e as indicated by the arrow, Fig. 34. In
this case, as with all turning operations, the first cut should be deep
enough to remove the hard outer scale at every part of the hole. Usually
a rough-cored hole is so much smaller than the finished size that
several cuts are necessary; in any case, the last or finishing cut
should be very light to prevent the tool from springing away from the
work, so that the hole will be as true as possible. Boring tools,
particularly for small holes, are not as rigid as those used for outside
turning, as the tool has to be small enough to enter the hole and for
this reason comparatively light cuts have to be taken. When boring a
small hole, the largest tool that will enter it without interference
should be used to get the greatest rigidity possible.

[Illustration: Fig. 37 (A) Setting Outside Calipers. (B) Transferring
Measurements to Inside Calipers. (C) Micrometer Gage]

=Measuring Bored Holes.=--The diameters of small holes that are being
bored are usually measured with inside calipers or standard gages. If
the pulley were being bored to fit over some shaft, the diameter of the
shaft would first be measured by using outside calipers, as shown at
_A_, Fig. 37, the measuring points of the calipers being adjusted until
they just made contact with the shaft when passed over it. The inside
calipers are then set as at _B_ to correspond with the size of the
shaft, and the hole is bored just large enough to admit the inside
calipers easily. Very accurate measurements can be made with calipers,
but to become expert in their use requires experience. Some mechanics
never become proficient in the art of calipering because their hands are
"heavy" and they lack the sensitiveness and delicacy of touch that is
necessary. For large holes, a gage _C_ is often used, the length _l_
being adjusted to the diameter desired. Small holes are often bored to
fit hardened steel plug gages (Fig. 38), the cylindrical measuring ends
of which are made with great accuracy to standard sizes. This type of
gage is particularly useful when a number of holes have to be bored to
the same size, all holes being made just large enough to fit the gage
without any perceptible play.

[Illustration: Fig. 38. Standard Plug Gage]

_Setting Work in the Chuck._--When setting a part in a chuck, care
should be taken to so locate it that every surface to be turned will be
true when machined to the finished size. As a simple illustration