)^t ^ ^l;^^ Digitized by the Internet Archive in 2007 with funding from IVIicrosoft Corporation http://www.archive.org/details/americsteelworkOOmarkri :^5 •'-;:? The American Steel Worker CO A TWENTY-FIVE YEARS' EXPERIENCE IN THE SELECTION, ANNEALING, WORKING, HARDENING AND TEM- PERING OF VARIOUS KINDS AND GRADES OF STEEL 9 CO BY E. R. Markham CO First Edition 1903 New York II fi n LIRRARr Copyright 1903 by E. R. Markham, Words are not adequate to express the debt I owe one, who, more than all others, has been instrumental in instructing, advising and assisting me along lines that have led to whatever success I may have attained. As an humble acknowledgement of my grat- itude, I dedicate this work To My Father, RUSSELL MARKHAM. The American Steel Worker. Q^<^=\ ,^=^n9 CO Introduction. An experience which covers twenty-five years of actual practice, in the various branches of machine shop work, has taught the writer that much more depends on the condition of the various cutting tools used, than mechanics in general realize. The various machines used in working iron and steel to shape have been improved, and made heavier in the parts subjected to strain, in order that heavier cuts and faster feeds might be taken to reduce the cost of production. If a tool is doing the maximum amount of work possible for it to do, when it is used in a light machine, it would be folly to purchase a heavier, stronger ma- chine and use the same tool in it. But it has been found in many cases that cutting tools could be made that would take heavier cuts and faster feeds than the older types of machines could carry. Consequently it has been necessary to re-design most types of machines iised to remove stock, in order to bring them into shape to be used as tools, parts of machines, and other apparatus. Competition has made it absolutely necessary that every possible means be taken to reduce the cost of an Cheapening cost of production. article without reducing the quality. Where possible the design is changed so the article may be made more cheaply. And as labor is, generally speaking, the princi- pal factor to be considered, it is necessary to reduce as far as possible the number of operations, or simplify those necessary, and so reduce the cost of the manu- factured article. If by the use of machinery especially adapted to the work to be done, it is possible to do in one opera- tion the work which formerly required four separate operations, then the amount paid for labor has been very materially reduced, without necessarily reducing the pay of the operator. In fact it is found possible in many cases to increase his compensation, and at the same time reduce the cost per piece of work very materially. Now, in order that improved machinery may do its maximum amount of work per day, it is necessary to have the cutting tools, fixtures, etc., made in a manner that allows them to do their part of the work. If a milling machine were bought and set up in a shop, and it was found that the fixtures formerly used in holding the pieces of work were not strong enough to hold them when the new machine was taking the heaviest cut possible, heavier fixtures would be made at once in order that the investment of money made in purchas- ing the machine might not be considered as having been thrown away. Following out the same line of reasoning, it would be necessary to make cutting tools of a design that made it possible to take as heavy cuts, and use as coarse feeds, as the strength of the machine and fixtures would allow. While manufacturers in general recognize the im- 8 Waste through improper handling. portance of having machines especially fitted for their needs, many times the good work stops right at this point. They are not educated to a point that makes it possible for them to comprehend the importance of having the cutting tools hardened in a manner that insures their doing the amount of work possible. While it is often necessary to re-design cutting tools to get added strength, many times this needed strength may be had by proper hardening. A manufacturer of a high grade tool steel, in con- versation with the writer, said, if he could have one per cent, of the value of steel in this country spoiled by improper hardening, he would not exchange his income for that of the President of the United States. By the value of steel, he meant its value at the time the article was hardened. A piece of steel which cost fifty cents in the bar, may be worth many dollars when ready for hardening, and represents to the manufacturer the total cost of steel and labor. This line of reasoning might be carried a great deal further. If a tool which is made to do a certain job is ruined, the time the machine or machines stand idle waiting for another one to be made, many times represents a greater loss than the money value of the tool. This is especially true where the time given to complete the job is limited. If a tool is hardened in a manner that makes it impossible for it to do as much or as good work as it ought, the loss may be greater than in either of the cases before cited, yet this loss is seldom taken into consideration. The writer's experience has convinced him that few mechanics realize the vast waste of time in many Increase of productive efficiency. shops, because tools are not capable of doing the amount of work possible were they properly hardened. Take for instance a milling machine cutter which runs at a periphery speed of thirty-six feet per minute, milling a mild grade of machinery steel. It is found necessary to stop this machine once in twenty working hours to sharpen the cutter, milling in the meantime five hun- dred pieces. A cutter is made from the same bar, and hardened by a process that makes it possible to run the tool at a periphery speed of eighty feet per minute, and it is then found necessary to grind but once in two hun- dred hours; milling in the meantime eight thousand pieces. Not only is the efficiency of this machine increased many fold, but the expense of grinding, and the necessary delay incident to stopping the machine, changing cutters and setting up, and the cost of tools per piece, is reduced very appreciably. Does some one ask. How is this trouble to be remedied? The answer is, men must be educated to see the enormous waste going on all the time; the waste of steel, of time required to make the tools, of the time valuable equipment is laying idle, and the small percentage of work produced per machine, all go to reduce dividends, and this because so little attention is given a subject which should receive as much con- sideration as any one branch of machine shop work. When the trouble is apparent, then it is necessary to find a remedy. The physician must necessarily un- derstand the human body in order that he may diagnose diseases. If one would be a successful hardener of steel, he must understand the nature and peculiarities of steel. As a study of drugs alone would not fit one to practice medicine, neither will practice alone fit one Necessity for the study of steel. to harden steel, especially if new problems are con- stantly coming up. At the present time when libraries are accessible to nearly every one, and books and mechanical journals, treating on steel and the proper methods of its manipu- lation, are within the reach of all, there is no good reason why ignorance of a subject so interesting, and at the same time of such vital importance to both manufacturer and mechanic, should be so general. A study of the nature of steel will convince one of the importance of extreme carefulness when heating either for forging, annealing or hardening. A man who understands the effect of heat on high carbon tool steel is often amazed at the careless manner which many old blacksmiths assume when heating a piece of steel. A difference of loo to 200 degrees of heat after the steel is red hot, does not, according to their idea, injure the steel in the least, but in reality it makes a vast amount of difference in the strength of the piece. In some shops a man is called a successful hard- ener if he is fortunate enough to avoid cracking the pieces he is called upon to harden. Apparently no account is taken of the capability of the tool to perform a satisfactory amount of work. A man who devotes his attention to hardening steel in a manner to avoid cracking, regardless of the utility of the tool, is not worthy of the title of a successful hardener ; he should be styled, as an eminent mechanic calls this class, a non-cracker. Now, it is possible to harden steel in a manner that does away with the liability of cracking, yet gives it the amount of hardness necessary, in order that it may do the amount of work expected of it. A study of the effects of expansion and contraction II Expansive properties of steel. of steel in the fire and baths is necessary in order to select the proper forms of furnaces and bath, so that the best results may be obtained. Suppose a micro- meter is left for some time in a room where the tem- perature is 40 degrees Fahr. , a piece of work is placed between the contact surfaces, as shown in Fig. i. Figure 1 Illustrating expansion of steel. Now grasp the micrometer by the frame at the portion marked by with a warm hand; in a few seconds the metal will have expanded to a degree that allows the work a to drop from the gauge, thus proving that but a very small amount of heat is needed to expand the steel sufficiently so the contact points no longer touch the piece between them. Now, if a few degrees of heat will expand steel so it can be readily observed, it is apparent that a heat of 900 to 1,200 degrees Fahr. must cause the process of expansion to be carried to a much greater extent. The amount of heat necessary to give steel, in order that it may harden when plunged in some cooling bath, varies with the make of steel, the percentage of carbon it con- Desirability of not overheating. tains, and also on the percentage of other hardening elements in the steel. Jarolinech places the critical temperature at 932 degrees Fahr. (500 Centigrade) as determined by him experimentally. The lowest heat at which a piece of steel will harden satisfactorily is termed the refining heat, because the effect of the operation of suddenly cooling steel heated to this tem- perature is to refine the grain, making it the finest pos- sible. The writer does not propose giving a scientific explanation of the changes which take place in a piece of steel when it is heated to the hardening heat, and quenched in the cooling bath, but the practical sides of the question will receive careful attention. Every man and boy working in a machine shop knows that steel heated red hot and plunged in water, will harden, but it is necessary to know how hot it must be heated in order that satisfactory results may follow. We should thoroughly understand the action of too great an amount of heat on the structure of steel, in order that overheating may be avoided. It is also necessary to have a correct understanding of the effects of baths of various kinds on steel, if it is dipped in them when red hot. It is an acknowledged fact that the lowest possible heat at which steel will harden, leaves it the strongest This is illustrated elsewhere. Knowing this, it will be seen that an article made of steel is very much less liable to crack when hardened at a low heat, than if it were heated to a temperature which caused it to be brittle. Commencing with cold steel, every degree of heat applied changes in a measure the size and structure 13 Uniform expansion in heating. of the piece, until a certain limit is reached. Now, if a change in temperature of a few degrees changes the size of a piece of steel, the reader is asked to imagine the change in size and structure which must take place when it is heated red hot. This means a change in temperature of about i,ooo degrees, and the effect of heat on steel is to expand it, while the opposite effect is accomplished when it is cooled. The more rapidly it is cooled the harder it will be. It is indeed wonder- ful that a piece of steel can undergo the changes which take place in its size and structure, and remain intact. When steel is cooled in the hardening bath, the outside of course chills and hardens first, while the inside is hot and consequently soft for some little time after- ward. Now, the outside, being hardened, is practically inflexible, while the inside continues to change in structure until cold. This is especially true of pieces having teeth or projections on their surface. Understanding the fact that heat causes steel to expand, it will readily be seen that it is absolutely necessary that it should expand uniformly throughout the piece. If the corners and edges are hotter than the balance of the piece, then it is unevenly expanded, and consequently will contract unevenly. Now, if one part of a piece of steel contracts more than another, or not uniformly with another part, it is liable to crack from the effects of the unequal contraction; if it is not cracked when taken from the hardening bath, it is liable to crack at some future time for no apparent reason. This applies especially to large pieces, and steel having a high percentage of carbon. 14 The Workman CO The writer's professional experience in the various methods of working" steel, brings him in contact with men of all degrees of intelligence. Some men are really skillful in the particular line they are engaged in; that is, they are very careful when heating and dipping in the bath, and get excellent results. But they do not know the difference between a steel of ^ per cent, carbon and one of i ^ per cent ; in fact, they do not know anything about percentages of carbon, and don't care ; they say so in as many words. The steel they use is always the same make and temper. They have never used anything else. If they should get hold of another make, that worked differently from that they had always used, they would condemn it, saying it was no good, because it didn't act just like the steel they were accustomed to handling. Now, if anything should happen to the steel mill making their particular brand, they would be obliged to learn the art of hardening all over again, or go out of business. When it becomes necessary, or the con- cern who employs these men considers it advisable, to change the steel used; or if it is necessary to have the composition changed to get some desired re- sult, this poor fellow is all at sea. He doesn't know 15 The workman who "knows it all." what to do, and he doesn't want anyone to tell him what to do. His only cry is, *' The steel isn't good for anything," when in reality it may be the best on the market. Such a man is to be pitied, but he is a very expensive man for those in whose employ he happens to be, and a very unpleasant fellow to attempt to teach anything. Another example is the man who banks on his twenty or fifty years' experience, and considers that because he has been allowed to exist for that length of time and occupy a position as blacksmith, or hardener, that he must necessarily know it all. To him steel is steel; he treats it all alike. If there is some particular steel good-natured enough to stand his treatment, that is the only brand on the market fit to use — according to his way of thinking — and he gener- ally has such an unpleasant and forcible personality, that he either has his say or goes where he can. He never investigates the merits of different makes of steel ; simply condemns every make that will not stand his abuse. If every man of the type under consideration ad- vocated using the same steel, there might be a plausi- ble excuse for looking into the merits of that particular brand, to the exclusion of every other, but you will hardly find two of them advocating the use of the same steel. I am happy to say this class of hardener is not in as great a majority as formerly; their number is gradually diminishing. It is impossible to teach him anything, because that long experience of his stands in the way ; it is his only stock in trade, and he presents it every time anything is said on the subject. Now, a long experience in any particular line of i6 The workman who doesn*t care. work is a good thing for a man, provided it has been a real experience, rather than an existence, and in no line of business is it more valuable than in the working of steel, if the man has kept pace with the procession. If not, then he is no farther advanced than when he fell out of line, and as it is a law governing all our lives, that no man stands still, he must of necessity either advance or go backward. The man who has not kept pace with the progress of events, must necessarily go backwards. Another class we meet with is the jolly, good- natured fellow, who wants to please everybody, but does not know how, and is too lazy to find out. He had rather tell a story than to keep his eyes and attention on the piece he is heating, consequently he has all kinds of luck. There is no remedy known for this chap. He is willing to be told how to do, but is too lazy to assimilate and put in practice what is told him. A class of hardeners which are few in numbers, but who should get into some other business as soon as possible, consists of men who are practically color blind. They cannot distinguish between the various shades of red, neither can they discern the temper colors as closely as they should. Some of them are extremely intelligent, capable men, but they have missed their calling, and missed it most decidedly, because a man to be a successful blacksmith or hard- ener, must have good powers of distinguishing colors and shades. There are many other classes that might be con- sidered, but it would be a waste of time, so we will look in upon the successful hardener. There are vari- ous degrees of success, but we will consider the man 17 The successful steel worker. who is a success according to the generally accepted idea. The successful hardener is one who finds out what is wanted or expected of the article he is to harden; whether extreme hardness, toughness or elasticity, or a combination of two of these qualities. He also under- stands the nature and pecularities of the steel he is using ; he considers the fire he is to use, and the bath in which the steel is to be quenched after it is heated. His spare moments are not spent hanging around street corners, or saloons, but in reading and studying such books and mechanical journals as treat on subjects in his line. In this way he becomes familiar with the nature of steel and knows what to do when certain conditions which are out of the ordinary arise ; he gets the experience of others and his knowledge makes it possible for him to discriminate between that which will be of value to him, and that which will not. When a piece of work is given him he studies the shape of the piece, the best method of heating and quenching, in order to get the desired results. To him steel is not simply steel, which must be treated just like every other piece of the same metal, but it is a valuable tool or piece of machinery which he takes pride in hardening in the best possible manner. If he hears of a brand that is giving some one trouble, he is anxious to get a piece of it, and experiment and find out why they can not get good results from it. If he hears of a brand that some one claims gives extra good results when using, he is anxious to get a sample and test it, and see for himself if the steel is all the makers claim it is. He is not above learning, takes advantage of every i8 The two kinds of steel. opportunity to get the ideas and experience of others, especially men who have had a wide experience. To him the articles he is called on to harden represent so much money entrusted to his care, and he takes every means possible to get it out in a satisfactory manner. Does some one ask, where do you meet such men? The writer is happy to say such men are not the ex- ception. To be sure they are not in the majority, but the number of men who are making a careful study of this subject is really encouraging. Steel. CO Although there are many makes of steel and, in most cases, several grades of the same make, yet to the average mechanic there are two kinds of steel, viz., machinery steel and tool steel. Machinery steel is used in making such parts of machines, apparatus or tools as do not require harden- ing in order to accomplish the result for which they are intended. Or, if they require hardening at all, it is simply a surface hardening, the interior of the piece being soft with a view to obtaining greater strength. This class of steel is of a lower grade than tool steel. It is softer, works more easily, both in the operations of forging and machining, and can be safely heated to a higher temperature without harm to the steel. It 19 Tool steel — what it is ; what it's for. resembles more closely wrought iron and is sometimes scarcely to be distinguished from it. Machinery steel is used whenever it will answer the purpose, not only on account of its being more easily machined, but its first cost is only ^ to -j^ that of ordinary tool steel, and for most purposes where it is used, it answers the purpose as well or better. Although it is considered advisable to group steel under two heads, as mentioned, namely, machinery steel and tool steel, yet on account of the different grades of the article under each head it will be neces- sary to distinguish them somewhat as they are con- sidered under the various processes of hardening. Tool steel is made with the idea in view that it is to be made into such tools, appliances or parts of machines as require hardening in order to accomplish the desired result. Although the term "tool steel" is applied to steel intended to be made into cutting tools, there are many makes of this article, each make differing in some respects from every other make. Not only is this so, but most makers put out tool steel of different tempers. Now, the word "temper," as used by steel makers, means the quantity or percentage of carbon the steel contains. It is low temper, medium, or high, or number or letter so and so, according to the understanding of the marks in each particular mill. The following are considered by steel makers as the most useful tempers of tool steel : Razor temper (i^ per cent, carbon). This steel is so easily burnt by being overheated that it can only be placed in the hands of very skillful workmen. When properly treated it will do many times the work of ordinary tool steel when working hard metals, etc. Percentages of carbon in tool steel. Saw file temper (i|^ per cent, carbon). This steel requires careful treatment, and although it will stand more heat than steel of i ^ per cent, carbon, it should not be heated hotter than a low red. Tool temper (i ^ per cent, carbon), A very useful temper for turning tools, drills and planer tools in the hands of ordinary workmen. Spindle temper {i}i per cent, carbon). A very useful temper for mill picks, circular cutters, very large turning tools, screw thread dies, etc. Chisel temper (i per cent, carbon). An exceed- ingly useful temper, combining, as it does, great toughness in the unhardened state, with a capacity of hardening at a low heat. It is well adapted for tools where the head or unhardened end is required to stand the blow of a hammer without snipping off, and where a hard cutting edge is required, such as cold chisels, etc. Set temper (^ per cent, carbon). This temper is adapted for tools where the surface only is required to be hard, and where the capacity to withstand great pressure is of importance, such as stamping or pressing dies, etc. The following also gives the steel maker's mean- ing of the word ''temper " : Very hard 150 carbon -f Hard loo — 120 carbon Medium 70 — 80 carbon In order that the reader may understand some- thing of the significance of the terms used to designate the amount of carbon a piece of steel contains, the fol- lowing brief explanation is given. A point is one hundreth of one per cent, of any element. 100 points is one per cent. A 40 point carbon steel contains forty 21 Peculiarities of tool steel. one-hundreths (.40) of one per cent, of carbon. The same explanation applies to any element that goes into the composition of steel. The steel is sometimes desig- nated by the number of points of carbon it contains — as 20 carbon or 60 carbon steel. The amount of carbon the steel contains does not necessarily determine the quality of the steel, as the steel maker can give an ordinary low grade stock a very high percentage of carbon. This would harden under the ordinary condi- tions, but would be practically useless if made into cutting or similar tools. It becomes necessary many times to procure a low grade steel having as low a percentage of carbon as possible. Then again it is advisable, where a greater amount of strength is required, to give the steel a higher percentage of carbon. This will be briefly alluded to from time to time under the various topics. The reader will readily see from the foregoing that it is the presence of carbon in steel that causes it to harden. The amount of hardness and the degree of heat necessary when hardening depending on the quantity of carbon the steel contains. Tool steel is hardened by heating it red hot and plunging into some coeling bath. The more quickly the heat is extracted the harder the piece will be. Tool steel has certain peculiarities which must be understood if one would be a successful hardener. The outside surface of a bar of steel, as it comes from the steel mill or forge shop, is decarbonized to a consider- able depth. This is because the action of the oxygen in the air causes the carbon to be burned out of the steel at the surface during the various operations when the steel is red hot. In order that the decarbonized Decarbonized surface of steel. portion may not give trouble, it is necessary to cut away enough of the surface to remove this portion before hardening. If a tool which is to finish ^ inch diameter is to be made out of round steel, it is neces- sary to select stock at least -jV inch diameter larger than the finished tool, or the outer surface will not harden sufficiently. For sizes from ^ to i inch diameter, select stock -^ to }i inch larger. For sizes from i to 2 inches diameter, select stock from }i to -^q of an inch. For sizes above 2 inches, about ^ of an inch should be cut off. It is necessary when centering round steel to have the center hole very near the center of the stock, as shown in Fig. 2, in order to take off an equal quantity Figure 2, Figure 3. Proper and imnroper centering. of the decarbonizing surface all around. If a piece is centered, as shown in Fig. 3, the decarbonized surface will be entirely removed from one side of the piece and scarcely any of it taken from the opposite side ; consequently, the side from which it was removed will be hard, while the opposite side will not harden, or at least will not be as hard as the other side. Extravagant economy. So it will be very readily seen that this simple fact, which is often entirely overlooked in machine shops, is a cause of a great amount of trouble. Tool makers, as a rule, understand this fact in regard to steel, but some one in authority, wishing to save money for the manufacturing concern, gives the job of centering to the "tool room kid, " as he is termed many times. He fails to instruct him in the proper manner, the boy does not understand the nature of steel, and as a consequence, it is centered, as shown in Fig. 3- Now, if the tool maker were given the job, he would readily see that it was centered wrong. But the spirit of economy still prevails, and the boy is allowed to rough out the piece. As a consequence, the outside surface is removed, and all traces of the eccentric cen- tering are eliminated. The piece is made into a reamer or some other tool, and when hardened it is soft on one side, the other side being hard enough. There is no one that can be blamed but the hardener, so he, poor fellow, has to "catch it." It wouldn't be human nature to stand by and say nothing when blamed for something one didn't understand, so he, in turn, says the steel is no good. As a consequence, the make of steel is often changed and another kind is procured, and as it is desirable to test the steel before making any quantity of it into costly tools, the tool maker is told to cut off a piece of the stock and make a reamer just like the one that wouldn't harden properly. He centers the piece, as shown in Fig. 2, turns it to size, cuts the teeth and gets it ready for hardening. It comes out all right. The steel is pronounced O. K. and a supply is No mysteries in steel handling. ordered. A large batch of reamers is made up and the same boy is given the job of centering and ** roughing " them, and the results