.

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,
be set with its cutting point above the center.

THE CLEARANCE.--Now, in gr