CHAPTER XXX 
the making and sharpening of tools. Carbon steels—Alloy steels—Forging—Hardening—Tempering—Temper ing in metal bath—Grinding—Sharpening. 

Although you may buy ready made, or have made to your order, tools of any shape, yet some experience in the making of the simpler kinds is very desirable. A repousse tool of some special shape is required, a small chisel, a mandrel for winding wire upon. Days or weeks might pass before the right tool could be obtained. Yet it could be made in a few minutes, in half an hour. Let us try. But first a word or two about the material of which it is to be made. Knives, chisels, files, drills, cutting tools generally, and many other types of tool are made from steel. This material is iron, made stronger and tougher by the addition of small per centages of carbon, tungsten, nickel, chromium, vanadium, etc. The actual proportions used to produce what is known as tool steel are often trade secrets. But tool steels may be roughly divided into two great groups : " Carbon steels," and what are known as " alloy or high speed steels." The former contain from 1^ to f per cent, of carbon. They were in general use up to 1894, and are still very widely used for general purposes. Carbon steels, however, begin to lose their hardness at a temperature of 260° C, so, though quite suited for all the ordinary tools used by metalworkers, they cannot be used for high speed work on lathes and milling machines. There is no convenient way known in which they may be kept cool enough to retain their temper. Alloy or high speed steels are those in which the iron is mixed with a small percentage of tungsten, or one or more of the other metals mentioned above. These steels will keep their hardness even when red hot, for they may become heated up to about 650°O, a dull red heat, without their cutting capacity being seriously impaired. However, carbon steels are those which one is most likely to meet with. They are made in different brands for various kinds of tools. Those containing much carbon Avill stand less J heating than those with less. But none should be heated more often than absolutely necessary, for with repeated heatings the carbon is burnt out and the quality of the steel impaired. 

Tools made from steel are hardened and tempered as described below. Tools made from iron cannot be hardened to the same degree, though there is a process, known as case-hardening, by which the surface of an iron tool can be turned into steel, so that it may be afterwards hardened. But this process takes a good deal of time, and is unsuited for the work we are discussing. Brass also is too soft for cutting tools. It is sometimes used for repousse tools, but those made from this material should be avoided. They are liable to get bent or otherwise damaged. Let us there fore take tool steel for the work we have in hand—a small chisel, shall we say. Tool steel may be bought in rods, round, square, hexagonal or octagonal, of almost any size. Take a -fe inch octagonal rod and cut off 3\ inches. To file it to shape would take too long and would wear out the file unnecessarily. To hammer it to shape when cold would be almost impossible, for it is so hard that it would probably crack in the process. It must be forged when hot. Any good fire will supply sufficient heat, but the work can be done in a furnace or with a blowpipe. Take a pair of strong pliers or tongs with which to hold the tool you are making, and put the end of the piece of steel rod in a clear part of the fire. Now tool steel can be forged when red hot, but it should not be brought to a pale yellow or white heat, such as the brightest part of a good fire, more than a few times. Nor must hammering proceed when it has cooled down to a dull red heat. In the former case it will become technically " burnt," and in the latter it is liable to be cracked. When the steel is at the right temperature hold it with the tongs and hammer it to shape on an anvil or some heavy stake, using any suitable hammer. If it gets cool before you have finished, heat it again. It may be finished with a file where necessary. Then reheat it to a cherry red and allow it to cool down quite slowly before hardening and tempering. 

To harden a steel tool. Prepare a vessel or bath of water in which to cool the tool. It should be large enough for this to be done without any appreciable heating of the water. Add some salt to the latter. Salt water or brine gives greater hardness than pure water. The temperature of the bath should not be below 60° F. (16° O). Heat the tool to a bright red colour. Stir the water so that it is going fast round and round in the pail or whatever vessel you are using. Then plunge the tool straight down into the swirl, holding it in the tongs and moving it about until cold,—the object being to get the tool cooled as quickly and evenly as possible. Moving water does this quicker than still water. Tools are sometimes quenched in oil, mercury or other liquids : small ones by sticking the point into a tallow candle. The use of oil or tallow for this purpose makes for toughness in the tool rather than for great hardness. Tools made from alloy steel are usually hardened in oil, though for some brands a blast of cold air is used instead. To return to our work. The tool is now hardened, but it is extremely brittle. If used in its present condition its edge would break almost at once. Before it can be safety used it must be tempered. 

To temper. First clean up one side of the tool by grinding it on a stone or on emery paper. It is too hard to use a file upon,—you would only spoil the file. The tool should be made quite bright and clean. Next apply heat to one end or the middle of the tool, but not to the point. This may be done with a blowpipe, or by laying the shank of the tool on a piece of red-hot iron, but 
in no case must the point be heated directly. It will get gradually heated as the warmth creeps up the tool. As the tool becomes hot the colour of the polished side changes. Bands of different colours appear close to where the heat is applied and creep down the tool towards the point. First pale yellow, then straw colour, then brown and finally blue like that on a clock spring. These colours indicate different degrees of hardness. Steel, tempered pale yellow, is very hard but very brittle. It is useful for razors and fine cutting tools, but it is too brittle to stand any hammer ing. Chisels are tempered to a brownish yellow or dark straw colour at the point, the shank of the tool being not quite so hard. For, the tempering being done as above described, the shank of the tool gets hotter, and softer, in the process than the point does. Saws are tempered blue, as they must be flexible and not brittle. When the colour at the point of the chisel indicates that the temper has been " let down " sufficiently, any further softening is stopped by putting the tool in cold water again. The chisel has now been hardened and tempered. It must yet be ground and sharpened for use. 

