Practical Mechanics for Boys | Page 7

bench should be elevated above the front planks several inches, on which the various tools can be put, other than those which are suspended on the rack above.
The advantage of this is, that a bench will accumulate a quantity of material that the tools can hide in, and there is nothing more annoying than to hunt over a lot of trash to get what is needed. It is necessary to emphasize the necessity of always putting a tool back in its proper place, immediately after using.
CHAPTER II
HOW TO GRIND AND SHARPEN TOOLS
It is singular, that with the immense variety of tools set forth in the preceding chapter, how few, really, require the art of the workman to grind and sharpen. If we take the lathe, the drilling machine, as well as the shaper, planer, milling machine, and all power-driven tools, they are merely mechanism contrived to handle some small, and, apparently, inconsequential tool, which does the work on the material.
IMPORTANCE OF THE CUTTING TOOL.--But it is this very fact that makes the preparation of that part of the mechanism so important. Here we have a lathe, weighing a thousand pounds, worth hundreds of dollars, concentrating its entire energies on a little bit, weighing eight ounces, and worth less than a dollar. It may thus readily be seen that it is the little bar of metal from which the small tool is made that needs our care and attention.
This is particularly true of the expensive milling machines, where the little saw, if not in perfect order, and not properly set, will not only do improper work, but injure the machine itself. More lathes are ruined from using badly ground tools than from any other cause.
In the whole line of tools which the machinist must take care of daily, there is nothing as important as the lathe cutting-tool, and the knowledge which goes with it to use the proper one.
Let us simplify the inquiry by considering them under the following headings:
1. The grinder.
2. The grinding angle.
THE GRINDER.--The first mistake the novice will make, is to use the tool on the grinder as though it were necessary to grind it down with a few turns of the wheel. Haste is not conducive to proper sharpening. As the wheel is of emery, corundum or other quickly cutting material, and is always run at a high rate of speed, a great heat is evolved, which is materially increased by pressure.
Pressure is injurious not so much to the wheel as to the tool itself. The moment a tool becomes heated there is danger of destroying the temper, and the edge, being the thinnest, is the most violently affected. Hence it is desirable always to have a receptacle with water handy, into which the tool can be plunged, during the process of grinding down.
CORRECT USE OF GRINDER.--Treat the wheel as though it is a friend, and not an enemy. Take advantage of its entire surface. Whenever you go into a machine shop, look at the emery wheel. If you find it worn in creases, and distorted in its circular outline, you can make up your mind that there is some one there who has poor tools, because it is simply out of the question to grind a tool correctly with such a wheel.
[Illustration: Fig. 18. Hook Tool.]
[Illustration: Fig. 19. Parting Tool.]
[Illustration: Fig. 20. Knife Tool.]
[Illustration: Fig. 21. Right-hand Side Tool.]
[Illustration: Fig. 22. Internal Tool.]
[Illustration: Fig. 23. Left-hand Side Tool.]
Coarse wheels are an abomination for tool work. Use the finest kinds devised for the purpose. They will keep in condition longer, are not so liable to wear unevenly, and will always finish off the edge better than the coarse variety.
LATHE BITS.--All bits made for lathes are modifications of the foregoing types (Figs. 18, 19, 20, 21, 22, 23).
As this chapter deals with the sharpening methods only, the reader is referred to the next chapter, which deals with the manner of setting and holding them to do the most effective work.
When it is understood that a cutting tool in a lathe is simply a form of wedge which peels off a definite thickness of metal, the importance of proper grinding and correct position in the lathe can be appreciated.
ROUGHING TOOLS.--The most useful is the roughing tool to take off the first cut. As this type of tool is also important, with some modifications, in finishing work, it is given the place of first consideration here.
[Illustration: Fig. 24. Tool for Wrought iron. Fig. 25. Tool for Cast iron.]
Fig. 24 shows side and top views of a tool designed to rough off wrought iron, or a tough quality of steel. You will notice, that what is called the top rake (A) is very pronounced, and, as the point projects considerably above the body of the tool itself, it should, in practice,