f the one which follows. While it is true that all
artificially made grinders will wear unevenly, even when used with the
utmost care, due to uneven texture of the materials in the stone,
still, the careless use of the tool, while in the act of grinding, only
aggravates the trouble.

Another fault of the careless workman is, to press the bit against the
stone too hard. This cuts the stone more than it wears off the tool, and
it is entirely unnecessary. Furthermore, it heats up the tool, which
should be avoided.

CALIPERS.--A true workman, who endeavors to turn out accurate work, and
preserve his tools, will never test the work with his calipers while the
piece is turning in the lathe. A revolving cast iron disk will cut ruby,
the hardest substance next to the diamond, so it is not the hardness of
the material which resists wear, but the conditions under which it is
used.

CARE IN USE OF CALIPERS.--The calipers may be of the most hardened
steel, and the work turned up of the softest brass, the latter, when
revolving, will grind off the point of the tool, for the reason that the
revolving piece constantly presents a new surface to the point of the
calipers, and when tests are frequently made, it does not take long to
change the caliper span so that it must be reset.

As stated elsewhere, the whole energy of the lathe is concentrated on
the bit or cutting tool, hence, in order to get the most effective work
out of it requires care; first, in grinding; and, second, in setting.

MACHINE BITS.--It does not always matter so much whether you use a
square, pointed, or a round-nosed bit, provided it is properly ground
and set in the tool holder. As a rule, the more brittle the metal the
less the top rake or angle should be.

In the chapter relating to the grinding of tools, references were made
as to the most serviceable bits for the various metals. We are concerned
here with the setting or holding of these articles.

[Illustration: _Fig. 30. Plain Hook Tool_ _Fig. 31. Plain Straight
Tool._]

The two illustrations here given show a pair of plain bits, in which
Fig. 30 represents a hook-shaped formation, and Fig. 31 a straight
grind, without any top rake. The hooked bit would do for aluminum, or
steel, but for cast iron the form shown in Fig. 31 would be most
serviceable.

Then the side bits, such as the round-nosed, Fig. 32 and the square end,
Fig. 33, may be ground hooked, or with a top rake, or left flat.

The too