are the same or worse than when the former lot was hardened. Now, it is evident to every one that the hardener must be to blame. He hardened one reamer from this same steel and it was satisfactory. Well, the only conclusion is that he made a mistake when he did that one^ and isn't on to his busi- ness, so he is nagged and found fault with until he can stand it no longer and gets out. The next man has the same results, and those in charge say, * * You can't get a decent hardener now-a-daj^s. " All this trouble and expense because some one wanted the reputation of being a good manager. Now, a boy can center and rough out stock and do it all right, but he must be told how and he must be watched. If a make of steel that gives satisfaction suddenly shows freaks, do not at first condemn the steel, but look for the cause. Many people have the idea that there are unaccountable mysteries connected with tool steel, and that hardening is a thing which must be attended with luck, or bad results follow. Now, as a matter of fact, if a good steel is used, the cause may be found for all troubles which occur when it is hardened, and many times they will be found to result from some penny wise and pound foolish notion. Another peculiarity of steel is that if the position of any of its molecules is disturbed when the steel is cold, there is apt to be trouble when the piece is hardened. For instance, if a piece of steel that is to be hardened for any given purpose is cut from a bar of tool steel and it is found to be so bent that it would be impossible to turn and make straight and remove Steel of difFerent makes vary. all the decarbonized surface, the piece should be heated red hot and straightened. If it were straightened cold, then finished to size and hardened, it would be almost sure to spring. The writer has seen men at work making blanking dies for punching press work who, when they made the openings too large at any point, would take a hammer and pene the stock into the opening without heating the die. They would plane the top of the die for shear and then finish it and swear about the hardener when the piece cracked in harden- ing directly under where they pened. Possibly, it would not show any bad results at that time, but when the die was used, the portion referred to would crack off. Or if the punch were a tight fit, it would lift a piece of steel from the face of the die the shape of the hammer pene or of the set used. Steels of different makes vary in their composition. A successful hardener will experiment with a new steel and find out just what he can do with it. One make of steel will harden at an extremely low heat ; another make will not harden in a satisfactory manner at that heat. It requires a higher heat in order to harden it. Now, if we were to heat the first steel as hot as we were obliged to heat the other, we should ruin it, or at least harm it. For this reason it is not advisable, generally speaking, to have a half a dozen different kinds or makes of steel around a shop, unless someone knowing the nature and peculiarities of each is to do the harden- ing. And even then trouble will follow unless a ticket accompanies each tool stating the kind of steel, and this in the ordinary machine shop would lead to end- less confusion. A steel which gives satisfactory results should be a6 Steel is usually all right. selected and then used until convinced that some- thing better is to be had. The judgment of an ex- perienced hardener is not always to be relied upon as to the best brand of steel for a particular purpose. It may be that he has had excellent results with a certain brand because he has methods of hardening particularly fitted to that brand of steel; but it may be true that were he to change his methods to adapt them to another steel, much better results would follow. The writer was at one time brought in contact with a hardener whose complaints in regard to the steel furnished had caused the superintendent of the shop to change the make of steel several times. Each time a new steel came into the shop the result was the same, until finally by the advice of one of the steel manu- facturers several tools similar to those previously hard- ened with unsatisfactory results were made from each of the condemned steels and given to a man who was considered an expert hardener. When they were hard- ened and returned they were all found to be in a satis- factory condition, not a crack visible in any of them. They all gave good satisfaction, proving that the man rather than the steel was at fault. Almost any of the leading makes of steel in the market will give good results if treated properly, but the same treatment will not answer for all makes. Some makes are more satisfactory than others for certain purposes, but better results may be obtained from most of them than is often the case. Steel may be purchased in bars of various shapes. The more common shapes are round, square, flat and octagon. If steel is to be cut from the bar and ma- chined to shape, it is advisable to purchase bars wliich »7 The choice of proper steel. allow of machining to the desired shape, at the least expense and with as little waste of material as possible. Always remember that it is necessary to remove the decarbonized portions previously mentioned. If a tool which is to be cylindrical in shape is to be made, use a piece of round steel. If an article which is to be finished square, use a piece of square steel, etc. Steel of the same quality and temper is furnished in all the common shapes on the market. It v/as for- merly considered necessary, if best results were de- sired, to use octagon steel when making cylindrical pieces of work, but now all steel makers claim to make round steel of exactly the same quality as the corresponding sizes of octagonal shape, and the exper- ience of every mechanic who has tested the two under similar circumstances substantiates the claim. The steel maker puts on the market steel of dif- ferent tempers, but he advocates the use of the par- ticular temper which he considers best adapted to the work in the individual shop. As a rule he does not make any mention of any other temper, because he knows that if steel of several different tempers are kept in stock, that in all probability the labels will be removed in a short time and any distinguishing marks be thrown away. Then no one in the shop will know one temper from another, and when a piece of ^ per cent, carbon steel is made into a shank mill or similar tool, and a piece of i ^ per cent carbon steel is made into some tool that must resist the action of heavy blows, trouble will follow and the steel be condemned. For this reason it is considered advisable to advocate the use of a temper that will give satisfactory results when put to most uses. But the fact remains that aS Carbon necessary to proper results. steel, in order to give best results, should contain the proper percentage of carbon for use on the particular job. In shops where detail is followed very closely, the steel is kept in a stock-room, each different temper by itself, and so marked that there is no danger of it get- ting mixed. Much better results are then obtained, provided a competent man does the hardening, than if one temper was . used for everything. But in a shop where there is only one rack, and sometimes no rack, the stock, machinery steel, tool steel, and everything else is kept on this one rack, or in a pile on the floor, it is not advisable to have steel of different tempers lying around, or results anything but satisfactory are sure to follow. Percentage of Carbon Necessary to Produce Desired Results. In the first part of this section is given a table of percentages of carbon present in steel for various pur- poses. This table is generally accepted as a guide to those desiring steel for any given purpose, and, gen- erally speaking, it is safe to use stock of the tempers given, but modem competition has made it necessary to harden steel harder and yet have it able to stand more than was formerly the case. When these condi- tions prevail, it is necessary many times, especially in the case of cutting tools, to use steel having a higher percentage of carbon than is given in the table. When steel containing a higher percentage of car- bon is used, then extra care must be observed when heating. For the operations of forging, annealing, or 29 No one steel best for all purposes. hardening high carbon steels should not tinder any cir- cumstances be given to a careless workman, or to one not thoroughly familiar with the effects of heat on steel of this character. When high carbon steels are used and treated properly, they will do more work than steels contain- ing a lower percentage, but unless they are to be handled by a competent man, they generally prove to be a very unsatisfactory investment. When long articles which are to be hardened are made of tool steel, the writer has had excellent results by taking the steel as it came from the bar, or after it was roughed out for annealing, or even after it was forged in the smith's shop, by heating it to a forging heat. Then, standing it on end on the anvil, or on a block of iron on the floor — if it were long — and giving it one or more blows on the end with a hand hammer or sledge; the weight of the hammer depending on the size of the piece. This operation is sneered at by many expert steel workers, but the writer's experience con- vinces him that better results will follow when the piece is hardened, if this precaution is taken, the ten- dency to spring is apparently greatly reduced. Should the piece be bent by the operation, it should be straight- ened while red hot, because if straightened cold, it most surely will spring when hardened. The writer has no intention of advertising any make of steel, as he does not believe any one make is best for all purposes, but experience has convinced him that some makes of steel give better results for certain purposes than others, also that some makes are better adapted for ♦* all around " use than others. If a party is using a steel with unsatisfactory 3° Cheap steel not necessarily cheap. results, it is advisable to take measures to ascertain whether the trouble is in the steel, or in the method of working it. The writer has seen one of the best steels on the market condemned and its use discontinued, because the workman who did the hardening had been accustomed to a steel containing a lower percentage of carbon. The steel he recommended was adopted, the results so far as hardening were concerned were satis- factory, but the tools did not produce nearly the amount of work they should. After a time, the services of an expert were sought. He advocated the use of the very steel they had dis- carded. A tool was made from it, the expert harden- ing the tool. When put to actual use, it proved itself capable of doing many times the amount of work between grindings that could be obtained from low carbon steel. The hardener, like a sensible man, allowed the expert to instruct him in the proper methods to pursue, with the result that he became one of the best hardeners the writer has ever had the pleasure of meeting. A steel should never be selected because it is cheap^ becaiise it often happens that the steels which sell for the least money are the dearest in the end. It is possible to put $100.00 worth of work on a piece of steel costing 25 cents. Now, if the tool was found useless when hardened, then $100.25 ^^^ been expended in vain. On the other hand, if steel adapted to the purpose had been used, and it had cost 50 cents, there would have been a clear saving in money of nearly $100.00. This is not an exaggerated comparison, as such cases are frequently met with by the writer. On the other hand, it is folly to pay 75 cents a 31 "Pipes" in steel bars. pound for steel, when i6 cents will buy one exactly- suited to the job. Good steel is cheaper at any price it would be apt to bring in the open market, than steel not adapted for the purpose would be if it were a gift. A steel not adapted to the purpose is dear at any price. The writer has had charge of tool rooms employ- ing large numbers of tool makers, and experience has convinced him that it is a saving of money in every case to test every bar of tool steel received into the shop that is to be made into tools. If the steel is kept in the stock-room, the stock keeper can — when the hack saw, or cutting off machine is not in use — cut a piece from the end of each bar, stamping the piece cut off and the bar alike. These pieces can be given to an experienced hardener, to heat them to the proper hardening heat, and quench them in a bath of water or brine. After they are thoroughly dry, break as near across the center as pos- sible, examining the center of fracture for pipes. A pipe is a cavity which of course makes the bar un- sound. It may run the entire length of the bar. If a bar having a pipe is discovered, the steel maker will gladly replace it with a sound bar. Any make of steel is liable to have cavities of this kind, although the inspector at the mill generally discovers it in the ingot, thus preventing it being made into bars ; but it some- times escapes even the most careful inspection. If a tool costing $50.00 were made from a bar that was piped, it would in all probability go all to pieces in the bath when hardened, unless the tool were of a character that allowed the piped portion to be re- moved. It is safer, however, to inspect the bar before any costly tools are made from it. If the bar proves 3» Inspection an economy. sound, the grain should be examined; if this is fine, and of the proper appearance, it may be tested for hardness with a file. If the piece proves to be all right, the bar may be stamped O. K. or given some distinguishing mark; should it prove otherwise, the manufacturer should be notified and the steel returned to the mill. This system of inspection may seem like a need- less waste of money, but the cost of one tool which is of no use when finished, would pay the necessary expense of testing all the steel used in a machine shop of the ordinary size in five years. When a tool is required to do extra hard work, that is, cut hard stock, or run at a higher speed than is ordinarily employed in the shop, it is advisable to get a steel having a greater percentage of carbon than the steel used for tools for ordinary work. When high carbon steels are bought, they should be distinctly labeled or stamped, and kept by themselves away from the rest of the steel, because if the identity of the piece is lost, it is liable to be made into tools and hard- ened without the hardener knowing that it differs in composition from the steel ordinarily used. As a con- sequence he would heat it to the same temperature he was accustomed to give the steel regularly used, and it would in all probability be cracked from the heat which was higher than was necessary. 33 Methods of Heating. c-o The method employed when heating steel for any- particular purpose depends on the facilities furnished by the individual shop. As it is not, generally speak- ing, the office of the hardener to purchase the equip- ment of the shop ; biit to use such equipment as may be furnished him, it is necessary that he adapt himself to circumstances as he finds them. The successful man is one who makes the best use possible of the equipment furnished him. If there are but a few tools to harden, and they are of a character that could be treated in a satisfactory manner in an ordinary blacksmith's forge, it would not be considered advisable to purchase a costly furnace, even though it were known that the work could be done more cheaply per piece, because the limited number of pieces would not warrant the extra outlay of money for equipment. On the other hand, if work was to be done in large quantities, it would be wise to procure the necessary equipment to do the work in a satisfactory manner at the least cost possible. If the total amount of harden- ing done in a shop in any one year was 6 or 7 diamond point turning tools and 2 or 3 side tools, it would be folly to invest several hundred dollars in a muffle fur- nace and an elaborate system of baths. But if the pro- duct of the shop was several hundred taps, reamers or 34 Hardener should do his best. similar tools per day, it would not be considered gooJ business policy to heat tliem for hardening in an ordin- ary blacksmith's forge. It would not be possible to do the work as cheaply, neither would it be done in as satisfactory a manner as though apparatus especially adapted to this class of work were used. But, as previously stated, the hardener should make the best possible use of apparatus furnished him. If obliged to use a blacksmith's forge for heating steel either for forging or hardening, he should see that his fire is clean and that it is high enough above the blast inlet so no jet of air can strike the heated steel. It is possible to heat comparatively small articles in a satisfactory manner in an ordinary forge by using care in regard to the size and condition of the fire and the location of the piece of work in relation to the blast inlet. It is always advisable to build a fire large and high enough so that the portion of the piece being heated will be covered to a considerable depth by the coals. Otherwise the action of the oxygen in the air would cause the carbon to be burned out of the surface of the steel, leaving it decarbonized ; in this condition it can- not harden. If the cold air from the blast strikes heated steel, it causes it to crack, particularly if there are teeth or projections, as these are more susceptible to the action of heat and cold than the heavier portions. The steel would expand from the action of the heat, the air striking the projections would cause contraction, and the repeated expansion and contraction would cause the steel to crack. If large pieces are to be hardened, a large high S5 Action of charcoal on steel. fire should be built, as a low fire in a forge having a tuyere — blast inlet — of the ordinary size would not be sufficiently large to heat the piece uniformly. It is always advisable when heating large pieces to use a fire of new coals if charcoal is used as fuel, as coals which have been used for some time are burned to the extent that the fire is dead unless considerable blast is used, in which case the result would be a lot of cracked work. Charcoal is generally considered the ideal fuel to use when heating tool steel. As it is a form of carbon, it is generally given credit for imparting carbon to the steel heated in it. Now, this is the case, if low carbon steels are packed in a tube or box with a good quality of charcoal, away from the action of the fire and air, and run for a considerable length of time. Carbon will then be absorbed by the steel. Before the process of making crucible steel was discovered, iron bars or rods were packed in tubes with charcoal and run for a suffi- cient length of time to charge the iron with carbon, thus making a union of iron and carbon, or steel, as it is familiarly known. This process is known as "cementation." It does not seem probable that a piece of tool steel, high in carbon would absorb any extra carbon in the brief time it was exposed to the action of fire, in heat- ing for hardening. On the contrary, if a piece of high carbon steel is heated in this manner, it is apt to lose some of the carbon at the surface. For this reason, a piece of high carbon steel is not so liable to have sur- face cracks if heated for hardening in a charcoal fire. But from experiments, it can, I think, be truthfully claimed that a piece of 1.5 per cent, carbon steel will 36 The use of mufHe furnaces. not be as hard on the surface if heated in a charcoal fire, as if heated in a fire burning coke. But if steel must be heated in a fire, exposed to the action of the burning fuel, it is advisable in most cases to use charcoal, because it does not contain im- purities injurious to the steel. On the other hand, high carbon steel will not be as hard on the surface if heated in a charcoal fire, as if heated in some form of furnace where the article is not exposed to the action of the burning fuel, and as most of the other fuels contain impurities injurious to the steel, it is best to heat in a manner that removes it from the action, not only of the burning fuel, but also from the action of the air. In order to accomplish the desired result, the article may be placed in a tube or iron box, or a muffle furnace may be used. If many pieces are to be hardened, it is advisable to procure a furnace especially adapted to the class of work. The neatest, most easily managed furnace, and the one which gives as good satisfaction as any, is a form made to bum illuminating gas as fuel. These can be procured of almost any size. A very satisfac- tory style of this type is known as a muffle furnace, from the fact that the piece of steel to be heated is placed in an oven or muffle. The flame circulating around the muffle heats it to any required degree of heat. The steel is heated by radiation, consequently it is not subjected to the injurious effects of the products of combustion; and as the door may be closed, there is little danger of oxidation of the heated surface. If the furnace is not provided with some means whereby the work being heated may be readily observed without removing the door, it is advisable to drill one or two 37 Types of muffle furnaces. one-incli holes in the door, covering them with mica. These furnaces are by far the most satisfactory for general use of any form the writer has used. Figs. 4 and 5 represent two styles of these furnaces. If it is not con- sidered advis- able to purchase a furnace of this description and one is to be made on the premises, it is possible to make a very satisfac- tory furnace quite cheaply. If large or long pieces are to be heated and a furnace is to be made of a type where the steel is placed in con- t a c t with the fuel, it is advis- able to use char- coal, as either coke or coal do Figure 4. Muffle furnace for hardening. ^^^ fumish a satisfactory means of heating under the circumstances mentioned. The grate should be made the size of the 38 'TheDerryCoUariCo.- Muffle furnace for hardening. Types of muffle furnaces. inside of the furnace, as in this way a uniform heat may be maintained in all parts of the furnace, and it will not be necessary to use a blast. A natural draft will be found sufficient. Fig. 6 shows a furnace of the type mentioned, the dimensions depending on the size and character of the work to be heated. A damper should be placed in the smoke pipe in order to check the fire if there is danger of its becoming too hot. This damper should not be of the type usually put in the pipe of a coal stove, as these dampers are made with a hole to allow for the escape of gas. It is not desirable to have this hole in the damper, as it is impossible to check the fire on a windy day. The lower door must also be fur- nished with a damper, in order to furnish Figure 5. Muffle furnace for hardening. draft when desired. It is possible with this furnace to do very excellent work. If it is desirable to build a muffle furnace, one may be made to use either charcoal, coke, or hard coal as fuel by taking the one represented in Fig. 7 as a model, and changing the design to meet the require- 39 "Home-made" muffle furnaces. ments. The interior of the muffle is represented by A, B is the fire box, C the ash pan. The heat and smoke passing up from the fire box follow the direction of the arrow passing under the muffle and out of the smoke pipe at D. A damper should be placed in the smoke Figure 6. A '*home-made" furnace. pipe and one in the ash chamber door. By means of these dampers the draft can be regulated very nicely. This form of furnace works very nicely in heating dies and similar work. When small articles are hardened in large quan- tities a furnace may be made of the design shown in 40 "Home-made" muffle furnaces. Fig. 8, where a represents the fire box which bums hard coal, charcoal or coke ; b the ash box ; and c the chamber for heating the work. The front plate has a number of holes corresponding to the number of tubes it is considered advisable to heat at a time. The tubes are made by taking a gas pipe, plugging one end as The Derry Oollard Co. Figure 7. A "home-made" furnace for burning charcoal, coke or hard coal. shown as Fig. 9, the other end being left open. A number of pieces of work may be placed in each tube and the tubes placed in the openings. The tubes at the bottom will heat more quickly than those at the top, so it is advisable when a tube in the bottom row is taken from the furnace to fill its place with one from one of the top rows. The tubes as they are filled may be placed in the top rows and allowed to heat gradually 41 "Home-made" muffle furnaces. and later removed and placed in the lower row. By following this plan it is possible to heat the work o o o o o o o o o o o liw Ddrry CoUard Co. Figure 8. A "home-made" furnace for heating small pieces. gradually and yet harden a large amount of work in a given time. The tubes should be turned occasionally in order to insure even heating and satisfactory results. When but a few small pieces are to be hardened *f /w/////ww///w///^vw . '//WA'w;/w////w//////w/w///^ ^ ^^^ The Derry ColUrd Co. Figure 9. Construction of tubes in "home-made" furnace. a gas blast of the form shown in Fig. lo answers very nicely. If the pieces are of a size that guarantee their 42 Apparatus for heating small number of pieces. heating quickly it is safe to hold them in the flame, having a piece of fire brick to reflect the heat. By this means the heat is utilized to much better advan- tage than if nothing were placed back of the work. It Tlw Deny C«U*rd C5o, Figure lo. Gas blast for heating a few pieces. is possible by forming a cavity in the brick or making a small oven as shown in Fig. 1 1 to heat a much larger piece of work in an ordinary blow pipe than would otherwise be the case. Figure x i . Another form of gas blast for heating A crude but satisfactory method of economically heating small pieces is furnished by the idea presented in Fig. 12, in which case a small oven is built of fire brick, or a casting of the desired shape may be 43 Gas blasts for heating a few pieces. obtained. In either case a flame from gas blast should enter at one or both sides through holes provided. Small articles may be heated by using a Bunsen Figure 12. Small "home-made" gas blast oven. burner, as shown in Fig. 13, which can be applied to a gas pipe in place of the ordinary burner, or may be connected by means of a piece of rubber tube. When using a burner of this description the work can be heated more readily if a piece of sheet iron is placed over the burner at the proper height, the article to be heated being placed beneath this, the sheet metal reflecting the heat and thus increasing its utility. It is also possible by means of a blow pipe to heat very small articles sufficiently for hardening by means of an ordinary gas jet or the flame of a spirit lamp, as shown in Fig. 14. This is an expensive method when work is heated in quantities, but answers very nicely for one or two pieces. When heating for forging or any work where the outside of the steel is afterwards to be removed it is Heating small articles. advisable to use a form of furnace where the direct heat of the fire comes in contact with the steel, as it is much more economical and is, generally- speaking, a quicker method than heating in a muffle furnace. It is advisable many- times when heating large pieces of steel for hardening, to use a furnace, as de- scribed, on account of economy. In case /, The Derry CoUard Co. Figure 14. The blow pipe way of heating. the outer decarbonized surface is to be ground away, the results will be satisfactory ; but if the outer surface must be hard, then it is necessary to protect the surface from the action of the products of combustion. This may be accomplished by several different methods. The Derry CoUard Co Figure 13. Bunsen burner, for heating small articles. 