urret makes it possible to quickly
place any tool in the working position. Turret lathes also have systems
of stops or gages for controlling the travel of the turret carriage and
cross-slide, in order to regulate the depth of a bored hole, the length
of a cylindrical part or its diameter; hence, turning machines of this
type are much more efficient than ordinary lathes for turning duplicate
parts, unless the quantity is small, in which case, the advantage of the
turret lathe might be much more than offset by the cost of the special
tool equipment and the time required for "setting up" the machine. (See
"Selecting Type of Turning Machine.")

[Illustration: Fig. 1. Bardons & Oliver Turret Lathe of Motor-driven
Geared-head Type]

=General Description of a Turret Lathe.=--The turret lathe shown in Fig.
1 has a hexagonal shaped turret _A_ with a hole in each side in which
the tools are held. This turret is mounted on a slide _B_ which is
carried by a saddle _C_ that can be moved along the bed to locate the
turret slide with reference to the length of the tools in the turret and
the room required for indexing. The turret slide can be moved
longitudinally by turning the pilot wheel or turnstile _D_, or it can
be fed by power. Ordinarily, the hand adjustment is used for quickly
moving the carriage when the tools are not cutting, although sometimes
the hand feed is preferable to a power feed when the tools are at work,
especially if the cuts are short. After a turret tool has finished its
cut, the turnstile is used to return the slide to the starting point,
and at the end of this backward movement the turret is automatically
indexed or turned one-sixth of a revolution, thus bringing the next tool
into the working position. The turret is accurately located in each of
its six positions by a lock bolt which engages notches formed in a large
index ring at the turret base. A binder lever _E_ at the top of the
turret stud is used to clamp the turret rigidly to the slide when the
tools are cutting.

The forward movement of the slide for each position of the turret is
controlled by stops at _F_, which are set to suit the work being turned.
When parts are being turned from bar stock, the latter passes through
the hollow spindle of the headstock and extends just far enough beyond
the end of the spindle to permit turning one of the parts. The bar is
held while the turning tools are at work, by a chuck of the collet type
at _G_. This chu