Section 13. qxd

Turning Recommendations
Recommendations for tool materials,
depth of cut, feed, and cutting speed for turning a variety of materials
are given in Table 13.4.4. The cutting speeds for high-speed steels for
turning, which are generally M2 and M3, are about one-half those for
uncoated carbides. A general 
troubleshooting guide
for turning opera-
tions is given in Table 13.4.5. The range of applicable cutting speeds
and feeds for a variety of tool materials is shown in Fig. 13.4.12.
High-Speed Machining
To increase productivity and reduce
machining costs, there is a continuing trend to increase cutting speeds,
especially in turning, milling, boring, and drilling. High-speed machin-
ing is a general term used to describe this trend, where speeds typically
range as follows: High speed: up 6,000 ft/min (1,800 m/min): very high
speed: up to 60,000 ft/min (18,000 m/min); and ultrahigh-speed, higher
than this range. Because of the high speeds involved, important consid-
erations in these operations include inertia effects, spindle design, bear-
ings, and power; stiffness and accuracy of the machine tools; selection
of appropriate cutting tools; and chip removal systems.
Hard Turning and Machining
As workpiece hardness increases, its
machinability decreases and there may be difficulties with traditional
machining operations regarding surface finish, surface integrity, and
tool life. With advances in cutting tools and the availability of rigid and
powerful machine tools and work-holding devices, however, it is now
possible to machine hard materials, including heat-treated steels, with
high dimensional accuracy. Hard machining can compete well with
grinding processes and has been shown to be economical for parts such
as shafts, gears, pinions, and various automotive components.
Ultraprecision Machining
To respond to increasing demands for
special parts with surface finish and dimensional accuracies on the
order of a nanometre (10
9
m), several important developments have
been taking place in advanced machining. A common example of ultra-
precision machining is