45 Covering paste, and how to make it. One method is to place the portion of the piece, which must not be decarbonized, in a box with carbonaceous materials — as charcoal or charred leather — and subject to heat until the piece has reached the desired uniform temperature, being- careful that the part which is exposed to the direct heat of the fire does not get over-heated. Another method which is used when an article must be hard on all its surfaces is to cover the piece with a carbonaceous paste, consisting of the following ingredients : Pulverized charred leather 2 parts. Fine family flour 2 *' Fine table salt i part. Mix thoroughly while in a dry state. Water is then added slowly to prevent lumps ; enough water may be added to make it of the desired consistency, which depends on the nature of the work and the length of time it must be exposed to the action of the fire. If the articles are small and will heat to the proper temp- erature for hardening in a few minutes, it should be of the consistency of varnish. If, however, the pieces are large and require considerable time for heating, it must be made thicker. Various substances are heated red hot in crucibles or iron dishes, and pieces to be hardened are heated in them. These exclude the air and so prevent oxidation and decarbonization of the surface of the steel. Among the substances used are lead, tin, glass, cyanide of potassium, a mixture of salt and cyanide of potassium. Lead is heated in a crucible in a furnace of the forms shown in Figs. 15, 16. It furnishes a very excel- 46 Heating in molten lead. lent means of heating- work which is hardened in large quantities. When making furnaces to heat lead red hot for use in hardening steel, some means should be provided for carrying off the fumes of the lead, as they are very injuri- ous to the work- man. They are especially hard to dispose of, as they are heavier than the atmos- pheric air ; conse- quently cannot be disposed of as readily by means of a ventilating shaft as other fumes. It is nec- essary to furnish a pipe connected with an exhaust fan. This pipe may be at the back of the furnace instead of over it, as is generally the case when gases or smoke are to be carried off. It should not be arranged in a manner that will cause the surface of the lead to become cooled by a current of air passing over it. If illuminating gas can be procured at a reasonable rate, it furnishes an ideal method of heating a crucible of lead. Furnaces burning illuminating gas can be pro- cured of a size and shape adapted to the work to be done. If, however, it is considered advisable to make a furnace for this purpose, one may be made which The Derry Collard Co. Figure 15. Lead hardening furnace. 47 Heating in molten lead. will give good satisfaction. It can be made to bum oil, coal, charcoal or coke. If oil is the fuel to be used, it is advisable to install a system especially for this method, and as circulars and full explanations can be The Derry Collard Co. Figure i6. Lead furnace for hardening. procured from manufacturers who make these outfits, it would not be wise to go into their details here. If it is considered advisable to make a furnace burning charcoal, hard coal or coke, the design shown in Fig. 17 may be used or changed to adapt it to these fuels. The outer shell may be made of cast iron, although it may be possible to procure an old 48 ^Home-made" lead heating apparatus. BACK HALF. TOP PLATE FRONT HALF boiler, which can usually be bought very cheaply. A piece the desired length may be cut from this, that an- swers the purpose very nicely. A round grate and the neces- sary frame to support it may be procured from a stove dealer. The form of grate mill I ■ 'Hi ll 2:^ Figure 1 7. Coal, coke or charcoal furnace for lead heating. 49 "Home-made" lead heating apparatus. used in the ordinary cylinder parlor stove will answer every purpose. The frame should be attached to the shell or blocked up from the bottom of the ash box, to allow the grate to be turned in dumping the contents of the furnace. The interior of the furnace may be made of circular fire brick, which may be supported by the slab which forms the base or bottom of the ash box and designated as the bottom plate. In case fire brick are used, the grate frame may be built into the brick work as shown. If, however, a stove lining of the desired size can be procured, the bricks need extend only up to the frame, the lining extending from the frame to the top of the shell. It is necessary to cut an opening in the ash box in the front of the shell. This should be covered with a swinging door, containing a sliding damper. This door is necessary in order to remove the ashes. A smoke pipe must be provided to carry off the smoke and gas from the fire. This should be con- nected with the shell at the top on the back side of the furnace. Over the top of the furnace must be placed a plate, having a hole in the center about one half inch larger than the size of the crucible to be used. This plate should be cast in two pieces, having more than one-half of the hole in the part that goes at the back. The smaller or front half may be moved forward, thus affording an opening to feed the coal to the fire. The object in having more than one-half the opening in the back part of the cover is to prevent the crucible from tipping over when the front plate is removed, when there is not sufficient coal in the furnace to support it. It is necessary to place a piece of fire brick in the center of the grate for the crucible to rest on in order so Cyanide of potassium furnace. that the fire may be beneath it. The smoke pipe should be provided with a damper, to enable the operator to properly control the fire. This form of furnace gives best satisfaction when hard coal is used as fuel. Red-hot c y a - nide of potassium is used with ex- cellent results in heating tools for hardening. It not only heats the steel uniformly, but, being lighter than steel, the latter sinks in the fluid, thus effect- ually excluding the air from the surface of the steel. It also has the effect of mak- ing the surface somewhat harder than it otherwise would be, without making the steel more brittle. It should be borne in mind that cyanide of Derryt3ollard Co, Figure 1 8. Furnace for heating in cyanide of potassium. 51 Heating cyanide by gas furnace. potassium is a violent poison, and great care should be exercised in its use. Not only is it poisonous when taken into the stomach, but the fumes are highly in- jurious to the workman if inhaled. However, if fur- naces are properly designed and set up, the fumes may be disposed of in a manner that does away with this trouble. In Fig. 1 8 is shown a form of furnace made es- pecially for use in heating in cyanide of potassium. The fuel used is illuminating gas, the products of combustion passing up the pipe E to the main pipe F which also conveys the fumes of the melted cyanide into the chimney or ventilating shaft. The burners enter the furnace at A and heat the crucible B, which contains the cyanide. A hood C, which is provided with a door D, keeps the fumes from entering the room as they are conveyed into the pipe F. The lighting holes G G are closed by the plugs shown when the fire is well under way. When a comparatively small number of small pieces are to be hardened, it is possible to heat the necessary amount of cyanide in a small iron dish in an ordinary forge. The pieces may be held in this until the desired effect has been accomplished, when they may be quenched. As the work heated in this manner is usually hung from the edge of the crucible by means of wire hooks, it is generally considered advisable to use a square crucible rather than a round one when work is done in large quantities. When a furnace is to be made for this purpose, the form represented in Figs. 19-20 will be found to give good results. This furnace burns hard coal. The cruci- 52 "Home-made" cyanide furnace. ble which is made of cast iron is square in shape and hangs from the flange, which is cast around the upper edge. The top of the crucible is below the top of the back of the furnace. An opening into this allows the fumes to es- cape into the chimney. A quantity of salt is placed in a crucible and heated red hot. To this is added cya- Figures 19-20. A "home-made' cyanide heating furnace. Crucible ??vi???7?????rr;rrr1 prevents this portion springing when the face is hardened, but it allows the heat to run to the face of the die. /Imk Figure 56. Bath for hard- ening dies. After the tongue side is sufficientl}'- cooled, the die is turned over and the stream of water is di- rected against the face; the o V er flo w is checked suffi- ciently to allow the water to rise several inches above the face, on the sides of the die ; that is, it is immersed several inches in the bath; the depth of immersion depending on the character of the die and the custom in the individual shop. When dipping large, heavy dies in the bath, it is advisable to hold the die with a pair of grappling hooks, as shown in Fig. 57. These should be attached to a rope or chain and operated by a pulley, in order The Deny Collard Co. Overflow 135 Tongs for handling heavy dies. that the die may be raised and lowered somewhat in the bath. Then again, it would not be advisable for the workman to dip so large a piece of steel with tongs that necessitated holding his hands and arms over the bath, as the im- ^^ Excellent results mense volume of vw/ may be had by the steam would be // \ ^^^ ^^ ^ furnace built liable to burn // >\ expressly for this him; neither /^ \V\ class of work (see could he properly \ I / / Fig. 58). The die A support the die \ \ / I is supported on a in the bath. Figure 57. Tongs for handling heavy dies. platform B, and is raised mechan- ically, so that the amount which it is nec- essary to hard- en is in the furnace, while the rest of the die is below and removed from the action of the heat. The heat- ing chamber is on top, with burners entering opposite sides and projecting the flame against the top lining and distributing it evenly. The die should not be placed on the platform until the furnace is evenly heated, when it may be raised by means of the lever D, until the face enters the furnace the desired amount. The face of the die can be observed through the open- 136 Heating dies with a gas furnace. ing- C. When heated to the desired degree, the plat- form is lowered, the die withdrawn and quenched. The weight of the die is counterbalanced by the weight shown, which can be shifted as occasion requires. Dies used in making molds for hard rub- ber and similar work, whose faces are en- graved, may- be packed as described and represented in Fig. 54, and run until the required heat is attained. After the heat becomesequal- ized — /. e.y the same through- out — the die may be dipped in the bath of brine, using the arrange- ment shown in Fig. 57. It is necessary to get the die in the bath as soon as possible after removing from the packing material in order to prevent oxidation of the face containing the engraved work. Figure 58. Gas furnace for heating dies. 137 Punching press dies. Dies for punch press work, especially those used for blanking — that is, punching blanks from sheet or other stock — occasion a vast amount of trouble in many- shops when they are hardened. Observation has led the writer to believe that most of the trouble is caused by uneven heats. The corners and edges of the block and the edges surrounding the openings will heat much more rapidly than the balance of the die block unless extreme care is used. Before putting the die in the fire, all screw and dowel pin holes and holes for guide pins (stops) should be filled with fire-clay, mixed with water to the consis- tency of dough. This prevents the contents of the bath entering the holes, and reduces the tendency to crack. The die should, if possible, be heated in a muffle fur- nace, not heating the furnace much, if any, hotter than the desired heat for the die. When it is to the proper heat and uniform throughout, remove from the fur- nace, catch by one end with a pair of tongs and lower into a bath of brine. Swing slowly back and forth in the bath, in order that the contents of the bath may pass through the openings. This insures the harden- ing of the walls, as otherwise the steam generated would force the contents of the bath away from the die until it had cooled to a point where it would not harden. When the die ceases to sing, it may be removed and plunged into a tank of oil. There is not much danger of a die cracking when dipped in a bath, provided it was annealed after the blank had been machined all over and the openings blocked out somewhere near to shape. But it is ex- tremely essential that the utmost care be taken when heating for hardening. Be sure that no part of the die 138 How to prevent cracking of dies. block is heated any hotter than it should be. The heat must be uniform throughout the piece. If the shape is one that betokens trouble, it is advisable to heat the contents of the bath considerably. Generally speak- ing, it is not advisable to use an extremely cold bath on this class of work. The writer prefers using a tank of generous pro- portions, so the contents would not be materially affected by the heated piece, and heating the liquid to a degree that does away with any tendency to crack the piece. An excellent method to prevent the ten- dency to crack from internal strains, consists in placing the die, after hardening, in a kettle of boiling water, keeping the die in the water at this temperature for one or more hours, according to the size of the die. If the temper is to be drawn immediately after the die is taken from the bath, a flat piece of cast iron or scrap steel may be heated while the die is being heated, and quenched. It is customary with some hardeners to heat the piece red-hot. Brighten the face of the die and lay it on the heated iron. The die should be moved around on the heated piece and turned over occasionally to heat both sides alike. When the temper has been drawn the desired amount, the die may be immersed in oil, thus preventing the temper being drawn too much. While it is the custom of many hardeners to heat the drawing plate red-hot, as explained, before placing the die on it, the writer considers it better practice to heat the plate somewhat^ leaving it over an open fire. Place the die on the plate and gradually raise the heat. It is rather rough treatment for a piece of unyielding hardened steel to be brought in direct contact with 139 Don*t bring steel to sudden heat. extreme heat, and is liable to crack the surface of the steel in innumerable places, especially if the operatoi is not thoroughly experienced in this line of work. The amount necessary to draw the temper of a blanking die depends on the steel used in its construc- tion, the temperature it was heated to when hardened, and the nature of the work to be performed by it. Generally speaking, it is advisable to refer the matter of how hard the die or punch should be to some one familiar with the requirements of the work to be done. In some cases it is desirable to have the punch the harder of the two, although, generally speaking, the die is left harder than the punch. In some shops, the one that requires the greater expense in making is left the hardest, in order that it may be the least injured in case they strike together when in use. In such cases it is necessary to draw the one that is desired softest considerable lower than the other. But as the circumstances must govern the relative hardness of the two, no hard and fast rule can be given. It is customary to draw to a temperature varying from that which produces a faint straw color, to a brown with purple spots. Probably no one class of tools used in machine shop work requires greater care on the part of the hardener than the hardening and tempering of punches and dies ; and probably no class of tools involves a wider range of methods of hardening and degrees of hardness essential to produce desired results in the individual shop. The hardener who is desirous of giving satisfac- tion will study the conditions in the shop where the tools are to be used. He will also consider the steel 140 Hardening the punch. used in the construction of the tools and the nature of the stock to be machined. It will be necessary also to get the experience of men familiar with the work to be done, because a die and punch hardened and tempered in a manner that insured satisfaction in one shop would not meet the requirements in some other shop. When hardening the punch, use extreme care in heating. If the punch is strong and is to be used for punching comparatively light stock, it is not necessary to harden it the entire length. Take, for instance, the punch shown in Fig. 59, to be used for punch- ing sheet steel ■^Q inch thick. This will work satisfactorily if hardened to the dotted line shown. When, how- ever, it is neces- sary to harden a piercing punch of the design shown in Fig. 60, it will be found neces- sary to harden the entire length of the end a^ if the punch is to be used on heavy stock. Should J ' ■ = Figure 59. Punch for ^ inch steel plates. ) 141 Kind of steel to use for punches. the hardness extend only to the dotted cross line, it would buckle, as shown in Fig. 6i, when punching stock as thick as the diameter of the punch. When making punches that are heavy and strong, and which must retain a good edge, it is advisable to use a steel of comparatively high carbon. But if Figure 60. Piercing punch for heavy work. punches are made of the form shown in Fig. 60, best results will follow if a comparatively low carbon steel is used, as it is not as liable to crystallize as if a higher The Derrjr CoUard Co. Figure 61. Result of hardening only as far as the dotted line, as shown in Figure. 60. Steel were used. As a rule, drill rod does not give good results when used in making tools of this de- scription. When punches are sufficiently strong, it is advis- able to apply the heat at the shank end when draw- ing the temper. A block, as shown in Fig. 62, having several holes a trifle larger than the shanks of the punches may be heated red hot and the punches placed in these holes. When the desired temper color is visi- 144 How to heat slender punches. ble at the cutting end, the punch may be taken from the block and dropped in oil to prevent its becoming too soft. The upper end of punch will, of course, be softer than the cutting end. When a long, slender punch, of the design shown in Fig. 60, is to be tempered, and the punch is to be The Derry CoUard Co. Figure 62. Heating block for tempering long, slender punches. subjected to great pressure, it must be hardened the entire length, and the temper drawn equally the whole length. This can be accomplished by heating in a heating machine of the design shown in Fig. 48, or the punches may be placed in a pan containing sand and drawn over a fire. Or they may be placed in a kettle of hot oil, gauging the heat by means of a thermometer. If intended for piercing a heavy, tough stock, they will be found to work very satisfactorily if drawn to a full straw color, 460°. Many hardeners and others look askance at ther- mometers and always associate them with theory rather than practice, with the laboratory rather than 143 Forming and ring dies. the workshop. In reality they are just as practical a tool as a steel scale or a micrometer, and, like them, enable us to measure rather than to guess. Forming Dies. When hardening forming dies or dies for compres- sion work, if a great amount of pressure is to be exert- ed in order to perform the necessary work, the dies will not stand up as well if hardened at a low heat as though heated somewhat hotter. The outside surface will be hard, but under pressure this surface will be forced or crushed in, the interior not being hard enough to resist the pressure on the outer surface. It is, as stated, sometimes necessary in such cases, to heat the block somewhat hotter than if it were a cutting tool, yet care must be exercised that the piece be not overheated. But while it may be advisable to heat somewhat hotter than is the case with most tools, the heat must be uni- form throughout the die. It is not, generally speaking, advisable to draw the temper very much on tools of this description, but it is necessary to remove the tendency to crack from in- ternal strains. This is done by heating the die over a fire until it is at a temperature that makes it impossible to hold the hand on it, yet not hot enough to percep- tibly start the temper, or it may be boiled in a kettle of water for several hours. Ring Dies. When hardening large ring dies or pieces of a cir- cular shape, whose size and weight make it impracti- 144 Furnace for ring dies. cable to harden by ordinary methods, it is a good plan to heat in a furnace made especially for this class of work. Such a furnace is seen in Fig. 63, which shows a circular block A in position for heating. It is resting on strips of iron C supported by pieces of fire-clay B. The circular piece be- ing heated should be in the center of the furnace — i. e.y evenly dis- tant from the inner walls. The cover D is attached to the mecha- nism for rais- ing the cover, and held by the chains EE. It is possible, by using prop- er care, to heat work very uni- formly in a furnace of this description. A method the writer has used with ex- cellent results when harden- ing work of this character, consists in placing the ring or circular die in an iron box two or three inches larger each way inside than the circular piece. A cir- cular box gives better results than a square one, as The Ocrry ColUird ( Figure 63. Gas furnace for ring dies and similar work. »4S Box for heating ring dies. Figure 64. Method of removing ring dies when heated in boxes. more uniform heats may be obtained. Place i>^ inches of a mixture of equal parts granulated charred leather and charcoal in the bottom of the box. Place the piece of work on this, cover with the mixture to a depth of an inch or so, put the cover on the box and place in the furnace. When the piece is of a uniform red heat, the box may be removed from the furnace and the piece of work taken out by grasping it with tongs on opposite sides, as shown in Fig. 64. Place it on a device which consists of a ring having three han- dles, as represented in Fig. 65. Have the ring (which should be made of iron or machinery steel) considerably thinner than the thickness of the piece to be hardened, but wide enough to screw the handles in as shown. The handles b b are threaded on one end and bent; they are then screwed into the ring, as shown. A stud c having a tapped hole is screwed in also. The third handle is screwed into this. The object of making it by this method is, the handle may be unscrewed from the stud c and the piece to be hardened put in place. The handle may then be screwed into the hole in stud. If the piece of work is very large and heavy, a man may 146 Device for handling large ring dies. be stationed at each handle. If not very heavy, two men can handle it all right. The operators should protect their hands and arms in some manner to pre- vent being burned by the steam generated when the red hot piece comes in contact with the water. It will be necessary to use a bath having a jet of water coming up from the bottom, so as to cool quick- ly, when harden- ,b ing work of this description. Be- fore immersing, the water should be turned on, and at the minute the piece is dipped, a quantity of table salt (about a pint) should be thrown into the water. The ring should be worked up and down in the bath. When the * * sing- ing" ceases, the supply valve may be closed. The water in the bath may become somewhat warm, but it will reduce the lia- bility of cracking. As soon as the piece of work is reduced to the temperature of the bath, it may be re- moved, placed over a fire and heated to prevent crack- ing from internal strains. If it is necessary to draw the temper, the piece of steel may be brightened while heating and the temper drawn at this time. It is advisable when drawing the temper of articles Th* Denry ColUrd Co. «47 Forms of screw cutting dies. of this description to heat very slowly^ so as to have all parts of an equal temperature. If possible, have the heat so uniform that it will not be necessary to quench the article when the desired heat is reached. Should the temper colors, however, run so fast that it seems necessary to quench in order to keep it from becoming too soft, it should be dipped in oil or hot water, as, if dipped in cold water, it would have a tendency to cause brittleness. Screw Threading Dies. There are several forms of the die under considera- tion. They are sometimes made square, then again they are made round in shape, with no means of ad- justment. They are then termed solid dies. Most square dies are made solid. The Derry OoUard Co. Figure 66. Various styles of screw threading dies. When it is necessary to cut a screw to size or to gauge, it is generally considered advisable to make the finish die of a form known as an adjustable die. The forms referred to are shown above, in Fig. 66. The solid square die, being used mostly for thread- ing bolts and similar work where accuracy is not essential, are usually made to cut small enough, and no particular pains taken when they are hardened. How- 148 Holder for hardening screw dies. ever, if a die of this form is hardened all over, the con- traction from the outside edges is very unequal, on ac- count of the corner containing more stock than the portion between. Owing to the unequal contraction, the cutting edges do not have an equal amount of work to do, so one cutting edge dulls more rapidly than the other. Every tool maker knows the secret of success in making a screw threading die that will work satisfactory, lays in having each cutting edge cut its proportional amount. It will readily be seen that any unequal contraction or wear, which causes an upsetting of this equality in cutting, must reduce the usefulness of the tool. Too often no account is taken of the amount of work a tool will do after it is hardened. If it survives the ordeal of going through the fire and water, and will cut, it is considered a successful job of hardening. From the preceding it will be seen that it is neces- sary, in order that best re- sults may follow, that the die be in (as near as possi- ble) the same shape, and the location of the cutting edges be the same as be- fore hardening. Now, in order to accomplish this result, it is necessary to treat the die in a manner that will cause the cutting portion to harden ^/-j/. By so doing, the contraction Figure 67. Device for cooling screw ^^ the OUtcr portioU doeS threading dies. UOt SCrioUSly aff CCt the CUt" '^% How to prevent "twist" in screw dies. ting qualities of the tool. When hardening a square or a solid round die, it is sometimes considered advis- able to place the die in a fixture, as shown in Fig. 67. It is then immersed in the bath and swung slowly- back and forth in order that the liquid may readily pass through the opening, thus insuring the hardening of the cut- ting teeth. The por- tion near the circum- ference is, of course, soft. This is rather to be desired than otherwise in the form of die under consid- eration. When adjustable dies are hardened, it is generally consid- ered necessary to harden the outer portion in order to furnish a certain amount of elasticity, in order that the die may open uniformly when ex- panded. The necessity of this depends on the design of the die. If stock enough is left at the portion where the die is supposed to spring, the stiffness of the stock will give it sufficient tension. Should it be necessary to harden the outer portion somewhat, the fixture may be cut away in a manner Figure 68. Method of preventing "twist' in screw threading dies. Figure 69. Example of "twist* in screw die. ISO Cooling dies for screw cutting. that allows the contents of the bath to come in contact with the steel nearer the outer edge. Adjustable dies of the description shown should not be cut entirely through at the point where pressure is applied to open them, but may be cut nearly through, Figure 70. Method of cooling dies for thread cuttmg. commencing at the inside and cutting toward the out- side, leaving a thin partition, as shown in Fig. 68. This partition holds the die in shape, preventing the tendency to twist, shown in Fig. 69. When it is not considered advisable to make or use a fixture as described, the die may be grasped, after being heated, with a pair of tongs, as shown in Fig. 70, and quenched in a bath of lukewarm water or brine, swinging it slowly back and forth, as repre- sented. When hardening any tool of this description, Drawing the temper of a "spring" die. bear in mind the fact that the article should never be heated in a manner that allows the cutting teeth to become oxidized by exposure to the air while heating. Best results are obtained by heating in a muffle or a piece of pipe. If the surface of the teeth become covered with a scale of oxide, this raises, and keeps the contents of the bath from acting, thus causing soft spots, which render the tool practically useless. An excellent plan consists in heating the dies in an iron box having a half inch of charred leather in the bottom. Fill the opening in the die with the same material. When the die reaches a uniform tempera- ture which is right to produce the desired result, quench in the bath. When hardening ** spring" dies, or, as they are familiarly termed in some shops, *' hollow mill dies," best results are obtained by dipping in the bath with the cutting end up- permost, as de- scribed under Hard- ening Hollow Mills. Figure 71. Drawing the temper of ' 'spring' Generally speaking, it is not necessary to heat the die much beyond the length of the threads. 