pulley running at a constant speed, can he driven equally well by a belt
drive from a countershaft or by a motor. Feeds arc seldom taken now
from a '* hack-shaft ", hut from a " feed-shaft " in front of the lathe.
Another innovation the hollow spindle-•• allows stock bars to he passed
through iron) the rear of the headstock to be* gripped in a chuck at the front.
It has caused many changes, in the design of spindle journals and bearings,
which are of value,
In all the common lathes a single tool is mostly used. This is so
severe a handicap on production that a large- number of lathes have been
built for multiple-tool cutting. Some of these are automatic in opera-
tion. The distinguishing feature oj these is the mounting of a battery of
tools in the holder of the slide rent to cut simultaneously or in rapid suc-
cession. These arrangements are used chiefly in the manufacture of articles
in which several different diameters occur, with shoulders and faces.
Turret Lathes and Screw Machines.-.........-The difference between a
turret and :i capstan lathe IH that in the former the tool holder is mounted
on a saddle that slides along the bed; in the hitter, the tool holder slides
along a saddle that in fixed to the bed. The practical result is that the range
of movement of the turret in more extensive than that of the capstan. The
first is also made* in larger dimension}* than the second. The difference
between a screw machine and a capstan lathe in that the first is fully auto-
matic in action -•• hence often termed an 4* automatic "......while the hitter is not.
The movements of the first art* canned by cams mounted on drums and on
disks. The movements of the second are produced generally by gears,
feed rods, &e. The screw machine may or may not be equipped with a
turret. The work-holding spindle is most commonly single, but many
lathes now have four, five?, or HIX spindles, each carrying its piece of work
which in brought round in turn to the tools.
Although many common lathes are fitted with turrets, the ** turret lathe "
in a distinct type. It has a hollow spindle fur bar work, and in many
has a chuck for face work, though the tendency now in to allot these functions
to distinct lathes* It has a cross-slide, with a tool at front and at rear.
A chasing saddle ia frequently included for cutting of greater length
than can be done conveniently from the turret. The hexagonal turret, with
mounted on face, arid with its rotational movements synchronized
with flume nf the work, far outdistances flit* common lathe in speed of pro-
duction. It is usual to scheme the* operation* in such a way that a complete
cydk* turning, drilling, minting with rough and finishing cuts, tapping, &c.
' can he finished on a piece during ow* rotation, In the simpler
article**) more than one piece can be tooled during rotation.
Stops. A feature common to all turret is the fitting of to
the and of the machined. This avoids
Originally a was used. This is