To temper a small drill. With the pliers hold a piece of sheet copper, measuring about 3 inches by 1, over a Bunsen burner or small gas jet. With another pair of pliers hold the drill by the shank over the copper. Let part of the shank of the drill touch the edge of the copper. The copper will protect the drill from direct contact with the flame, yet sufficient heat to temper it properly will reach the drill through its place of contact with the copper. Proceed as described above. 

To temper a spring. Cover the spring with two layers of iron binding vdre, about 26 Standard Wire Gauge, coiled quite closely. Dip it into sweet oil, olive oil, linseed oil—which ever you have by you. Hold it over a flame until it catches alight. Let it burn itself out. At once uncoil the wire, and the spring will be found to be properly tempered. It is not necessary in this case to dip the work in water to stay the tempering. If twoor three strands of the wire are coiled on the spring at once the work is done quicker. 


The colours to which steel tools are tempered for various purposes are given below with temperatures— 
Cent. Fahr. 
Light straw colour Dark straw  221° 243  430° 470  Razors. For wood, ivory and vulcanite  
tools.  
Brown yellow.  260  500  For gravers and tools for metal-cutting.  
Bright blue  .  288  550  For springs and saws.  

A method by which the temperature—and hardness— of the steel may be accurately regulated is that by which the tempering is done in a bath of molten metal. Different alloys of lead and tin can be made, the melting points of which correspond with the various degrees of temper required in the steel. 

Composition of Bath. Melting-point. Colour ol Steel at Temperature given. 
Lead.  Tin.  Cent.  Fahr.  
14  8  215°  420°  Very faint yellow.  
15  8  221  430  Faint yellow.  
16  8  227  440  Light straw.  
17  8  232  450  Straw.  
18-5  8  238  460  Full straw.  
20  8  243  470  Dark straw.  
24  8  249  480  Old gold.  
28  8  254  490  Brown.  
38-8  8  266  510  Brown with purple spots.  
60'8  8  277  530  Purple.  
96  8  288  550  Deep purple.  
200  8  293  560  Blue.  
Boiling linseed oil. Melted lead.  316 322  600 610  Dark blue. Grey blue.  
Melted lead.  332  630  Greenish-blue.  

To grind a chisel. The angle between the two faces at the cutting edge of a chisel varies with the material which is to be cut. The harder the material, the greater the angle between the two faces. Thus for paring soft wood an angle of 15° or less may be used, but it would not be safe to use the mallet with so slight an edge. Much depends upon the thickness of the tool a little way behind the edge. The edge of a good hollow-ground razor in working order has an angle of about 16°, for in setting a razor the thickness of the back regulates the angle at which the edge is ground. An angle of about 25° is safe to use with a mallet in hard wood, if the tool is tempered rightly. For metal the angle at which the chisel point is ground must be blunter still. For work on thick metal the thickness of the point a little way from the edge is perhaps as important as the actual angle of the cutting edge. For the blows given are fairly heavy, and they drive a narrow chisel deep, whatever the form of its edge may be. 

Grinding is done on a grindstone or an emery or cor undum wheel. So great is the amount of heat produced in this process, that unless the stone is kept wet, in the course of a few seconds the tool will get so hot that its temper will be spoilt. In that case it must be hardened and tempered afresh. Tools may be ground with the grindstone running either towards or from you. The stone " running towards you " means that when you are in the position for grinding a tool, that part of the grindstone between the top of the stone and your hands is travelling towards your hands. It is a little more difficult to hold a tool when the stone is running towards you, but the work is done quicker. Each of the two sides of the chisel which meet at the cutting edge, should be ground quite flat, or even slightly concave (follow ing the curve of the grindstone), but never convex. The tool is held in the right hand, and its further end is pressed against the stone by the first two or three fingers of the left hand. The angle at which the tool meets the stone can be adjusted by raising or lowering the hands. It is usual to move the tool from side to side of the grindstone as the work proceeds. This is done to avoid wearing grooves in the stone. It sometimes happens, in grinding with the stone running from you, that an edge of metal, as thin as a sheet of paper and quite flexible,is left at the extreme edge of the tool. This is known as the " wire edge " or " arris." It will generally break off in the course of sharpening and leave the tool quite keen. When the grinding has proceeded far enough the chisel may be sharpened on an oilstone. 

Sharpening is but a continuation of the process of grinding. It is done on smoother stones,—slower in cutting. But a finer edge is produced than it would be possible to obtain with grindstone alone. Lay the oilstone on the bench with its end to the front edge of the bench. Hold the tool as before, and rub from end to end of the stone. The middle part of a stone generally has more wear than the edges, and so gets worn hollow. Try to avoid this. Proceed with the sharpening until the rough scratches left by the grinding have been smoothed out, and the tool has a true, dull-polished surface at the extremity. The wire edge may still be present, but it will be rubbed off later on the strop. 

Stropping produces an extremely fine polished or burnished edge to a tool. The strop, like the oilstone and grindstone, acts by rubbing off some of the metal near the edge of the tool. The only difference is that it is less coarse than they. Use a mixture of tripoli, rouge and tallow on the strop. It is well to remember that in the case of any cutting tool whatsoever, whether it be a pocket-knife for peeling an apple, a drill, or a lathe for a 14-inch gun, the efficiency of the tool ultimately depends on the keenness and truth of the last hundredth, or twenty-fifth, or sixteenth of an inch, whichever you like, of that tool's cutting edge. All the rest of the tool is but handle, with various labour-saving devices, for applying that cutting edge to its work. It is well, therefore, to see to it that the cutting edge of your tool is correct in form and properly applied.