152 Tempering small dies. The temper may be drawn by placing the die on a hot plate, as shown in Fig. 71, drawing from the back end. On account of the shape of the cutting edge, which makes it stronger than the ordinary form of screw threading die, it is not necessary to draw the temper as much. A faint straw color making them about right, unless the cutting tooth is long and weak, in which case it may be drawn to a full straw color. If many dies are to be tempered at a time, the cost may be reduced very materially by heating in a kettle of oil, drawing them to a temperature which varies from 460° to 500°, according to the conditions pre- viously mentioned. When but one or two are to be done, it is advisable to brighten the sides and draw the temper by laying them on a flat plate, moving around on the plate, and turning them over occasionally. The temper color should be from a straw to a brown color. If it is con- sidered advisable to draw the temper of a large batch of dies by the hot plate method, the plate may be placed over a fire, in order to maintain a uniform heat. Quite a number of dies may be placed on the plate at a time. It is necessary to turn them occasionally, as mentioned. As one shows the proper temper color, it may be removed and placed in a dish of warm oil. By this method a skillful operator can temper a large batch of dies in a comparatively short space of time, but the results will not be as satisfactory as though heated in oil. The amount of work to be done will always deter- mine the most economical method of doing it, but it is better to err on the side of having too many convenien- ces. A few spoiled tools will pay for several improve- ments. «53 Cracking of dies from internal strains. Larg-e pieces of steel are more liable to crack as a result of internal strains than smaller pieces. On ac- count of the weight of the piece there is a tendency on the part of some hardeners to neglect reheating the piece to overcome this tendency to crack, due to various uneven heats the steel may have received. In order to overcome this tendency, the die should be reheated in a uniform manner to a temperature that allows the various portions to conform to any strains in the piece. This may be accomplished by placing the die in the fire, turning it occasionally, in order that it may be uniformly heated, and heating until moisture applied to the surface forms steam. This method when applied to large pieces is not apt to result in the center of the piece being heated as hot as the outside. Con- sequently better results will follow if the die is placed in a kettle or tank of boiling water (212°) and left there until heated uniformly throughout. If the die is large this will necessitate leaving- it in the water at the boil- ing point for several hours, as it takes longer to heat a large piece of steel throughly than we realize. It pays to be very careful about these little points, as these dies are often expensive. Hardening Long Articles. Most hardeners dread hardening long, slender articles, on account of the uncertainty attending the operation, so far as results are concerned. If the article is a reamer or similar tool, having teeth on the outer surface, it will not require as great an amount of heat as though it were a solid piece. In any case, however, do not heat any hotter than is necessary to 154 Proper way to harden long articles. accomplish the desired result, always remembering that even heats are the secret of success when heating steel for hardening. If the tools are hotter on one side than the other, unequal contraction must take place ; consequently, the article will be crooked. When hardening long reamers and similar tools, it is necessary that the Wrong Right heat should be uniform and as low as possible. It must be the same on each side. If one side be a low red and the opposite side a bright red, and it is quenched in the bath, it is sure to come out crooked. A piece of this description must be dipped in the bath in as nearly a vertical position as possible, as shown in Fig. 72, in order to cool both sides uniformly. If it be dipped at very much of an angle, as shown in example marked * 'wrong, " it will surely spring, on account of the uneven contraction of the two opposite sides. It is necessary to work such pieces up and down in the bath, changing the location occasionally in order to avoid the effects of the steam generated. These may seem like unnecessary precautions, but the results obtained will show that it is worth while Figure 72. The Derry CoUatd Co. Proper method for dipping long articles. 155 Advantages of heated baths. observing them as thorouglily as possible. It's the little things that count in successful hardening and tempering. Condition of the Bath. If the tool is of a design that makes springing a possibility when the article is quenched, it will be necessary to warm the contents of the bath consider- ably, the degree to which it should be heated depend- ing on the shape of the tool and the temper of the steel used. Excellent results are many times obtained with a bath heated to a temperature of ioo° to 150°. The writer has had excellent results when harden- ing articles of this description by placing them in tubes one inch larger inside than the piece to be hardened. It should be placed in the center of the tube, the space between the article and the tube being filled with charred leather. The ends should be stop- ped and sealed with fire-clay. The tube is then placed in the fire and given a uniform heat for a period that insures the article being evenly heated to the desired temperature, when it may be removed from the tube and plunged in a warm bath of brine or the citric acid solution. Hardening Taps. It is necessary to take into consideration the design of the tool, the steel used, and the nature of the work to be done by the tap. If the tool is very long and it is necessary to harden but a small portion of the length, it is not necessary to heat it any farther up than the 156 The hardening of taps. length wliicli requires hardening. In such cases it is a comparatively simple job. When a long tap requires heating and hardening its entire length, it is necessary to devise some way of uniformly heat- i-5^2Z%r:*L^^_ The Derry Collard Co. ing the piece. It is also neces- sary to quench in such a man- ner that all por- tions will cool as uniformly as possible, to avoid unequal contraction, thus preventing springing or cracking. When hard- ening taps, care should be exer- cised that the teeth are heated no hotter than the refining heat, or they will be brittle. If heated hotter than nec- essary, it must have the temper drawn very low, or the teeth will snap off when used. If the temper is drawn low, as described, the tap is too soft to perform its full share of work. When hardening tools having teeth or projections, it is essential that the heat be the lowest possible. It is advisable to heat in a muffle furnace or enclosed in some receptacle to remove it from the products of combustion in the furnace and from oxidation by the action of the air. When it Supply Pipe Figure 73. Bath for hardening taps. 157 Bath for hardening taps. reaches a low, uniform heat, dip in the bath of water or brine, preferably the latter. Work up and down rapidly, to bring" the contents of the bath in contact with the teeth; or, better still, use a bath as shown in Fig. 73, having inlet pipes on opposite sides of the tank, these pipes being perforated, as shown. It is advisable to have the piping so designed that the upright perforated pipes may be placed against the side of the tank or moved toward each other, in order that the jets coming out of the holes may strike the object with sufficient force to drive the steam away, thus allowing the liquid to act on the steel. Long taps give best results if packed in a tube with carbon, in the form of charred leather, as de- scribed in hardening reamers. When it has reached the proper uniform hardening heat, it may be hardened by immersing in the form of bath represented in Fig. 73. If a bath of this description is not at hand, very satisfactory results may be obtained by dipping in an ordinary bath of the desired temperature, and revolve the piece rapidly in the bath to insure uniform results. This will in a measure imitate the bath mentioned. A bath of brine, or the citric acid solution, give excellent satisfaction for hardening tools of this descrip- tion. Unless the tap is of large diameter, do not use a cold bath. Hardening Small Taps, Reamers, Counterbores, Etc. When small articles of this description are hardened in great quantities, it is necessary to devise means 158 Muffle furnace for heating taps. whereby they may be hardened cheaply, yet the work must be done in a satisfactory manner. Various methods are employed to accomplish this, and one of the most successful methods that has come to the writer's attention consists of a furnace made with a r/////y//y///yy/^^^^^^^ Muffle b ml Fire Box ,J,^^,^/>,^,,,,^„,,^,,^y,^^,j-,^^/^/'^/\yy, Ash Box Smoke Pipe '/////////////////////////////////////////////////A \ (? ■NN ^ J ^ ' °i-- =o <: OD^DD -V ^~- V 1 The Derry Collard Co. Figure 74. Muffle furnace for heating taps. muffle. The heat was furnished by burning illuminat- ing gas, or it may be designed to bum coal. The muffle was made as shown in Fig. 74. Cleats are cast on to the walls of the muffle, which in this case was cast iron. On these cleats shelves were placed, and on these shelves the pieces to be hardened were heated. It was necessary to turn the pieces over occasionally to insure uniform results. When a piece was heated to the proper tempera- ture, it was taken by means of a pair of tongs and dropped into a bath, which consisted of a tank having 159 Bath for hardening taps and reamers. several tube-shaped pieces of wire netting, as shown in Fig. 75. The tubes were slightly larger inside than the diameter of the largest part of the tool being hardened. Tubes of various sizes were used, the size depending on the diameter of the tools to be hardened. The tank had a supply pipe coming up fam\\\\\^^^^^^ Tlw-Detry CoUard Co. Figure 75. Bath for hardening taps and reamers. from the bottom. This was connected with a supply tank overhead. A pump was used to force the water into the supply tank. It was possible to use a bath of clear water, brine, or any favorite hardening solution. In this case, the bath consisted of the citric acid solution, described under ** Hardening Baths." It was kept at a temperature of about 60°. As fast as the pieces were heated to the desired temperature, they were taken with tongs and dropped into one of the tubes, the cutting end being down. They 160 How to brighten taps to show color. passed down through the tubes on to an incline, and then into a catch pan, as shown. The distance the pieces traveled in the bath was considered when designing it. It was found by experiment that the largest piece to be hardened would cool below a red heat in falling a distance of two feet in the bath. To make satisfactory results a certainty, the depth of the part of the tank through which the pieces passed was made 36 inches. If the tools had struck the bottom and Figure 76. Grinding to show temper color. turned on their side before the red had disappeared from the surface, they would have, in all probability, sprung ; but, as it was, excellent results were obtained. When taps are brightened, in order that the temper colors may be visible, it is not advisable to use a piece of emery cloth on a stick or round file, as is often done, because unless the operator is extremely careful, he is apt to cut away the cutting edge of the teeth, thus rendering the tool unfit for use. If possible, use an emery wheel of the shape of the groove, as shown in Fig. 76. It is not absolutely necessary to use a fixture, as the tap may be held in the hands for brightening. 161 Other ways of heating taps. In this way, not only is the steel brightened, so the colors may be readily seen, but the cutting edges are ground sharp, and any burrs thrown up between the teeth are ground away. When but a few taps are to be tempered, it is pos- sible to heat them sufficiently in a gas jet or the flame of a Bunsen burner ; sometimes the flame of a candle is used when the article is very small, as in Fig. 77. With a blowpipe, a hot flame can be produced. When the taps are made in quantities suffi- ciently large, it is much more economical to draw the temper by placing in a kettle of oil, gauging the temperature with a thermometer. The amount necessary to draw the temper of a tap in order to get desired results, de- pends, as with most other cutting tools, on the steel used, the heat given when hardening, and the use to which they are to be put. Very small taps that are to be used by hand may be left harder than those intended for The oerry' couard co. use in a screw machine. Taps Figure 77. One way to used by hand should be drawn ^^^ ^"^^ ^^^^' to deep straw or brown color, while those used on screw machine work need drawing to a deep brown, and in some cases to a purple. Half Round Reamers. These should be heated very carefully in a pipe or muffle furnace to the lowest heat possible to harden. 162 Method for cooling half-round reamers. When dipping in the bath, the reamer should be in- clined somewhat from a perpendicular position, the heavier portion being on the lower side, as shown in Fig. 78, to avoid a tendency to spring. The contents of the bath should be heated as warm as is consistent with good results, as this will help keep it straight. Should the ream- er spring somewhat in hardening, it may be straight- ened by reheating and exerting a pressure on the convex side. If the projection has been left on the end, as shown in Fig. 79, the reamer may be placed be- tween centers and straightened, as represented else- where. Should it be a reamer having no center at the small end, it may be placed on two V blocks, as shown in Fig. 80. Apply heat by means of a gas jet, spirit lamp, or any other means to the lower side, heat until oil placed on the surface commences to smoke. Now apply pressure at P, on top side. When it has been sprung the proper amount, cool by means of wet waste. The possibility of straightening reamers and sim- ilar work means such a saving in many shops that it 163 Figure 78. Proper method for cooling half-round reamers. Hardening milling cutters. will pay to have special attention paid to it, as crooked tools of any kind cannot do accurate work. It will pay to rig up fixtures especially for this, as the saving is far greater than the cost. Small, half-round reamers should be drawn to a full straw, or a brown color for most work. Hardening Milling Machine Cutters. As most shops have at least one milling machine, and many shops hundreds, there are probably more cutters hardened for this class of work than for any other. In hardening this class of tools, it is necessary to The Derry CoUard Co. id Figure 79. Half-round reamer. have them hard enough to cut the metal being machined, yet tough enough to stand up under the strain to which it must be subjected. Milling machine cutters should be hardened at a lower heat than a solid piece of the same size. The teeth, being slender and projecting from the solid body, take heat very readily. When possible, tools of this description should be annealed after a hole some- what smaller than the finished size has been drilled and the tool blocked out to shape in order to overcome the tendency to crack from internal strains. If it has not been possible to do this, or if for any reason it has 164. Care in heating milling cutters. not been considered advisable, the cutter may be heated to a low red and laid to one side and allowed to cool until the red has disappeared, when it may be reheated and quenched. It is always better, however, to anneal after blocking out if it can be planned so as to take the time necessary to do this. The results are more satisfactory in every way. It may be well to again caution the reader in regard to the heats. The teeth of this form of tool being thin, are apt to absorb heat faster than one realizes, and as a consequence, they become too hot. If a cutter is The Derry Collard Co. Figure 80. Straightening a half-round reamer. overheated, it will not do as much nor as satisfactory work as though properly heated ; but should the teeth by any carelessness become overheated, do not quench at that heat, thinking no one will know the difference. While it is possible to misrepresent the condition of the heat when describing it, the texture of the steel always tells the truth in regard to what the operator has done with it when in the fire. Neither is it a good plan to hold it in the air and let it cool until the color shows about right, because it is hotter inside than on the outside ; and then again, the grain will be as coarse 165 How to cool milling cutters. as thougli it were dipped at the higher heat. It should be allowed to cool off and then heated to the refining heat and quenched. When this form of tool is ready to harden, place it on a wire, bent as shown in Fig. 8i. The wire should be large ^ enough to hold the cutter without bending, ^,^ but not much larger, as it should not impede ^^ the circulation of the fluid through the hole of the ^^ cutter. Neither should any con- siderable sized ^^ piece of steel rest against the side of the cutter, ^^ as the action of the bath would not be uni- ^^ form if it were kept away from some portions ^^ of the piece. The cutter should be worked ^^^ around well in the bath until the teeth are hard, ^^^ when it may be re- moved and plunged in oil ^^^ and left until cold. It should then be taken and ^^ held over a fire and heated sufficiently to re- ^. move any ten- dency to crack from internal ^ strains. The temper may now be drawn the re- quired amount. A method in use in many shops, con- sists in dipping the cutter in a bath of water having one or two inches of oil on the surface. The cutter is passed down through the oil into the water. Fig. 82 shows a bath of this description. The oil does away with the first sudden shock, which results when hot steel is plunged into cold water, and as a small portion of the oil adheres to the teeth, especially in the comers where the teeth join the body of the material, 166 liM-Drnj CoUard Co. Figure 81. Proper way to cool milling cutters. Drawing temper of milling cutters. the action of the water is not as **rank" as would otherwise be the case. Where the teeth are long or the mill is of irregular contour, it is advisable to heat the water somewhat. Water or brine, heated luke- warm, works fully as well as though cold on tools of this description and is not as likely to crack them. When the outline is very irregular and the tool is made of high carbon steel, the writer has had excellent suc- cess using a bath of brine heated to 80° Fahr. The idea that a bath must be as cold as possible has prob- ably ruined more steel than we realize. Drawing Temper of Milling Machine Cutters. iiiiiiiiiiiii !i|!i!!i|!l!| I II I I I I I II I ■'i|l |i||i|0 |li|l""' ' III I !i i:i.!!i! III :| niTg r^ri^-zznWatec: A method in very general use for drawing temper of milling machine cutters, consists in placing the hardened cutter on an iron plug of the form shown in Fig. 83, the plug having been pre- viously heated suffici- ently to draw the tem- per of the cutter. The plug, when heated, should not fill the hole in the cutter. In order to heat the cutter uniformly, it should be turned con- stantly on the plug. It is, of course, necessary to brighten the backs 167 7////////////////////////////////^////////////^^^ TTut T>errv Collard Co. Figure 82. Oil and water bath for milling cutters. Heating milling cutters on a plug. of the cutter teeth in order that the temper colors may be readily discerned. The writer has had best results by holding the cutter over a fire, or a hot plate, and warming the circumference to a degree that made it impossible to Figure S3. Plug for heating milling cutters. hold the hand on it, previous to placing the cutter on the plug. It was then placed on the plug and turned constantly until the proper temper colors showed, when it was plimged in oil to prevent its getting too soft. The object attained in heating the outer surface first, was that the heat given was sufficient to make the steel at this point somewhat pliable; whereas, if the cutter had been placed when cold on the red hot plug, the cutter absorbing the heat would tend to expand the steel toward the outer, rigid surface. If this expansion should prove, as it does many times, to be greater than the steel could stand, cracks would result. The amount of heat necessary to give a milling machine cutter when drawing temper can not be stated arbitrarily. It is desirable to leave it as hard as possi- 168 Hardening shank mills. ble, and yet not have it too brittle to stand up when in use ; consequently, it should not be heated any hot- ter than necessary when hardening. It should not be plunged in a bath of extremely cold fluid, neither should it be checked in cold water when the temper has been drawn sufficiently. While it is not considered advisable by many mechanics to make cutters of this description of a high carbon steel, the writer's experience has convinced him that better results are obtained by using a high carbon steel extremely low in phosphorus, and using extreme care in the heating. Then quenching in a bath of warm brine, 80° to 100° Fahr. For ordinary work, a faint straw color (430**) gives best results, although it may be necessary at times to draw to a full straw color, 460°. A kettle of oil, heated to the desired temperature, furnishes an ideal method of tempering cutters of this description. This method has been ftdly described under the proper section on pages 121 and 122, and should be carefully considered in connection with tools of this character Hardening Shank Mills, The percentage of carbon necessary to give the best results, depends on the make of steel. For ordin- ary work, however, a steel having i % per cent, gives good results. The methods employed in heating and quenching shank mills when hardening, depend in a measure on the form of the mill and the custom in the individual shop. Mills of the form shown in Fig. 84, may be 169 Best way to harden shank mills. heated to a uniform low red heat for a short distance above the teeth, stopping the heat in the necked portion, marked a. In some shops it is the custom to leave the shank quite a little larger than finish size in order that it may be turned to size in the lathe and fitted to Figure 84. How to harden shank mills the collet or spindle after hardening. In such cases it is necessary to leave the shank soft its entire length. In other shops it is the custom to turn the shank nearly to size before hardening, leaving on just enough to allow for grinding to a fit and remove any untruth resulting from springing in hardening. If it is neces- sary to leave the shank soft its entire length, care should be exercised in heating and dipping in the bath that the shank is not hardened in the least. If it is to be ground to a fit, the same care is not necessary, although greater care must be exercised in grinding if the shank is hard for a short distance and the balance is soft ; but if careful when taking the finishing cuts on the grinder, no trouble need be experienced. If the cutter is made as represented in Fig. 85, it will be necessary, in order to harden the teeth the entire length in a satisfactory manner, to harden the shank for a short distance. When hardening a cutter of the description shown 170 Treatment of holes in shank mills. in Fig. 86, having a recess of considerable depth in the end, much better results will be obtained if it is dipped in the bath with the hole uppermost, as shown in Fig. 87 — that is, provided it is necessary to harden the walls of the hole. If this were not desirable, then it would be safest to fill the hole with fire-clay, mixed with water, to the consistency of dough, and the cutter dipped as shown on next page. If the hole was not filled and the cutter was dipped in the bath with the hole down, the steam generated would drive the water away from the teeth at end; and furthermore, the steam would very likely cause the thin walls to crack. TtM Shrry C«lUrd Co. Figure 85. Figure 86. Shank mills. When hardening cutters of the form shown in Fig. 88, known as T slot cutters, it is necessary to harden the entire length of portion necked below size of shank for several reasons. When the neck portion is slender, this is necessary, in order to strengthen this 171 Treatment of T slot cutters. portion so it will not spring or twist off when the cutter is in operation. If the cutter is of a size that makes the necked portion large and strong enough to resist the cutting strain, it might not appear at first thought necessary to harden this. But as it ^ is g e n e r ally made but a few thousandths of an inch smaller than the slot it travels in, it will, if left soft, become roughed up by the fine cast iron chips, which are liable to get between the walls of the slot and the stem. Con- sequently, it will be readily seen that in most cases it is advisable to harden the entire length of the necked portion. If there is considerable dif- erence between the size of the cutting portion and the shank of the tool, the cutter should be made, if possible, with a fillet in the comer, as shown at a^ in sectional view of Fig. 89. If, however, this precaution has not been taken, or it has not been possible to do it, a piece of iron wire may be wound around, as shown at 5. This wire being red- hot when the cutter is dipped in the bath, has the effect Figure 87. Proper method for treating shank mills. 172 Tlie Derry Collard Co. Figure 88. T slot cutter. Fillets for T slot cutters. of keeping the contents of the bath away from the sharp comer until the larger and smaller portions of the mill have become hardened to a degree, thus reduc- ing the liabil- ity of cracking at this point. When the cut- ter has been heated to a low red, it should be plunged into a bath of water or brine from which the chill has been removed ; work around well in the bath until it is of the same temperature as the bath, when it may be removed and the temper drawn. If it has not been possible to heat the cutter in a muffle or in a piece of pipe or other receptacle, it will be found an excellent plan to have a strong solution of potash and water, which should be heated quite warm. Before the cutter is heated, it may be plunged into the potash solution. Place it in the fire and heat to the proper hardening temper- ature and plunge in the hardening bath. The effect of the potash is to cause any thin scale of oxide which may have formed on the surface to drop off the instant the tool touches the bath. If this scale adheres to the piece, it has a tend- ency to rise in the form of a blister when in contact with a cool liquid, and consequently it keeps the con- tents of the bath from acting on the steel directly underneath. Figure 89. Fillets for T slot cutters. 