ld be out, in a central position, or
in.

In order to find what the position of lever _L_ and knob _K_ should be
for cutting any given number of threads to the inch, find what "stop"
number is directly above the number of threads to be cut, which will
indicate the location of lever _L_, and also what position should be
occupied by knob _K_, as shown in the column to the left. For example,
suppose the lathe is to be geared for cutting eight threads to the inch.
By referring to section a we see that lever _L_ should be in position 4
and knob _K_ in the center, provided the idler gear _I_ were in position
_A_, as it would be ordinarily, because all standard numbers of threads
per inch (U. S. standard) from 1/4 inch up to and including 4 inches in
diameter can be cut with the idler gear in that position. As another
illustration, suppose we want to cut twenty-eight threads per inch. This
is listed in section _c_, which shows that lever _L_ must be placed in
position 3 with knob _K_ pushed in and the idler gear shifted to the
left as at _C_.

The simplicity of this method as compared with the time-consuming
operation of removing and changing gears is apparent. The diagram _D_ to
the right shows an arrangement of gearing for cutting nineteen threads
per inch. A 20-tooth gear is placed on the spindle stud (in place of the
regular one having 16 teeth) and one with 95 teeth on the lead-screw,
thus driving the latter direct as with ordinary change gears. Of course
it will be understood that the arrangement of a quick change-gear
mechanism varies somewhat on lathes of different make.

CHAPTER V

TURRET LATHE PRACTICE

Turret lathes are adapted for turning duplicate parts in quantity. The
characteristic feature of a turret lathe is the turret which is mounted
upon a carriage and contains the tools which are successively brought
into the working position by indexing or rotating the turret. In many
instances, all the tools required can be held in the turret, although it
is often necessary to use other tools, held on a cross-slide, for
cutting off the finished part, facing a radial surface, knurling, or for
some other operation. After a turret lathe is equipped with the tools
needed for machining a certain part, it produces the finished work much
more rapidly than would be possible by using an ordinary engine lathe,
principally because each tool is carefully set for turning or boring to
whatever size is required and the t