o the left (in this case 1/7
inch for each revolution of the work) and cuts a winding groove as at
_A_, Fig. 5. When the tool has traveled as far as the thread is wanted,
it is withdrawn by a quick turn of cross-slide handle _e_, and the
carriage is returned to the starting point for another cut. The tool is
then fed in a little farther and a second cut is taken as at _B_, Fig.
5, and this operation is repeated as at _C_ and _D_ until a "full"
thread is cut or until the top of the thread is sharp. The thread is
then tested for size but before referring to this part of the work, the
way the carriage is returned to the starting point after each cut should
be explained.

[Illustration: Fig. 5. Thread is formed by taking a Number of Successive
Cuts]

When the tool is withdrawn at the end of the first cut, if the carriage
is disengaged from the lead-screw and returned by hand, the tool may or
may not follow the first cut when the carriage is again engaged with the
lead-screw. If the number of threads to the inch being cut is a multiple
of the number on the lead-screw _S_, then the carriage can be returned
by hand and engaged with the lead-screw at random and the tool will
follow the first cut. For example, if the lead-screw has six threads per
inch, and 6, 12, 18 or any number of threads is being cut that is a
multiple of six, the carriage can be engaged at any time and the tool
will always follow the original cut. This is not the case, however, when
the number of threads being cut is not a multiple of the number on the
lead-screw.

One method of bringing the carriage back to the starting point, when
cutting threads which are not multiples, is to reverse the lathe (by
shifting the overhead driving belts) in order to bring the tool back to
the starting point without disengaging the carriage; in this way the
tool is kept in the same relation to the work, and the carriage is not
disengaged from the lead-screw until the thread is finished. This is a
good method when cutting short threads having a length of say two or
three inches; but when they are longer, and especially when the diameter
is comparatively large (which means a slower speed), it is rather slow
as considerable time is wasted while the tool is moving back to its
starting point. This is due to the fact that the carriage is moved
slowly by the lead-screw, but when disengaged, it can be traversed
quickly by turning handle _d_, Fig. 2.

A method of returning the ca