173 Drawing temper of T slot cutters. When drawing the temper of a tool of this descrip- tion it is necessary, in order that the necked portion be as strong as possible (especially if it is slender), to draw it to a purple or even a blue color, while the cut- ting teeth need drawing to a straw color. It is surprising to one not thoroughly posted in the effects of different degrees of heat on steel to find how hard a cutter of this kind may be left if it was properly heated when hardened. This is best seen by compar- ing with one that was heated a trifle too hot, yet not to a degree that is generally considered harmful to the steel. In the case of the cutter properly heated — that is, to the refining heat — it may be left when tempering at a faint straw color, while if given a trifle more heat, it is necessary to draw it to a full straw, a difference of 30° of heat, and a vast difference in the amount of work it will do between grindings. In order to suc- cessfully draw the temper, the necked portion may be placed in the flame of a gas jet, a Bunsen burner, the flame of a spirit lamp ; or, if none of these are avail- able, and it is necessary to use a blacksmith's forge for all work of this description, a piece of sheet iron having a hole in it may be placed over the fire. A jet of flame will come through the hole, which may be made to strike the necked portion. In this way the desired temper may be obtained. Hollow Mills. When articles having a hole running part way through them, as, for instance, the hollow mill shown in Fig. 90, are to be hardened, it is advisable to dip 174 Hardening hollow mills. them in the bath, with the opening uppermost, as re- presented in Fig. 91. If the mill were dipped with the opening down, it would be almost impossible to get water to enter the hole for any considerable distance, Figure 90. A hollow mill. as the steam generated would blow the water out. As a consequence, the walls of the hole would not harden, and the steam would in all probability cause the steel to crack. Then again, best results will follow if the frail end is not chilled until after the heavier, solid portions have contracted somewhat. If the lighter portions are chil- led and contracted before the heavier ones, the tend- ency is for the heavier parts, which are stronger than the lighter, to pull them into conformity with them- selves, and as the steel is hard and rigid, it must crack. While this principle is explained elsewhere in this work, it seems wise to show the adaptability of this peculiarity of steel to pieces of this description. When making articles having holes, as shown, if the piece is to be hardened, the liability of cracking will be lessened if the stock at the end of hole is left, as shown in Fig. 92. If, however, the piece is made »7S Tepid water for hardening hollow mills. with a sharp comer, as shown in Fig. 93, it is advisable to fill in this sharp comer with fire clay, or graphite, in order that there may be no pronounced difference in the contraction of the two portions. When hard- ening pieces of this character, it is, generally speaking, good practice to use a bath of tepid water or brine. When it is con- sidered desirable to harden a piece a certain dis- tance, and no far- ther, and the fa- cilities for heat- ing do not allow of heating ex- actly the right distance, it is necessary to dip in the bath with the teeth down. In order to over- come the tendency of the steam to blow the water from the hole, a small vent hole is drilled through the wall of the piece, as shown in Fig. 94. If this hole is large enough to allow the steam to escape, good re- sults will follow if a bath is used having a jet of water coming up from the bottom, as, by this means, water is 176 The Derry Collard Co» Figure 91. Method for hardening hollow mills. Various types of hollow mills, forced into the hole. However, the operator should bear in mind that it is never good practice to have Figure 92. Hollow mill with rounded corners. The Derry CoUard Co. the hardening stop at a shoulder, either inside or out- side of a piece of steel. Where possible, stop the Figure 93. Hollow mill with sharp corners. hardening somewhat short of the shoulder, but if this does not meet the requirements, harden a trifle Figure 94. Hollow mill with hole to allow escape of steam. beyond the shoulder. This may seem like a little thing to bother about, but it generally means the dif- ference between a good job and a poor one, and it's 177 Hardening thin articles. one of the little points that count in making a success- ful hardener. Thin Articles. Thin articles, as screw slotting saws, metal slitting saws, etc., may be hardened between two plates whose faces are covered or rubbed with oil. If reasonable care is exercised in the operation, they will be very straight. It is essential, in order to get good results, to heat the pieces on a flat plate. They should be heated no hotter than is necessary to accomplish the desired result. When at the proper heat, the saw may be taken by a pair of tongs, of the form shown in Fig. 95, and placed on a plate whose face is covered with lard, sperm or raw linseed oil. The advantage derived from using tongs of this description is, the saw is held by the por- tion near the hole, rather than by the teeth, as would be the case if a pair of the ordinary style were used. In that case, the teeth grasped by the tongs would not be of the same temperature as the balance of the saw ; and, as a consequence, the hardening would not be uniform. Another plate, whose face has been treated in a similar manner, may be placed on top of the saw and held there until the saw is cold. It is necessary to Figure 95. The Derry Coiiard Co. Tongs for holding flat plates. place the top plate in position as quickly as possible, after the saw has been placed on the lower plate. If the saw should become chilled before the upper 178 Method of cooling flat plates. plate is placed on it, it will spring somewhat, and the upper plate cannot straighten it. Should it be sprung II II II II II II II II II y/////f//^^/^/^////j//M f/^//wj,j//:r//f/. Figure 96. Device for cooling thin, flat work 'The Derry Coltard Co. very much, the pressure applied to the upper plate will, in all probability, break the saw, as it would be hard and unyielding. If many pieces of the description mentioned are to be hardened, it is advisable, for the sake of economy, to make a special device for chilling the work, as when two plates are used, it is necessary to have the services of tvv^o men, one to handle the saws, and one to work the movable plate. If the number of pieces to be hardened does not warrant an expensive apparatus, two flat plates may be used, drilling two holes in each plate, as shown in Fig. 96. The holes in the lower plate should be a driving size for ^ inch wire, while those in the upper plate should be -^ inch larger than 179 Devices for hardening thin plates. the size of the wires. A cord should be attached to the upper plate, as shown. This cord should pass over a pulley and return to a treadle. The operator, a u Qel r: r.z: i x*> '.-.: O Q: lerffjri ^ inches of packing material in the bottom, then lay a row of work on this, being careful that no pieces come within ^ inch of each other, or within i Yz inches of the walls of the box. Cover this row of work with packing material to the depth of ^ inch, put in another row of work, and continue in this way until within i % inches of the top of the box. After covering each row of work with the packing material, it should be tamped down lightly to insure its staying in place. When the box is filled to within the distance of top mentioned (i}^ inches), the balance should be filled with packing material, the cover put in place and sealed with fire- clay mixed with water to the consistency of dough, and allowed to dry before placing in the furnace. Before the articles are packed in the box, a piece of iron binding-wire should be attached to each piece of work in such a manner that the article may be removed from the box and dipped in the bath by this means, unless the piece is too heavy to be handled in this man- ner, in which case it must be grasped with a pair of tongs. The wires should extend up the sides to the top of the box and hang over the edge, in order ao7 Figure 115. The wrong way to pack harden. Pack boxes with similar articles. that the operator may readily see them when removing the articles from the box. If several rows of work are placed in the box, it is necessary to place the wires in a manner that allows the different rows to be readily distinguished. As it is necessary to draw the pieces on the top row first, each succeeding row should be drawn in its order, because if an article were drawn from the bottom row first, it would probably draw one or more of the pieces located above along with it. As a conse- quence they would lay on the top of the box exposed to the action of the air, and would cool perceptibly while the first piece was being quenched in the bath. For this reason it is advisable to draw the pieces in the top row first, as described. As the length of time a piece of steel is exposed to the carbonaceous packing material after it is red-hot determines the depth of hardening, articles packed in a box should all be of a character that need carbonizing alike, or some pieces will not receive a sufficient depth of carbonizing and others will receive too much. Know- ing this, one may select the articles accordingly, pack- ing those requiring charging for one hour in one box, those requiring two hours in another, and so on. A little experience will teach one the proper length of time to give a tool of a certain size to accomplish a given result. The Derry-Collard Co. ao8 Boxes for pack hardening. Attention must be paid to the shape of the piece when packing in the box. If it is long and slender, it should not be packed in such a manner that it will be necessary to draw it through the packing material, as shown in Fig. 115, or it will surely spring from doing so, it being red-hot, and consequently easily bent. If but a few pieces of this character are to be hardened, it would not be advisable to procure a box especially Figure Ii6. Box for pack hardening. adapted to it. In that case the articles could be packed two or three in a box. When they have run the proper length of time, the box should be removed from the furnace, turned bottom side up on the floor, provided the floor is of some material that will not catch fire. The piece of work may be pulled out lengthwise from the mass, and in that way all danger of springing is done away with. If, however, quite a number of pieces are to be hardened, it is advisable to procure a box adapted to pieces of this description. This may be done by adopt- ing a design opening at the end, as shown in Fig. n6. This may stand on end with the opening uppermost while packing the pieces. If a furnace of the design 209 How to tell when heated. shown in Fig. 1 1 7 is available, it should be used, as the box can stand on end. If this form of furnace is not at hand, the box may be placed on its side in any fur- nace large enough to receive it. If necessary to use a furnace where the box must lay on its side, it will be advisable to provide some way of fastening the cover in place. This may be done by drilling a j^ inch hole on opposite sides of the box and running a rod at least -jV of an inch smaller than the hole across the face of the cover, Fig. 118, before sealing with fire-clay. This rod can easily be removed when the articles are ready for immersion in the bath. In order that the exact time at which the work be- comes red-hot may be ascer- tained, it will be necessary to use test wires. Several % inch holes may be drilled near the center of the cover, a -f^ inch wire run through each of these holes to the bot- tom of the box, as The Derry Collard Co. Figure 117. Furnace for use in pack hardening. shown in Fig. 26. When the work has been in the furnace for a sufficient length of time to become heated through, according to the judgment of the . operator, one of the test wires may be drawn and its The length of time work should be run. condition noted. If it shows red-hot the entire length, note the time. If not, wait a few minutes (say, 15 minutes) and draw another wire. When one is drawn that shows the proper temperature, time from this. The length of time the pieces should be run cannot The Derry Colliwd Co. Figure 118. Method of fastening cover in place. be Stated arbitrarily, as the character of the work to be done by the tool must, in a measure, determine this. However, if the pieces are ^ inch diameter, and are to cut a soft grade of machinery steel, one hour may be found sufficient. If a harder surface is required, it is necessary to run somewhat longer (say, 1% hours). When the work has run the required length of time, the box may be removed, the cover taken off, and the ar- ticles taken out one at a time and dipped in a bath of raw linseed oil. When the articles are long, it is ad- visable, if possible, to use a bath having a perforated pipe extending up two opposite sides of the tank, as shown in Fig. 119. A pump should be connected with the oil in the bath, pumping it through a coil of pipe in a tank of water and forcing back into the tub through the upright perforated pipes shown. This method insures evenly hardened surfaces, as the jets of oil forced against the sides of the article drive the vapors away from the piece, thus insuring its hardening. It is necessary to move the work up and down and to turn How to treat milling cutters. it quarter way around occasionally in order to present all sides to the action of the oil. When milling machine cutters, or similar tools having projections, are to be hardened by this method, they should be packed in the box, using the packing Figure 119. Bath for use in pack hardening. Tbe Deny Collard Co. material mentioned. Previous to placing the cutters in the hardening box, a piece of iron binding- wire should be attached to each cutter and allowed to project over the edge of the box. Test wires should be run down through the holes in the cover, as shown in Fig. 26. The length of time the cutters should run is determin- ed by the character of the work they are to do ; but for Milling cutters needing no tempering. ordinary milling, a cutter 3 inches diameter, if of the ordinary design, should run about 3 hours. If the teeth are heavy, of the style known as form- ed mills, Fig. 120, they should be run 4 hours after they are red-hot. When the box is removed from the fur- nace, the cutters may be removed one at a time, placed on a bent wire of the form shown in Fig. 81, and im- mersed in the oil, working them around well until all trace of red has disappeared, when they may be dropped to the bottom of the bath and left until cold. A milling machine cutter of the form shown in Fig. 120 will not as a rule require tem- pering. The teeth may be left as hard as they come from the bath, but those of the ordinary form of tooth should have the tem- per drawn. This may be done by the method described under Hard- ening and Tempering Milling Machine Cutters, or, if there are . . The Derry ColUrd Co. many cutters, a savmg of time will result if the articles are igure 12,0. orme -1 • -I 1 f '^ 11 milling cutter. placed m a kettle of oil and the temperature gauged by a thermometer, drawing them to 430 degrees. Punch press blanking dies give excellent satisfac- tion if hardened in this manner. The die is packed in a box. Test wires are run down through the opening in the die to the bottom of the box. "When drawing the wires to test the heat, do not draw them way through the cover. After observing the heat, place the wire back in its original position. A wire can be raised from time to time, the amount of heat observed and the wir^ 213 Treatment of blanking dies. returned. In this way the operator can tell from time to time the exact temperature of the piece being heated, and as the same laws governing the heating of steel in the open fire apply when heating to harden by this method, it is advisable to keep the heats as low as pos- sible ; for steel treated by this method will harden in oil at a lower heat than if treated in the ordinary way and hardened in water. Blanking dies for the class of work usually done on punch presses (if they are i inch to i j^ inches thick) Figure 121. Bath for blanking dies. vx/i>)<;>./^y/yyyyx^z^xy^^^y^yyy^///yy/x^^^^^ Tlie Perry Collard Co. should run about four hours after they are red-hot. At the expiration of that time the box may be removed from the furnace, the die grasped by one end with a pair of tongs and immersed endwise down into a bath of raw linseed oil. It is a good plan to have the bath rigged as shown in Fig. 121. A pipe is connected with the tank near the top, and runs in a coil through a tank of water. A pump draws the oil from the tank through the coil, and forces it back into the bath, as represented. 214 Handling of dies and taps. The inlet pipe may be so situated as to cause the oil to circulate with considerable force through the bath. This, striking the face of the die, passes through the opening, insures good results. If no means are pro- vided for the cir- culation of the oil, the die may- be swung back and forth in the oil, and it will harden in a satis- factory manner. Forming and bending dies, if hardened by this The Derry Collard Co. Figure 1 22. One method of packmg snap gauges. method, must be run longer, and heated somewhat hotter, yet not hot enough to injure the steel. Pack hardening fur- nishes a method whereby taps may be hardened without altering the pitch very perceptibly; neither will the diametrical measurements be changed, provided the blanks were annealed after blocking out to shape, and by this method the teeth are made exceedingly hard without being brittle. A tap from one to two inches Figure 123. Another method of packing snap gauges. 215 Pack hardening for gauges. in diameter should be run about two hours. It should be worked around rapidly in the bath, in order that the teeth may be hardened. For general machine shop work, taps do not require the temper drawn as low as if they were hardened by heating red-hot and plunging in water. Generally speaking, 430 degrees (a faint straw color) is sufficient, provided a low heat was maintained in the furnace. This is an ideal method of hardening gauges and similar work, as the liability of cracking is eliminated and the danger of springing is reduced to the minimum. If the gauge is of the plug or ring form, it is not neces- sary to allow as great an amount for grinding as would otherwise be the case, as there is little danger of springing. When hardening snap gauges, especially if they are long, it is advisable to pack as represented in Fig. 122, provided a box deep enough is at hand. If obliged to pack in a box so that the gauges lay lengthwise in the box, they should be so placed as to have the edges up and down, as shown in Fig. 123, thus doing away with the tendency to spring when they are drawn through the packing material. Articles of a form which betokens trouble when hardening can, if proper precautions are taken, be hardened by this method in a very satisfactory manner. Take, for instance, the shaft shown in Fig. 124. This was made of ^ per cent, carbon crucible steel, and turned within a few thousandths of an inch of finish size. It was packed in a mixture of charred leather and char- coal, and subjected to heat for i^ hours after it was red-hot. It was then dipped in a bath of raw linseed oil, heated to a temperature of 90°. It was found zi6 Treating difficult subjects. upon being tested between centers to run nearly- true. The designer does not always take into consideration the difficulties which may be encountered when a piece of irregular contour is hardened, consequently we some- times run across articles which call for serious study on the part of the hardener when the article reaches him. Then again, such articles are many times made The Derry Collard Co. Figure 124, A peculiar piece to harden. of a high carbon tool steel, when a low grade steel would answer the purpose as well, and not cause nearly as much trouble. At one time the writer was called to a shop where they were experiencing all kinds of trouble in an attempt to harden a gauge of the description shown in Fig. 125. As it was not practical to grind the interior of this gauge with a grinding machine, it was necessary that it should retain its shape when hardened. In order to accom- plish this, the gauge was surrounded with a mixture of fire-clay, to which was added sufficient hair (obtained from a plasterer) to hold it together. It was moistened with water to the consistency of dough. The hole in th e gauge was filled with finely granulated charred leather. It was then placed in a small hardening box, in the bottom of which was placed 2 inches of granulated wood ai7 How the "teaser" was hardened. charcoal. The box was filled with charcoal, the cover placed in position, and sealed with fire-clay. The box was subjected to heat for one hour after the contents were red-hot, this being ascertained by means of the test wires, as described. The gauge was then taken from the box, the leather removed from the hole, and a jet of raw linseed oil Figure 125. A "teaser" for hardening. TheDerry CoUard Co. forced through the hole until the piece had cooled off. The walls of the hole were very hard, and the gauge was found by test to have retained its shape. The coating of fire-clay prevented the exterior hardening of the piece, thereby eliminating the tendency to spring or go out of shape. The walls of the hole, hardening first, retained their shape, and the balance, being red-hot, conformed to this portion. While it would be impossible to enumerate the various articles of irregular contour that may be hard- ened by applying this principle — namely, protecting the portions that do not require hardening, by the use of a mixture of fire-clay and water, adding sufficient hair to hold it together — it can safely be said that many thousand dollars' worth of tools are ruined annually, which might have been saved had this precaution been observed. zi8 Pack hardening for mandrels and arbors. As this process of charging the surface of the steel with carbon is a process of cementation, it is necessarily- slow. When extremely high carbon steel is used in making tools, it is considered advisable by some to use hoofs and horns as packing material rather than leather. At times it is not considered desirable to subject the articles to heat for so great a length of time. In such cases it is necessary to treat the surfaces to be hardened with some material that will act more quickly than charred leather. In fact, at times it is necessary to prevent any portion other than the ones to be hard- ened from becoming red-hot. This can be effected by covering the parts with the fire-clay mixture to a considerable depth, applying heat to the portions that need hardening. When it is not desirable to subject the article to heat for a length of time sufficient to charge the steel with the necessary amount of carbon to cause it to harden (if it was to be carbonized by means of charred leather), excellent re- sults may be had by the use of a mixture of 5 parts of rye flour, 5 parts table salt, 2 parts yellow prussiate of potash, filling the hole or covering the portions to be hardened with this. Mandrels, or any form of arbor which it is consid- ered advisable to harden, will harden in a more satis- factory manner by this method than by any that has come to the writer's notice. If the article is long and slender, do not pack in the box in such a manner that they will spring when drawn out ; but if the shape of the box is such that this cannot be avoided, the box may be turned bottom side up on the floor when the articles are ready for hardening, as previously explained. If, however, the mandrels are made of the proportions 119 How to dip mandrels and arbors. tisually observed when making for general shop usd, there is very little liability of springing when drawing them through the packing material. The mandrel may be wired as represented in Fig. 126, or it may be grasped with a pair of tongs of a form that allows the contents of the bath to have ready access to the end of piece ; but as tongs of this form are not in general use, the wires will answer unless the pieces are very heavy. In this case it is advisable to procure tongs of a suitable shape rather than to have an un- satisfactory article when it is finished. As stated under Examples of Hardening, it is never advisable to hold a mandrel with any form of tongs that in any way interfere with the hardening of the walls of centers in the ends of a mandrel. If the work is wired, it should be done in a manner that makes it possible to dip the mandrel in the bath in a vertical position, to avoid any tendency to spring. The wires may be grasped by means of tongs which close together very nicely, as shown in Fig. 126, in order that they may not lose their grip and the piece fall to the bottom of the bath before the red had disappeared from the surface. It should be worked up and down in the oil until all trace of red has disappeared, when it may be lowered to the bottom and left until cooled to the temperature of the bath. Circular forming tools, especially those having long, slender projections and sharp comers, as shown in Fig. 127, are safely hardened by this process, as they n r Stay-bolt taps and the like. can be given any degree of hardness desirable without making them brittle. Being solid in form, they must be heated for a longer period of time than if there were teeth on the surface — as a milling machine cutter. As with other cutting tools, the length of time a tool of this form should be subjected to heat depends on the nature of work to be performed by it. A tool 4 inches in diameter and 2 inches wide for ordinary work should run about 4 hours after it is red-hot. If there are slender projec- tions from the face of the tool, it will be found necessary to draw the temper somewhat ; but as a rule it should not be drawn as low as if it were hard- ened by the methods ordinarily employed. The writer has in mind a forming tool of the same general outline as the one represented in Fig. 127, which gave excellent results when drawn to 350 degrees after hardening by the method under consideration. It was hard enough to stand up in good shape, and yet tough enough to stand very severe usage. If the formed surface is of a shape that insures strength — that is, if there are no projections — the cut- ter should be left as hard as when it comes from the bath. Stay-bolt taps and similar tools may be packed in a box of the proper shape and run for a length of time, depending on the size of the piece. They should then Tlw Derry Collard Co, Figure 127. A forming tool. 221 Precautions to be taken on large work. be taken one at a time and immersed in a bath of raw linseed oil and worked up and down in a vertical man- ner, moving to different parts of the bath, unless there is a jet of oil coming up from the bottom. Or, better still, having perforated pipes coming up the sides of the bath, as represented in Fig. 119. In either case it is advisable to work the articles up and down, to avoid the vapors which always have a tendency to keep the contents of the bath from acting on the heated steel. If the articles are long, a deep tank should be used for the bath. If the taps are 24 inches long, there should be a depth of 40 inches of oil. If the articles are longer, the tank should be proportionally deeper. A precaution that should always be observed when hardening large pieces of work, when they are to be quenched in a bath of oil, consists in protecting the hands and arms of the operator to prevent burning from the fire, which results when a piece of red-hot steel is immersed in oil. This is, of course, simply a burning of the surface oil as the steel passes through it, but it is liable to flash high enough to bum the hands and arms unless they are protected in some manner. When hardening long articles, it is found much more convenient if the tanks containing the cooling liquid are so located that the tops of the tanks are nearly on a level with the floor — say 12 or 15 inches above it. The toolmaker should, when making adjustable taps, reamers, etc., of the description shown in Fig. 128, leave a portion on the end solid, as shown in Fig. 129, to prevent the tool springing out of shape. The hole for the adjusting rod should be filled with fire-clay, the article packed with the mixture of charcoal and How to harden an adjustable reamer. charred leather, and subjected to a very low red heat, and dipped in raw linseed oil, warmed to about 90 degrees Fahr. The length of time it should be sub- jected to heat after it is red-hot depends on the size, § Figure 129 of reamer. The Derry CoUard Co. Solid portion Figure 128. An adjustable reamer. quality of steel used, and the work it is to do. It will vary from i to 2^ hours. The temper may be drawn to a light straw or a full straw color. The shank, and ends of flutes nearest the shank, should be drawn to a blue. When drawing the temper, the reamer or tap may be placed in a kettle of oil heated to the proper degree for the cutting edges. The shank may be drawn lower in a flame, or heat may be ap- plied at the shank end by means of a flame from a gas jet, Bunsen burner, or any other means, allowing the heat to run toward the cutting end. After the reamer has been hardened and ground to size, the extreme end may be ground off enough to allow the slots to extend to the end. Dies used for swaging tubing are a source of an- noyance when hardened by methods usually employed, as the unequal sizes of the different portions cause them to spring out of shape, and their shape is such that it is next to impossible to grind them in a manner that insures satisfaction when they are used. Pack hardening furnishes a method whereby this aa3 Box for heating swaging dies. class of work can be made hard enougli to do the work required of them, and they do not alter in shape enough to require grinding. For this reason the extremely hard surface, which comes in contact with the contents of the bath, need not be removed by grinding. When making swaging dies of the description mentioned, best results will follow if they are made of tool steel of i^ to I }4^ per cent, carbon. . Block to shape, anneal thoroughly, and finish to size. When harden- ing, the dies should be wired and packed in a box, as shown in Fig. 130, placing charred leather all around the die for a distance of % inch to i inch. The balance of the box may be filled with ^^^ ^'^"'"^ ^3°- packing mixture ^8\i Box for hardening that has previously 1 V* swaging dies. ^v been used. Run for about 4 hours after they have reached a medium red heat. It is necessary to give articles of this description a trifle higher heat than if hardening cutting tools made from the same stock. As hardness is the required quality, the dies should be left as hard as when taken from the bath, which should be raw linseed oil at a temperature of about 60 degrees Fahr. A careful study of the pack hardening method will help every one handling steel. It often makes possible the use of lower grade steels, and it enables pieces to be made of any desired shape with the knowl- edge that they can be hardened without cracking. Tke Derry Collard Co. 224 Case Hardening, 6--^=^ .