Practical Mechanics for Boys | Page 7

to the elbows, when
they are held in that position.
THE PROPER DIMENSIONS.--This plan will give you a sure means
of selecting a height that is best adapted for your work. The regulation
bench is about 38 inches high, and assuming that the vise projects up
about 4 inches more, would bring the top of the jaws about 42 to 44
inches from the floor. It is safe to fix the height of the bench at not less
than 34 inches.
This should have a drawer, preferably near the right-hand end of the
bench. The vise should be at the left side, and the bench in your front
should be free of any fixed tools.
HOW ARRANGED.--Have a rack above the bench at the rear, for the
various tools when not in use, and the rear board of the 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