tting edge. Very often broad tools cannot be used for
finishing cuts, especially when turning steel, because their greater
contact causes chattering and results in a rough surface. An old and
worn lathe is more liable to chatter than one that is heavy and
well-built, and as the diameter of the work also makes a difference, a
broad tool cannot always be used for finishing, even though,
theoretically, it would be preferable. After one side of the disk is
finished, it is reversed in the chuck, the finished surface being placed
against the jaws. The remaining rough side is then turned, care being
taken when starting the first cut to caliper the width of the disk at
several points to make sure that the two sides are parallel.

[Illustration: Fig. 35. Tools Ground so that Top Slopes away from
Working Part of Cutting Edge]

=Example of Boring.=--Another example of chuck work is shown at _B_,
Fig. 34. In this case a cast-iron pulley is to have a true hole _h_
bored through the hub. (The finishing of internal cylindrical surfaces
in a lathe is referred to as boring rather than turning.) The casting
should be set true by the rim instead of by the rough-cored hole in the
hub; this can be done by the use of chalk as previously explained. Even
though a universal type of chuck were used, the jaws of which, as will
be recalled, are self-centering, it might be necessary to turn the
pulley relative to the chuck as a casting sometimes runs out because of
rough spots or lumps which happen to come beneath one or more of the
jaws.

[Illustration: Fig. 36. Boring Tool]

The shape of tool _t_ for boring is quite different from one used for
outside turning, as shown by Fig. 36. The cutting end of a solid type of
tool is forged approximately at right angles to the body or shank, and
the top surface is ground to slope away from the working part _w_ of the
cutting edge, as with practically all turning tools. The front part or
flank, _f_ is also ground away to give the edge clearance. This type of
tool is clamped in the toolpost with the body about parallel with the
lathe spindle, and ordinarily the cutting edge would be about as high as
the center of the hole, or a little below, if anything. When starting a
cut, the tool is brought up to the work by moving the carriage and it is
then adjusted radially to get the right depth of cut, by shifting the
cross-slide. The power feed for the carriage is then used, the tool
feeding back through the hol