^=^=^>© CO When wrought iron or machinery steel — especially the latter — will answer the purpose as well as tool steel, they are generally used. The first cost is less, and it can be machined much more cheaply, and in many cases it is better adapted to the purpose. Machinery steel is made by two entirely different processes, namely: the Open Hearth and the Bessemer processes. Each method produces steel adapted to certain classes of work. There are many grades of steel made by each of these processes, these being de- termined by the amount of carbon or other elements present in the steel. Machinery steel is not only valu- able to the manufacturer on account of its low first cost, as compared with tool steel, and the ease with which it may be worked to shape, but it possesses the quality of toughness, and is not so susceptible to crystalliza- tion from the action of shocks and blows. A very valuable feature is, that by subjecting it to certain processes, the surface may be made extremely hard, while the interior of the steel will be in its normal condition, thereby enabling it to resist frictional wear and yet possess the quality of toughness. The hardening of surfaces of articles made of wrought iron and machinery steel is generally termed 225 Case hardening a few pieces. **case hardening," and consists in first converting the surface of the article to steel, then hardening this steel surface. In order to convert the surface to steel, it is necessary to heat the piece red-hot, then treat it while hot with some substance which furnishes the necessary- quality to cause the steel to harden when plunged in a cooling bath. Most machine shops have some means whereby they can harden screws, nuts and similar articles. Where there is only a limited .number of pieces to harden, it is customary to heat the work in a black- smith's forge, in a gas jet, or in any place where a red heat can be given the piece. When hot, sprinkle with a little granulated cyanide of potassium, or some yel- low prussiate of potash, or a mixture of prussiate of potash, sal ammoniac and salt. If cyanide of potassium is used, it is advisable to procure the chemically pure article, as much better results may be obtained. The reader should bear in mind that this is a violent poison. Re-heat to a red and plunge in clear, cold water. When there are large quantities of work to harden, this is an expensive as well as a very unsatisfactory way. To case harden properly, one must understand the ma- terial of which the article is made and the purpose for which it is to be used — whether it is simply to resist friction or wear, or to resist sharp or heavy blows, a bending or twisting strain, or whether it is merely de- sired to produce certain colors. We will first consider the case hardening of work that simply needs a hard surface, with nothing else to be taken into consideration. Pack the articles in an iron box made for this purpose, as shown in Fig. 131. The size and shape of the box used depend, as a rule, 226 Case hardening in a gas pipe. on what can be found in the shop. But when results are to be taken into consideration, it is advisable to procure boxes adapted to the pieces to be hardened. It is not policy to pack a number of small pieces, which do not require a deeply hardened portion, in a large box, especially if it is desirable to have a uni- formity in the hardened product, as the pieces which Figure 131. Box for case hardening. are near the walls of the box will become red-hot long before those in the center. And as steel or iron absorbs carbon only when red-hot, the pieces nearest the outside would be hardened to a greater depth than those near the center of the box. For small articles, where but a few pieces are to be hardened at a time, a piece of gas-pipe may be used. Screw a cap solidly on one end or plug the end with a piece of iron, using a pin to hold it in place. The outer end may be closed by means of a piece made in the form of a cap to go over the end, or it may be a loose-fitting plug held in place by a pin, as shown in Fig. n8. When a hardening box of the description shown in Fig. 131 is used, the heat may be gauged nicely by running test wires through the cover to bottom of tube, as shown in Fig. 126. Pack the pieces of work in a mixture of equal parts, by measure, of az7 How to pack for case hardening. granulated raw bone and granulated charcoal mixed thoroughly together. Cover the bottom of the harden- ing box to a depth oi 1% inches with the mixture, pack a row of work on this, being sure that the arti- cles do not come within X ^^ ^ i^^^ of each other, or within i inch of the walls of the box. Cover this with the packing material to a depth of half an inch. Test wire! Test wire I QL The Deny Collard Co. Figure 132. A method of using test ynttz. Tamp down, put on another layer, and so continue until the box is filled to within i inch of the top. Fill the remaining space with refuse packing material left over from previous hardenings, if you have it. If not, fill with charcoal or packing material, tamp well, put on the cover, and lute the edges with fire- clay to prevent as much as possible the escape of the gases. This is necessary, as the carbon is given off from the packing material in the form of a gas. Then again, if there are any openings, the direct heat will penetrate these and act on the work in a manner that gives unsatisfactory results. If the articles are so large that they would not cool below a red heat before reaching the bottom of the bath, they should be wired, as shown in Fig. 130, before put- 228 Figure 133. Bath for case hardening small pieces. o o 000 To case harden many small pieces. ting in the hardening box. Use iron binding wire, suf- ficiently strong to hold the piece when it is worked around in the bath. If the articles are too heavy for wiring, we must devise some other way of holding — either tongs or grappling hooks. If the pieces are small, they can be dumped directly from the box into the tank, sifting the work out of the box somewhat slowly, so that the articles will not go <^ into the bath in a body. If the tank is large enough, it is a good plan to have wires across from side to side, about 4 inches apart in horizontal rows. Have the rows 3 or 4 inches apart. Do not put any two consecu- tive rows of the wires underneath each other, but in such a manner that the work will strike the wires as it passes to the bottom of the tank. In striking these wires, the work will be separated, and any packing material ad- hering to it will be loosened by the jar. The work will also be turned over and over, thus presenting all sides to the cooling effects of the bath as it passes through. These wires can be arranged as shown in Fig. 133 by taking two pieces of sheet metal, a little shorter than the inside length of the tank, drilling holes in them as de- scribed in the arrangement of wires, and wires can be passed through these holes and riveted, thus making a .-"hS^ W<'<. Figure 140. Bicycle axle. Another method employed when hardening the ends of a piece of work and leaving the center soft, can be illustrated by the bicycle axle shown in Fig. 140. The ends are machined to shape, the center being left large, as represented at a. The axle is packed in the hardening box and charged with carbon, as described. The center is then cut below the depth of charging shown at d. The piece is ready for hardening. This can be accomplished by heating in an open fire, muffle furnace or lead crucible, and dipping in the bath. When it is necessary to harden the center of a piece and leave the ends soft, it can easily be accom- plished. If the ends are to be smaller than the center, 246 How to harden bicycle chain studs. the pieces may be packed in the hardening box with raw bone and charcoal. Run for a sufficient length of time to carbonize to the desired depth of hardening. Allow the pieces to cool off. When cool, machine the ends, as shown by lower cut in Fig. 141, the upper cut The Derry Collard Co. Figure 141. Method of treatment for chain studs. representing the piece of work before charging with carbon; the lower, after machining the carbonized portions at the ends. It may now be heated red-hot and dipped in the hardening bath in the usual man- ner. The center will be found hard. A method employed in making bicycle chain studs that are hard in the center at the point of contact with the block link and soft on the ends, in order that they may be readily riveted in the side links, consists in taking screw wire or special stud wire of the desired size, packing it in long boxes with raw bone and char- coal and running 3 or 4 hours after it is red-hot. Then allow it to cool off. The stock is now placed in the screw machine and cut to shape — that is, the ends are cut down to proper size. The center, being of the proper size, is not machined. The studs may be heated H7 An interesting experiment. in a tube in any form of fire and dumped in a bath of water or brine. The center will be hard enough to re- sist wear, while the ends will be soft, the carbonized portion having been removed. An interesting experiment can be tried, which in itself is of no particular value, except that it acquaints a & a b a b q The Derry Collard Co. Figure 142. An interesting experiment. one with the manner in which carbon is absorbed by- steel. Take a piece of open hearth machinery steel, turn it in the lathe to the shape shown in Fig. 142, neck- ing in every half inch to the depth of }i inch, leaving the intervening spaces }4 inch long. Pack the piece in the hardening box with raw bone and charcoal. Run five or six hours after the box is heated through. AVhen cold, turn the shoulders marked d to the size of a, leaving a the same size as before charging. Heat to a low red and dip in the bath. The portions marked a will be found hard, while the balance of the piece will be soft. When pieces are to be case hardened, and it is con- sidered desirable to leave a certain portion soft, it is accomplished many times by making tongs of the proper form to effectually prevent the contents of the hardening bath coming in contact with the portion men- 248 Case hardening to leave soft places. tioned Suppose, for example, a piece of the design shown in Fig. 143 is to be case hardened, and itisde- < PORTION-G^StRtD-SOFl The Derry Collard Co. Figure 143. Piece with portion desired soft. sired to leave the central portion marked soft. Make a pair of tongs to grasp the piece, as shown in Fig. 144. It will be seen that tioned is eff ect- the tongs. The in the bath, and until the red has it may be dropped tank and left until desirable to leave a the portion men- ually protected by piece may be dipped worked around well disappeared, when to the bottom of the cold. When it is portion of an article i ^ P Tba Dtfiry Collard Co, Figure 144. Tongs for handling piece shown above. soft, as shown in Fig. 145, it is sometimes accomplish- ed by covering the portion to be soft with fire-clay, as shown in lower view. The fire-clay may be held in place by means of iron binding wire ; sometimes the fire-clay is held in place by means of plasterers' hair, 249 The use of fire-clay for soft places. whicli is worked into the mass when it is mixed with water. The fire-clay prevents the carbon coming in contact with the stock where it is desired soft. The Derry Collard Co, Figure 145. The use of fire-clay for soft spots. A method employed in some shops consists in wrapping a piece of sheet iron around the article over the portion de- sired soft, as shown in Fig. 146. The sheet metal is held in place by means of iron binding wire, as shown. The Derry Oollard Co. Figure 146. Using sheet iron to prevent hardening. A very common method, which is costly when many pieces are to be treated, consists in forcing a 250 The use of a collar in case hardening. collar on to the piece over the portion desired soft, as shown in Fig. 147. The collar is removed alter the article is hardened. Piece to be hardened Collar The Derry Collard Co. Collar In position Figure 147. A collar for keeping portions soft. When machine nuts are to be case hardened, and for any reason it is desirable to have the interior threaded portion soft, it is accomplished by screwing a threaded piece of stock in the hole before the nuts are packed in the hardening box. As carbon can not penetrate a nickeled surface, articles are sometimes nickel-plated at portions desired soft; this, however, is, generally speaking, a costly method of accomplishing the desired result. It is sometimes considered necessary to harden the 251 Mow to produce toughness. Surfaces of pieces quite hard and leave the balance of the stock stiffer than would be the case where ordinary- machinery steel is used. In such cases many times an open hearth steel is selected, which contains suf- ficient carbon, so that it will become very stiff when quenched in oil. The writer has in mind a gun frame which, on account of the usage to which it was to be put, must have a hard surface, while the frame itself must be very stiff. They were packed in a mixture of charred leather and charcoal, placed in the furnace and run for a period of ij4 hours after they were red-hot. They were then quenched in a bath of sperm oil. The stock used was 30 -point carbon open hearth steel. Were the articles heavier or a greater degree of stiffness de- sirable, a steel could be procured having a greater per- centage of carbon. When toughness or strength is wanted in the case hardened product, a steel having much phosphorus should not be used ; in fact, the percentage of phosphorus should be the lowest possible, as steel containing phos- phorus, in connection with carbon, is extremely brittle. For this reason, articles which must be extremely tough should not be packed in raw bone, as this contains a very high percentage of phosphorus. At times a job will be brought around to be case hardened, and one particular part will be wanted quite hard, while the balance of the piece will not require hardening very hard or deep. In such cases, if the por- tion mentioned be a depression, it may be placed upper- most in the hardening box, and some prussiate of potash or a small amount of cyanide of potash placed at this point, the piece being packed in granulated raw bone or leather, and run in the furnace a short time. Furnaces for case hardening. The article may be quenched in the usual manner. The portion where the potash was placed will be extra hard. The 'Deny CoU«rd Co, Figure 148. Gas furnace for case hardening. The furnace used in case hardening should receive more consideration than is many times the case; an even heat that can be maintained for a considerable length of time is essential if desi results are desired. A very satisfactory form of furnace is represented in Fig. 148; it bums illuminating gas as fuel. When it is considered desirable to use hard coal as aS3 A "home-made" case hardening furnace. fuel, the furnace made by the Brown & Sharpe Co. , of Providence, R. I., gives excellent results. When it is considered advisable to construct on the Figure 149. ** Home-made" fiiinace for case hardening. premises a furnace burning charcoal or coke, the form shown in Fig. 149 will be found very satisfactory. However, the form and size of furnace depend in a great measure on the character and amount of work to be hardened. Baths for Case Hardening. The bath that is to be used for cooling work being case hardened must be suitable to the work being 254 Various styles of case hardening baths. hardened. Where work is case hardened in large quantities, it is customary in most shops to harden in iron boxes. When the work is in the proper condition, the box is inverted over a tank of water or some fluid, and the contents dumped into the bath. If the pieces of work are large or bulky, and the tank is shallow, they reach the bottom while red-hot, and, as a con- sequence, the side of the piece that lays on the bottom will be soft. In order to overcome this trouble, the tank must be made deep enough so that the pieces will be sufficiently chilled before reaching the bottom. If it is not considered advisable to have an extremely deep tank and the pieces are large, various ways are taken to insure their hardening. One method which the writer has used with excel- lent results is to have a series of rows of wire rods reaching across the tank, no two consecutive rows being in the same vertical plane, as mentioned in the previous section. The work as it descends into the bath strikes these wires, which turns them over and over, bringing all portions in contact with the contents of the bath. These wires also separate the pieces from each other and from any packing material which may have a tendency to stick to them. The wires also retard the progress of the articles, giving them more time to cool before reaching the bottom of the bath. In order to insure good results, it is necessary to have a jet of water coming up from the bottom of the tank. An outlet is provided near the top for an over- flow. The overflow pipe, of course, should be larger than the inlet pipe, and should be located far enough below the top edge of the tank, so that the contents will not overflow when a box of work is dumped into it. Bath with catch pan, I Perforated Catch Pan W/ /f^//^/y'^/^/^/////^////^///^/M^/7/?///. In order to get tlie hardened pieces out of the bath easily, it is necessary to provide a catch pan, as shown in Fig. 150. The bottom of this pan should be made of strong wire netting or a piece of perforated sheet metal, preferably the former. The holes in the pan allow the packing material to fall through to the bottom of the tank, and also allow the water from the supply pipe to circulate freely around the work and to the top of the bath. This catch pan should be provided with strong wire handles, as shown, in order that it may be readily raised. I was at one time requested to call at a shop where they were having very unsatisfactory re- sults with their case hardening. An examination showed they were dumping their product into a barrel of water to harden. The box containing the work was inverted over this barrel, and the work and packing material went into the water in a lump. Some of the pieces that hap- pened to get out of this mess were cooled sufficiently to harden somewhat, but the majority of the pieces were soft, or else they were hard on one side and soft on the 256 =s^ Tha Dtsrry Col lard Co. Figure 150. Case hardening bath with catch pan and steam pipe. How a temporary bath was arranged. other. An examination of the bottom of the barrel showed it to be considerably charred. In places the outline of the pieces was plainly visible. These pieces had reached the bottom red-hot, and had burned their way into the wood. It is needless to say that the side of the piece of work which was down did not harden. As those in charge of the work did not think it ad- visable, considering the limited amount which they had to case harden, to get a tank of the description shown in Fig. 150, we made a catch pan as described, blocked it up about 6 inches from the bottom of the barrel by means of bricks. We then bored a hole into the bottom of the barrel, screwed in a piece of pipe, and by this means were able to connect an ordinary garden hose, so as to get a jet of water coming up from the bottom. As the barrel was out of doors, we simply bored a two -inch hole about two inches from the top of the barrel for an overflow, and let the water run on the ground. When the work was ready to dump, we sifted it out of the box into the water gradually, rather than to dump it in a body. As soon as the box was emptied, we grasped the wire connected with the catch pan, and raised and lowered the pan in a violent man- ner, in order to separate any pieces that might have lodged together. The result was very satisfactory, and I think they are still using that barrel. Baths are made, when large quantities of work are hardened, with some means of keeping the work in motion after it reaches the bottom of the bath. This is sometimes done by mechanically raising and lower- ing the catch pan, and at the same time turning it around. Then again, it is done by means of several sweeps, which are attached to the lower end of a verti- 257 Baths with air pumps or perforated pipes. cal shaft, the shaft resting in a bearing in the center of the catch pan. These sweeps, or arms, revolving, keep the pieces in motion, turning them constantly, but un- less arranged properly, they have a tendency to gather the work in batches, thereby acting exactly opposite from what they are intended to do. Then again, they have a ten- dency to scratch the surface of the work, which is a serious objec- tion, if color Supply Pipe Figure 151. Bath for cooling slender case hardened articles. work is wanted. When it is de- sirable to get nice colors on case hardened work, an air pump may be connected with the bath, as shown in Fig. 134, the water and air entering the bath together. While it is not advisable to let air come in contact with the pieces to be hardened for colors while passing from the box to the water, yet the presence of air in the water would have the effect of coloring the work nicely. When hardening long slender articles or those liable to give trouble if a bath of the ordinary descrip- tion is used, excellent results may be obtained by the use of a bath with perforated pipes extending up the sides of the tank, as shown in Fig. 151. 258 Spring Tempering, G^<^ .^=^n9 CO When it is necessary to give articles made of steel a sufficient degree of toughness, in order that when bent they will return to their original shape, it is accom- plished by a method known as spring tempering. The piece is first hardened, then the brittleness is reduced by tempering until the article, when sprung, will return to its original shape. Generally speaking, it is not advisable to quench pieces that are to be spring tempered in cold water, as it would not be possible to reduce the brittleness suffi- ciently to allow the piece to spring the desired amount without drawing the temper so much that the piece would set. Steel heated red-hot and plunged in oil is much tougher than if plunged in water ; and as tough- ness is the desired quality in springs, it is advisable to harden in oil whenever this will give the required result. For many purposes a grade of steel made especially for springs gives better results than tool steel ; for in- stance, bicycle cranks made of a 40-point carbon open hearth steel will temper in a manner that allows them to stand more strain than if made of the finest tool steel, and the stock does not cost more than one-quarter the price of tool steel. When springs are to be made for a certain purpose, 259 How to harden clock springs. it is generally safer to state the requirements of the spring to some reliable steel maker, allowing him to furnish the stock best suited for the purpose, than to attempt to specify the exact quality wanted — unless, of course, the operator or manufacturer has, either by ex- perience or by study, acquired the knowledge necessary to qualify him to judge as to the quality needed. As previously stated, the hotter a piece of steel is heated for hardening the more open the grain becomes ; and as hardened steel is strongest when hardened at the refining heat, it is always advisable to heat no hot- ter than is necessary to accomplish the desired result. But as springs are generally made of a steel lower in carbon than ordinary tool steel, and as low carbon steel requires a higher heat to harden than is the case when tool steel is used, it is necessary to experiment when a new brand of steel is procured, in order to as- certain the proper temperature in order to produce the best results. When steel is heated to the proper degree, it may be plunged in a bath of oil or tallow and hardened, the character of the bath depending on the size of the piece to be hardened and the nature of the stock used. For ordinary purposes a bath of sperm oil answers nicely. In some cases tallow will be found to answer the pur- pose better. It is necessary sometimes to add certain ingredients to the bath in order to get the required de- gree of hardness. The following is used by a concern when hardening clock springs: To a barrel of oil add lo quarts of resin and 13 quarts of tallow. If the springs are too hard, more tallow is added. If, however, the fracture indicates granulation of the steel rather than excessive »6q Mixture for hardening springs. hardness, a piece of yellow bees'- wax of about twice the size of a man's fist is added to the above. The following mixture has been used by the writer with success in hardening springs which, on account of the thickness of the stock or a low percentage of carbon, would not harden in sperm oil : Spermaceti oil 48 parts. Neat's foot oil 46 ' ' I Rendered beef suet 5 ' ' Resin i * ' The proportion of the different ingredients may be changed to meet the requirements of the particular job. Resin is added to the oil to strike the scale. As the scale or oxidized surface of the steel, when subjected to heat, is liable to raise in the form of blisters, and as these are filled with gas, the contents of the bath can not act readily on the steel. A small proportion of spirits of turpentine is sometimes added, to the oil for the same purpose, but as it is extremely inflammable, it is somewhat dangerous to use unless great care is observed. The presence of resin in a hardening bath has a tendency to crystallize the steel, and on this ac- count is sometimes objectionable. A very good method, when neither resin nor turpen- tine are used to strike the scale, consists in having a dish of soft soap ; or, if that can not be procured, dis- solve some potash in water, dipping the steel into this before heating. It has the effect of preventing oxida- tion of the surfaces, and helps to strike any scale that may have been on the stock previous to hardening. When small springs are to be hardened, which, on account of their size, cool quickly, they can, if there are many of them, be placed in tubes and heated in a 261 Furnace for heating springs. furnace of the description shown in Fig. 152. When the pieces are heated to the proper temperature, a tube is removed and inverted over a bath. The contents should go into the bath in a manner that insures uni- form results, that is, the pieces should be scattered in the bath. If the tube was held in the position shown Figure 152. Furnace with removable tubes for heating springs. 