Section 13. qxd

TURNING
Turning
is a machining operation for all types of metallic and non-
metallic materials and is capable of producing circular parts with
straight or various profiles. The cutting tools may be single-point or
form tools. The most common machine tool used is a 
lathe;
modern
lathes are computer-controlled and can achieve high production rates
with little labor. The basic operation is shown in Fig. 13.4.10, where the
workpiece is held in a chuck and rotates at 
N
r/min; a cutting tool moves
along the length of the piece at a feed 
f
(in/r or mm/r) and removes
material at a radial depth 
d,
reducing the diameter from 
D
0
to 
D
f
.
is flush with the end of the bed. The maximum swing over the ways is
usually greater than the nominal swing. The 
length of the bed
is given
frequently to specify the overall length of the bed. A lathe size is indi-
cated thus: 14 in (356 mm) (swing) by 30 in (762 mm) (between cen-
ters) by 6 ft (1,830 mm) (length of bed). Lathes are made for light-,
medium-, or heavy-duty work.
All geared-head lathes, which are single-pulley (belt-driven or arranged
for direct-motor drive through short, flat, or V belts, gears, or silent chain),
increase the power of the drive and provide a means for obtaining 8, 12,
16, or 24 spindle speeds. The teeth may be of the spur, helical, or herring-
bone type and may be ground or lapped after hardening.
Variable speeds
are obtained by driving with adjustable-speed dc
shunt-wound motors with stepped field-resistance control or by electronics
or motor-generator system to give speed variation in infinite steps. AC
motors driving through infinitely variable speed transmissions of the
mechanical or hydraulic type are also in general use.
Modern lathes, most of which are now computer-controlled