riving members of the dog. The advantage of driving by
a two-tailed dog, as most mechanics know, is in equalizing the tendency
to spring slender parts while they are being turned.

[Illustration: Fig. 37. Lathe Knurling Tool having Three Pairs of
Knurls--Coarse, Medium and Fine]

In Fig. 36 another turning operation on a lathe of this type is shown,
the work in this case being a rear axle for a motor truck. The turning
of this part is a good example of that class of work where the rapid
removal of metal is the important feature. As the engraving shows, the
stock, prior to turning, is 3-1/2 inches in diameter and it is reduced
to a minimum diameter of 1-1/16 inch. This metal is turned off with one
traverse of the carriage or by one passage of the five tools, and the
weight of the chips removed from each end of the axle is approximately
12 pounds. The time required for the actual turning is about 9 minutes,
while the total time for the operation, which includes placing the heavy
piece in the machine, turning, and removing the work from the lathe, is
12 minutes. The axle revolves, while being turned, at 110 revolutions
per minute and a feed equivalent to 1 inch of tool travel to 60
revolutions of the work is used. It will be noticed that the taper
attachment is also employed on this part, the taper being turned by the
second tool from the left. As the axle is equipped with roller bearings,
it was found desirable to finish the bearing part by a separate
operation; therefore, in the operation shown the axle is simply roughed
down rather close to the finished dimensions, leaving enough material
for a light finishing cut.

=Knurling in the Lathe.=--Knurling is done either to provide a rough
surface which can be firmly gripped by the hand or for producing an
ornamental effect. The handles of gages and other tools are often
knurled, and the thumb-screws used on instruments, etc., usually have
knurled edges. A knurled surface consists of a series of small ridges or
diamond-shaped projections, and is produced in the lathe by the use of a
tool similar to the one shown in Fig. 37, this being one of several
different designs in common use. The knurling is done by two knurls _A_
and _B_ having teeth or ridges which incline to the right on one knurl
and to the left on the opposite knurl, as shown by the end view. When
these two knurls are pressed against the work as the latter revolves,
one knurl forms a series of left-hand ridges an