The results obtained from the use of high-speed steel tools are dependent in a very large measure on the way in which the tools are made and used. As they are principally valuable for roughing purposes, it is apparent that they should be made strong and of such shape as to bring as little strain as possible on the machine. When forging, the life of the tool should be considered, and a shape adopted that will permit a number of grindings. If the top of the cutting end of a tool is made of the same height as the top of the tool shank, it can be ground but a few times before it is necessary to dress it again, and the tool is consequently short-lived. If, however, the top of the cutting end of the tool is made higher than the top of the tool shank, it can be ground a number of times, so that the life of the tool is increased and the expense of forging proportionately lessened.
The use of high-speed steel for cutting tools has, as stated elsewhere, revolutionized machine-shop methods. Modern competition renders it necessary in many plants to reduce the cost of labor to the lowest possible limit, and the use of tools that allow extremely high speeds has done much toward making this reduction possible.
All steels are not equally good for all classes of work. Some work better on cast iron, while others are better adapted for steel cutting. In order to get the highest efficiency possible it is advisable, where several different metals are machined in quantities, to employ tools that are specially suited to the different kinds of work, each tool having the name of the steel from which it is made plainly stamped on it. However, when most of the material machined is cast iron, special tools for steel cutting need not be made as the tools used for cast iron will answer.
If several kinds of steel are used in a shop, each tool should be given a distinguishing mark, as one tool might be made from ordinary crucible steel, another from a steel containing a small amount of tungsten, and still another from high-speed steel. Tools made from each of these grades require different treatment and unless they are marked or a record of them kept, it is impossible after a time to distinguish between them.
Tungsten steels may be recognized, when grinding on an abrasive wheel, by the appearance of the spark, which will be blood-red in color and round in form; carbon steel, when ground, gives off a yellow spark which bursts in the air.