... do do Pins Pinion end bracket On front of case. For studs P74C. For studs P74D. For intermediate shaft. For lever shaft. For intermediate shaft. For armature shaft. Secure studs f P74D) in case. Secured to pinion end of magneto. P73B Rivets Screws, fllister head. For fastening spring to lever catch. Fasten nameplate to case. P76D P76C P76B P76B do do do do Clamps end of terminal end bracket. Conductor terminal to terminal end bracket. Pinion end bracket to magneto. Terminal end bracket to magneto. P75L Segment On intermediate shaft. P75D..... Segment spring ... . Between spring hanger and spring stud. In lever shaft. P75M Segment key Snlitpta.. . , For lever-catch pin. do For spring hanger. On segment. P75N Spring hanger P74P Spring stud Screwed and riveted to inside of case. P74C studs. : . . ::.:.... Fasten magneto to base. P74D do Connect base to case. P76A Terminal end bracket Secured to terminal end of magneto. T96EA... Terminal tube, complete Screwed into base. P75H Washer For lever-catch pin. P75K do For spring hanger. P76Q do For intermediate shaft. War Department, Office of the Chief of Ordnance, Washington, March 10, 1917. Form No. 1814. Ed. Aug. 27-17—500. NOU/SOd SIHl Nl SI d3A31 N3HN^ a39\/0N3 Xnnj HJ.33J. HOimO HJ.IM IVlNOZiyOH 39 01 3ynivu/ijv- 10 n STAMPED Je^W^®^ "Ara AN INITIAL FINS ni. o. OVE^OUE. "° *'°° ON THE SE^V^EWTr^J? iii YC 6437 Ca^ord Bros. Makers Syracuse, N. Y. pit; JAM. 21 .\m ^ d< UNIVERSrrY OF CAUFORNIA UBRARY