0000 000 0000 Jht D«nry ColUrd Co. at Uy in Fig. 153, the pieces would go into the bath in a lump; but if it were held as shown at ^, the pieces would become scattered, thus insuring good results. When springs larger than those previously con- sidered are to be hardened, an oven having some means of heating the articles in a manner that keeps them from coming in contact with the products of combus- tion should be used. Any form of a muffle having %6% An oil bath for spring hardening. Figure 153. How tubes shown ia Figure 152 should be emptied. sufficient capacity will do, or the pieces may be placed in a hardening box, having ^ inch powdered charcoal in the bottom, and a cover placed on the box — which need not be sealed. The box may then be placed in a furnace and subjected to heat. The cover may be raised from time to time and the contents of the box noted. This makes an excellent way of heating large coil springs and similar articles. If the oven is sufficiently large, several boxes may be heated at a a time. When a spring shows the proper tempera- ture, which should be uni- form through- out, it may be re- moved, placed on a bent wire and immersed in a bath of sperm oil, having a jet of oil coming up from the bottom, as shown in Fig. 154, A repre- | ^EiEp-EZIr^ senting the outer tank containing water, B the bath of oil, C the pump used in drawing the heated oil from the bath through the pipe D ; it is then forced through the coil of pipe in the water and back into the bath through the inlet E. F is the catch pan. The jet of 263 The DeiTy CoUardi €•• Oil bath for spring tempering. oil is forced toward the top of the tank, as shown at G. The spring should be worked up and down in the bath until all trace of red has disappeared, when it may be lowered to the bottom of the tank and left until the temperature has been reduced to that of the contents of the tank, or until a convenient time comes for their removal. As previously explained, it is not advisable to re- move articles being quenched from the bath until they "The J)erry Collwd Co. Figure 1 54. Oil bath for spring tempering. are of a uniform temperature throughout. While this procedure might not make as much difference with a piece of work hardened in oil as one hardened in water, yet it is not a good plan to remove articles from the bath until they are reduced throughout to the temperature of the bath. In order that the contents of the bath may be kept a uniform temperature, the pump shown in accompany- ing cut may be connected with the tank, as represented, the oil to be taken from near the top and pumped 264 How to heat heavy springs. through the coils of pipe in the outer tank, which should be supplied with running water. When steel contains carbon of too low a percen- tage to harden properly in oil or any of the mixtures mentioned, the writer has used a bath of water at, or nearly at, the boiling point (212°) with very gratifying results. It may be found necessary with certain steels to reduce the temperature of the water somewhat. Various methods are employed when drawing the temper. The one more commonly used than any other is to heat the spring until the oil adhering to the sur- face catches fire and continues to burn, when the piece is removed from the fire, burning until all the oil has been consumed. If this method is used, it will be found necessary to provide some means whereby a uniform heat may be obtained, or one part of the spring will be found to be too soft by the time the balance is rightly tempered. If the spring is of heavy stock, it is necessary to bum the oil off three and sometimes more times, in order to bring it to the proper degree of elasticity. The process of drawing the temper by heating the spring until the oil catches fire from the heat contained in the steel is familiarly known as "flashing." Hardeners say that it is necessary to flash oil off this spring three times, or it is necessary to flash tallow off this spring twice, some using the oil the piece was quenched in, while others prefer some other kind of oil or tallow. Springs hardened in boiling water may be coated with oil or tallow and the temper drawn as described, if it be found necessary. It is not policy to use a fire having a forced draft or blast when drawing articles to a spring temper. An open fire burning wood or 265 The thermometer in spring tempering. charcoal gives excellent results. A gas flame having no air blast also works very satisfactorily. Springs of unequal sizes on the various portions re- quire a very skillful operator, in order to get uniform results, if the above method is used. The thinner portions, heating faster than the heavier parts, be- come too soft before the other parts are soft enough. Consequently, it is advisable to temper these by a dif- ferent method. The spring may be placed in a per- forated pail, which in turn is set into a kettle of oil or tallow. This kettle is placed where a sufficient amount of heat may be obtained to draw the temper to the proper degree. The amount of heat given is gauged by a ther- mometer, and varies according to the nature of the steel and the character of the spring. It ranges from 560° to 630°. The exact amount of heat necessary must be ascertained by experiment. This method furnishes a very reliable way of tempering all kinds of springs. The kettle should be so arranged that a cover may easily be placed on it in case the oil catches fire, as otherwise the operator, or the building, might be burned, or the work in the oil spoiled, or the thermometer cracked. The cover should be made high enough to take in the thermometer. The cover should be provided with a long handle, in order that the operator may not be burned when putting it on the kettle. If it is not considered necessary to provide the cover mentioned, a piece of heavy sacking should be kept conveniently near for use. If this is placed over the top of the kettle, it will generally extinguish the flames. The thermometer should not be taken from the hot 266 Heating watch springs. oil and placed where any current of air can strike it, or the glass will crack. It is advisable to leave it in the oil, letting it cool down with it. If the furnace where the oil is being heated is located where any cur- rent of air will strike the thermometer, it must be pro- tected in some manner, or it will crack. If it is considered advisable to remove the pail of work from the oil before the pieces are cool, it may be done, and the pieces dumped into a wooden box, cover- ing the opening, so that the air will not strike the pieces. The pail may now be filled with fresh pieces requiring tempering. The pail of work should be placed in the kettle of oil. The kettle should not be placed in the fire again until the pieces of work have absorbed considerable of the heat that was in the oil, when the kettle may be placed in the fire and the operation repeated. When work is hardened in large quantities, it is generally considered advisable to devise methods that allow of handling the work cheaply, at the same time keeping the quality up to the standard. Watch springs are sometimes heated in a crucible containing melted cyanide of potassium or salt and cyanide of potas- sium heated to the proper degree. The springs are immersed in the mixture until uniformly heated, then quenched. It is stated, however, that this mixture will not do when heating the hair springs, as it causes the nature of the steel to change slightly. These springs are heated for hardening in a crucible of melted glass. When a make of steel is found that gives satisfac- tory results when made into springs and tempered, it is folly to exchange it for another make, unless convinced 267 The "second blue." that the other is better. A saving of a few cents, or even dollars, on an order of steel is quite often very- costly economy, as many times springs do not give out until in actual use, and in that case they are often- times many miles from the factory where they were made. When large numbers of springs that must receive severe usage are made, it is advisable to give them a test — at least, test an occasional spring. Give them a test somewhat more severe than they will be liable to get in actual use. By so doing it is possible to detect an improper method of hardening or tempering before the whole batch is done. "Second Blue-" When all springs were made of tool steel and hardened, and the temper drawn one at a time, it was customary with some hardeners to draw the temper to what is known as the * 'second blue." After harden- ing, the springs were polished, then placed in a pan of sand and held over the fire until the temper colors commenced to show, the pan in the meantime being shaken to keep the sand and springs in motion and insure uniform heating. The tempers will show in order as set forth in the color table given under Drawing the Temper. After the] colors had all appeared, the surface of the steel assumes a grayish appearance. When heated a trifle above this, it as- sumes a blue color again, which is known as the "second blue." When this color appears, the spring should be dropped in a tank of hot oil, leaving it to cool off with the oil. a68 Colors for springs — how obtained. Another method sometimes used when drawing the temper of heavy springs made from high carbon steel consists in heating the article until sawdust dropped on it catches fire, or a fine shaving left from a hard- wood stick, such as a hammer handle, being drawn across a comer of it, catches fire at the proper temper- ing heat. Mechanics are sometimes surprised when they ob- serve a spring in some conspicuous place which is drawn to a straw color, a brown or a light blue. It does not seem possible to them that a spring drawn to the tem- per represented by the color visible should be able to stand up to the work. The temper color shown is simply for appearance. The articles are first hardened and tempered to give them the necessary elasticity. This is ordinarily done by heating in a kettle of oil, gauging the heat with a thermometer. After heating to the proper temperature and cooling, they are polished. Any desired color can be given by placing the articles in a pan of sand and shaking over a fire until the desired color shows, when they may be dumped in warm oil to prevent running. This second operation does not affect the hardness or elasticity, provided they were not heated as hot as when the temper was drawn. Many times it is impossible to harden and temper a spring in a manner that gives satisfactory results, be- cause the spring was bent to shape when cold. Now, it is possible to bend most steel somewhat when cold, and yet have it take a good spring temper ; but it is impossible to bend it beyond a certain amount, which varies with the steel. The writer has seen large safety valve coil springs 269 Caution about annealing sheet steel. rendered unfit for use by coiling when cold. If a piece of the same steel was heated red-hot and coiled, excellent results were obtained. Many times it is necessary to anneal steel one or more times between operations in order to obtain good results. It was found necessary to anneal the spring shown in Fig. 155 after punch- ing the blank and before bending at all. The first operation of bending brought the spring nearly to shape ; it was then an- nealed, and the finish- ing operation taken. If it was bent to shape without annealing the second time, it would break in the comers when in use, if not in the operations of bending. When annealing sheet steely whether it be for springs or cutting tools, the utmost caution should be exercised. If the steel is allowed to stay in a red-hot condition for too great a length of time, the stock is rendered unfit for hardening. If heated red-hot and laid aside to cool slowly^ much better results will follow than if it were packed in an annealing box with charcoal and kept red- hot for a considerable length of time. These long heats apparently have the effect of throwing the carbon out of its proper combination with the iron. It will harden, but can never be made elastic or strong. Tlw Derry C«ll»rd Co. Figure 155. A peculiar case. ayo Making Tools of Machine Steel. 6^?=^ ^?=^s£) CO While it is considered advisable in most shops to make articles whose bearing surfaces must be hard, in order to resist frictional wear, of some form of machine steel, and give the surfaces sufficient hardness by case hardening, it is generally considered necessary to make cutting, forming and similar tools of tool steel. It is practical, however, to make cutting tools for certain classes of work of machine steel, and harden the cutting edges sufficiently to produce very satisfactory results. Steel is, as previously explained, a combination of iron and carbon. The grade of iron used in making tool steel is, however, vastly superior and much more expensive than that used in the manufacture of the or- dinary machine steel. Being much purer, it is much stronger when carbonized and hardened, and conse- quently can do many times the amount of work of tools made of the lower grades of steel, even when these are charged with the satnc percentage of carbon. It is also less liable to crack when hardened, as the impurities contained in the lower grades make it, when combined with carbon, very brittle when hardened. But notwithstanding the facts just presented, it is 471 How phosphorus affects steel. possible to make tools for cutting paper, wood, lead, brass and soft steel of a low grade of steel, and harden it by a process that gives results much more satisfac- tory than would be thought possible by one who had never tried it. This method recommends itself on ac- count of the comparatively low cost of the steel, and it can be worked to shape more cheaply than if tool steel were used. But it is usual, when the experiment is tried, to use any piece of low grade steel laying around the shop that will machine to shape in a satisfactory manner, not realizing that it is necessary, in order to get satisfactory results, to use steel adapted to the pur- pose. As phosphorus, when present in steel, and es- pecially when in combination with carbon, causes it to be extremely brittle when hardened, a grade should be selected that has the least possible percentage of this harmful impurity. If it is not necessary to have the hardened surface very deep, a steel having a low percentage of carbon may be used. If, however, the tool is to be subjected to great strains, it is advisable to use a steel containing sufficient carbon to cause the tool to harden enough to furnish the necessary stiffness or internal hardness. The extra amount of hardness necessary to insure the cutting portions standing up when in use, must be fur- nished by the process of hardening. The writer has seen reamers, counterbores, punch press blanking, forming and drawing dies, and many other forms of tools made of low grade steel, which, the parties using them claimed, gave the best of results. As before stated, when making tools which are not to be subjected to a very great amount of strain, or which will not be called upon to resist a great amount ^^^ Steel for slender tools. of pressure, a steel low in carbon may be used. Any desired amount of surface hardness may be given the piece. If, however, the tool will be subjected to tor- sional strain, as in the case of a long, slender reamer, or if it may have to resist a crushing strain, as in the case of a punch press forming die, it is necessary to use stock containing sufficient carbon to furnish the desired result when hardened. If the tool is not to be subjected to very great strain, almost any low grade stock that is practically free from impurities will do. If a long, slender reamer, or similar tool, is to be made, excellent results are claimed by using a low grade steel of 40-point (.405^) carbon. In the case of a forming die, or similar tool, use a steel of 60 to 80-point carbon. If, however, it was to be subjected to great pressure or very severe usage, the writer's experience leads him to advocate the use of tool steel specially adapted to this class of work. As it is necessary, in order to get satisfactory re- sults, to have the percentage of impurities as low as can be obtained, in order to have the hardened steel as strong as possible, do not allow it to come in contact with any form of bone when heating. The articles should be packed in a hardening box with a mixture of equal quantities (volume) of charred leather and granulated charcoal in the same manner as described under Pack Hardening. It will be necessary to subject the articles to heat for a longer period of time than if hardening tool steel. The length of time the articles are sub- jected to the action of the carbonizing element depends on how deep it is necessary to have the hardened portion. The test wires previously mentioned should be used to determine when the contents of the box are heated. a73 When in doubt about steel. If you are reasonably sure the steel used was prac- tically free from injurious impurities and is low in car- bon, it may be dipped in a bath of water or brine. Should there be any doubt as to this, dip in raw lin- seed oil. If the article being hardened is a cutting tool, or something requiring a fine, compact grain, better re- sults will follow if it is left in the box after being sub- jected to the action of carbon, the box removed from the fire, and the whole allowed to cool. When cold, the article may be reheated to a low red, and hardened. While the writer has used a low grade steel in making various forms of tools, and had excellent re- sults when they were put to the use for which they were intended, he cannot recommend its use, unless the parties doing the work select stock suited to the pur- pose and exercise due care when hardening. While this subject might properly be classed under the heading of Case Hardening, it has not seemed wise to the writer to do so, because case hardening, according to the interpretation usually given it by mechanics, is simply a process of transforming the surface of the article into a condition that allows it to become hard if plunged red-hot into water. Hardness is apparently the only object sought, but such is not the case when the subject is considered in its proper light. When applying this principle to tools, it is neces- sary to consider the requirements of the tools. Know- ing this, it is necessary to proceed in a manner that will give the desired results. If it is considered advisable to make certain tools of a low grade steel, treating it as described, it is necessary to select steel adapted to the tool to be made. 274 special steels. It is never advisable to use Bessemer steel bought in the open market, because it does not run uniform. Always use open hearth steel, procuring it, if possible, of a quality that will give satisfactory results. Steel, with a very small percentage of phosphorus and other impurities, may be obtained from any reliable maker, if the purpose for which it is to be used is stated when ordering. Special Steels. To one interested in working steel, the history of the development of this industry furnishes a remarka- bly interesting study. Steel may be grouped under four general heads, the name given each class being selected on account of the method pursued in its manufacture. Probably the oldest of all known steels is the cemented or converted steel. This steel is made by taking iron in the form of wrought iron bars, packing them in a fire-brick receptacle, surrounding each bar with charcoal. This is hermetically sealed, and heat is then applied until the whole is brought to a degree of heat that insures the penetration of a sufficient quantity of carbon. Experience proves that carbon will penetrate iron at about the rate of one-eighth of an inch in twenty-four hours; and as bars of about three-quarter inch thickness are generally used, it re- quires three days for the carbon to penetrate to the »75 Crucible cast steel. center of the bar (^-inch). The furnace is then al- lowed to cool, and the iron bars, which are converted to steel, are removed. They are found to be covered with blisters, hence the name. Blister Steel. When examined, the bars are found to be highly- crystalline, brittle steel. When this form of steel is heated and rolled directly into commercial bars, it is known as German Steel. If blister steel is worked by binding a number of bars together, heating to a high heat, and welded under a hammer, it is known as Shear Steel, or Single- Shear. If single-shear steel is treated as above, the finished product is known commercially as Double- Shear Steel. Until within a comparatively few years these three classes of converted steel were practically the only kinds known in commerce. Crucible Cast Steel. As this is the standard steel used for fine tools, a brief study of the methods used in its manufacture may be of interest to the reader. Benjamin Huntsman, a clockmaker, is supposed to have been the inventor of this process. It occurred to him that he might pro- duce a more uniform and satisfactory article than was to be had at that time for use in manufacturing springs to run his clocks. The method he had in mind con- sisted in charging into a crucible broken blister steel, v^^hich was melted to give it a homogeneous character. While Huntsman thus founded the crucible steel industry, which has been of incalculable value to the mechanic arts, he met with many difficulties. These have been overcome by later inventions, notably those 276 Alloy steels. of Heath and Mushet, until to-day it is possible, with skill and care, to produce a quality of steel which, for strength and general utility, has never been equaled, despite the claims of some blacksmiths that the steel of to-day is not as good as that produced 25 to 50 years ago. Competition has rendered it necessary to run cut- ting tools, or stock, as the case may be, much faster than was formerly the case, which made it necessary to make steel containing a higher percentage of carbon than was formerly the case. As stated in a previous chapter, when high carbon steels are used, it is neces- sary to exercise great care in heating for the various processes of forging, annealing and hardening. As high carbon steels are more easily burned than those containing a lower percentage, it is necessary to put them in the hands of skilled workmen, for, unless the steel is to be worked by men understanding its nature, it proves to be a very unsatisfactory investment, and is often condemned because it will not stand as much abuse as a steel of lower carbon; but if properly treated, will do many times the amount of work. Alloy Steels. In order to accomplish certain results, steel is made containing other metals. To distinguish them from steels, which depend on the quantity of carbon present for their hardening properties, they may properly be termed "alloy" steels, the amount of the hardening property present determining the quality of the steel. As these steels can generally be run at a higher periphery speed and cut harder metals than carbon steels, they are very valuable at times, and in some 277 Self-hardening steel. shops are used altogether. As a rule, they are more easily injured by fire than carbon steel, and, conse- quently, extreme care must be exercised when working them. When high carbon steel is alloyed with other hard- ening properties, a steel is produced which will be found more efficient for machining chilled iron than the regular high carbon steels. However, as the nature of steel of this character depends entirely on the amount and kind of the alloy used and the amount of carbon present, no fixed rule can be given for the treatment. It is always best to follow as closely as possible direc- tions received with the steel. The writer has seen milling machine cutters, punch press blanking dies, and other tools, which were to cut very hard, "spotty" stock, give excellent results, when made from a reliable alloy steel, where carbon steels would not stand up. If the amount of certain hardening elements be increased to a given point, the steel hardens when heated red-hot, and is exposed to the air. It is styled **Air Hardening Steel," more generally known, how- ever, as Self-Hardening Steel. Self-hardening Steel. It was not originally the intention of the writer to mention self -hardening steel, because there are so many different makes of the article, each differing from the other to an extent that the method employed to get sat- isfactory results, when using one make, would prove entirely unsatisfactory when applied to another. Self-hardening steel has a field of its own, and is very useful when made into tools for certain work. It 278 A common error. is used very extensively in cutting hard metals, and can be run at a high periphery speed, because the heat generated does not soften the tool, as is the case when carbon steels are used. No general instructions can be given for working the steel, because the composition of the different makes varies so much that the treatment necessary, in order that one brand may work satisfactorily, would unfit another for doing the maximum amount of work pos- sible for it to do. A very common error in shops where a make of this steel is used, and another brand is to be tried, con- sists in attempting to treat the new brand in the same manner they have been treating the other, regardless of instructions furnished. As previously stated, the treatment suited to one brand would render another unfit for use, and as the reputation of a brand depends on the results attained, the makers are very careful when selling steel to state plainly the treatment it should receive. The buyer should see that the directions are followed implicitly. When purchasing self-hardening steel, it is advisa- ble to investigate the merits of the different makes. In practice, certain brands prove best for cutting cast iron, while another brand, which will not do as much work when cutting cast iron, proves to be more desira- ble when working steel. Other brands, which give sat- isfaction when made into lathe and planer tools, prove useless when made into tools having projecting cutting teeth, as milling machine cutters, etc. As previously stated, the different makes of self- hardening steel require different methods of treatment. One gives best results when worked (forged) at a full 279 A few don*ts. red heat, while another requires a much higher heat. As the steel is less plastic when red-hot than most carbon steels, it is necessary to use greater care in re- gard to the manner in which it is hammered. A heavy hammer should be used, if a large section is to be forged, as it is necessary to have it act uniformly on the entire mass, or the surface portion will be drawn away from the interior, and, as a consequence, a rupture will be produced. Small pieces should be forged with lighter blows, or the steel will be crushed. Do not attempt to forge when the temperature is lowered to a point where the steel loses its malleability, or it will be injured. It is very necessary that a uniform heat be main- tained throughout the piece. Do not think, when work- ing a small section, that it is safe to forge when it has cooled to a low red, because some heavier portion has not cooled below a full red. Do not allow the steel to cool off from the forging heat. After forging, place the piece in the fire again, and allow it to come to a uniform bright red. Do not allow it to **soak" in the fire, but it should be heated at this time without the aid of the blast. When it has reached a uniform red heat, remove from the fire, and allow it to cool in a dry place, not exposed to the action of any draft. While most self -hardening steels will become hard enough when cooled in the air, it is sometimes necessary to have the tool extra hard. In such cases, it may be cooled in a forced blast. Some steels give better re- sults if cooled in oil, others require cooling in hot oil, while others may be cooled in hot or cold water. Gen- erally speaking, however, it is not advisable to bring 280 Different steels need different treatment. most brands of this steel in contact with water when red-hot. While it is generally admitted that self-hardening steels are principally valuable for lathe, planer, and similar tools, when cutting hard metals or running at high speeds, there are makes which give excellent sat- isfaction when annealed and made into such tools as milling machine and similar cutters. When it is necessary to have the stock in an an- nealed condition, it is advisable to procure it in this state, as the manufacturer, understanding the composi- tion and nature of the steel, is in a position to anneal it in a more satisfactory manner than the novice. How- ever, if it is considered advisable to anneal it in the factory where it is to be worked, it may be accom- plished. Different makes of steel require treatments differing from each other, the treatment depending on the element used to give it its hardening qualities. Some brands may be annealed sufHciently to work in the various machines used in working steel to shape by heating to a bright red and burying in green pine sawdust, allowing it to remain in the sawdust until cool. Most brands may be annealed by keeping the steel in an annealing furnace at a bright red heat for from twenty- four to forty hours, then covering with hot sand or ashes in the furnace, and allowing to cool. It should be about the same length of time cooling as it was ex- posed to the heat. It is necessary many times to machine it with tools made of the same quality of steel, on account of the natural hardness and density of the stock. It is claimed that tools made of certain brands of self-hardening steel give better results when cutting chilled iron than tools made of high carbon alloy steels. 