Most workmen find themselves, at times, compelled to forge and temper their own tools, such as drills, cold chisels, etc. The following hints will be of service:
Beware of over-heating the piece to be forged, and also be careful that the fire is free from sulphur. Small drills are easily heated in the flame of a lamp or candle; a Bunsen burner will heat sufficiently quite a good sized tool. Charcoal makes the best fire for all kinds of tools. If you are compelled to use common bituminous coal let the fire burn until most of the sulphur has been driven off. Do not hammer with heavy blows after the steel has cooled. By tapping it lightly, however, until it becomes black, the closeness of the grain is increased.
Heat it to a bright cherry red and quench it in water. Do this a few times and then forge it carefully, and it will be nearly as good as before. The various recipes for mixtures for restoring burnt steel are worthless.
Heat the steel to a bright cherry red and plunge it in water that has been thoroughly boiled and then allowed to cool. It will then be "as hard as fire and water will make it," and too hard for anything except hardened bearings, or tools for cutting and drilling glass and very hard metals.
Where very hard tools are required, as, for example, for cutting steel or glass, mercury is the best liquid for hardening steel tools. The best steel, when forged into shape and hardened in mercury, will cut almost anything. We have seen articles made from ordinary steel, which have been hardened and tempered to a deep straw color, turned with comparative ease with cutting tools, from good tool steel hardened in mercury.
To make it stand work without breaking, it must bo tempered. To do this, polish the surface on a grindstone or with emery paper, so that any change in the color of the metal may be easily seen. Then heat the tool until the cutting edge shows the proper color, as given below. Large drills and cold chisels are hardened and tempered at one operation, the cutting edge being cooled and hardened while the upper part is left hot. When taken from the water the heat from the shank passes towards the cutting edge and brings it to the right degree of softness. Small drills may be best tempered in the flame of a lamp. A spirit lamp is beet, and the neatest plan is to heat the drill a short distance from the point and allow the heat to flow towards the cutting edge. As soon as the right color is seen on the edge, the entire tool is plunged in water and cooled. In this way the shank is kept soft and the tool is not so apt to snap off.
The following are the degrees of heat (Fahrenheit) and corresponding colors to which tools for different purposes should be brought:
Very faint yellow.
Very hard; suitable for hammer faces, drills for stone, etc.
Pale straw color.
Hard and inelastic; suitable for shears, scissors, turning tools for hard metal, etc.
Brown with purple spots.
For tools requiring strong cutting edges without extreme hardness; as cold chisels, axes, cutlery, etc.
Grayish blue verg-ing on black.
Spring temper; saws, swords.
Bed hot lead is an excellent thing in which to heat a long plate of steel that requires softening or tempering on one edge. The steel need only to be heated at the part required, and there is little danger of the metal warping or springing. By giving sufficient time, thick portions may be heated equally with thin parts. The ends of wire springs that are to be bent or riveted may be softened for that purpose by this process, after the springs have been hardened or tempered.
The mode employed in bluing steel is merely to subject it to heat. The dark blue is produced at a temperature of 600°, the full blue at 500°, and the blue at 550°. The steel must be finely polished on its surface, and then exposed to a uniform degree of heat. Accordingly, there are three ways of coloring; first, by a flame producing no soot, as spirits of wine; secondly, by a hot plate of iron; and thirdly, by wood ashes. As a very regular degree of heat is necessary, wood ashes for tine work are to be preferred. The work must be covered over with them, and carefully watched; when the color is sufficiently heightened, the ,york is perfect.
Make a box of sheet iron; fill it with sand and subject it to a steady heat. The articles to be blued must be finished and well polished. Immerse the articles in the sand, keeping watch of them until they are of the right color, when they should be taken out and immersed in oil.