28X Get reliable steel. The writer cannot substantiate this claim, as he has never been able to get as good results as when using an extra high carbon alloy steel, properly treated. However, it is safe to say that used for machining (roughing) work in the lathe, planer, and similar machines, can be made to do many times the amount of work in a given time than would be the case were ordinary carbon steel tools used. Much better results may be attained, however, than is usually the case, if makers* instructions are implicitly followed. On account of the rapidly growing popularity of certain makes of this class of steel, many swindles have been perpetrated by unscrupulous parties, claim- ing to be representatives of a reliable house. A tool made, as they claim, from the steel they were selling is submitted for trial. It proves to be all that could be asked for, and a quantity of steel is ordered sent C. O. D. When this is received and paid for, it is found to be of no use. Parties purchasing steel of any but known and reliable steel concerns do so at a great risk, as a number of manufacturers have found to their sorrow. Steel for Various Tools. There is no one topic connected with this work that caused the writer so much anxiety as the one under consideration, because a temper of steel that gives en- tire satisfaction when used in one shop, would not answer when made into tools intended for the same, or 282 Phosphorus in steels. similar purposes, in a shop situated on the opposite side of the street. This is simply because in one case the operator who forged or hardened the tools under- stood handling the steel, and in the other case a man totally incompetent was entrusted to do the work. Then again, steels of certain makes are more free from harmful impurities than others. A steel contain- ing a low percentage of these impurities can safely have a higher percentage of carbon. Certain steels which are low in their percentage of phosphorus can have a greater amount of carbon than other steels which con- tain more of this harmful impurity. A tool made of 1.4 per cent, carbon steel low in phosphorus will not cause as much trouble as if made of a 1.25 per cent, carbon steel containing a greater amount of phosphorus, but its capacity for cutting hard metals, and holding its edge when running at high speeds, is much greater. Knowing the tendency in many shops to use a high carbon steel, and realizing the advantages of so doing, the writer would advocate the use of such steels, were it not for the fact in many cases the results have been anything but satisfactory, because men totally unfit for such work were employed to forge and harden the tools made from them. But it has seemed wise to give the tempers of tool steel suited for certain purposes, the reader bearing in mind that in many cases it is safe and advisable to use a higher carbon, provided due care is exercised when working it during the various operations of forging, annealing and hardening. As previously stated, steel of a certain make and temper giving excellent results in one shop does not always give satisfactory results in Z83 The degrees of hardness. some other shop on the same class of work. Knowing from experience that the variable factor is the man working the steel, rather than the steel itself, the writer has deemed it wise to quote the experience of various steel makers, rather than results of his own personal experience. Degree of Hardness Percent- age of Carbon Should be used for Very hard 1-5 Turning and planing tools for hard metals, small drills, gravers. Hard 1.25 Tools for ordinary turning and planing, rock drills, mill picks, scrapers, etc. Medium hard 1. Taps, screw thread dies, broaches, and various tools for blacksmiths' use. Tenaciously hard •85 Cold sets, hand chisels, ream- ers, dies, drills. Tough •75 Battering tools, cold-sets, shear blades, drifts, hammers, etc. Soft •6s Battering tools, tools of dull edge, weld steel for steeling finer tools, etc. While the foregoing table gives the tempers of steel that can safely be used for the purposes specified, it is many times advisable to use steel of a higher per- centage of carbon. Then again, it is sometimes best to use a low carbon steel of good quality, in order to get the maximum amount of toughness in the interior portions, packing the finished tool in a box containing charred leather, as 284 How to make steel extremely hard. explained under Pack Hardening, and running for a sufficient length of time to get an extremely hard sur- face when hardened. By adopting this method, it is possible to get a cutting surface that will stand up when running at a high rate of speed, and yet be strong enough to resist extremely rough usage. When it is desirable to get the steel extremely hard and very deep, in order to allow for grinding, and yet have the tool sufficiently tough to stand up, use a high carbon steel, pack in a box as described, running in the iire at an extremely low heat ; quench in a bath of raw linseed oil. In order to provide a guide for use in selecting steel suitable for various purposes, the following list is given. It is the result of the writer's experience, and information picked up here and there. A very notice- able fact, however, must be taken into consideration, namely: mechanics in the same class do not advocate the use of steel of like tempers, even when making tools of the same kind, to do the same class of work under the same, or similar circumstances, so no rule can be given arbitrarily. The reader should, however, bear in mind that steels, which contain impurities to any considerable de- gree, cannot safely be used with the percentage of carbon mentioned. But as most of the leading steels on the market have received their standing because they are practically free from these impurities, it is safe when using them to use the percentages of carbon mentioned. There are several makes of crucible tool steel on the market, which are exceptionally low in their percentage of impurities, and when using these, it is 285 About cast steel. safe to use a higher carbon than the one mentioned, provided due care is used when heating for the various operations of forging, annealing and hardening. In the following pages the term crucible steel is intended to denote crucible tool cast steel. The term cast steel is often misunderstood by me- chanics, and many are of the opinion that any cast steel is tool steel. Such, however, is not the case, for the products of the Bessemer and open hearth processes are cast steel in the same sense that crucible steel is, yet they are not understood as tool steels, although products of both processes which were highly carbon- ized have been sold to parties as tool steel. Arbors for saws. Saw arbors, and similar articles, when made from crucible steel are made from a stock containing .60 to .70 per cent, carbon. When made from open hearth steel the percentage of carbon is about the same, although some manufacturers claim good results when a lower percentage is used. Arbors for milling machines. Milling machine arbors when made from crucible steel give good satisfaction if a steel of .70 to .80 per cent, carbon is used. Unless they are to be hardened, better results are obtained if the steel is worked to shape without annealing, as it is much less liable to spring when subjected to strain in use. In shops where great numbers of these arbors are used crucible steel is considered very costly. In such cases open hearth steel containing .40 to .60 per cent, carbon is often used. Many times a stock containing a higher per- centage is used. Augers. Augers for wood-work are made from crucible steel of .70 to .80 per cent, carbon. Axes are made from crucible steel containing i.oo to 1.20 per cent, carbon. Barrels for Guns are made from crucible steel containing .60 to .70 per cent, carbon, while some manufacturers use an open hearth steel containing .50 per cent, carbon, and others claim to use the same steel with . 60 or even . 70 per cent. Centers for Lathes are made of crucible steel containing .90 to i.io per cent, carbon. Chisels for Working Wood are made from crucible steel containing 1.15 to 1.25 per cent, carbon. Chisels for Cutting Steel, where the work is light, give good satisfaction when made from crucible steel containing 1.25 per cent, carbon. Cold Chisels, for chipping iron and steel, work well if made from crucible steel containing .90 to i.io per cent, carbon. Trouble with cold chisels is more often the result of poor workmanship than an unsatisfactory steel. Chisels for Hot Work may be made of crucible steel of .60 to .70 per cent, carbon. a87 Chisels for Cold Work, for blacksmiths' use, are made of crucible steel con- taining .70 to .80 per cent, carbon. Chisels for Cutting Stone are made from .85 per cent, carbon crucible steel. Cutters for Milling Machine Work are probably made from a greater range of tempers than almost any other tool used in machine shop work, some manufacturers never using a steel containing over 1. 00 per cent, of carbon, on account of the liability of cracking. Cracking is, however, a result of careless working, and as much more work can be done in a given time with a cutter made from a high carbon steel, it is, generally speaking, advisable to use such steels. Cutters, 2 inches and smaller, may safely be made from crucible steel containing 1.25 to 1.40 per cent, carbon. Cutters, 2 to 3 inches, 1.15 to 1.25. Larger than 3 inches, or if of irregular contour, 1. 10 to i. 20 per cent, carbon. There are several alloy steels on the market which give excellent results when made into cutters of this character, provided extreme care is taken in heating. Cutters for Pipe Cutting may be made from crucible steel containing 1.20 to 1.25 per cent, carbon. Cutters for Glass are made from crucible steel containing 1.25 to 1.40 per cent, carbon. 288 Dies (Threading) for Bolts and similar work, made from stock having rough, un- even surfaces, may be made from crucible steel con- taining . 70 to . 80 per cent, carbon. However, when the dies are hardened by the process described under Pack Hardening, steel containing i.ooto i.io percent, works nicely, stands well, and holds a good edge. Dies for Screw Cutting, to be used by hand or in screw machine, may be made from crucible steel containing i.oo to 1.25 per cent, carbon. Dies for Blanking or Punch Press work are made from crucible steel containing .90 to I.IO per cent, carbon. When the articles to be punched are small, and the stock to be worked is hard, steel con- taining 1.00 to 1.25 stands better than the lower carbon steel for small dies. Some manufacturers use a steel containing 1.25 to 1.40 per cent, carbon, provided it is low in percentage of impurities. When the work is not of a shape that requires great strength on the part of the die, open hearth steel containing .40 to .80 per cent, carbon is used. The die in this case should be hardened according to directions given for hardening tools made from machine steel. Dies Used for Swaging metals are made from crucible steel, the percentage of carbon varying according to the character of the work to be done. When the die is not to be subjected to very severe usage, a steel containing .90 to i.io per cent, of carbon may be used. Where a deeply hard- ened portion is desirable, a steel containing 1.20 to 1.25 per cent, works nicely. 289 Drawinrr Dies o are made of crucible steel containing 1.20 to 1.25 per cent, carbon. Dies for Drop Forging. As the product of different steel manufacturers varies so much, and the requirements are so varied for work of different kinds, it is advisable to submit the article to be made to some reliable steel manufacturer, letting him furnish a steel especially adapted to the work to be done. Ordinarily a crucible steel is used containing .40 to .80 per cent, carbon. However, many manufacturers consider it best to use a good quality of open hearth steel containing the proper percentage of carbon. Small dies, or those having slender portions requiring great strength, are made of the higher carbon. Drills— (Rock Drills), for quarry work, are made of crucible steel containing 1. 10 to 1.25 per cent, carbon. Drills— (Twist). Sma// drills are made of crucible steel of 1.25 to 1. 50 per cent, carbon, while larger drills require a steel of 1. 00 to 1.25. Files are made of crucible steel of 1.20 to 1.40 per cent, car- bon. Files of inferior quality are made of open hearth steel. Hammers for Blacksmiths use are made from crucible steel of .65 to .75 per cent, carbon. S90 Hammers for Machinists' use are made from crucible steel of .85 to 1.15 per cent, carbon. For the ordinary sizes steel containing 1. 00 per cent, works nicely. Hardies for Blacksmiths are made of crucible steel of .65 to . 75 per cent, carbon. Hobs for Dies are made of crucible steel of .90 to i.oo per cent, carbon, when they are to be used for cutting a full thread in a die. If they are to be used for sizing only, a steel containing 1.20 to 1.25 may be used, as it will hold its size and form longer than if made of steel containing less carbon. Jaws for Bench Vises are made from crucible steel of .80 to .90 per cent, carbon. Open hearth steel is, however, extensively used for this purpose. Jaws for Chucks are strongest if made of crucible steel containing .85 to 1.00 per cent, carbon, although many times they are made from a good quality open hearth steel. Jaws for Cutting Pliers are made from crucible steel containing i.io to 1.25 per cent, carbon. When they are to be used for cutting piano or other hard wire, they are made from steel containing 1.40 to 1.50 per cent, carbon. 291 Jaws for Gripping work in various fixtures are made from crucible steel of . 80 to . 90 per cent, carbon. Jaws for Pipe Machines are made from crucible steel containing i.oo to 1.20 per cent, carbon. Jaws for Screw Threading Dies, having inserted jaws or blades, are made of crucible steel of 1.00 to 1.20 per cent, carbon. Jaws for Wire Pullers are made from i.oo to 1.20 per cent, carbon crucible steel. Knife Blades. When crucible steel is used, a stock containing .9 to I.oo per cent, carbon is selected. Knife Blades, to be used for whittling and general wood- working, are made from i.io to 1.25 per cent, carbon crucible steel. Knives — Draw Knives are made from crucible steel of 1.20 to 1.25 per cent, carbon. Many times, however, they are made of open hearth steel. Lathe Tools for ordinary work are made of crucible steel containing 1.25 per cent, carbon. For turning hard metals or running at high rate of speed, use steel containing 1.40 to 1.60 per cent, carbon. Lathe Tools. For turning chilled iron, a high carbon alloy steel works better than a straight carbon steel. When it is desirable to run at very high speeds, use a self -hardening steel. Machinery Crucible Steel contains .55 to .65 per cent, carbon. Mandrels. Custom differs in various shops. Some mechanics consider it best practice to make mandrels up to and including i inch of crucible steel, and for sizes above i inch advocate the use of machine steel, case hardened. Others claim best results from crucible tool steel for all sizes. Mandrels, however, do not require a steel containing as high a percentage of carbon as cutting tools. Small mandrels give good satisfaction when made from steel of from i.oo to i.io carbon, larger sizes made of steel containing .80 to i.oo per cent. When mandrels are hardened by the process known as Pack Hardening, a steel containing .75 to .90 per cent, will give excellent results. Mowers. Lawn mower knives, .90 to i.oo per cent, crucible steel, although in many instances they are made from open hearth steel. Planer Tools for Stone, •75 to .90 per cent, carbon crucible steel. Planer Tools for Wood-working machinery are made of crucible steel containing from I.IO to 1.25 per cent, carbon. 293 Planer Tools. If the tools are large and the metal to be machined is comparatively soft, crucible steel containing 1.25 works nicely. If, however, high speeds are desired or the metal to be cut is hard, a steel containing 1.40 to 1.50 per cent, carbon gives better results, provided care is exercised in heating for forging and hardening. If the stock to be cut is extra hard or it is desirable to run at speeds higher than is practical when using tools made from carbon steels, it is advisable to get a reliable self -hardening steel. Punches for Hot Trimming, . 85 to 1 . 00 per cent, carbon crucible steel. Some mechan- ics claim as good results if the punch is made of open hearth steel of . 60 to . 80 per cent, carbon, while others make both punch and die of open hearth steel. These tools may be hardened in the ordinary manner or they may be hardened according to directions for hardening tools made of machine steel. Punches for Blanking Work in punch press. The percentage of carbon desirable depends on the stock to be cut and the skill of the operators doing the hardening If crucible steel is used, a range of .90 to 1.25 per cent, carbon is allowable, de- pending on the character of the work. Many times, however, such punches, if of a shape and size that in- sures strength, are made of . 40 to . 80 per cent, carbon open hearth steel, and hardened as explained under Making Tools of Machine Steel. Punches for Blacksmiths should be . 80 to . 90 per cent, carbon crucible steel. 294 Punches for Railroad Track Work, about .85 per cent, carbon crucible cast steel is advis- able. Reamers. Small reamers, which are to be used continuously, should be made from crucible steel of 1.25 to 1.50 per cent, carbon. When they are to resist great strain, steel of 1. 00 to 1.25 per cent, may be used. Excellent results will follow if steel containing .90 to i.io per cent, carbon is used, and the reamer hardened by the method described under Pack Hardening. This is es- pecially true if the reamer is long or slender, or of a shape that betokens trouble when it is hardened. Saws (Circular) for Wood, about .80 to .90 per cent, crucible steel. Saws for Cutting Steel are made from 1.25 to 1.50 per cent, crucible steel. Scrapers for Scraping Surfaces, 1,50 carbon crucible steel. Although many scraper hands claim best results from using a high carbon alloy steel. Screw-Drivers, small, .90 to 1. 00 per cent, crucible steel; large, .65 to .80 per cent. Stamps for Stamping Steel, 1.25 to 1.50 per cent, carbon crucible steel. Shafts for High Speed Machinery are many times made from crucible steel, containing .65 per cent, carbon. Spindle Steel, same as shafts. 295 Springs for Ordinary Purposes are made from i.oo to i.io per cent, carbon crucible steel. For many purposes, an open hearth steel is used with satisfactory results. Springs for Locomotives are made by some manufacturers of crucible steel con- taining .90 to 1. 10 per cent, carbon, and by others of a steel containing .80 to .90 per cent., while in many cases very satisfactory results follow if open hearth steel, made especially for the purpose, is used. Springs for Carriages are made from crucible steel containing .80 to .90 per cent, carbon, but many more springs of this character are made from open hearth and Bessemer stock than from crucible, because it answers the purpose and is much cheaper. Taps are made of crucible steel containing i.io to 1.25 per cent, carbon in many shops, while others claim better results from steel containing 1.25 to 1.40 per cent. Taps for Tapping Nuts, generally called machine taps, give best results if made from steel containing i.oo to i.io per cent, carbon. 196 Causes of Trouble, CO While most of the causes of trouble when steel is hardened have been considered under the various topics presented, it has seemed wise to group together the more common causes, in order that they may be referred to more readily by the reader. Uneven Heats. Probably the most common cause of trouble is un- even heating of the piece in forging, annealing or hardening. As a consequence, violent strains are set up which cause the piece to crack or, in the case of heavy pieces, to burst. The different parts of the piece being unevenly heated, must, when cooled, contract unevenly; and when two portions of a piece adjoining each other attempt to contract unevenly — that is, one contracting more or faster than the other — and both being rigid to an extent that makes it impossible for them to yield one to the other, there must be a separa- tion at the point where the uneven temperature occurs. High Heats. A very common. cause of trouble consists in heat- ing steel too hot for the purpose. High heats open the pores of the steel, making the grain coarse and causing the steel to be weak. When the piece is broken, it has 497 Too rapid heating. a honeycomb appearance — looks full of holes, so to speak. Now, as there is but a very thin layer of steel over these holes, when pressure is applied the surface over the holes caves in, and the steel is unfitted for doing the maximum amount of work. Steel which has been overheated may be restored — unless the heat was high enough to burn or disinte- grate the steel — by reheating carefully to the refining heat and quenching ; but it can never do the amount of work possible, had it not been overheated. Yet, it will be much better than if left in the condition the high heat placed it. Then again, high heats have a tendency to cause the steel to crack when hardened. This is especially true if the piece be cylindrical in shape. Cylindrically shaped pieces will not stand the amount of heat that may safely be given a piece of almost any other shape without cracking, although the effect on the grain and the ability of the steel to stand up and do the maximum amount of work possible would be the same in any case, regardless of the form of th e piece or the method of applying the heat. Too Rapid Heating. While it is advisable to heat steel as rapidly as possible consistent with good results, it should not be heated too rapidly, as corners and edges will become overheated before the balance of the article has reached the proper heat ; and even if they are allowed to cool down to the proper heat (apparently), the grain has been opened at these portions, and violent strains are set up. This is one of the places where experience seems to be the only guide and where the instructor 298 Fire cracks — how to avoid. can only give suggestions, wliicli should be heeded and worked out by each hardener. Heating Too Slowly. In attempting to avoid heating too rapidly, do not go to the opposite extreme and allow the steel to **soak" in the fire, or soft surfaces will result, and the steel is not as good as if heated properly. Fire Cracks. There are a number of causes for steel cracking in the fire. Among the more common are, first, the cold air from the blast, if the work is heated in a black- smith's forge. Then again, it may be heated in a gas flame having an air blast. The air may be turned on too much, resulting in cold air jets striking the heated steel. If a charcoal fire is used, it is the custom of some hardeners to throw cold water on the fire. Now, if the steel is red-hot, the water has a tendency to cause it to crack in the same manner as if the air from the blast came in contact with it. Large articles plunged in a crucible of red-hot lead, cyanide of potassium, or any substance where they are exposed to violent heats, are very liable to crack, especially if there are heavy and light portions adjoining each other. The unequal expansion tears the steel apart at the point where the unequally heated portions adjoin each other. This may be avoided by heating the articles nearly to a red in some form of fire where it would heat more slowly, then plunge in the lead to bring to the desired heat ; or, the article may be im- mersed in the red-hot contents of the crucible, left for a moment and withdrawn, immersed again, leaving a 299 Improper forging. trifle longer, and so continue until it reaches the desired heat. If a piece of steel is immersed in a crucible of red- hot lead or similar material for a certain distance so that part of the piece is out of the red-hot material, it should be moved up and down in the molten mass, or the part below the surface will expand more rapidly than the adjoining metal. If the article were im- mersed and withdrawn, repeating this operation until the desired result is obtained, the heat being applied gradually, the expansion is more uniform, and the heat is imparted to the adjoining stock so it can yield to an extent that does away with any tendency to crack. Cold Baths. Extremely cold baths are the cause of a great deal of trouble when pieces of irregular contour are harden- ed. It is nearly always advisable, when hardening articles made of high carbon steel, to warm the con- tents of the bath somewhat. Many hardeners claim that oil heated to a temperature of loo degrees to 120 degrees will harden steel harder than if it were ex- tremely cold. It will certainly cause it to be tougher. Improper Forging. This is the cause of a great amount of trouble when steel is hardened. While the writer claims best results from steel properly forged, he is aware that much better results are obtained from steel machined to shape than if the articles were heated or hammered in any but a proper manner. Steel to be made into tools whose cutting edges are on or near the end should not be nicked with. a chisel 300 A few more don*ts. and broken, as the portions at the end are rendered unfit for cutting purposes. Do not straighten steel that is to be hardened without heating it red-hot. Do not attempt to harden a tool of irregular shape unless it has been annealed after blocking out to some- where near to shape. Do not take it for granted that because you have held a piece of steel in the fire and stuck it into water, it is necessarily hard. Try it with a sharp file before brightening the surface preparatory to drawing the temper, as much valuable time may be saved if the piece should prove not to have hardened. When you get a piece of steel that you are in doubt about, it is advisable to cut a small piece of it from the bar and harden it, noticing the amount of heat neces- sary to produce desired results. If this is not done, trouble may follow when the article is hardened. It is better to experiment with a small piece of steel than with a costly tool. Do not use any but chemically pure lead in a crucible intended for heating tools, or you will not get as good results as you might otherwise have. Do not think that because the surface of red-hot lead appears to be at about the proper heat, that the contents nearer the bottom of the crucible are neces- sarily of the same temperature; because, generally speaking, the deeper you place a piece of steel in the contents of the crucible the hotter it becomes. Being ignorant of this fact, workmen spoil many valuable articles, and then think the lead has an injurious effect on the steel, not knowing that it is the amount of heat given rather than the method used in applying it that 301 Things to remember. caused the trouble. Impure lead will injure the sur- face of the steel, but will not alter the appearance of the grain if the temperature is right. Remember that steel heated for annealing should not be subjected to heat for a longer period of time than is necessary to produce a 7iniform heat of the de- sired temperature. Steel overannealed does not work as well in the various operations of machining, neither will it harden and temper as satisfactorily as though properly treated. Remember that heating is a process of softening steel, and cooling is a hardening process. The slower the process of cooling is carried on the softer the steel will be; consequently, it is never advisable to place red-hot steel that needs softening in cold or damp lime or ashes. Always use a clean fire. Dirty slack fires are a source of a great amount of trouble, as they cause the surface of the steel to be covered with a sulphurous oxide. A fire of new coals should be used (when using a charcoal fire) for heating steel. Dead coals require more blast than is good for the steel. Ten pieces of steel are cracked as a result of uneven heating to every one that is the result of a defect in the steel. Do not think that because the surface of a hardened piece of steel is not scaled that it is not overheated. Every degree of heat given it above that necessary to produce the desired result unfits the steel for doing the maximum amount of work possible for it to do. Always harden on an ascending heat. Never heat a little too hot and allow to cool down to the /r^ ^^ >-k<» •330 ^OtD 1 3 P >- I cj«*P a3 >^u» a 3 cj am (s p o • g f- 3 TJ CO »*• • • H»fO 3 as lOQ >- ^ H'3 r- (OIJQ ^ <-• t-^fO C f-0 1 «• -• DT^ 3 V* POQ •0 O I* r- 'D M^- p 1 • O ^4 1 W{- ® *< • OQ M. p 3 3- o t (DPP X 3 'I "0 a (0 U) fv ;o U) 3 r-tO O . ?P r- 3 5C 3**« 0^ P I