Section 13. qxd

Workpiece speeds
depend on the size and type of workpiece material
and on whether it is rigid enough to hold its shape. In surface grinding,
table speeds generally range from 50 to 100 ft/min (15 to 30 m/ min);
for cylindrical grinding, work speeds from 70 to 100 ft/min (20 to 30
m/min), and for internal grinding they generally range from 75 to 200
ft/min (20 to 60 m/min).
Fig. 13.4.18
Standard marking system chart for aluminum oxide and silicon carbide bonded abrasives.
Fig. 13.4.19
Standard marking system chart for diamond tool and cubic boron nitride (cBN) bonded abrasives.
Section_13.qxd 10/05/06 10:32 Page 13-67

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13-68
MACHINING PROCESSES AND MACHINE TOOLS
Cross-feed
depends on the width of the wheel. In roughing, the work-
piece should travel past the wheel 
to 
of the width of the wheel for
each revolution of the work. As the workpiece travels past the wheel
with a helical motion, the preceding rule allows a slight overlap. In fin-
ishing, a finer feed is used, generally 
to 
of the width of the wheel
for each revolution of the workpiece.
Depth of Cut
In the roughing operation, the depth of cut should be
all the wheel will stand. This varies with the hardness of the material
and the diameter of the workpiece. In the finishing operation, the depth
of cut is always small: 0.0005 to 0.001 in (0.013 to 0.025 mm). Good
results as regards finish are obtained by letting the wheel run over the
workpiece several times without cross-feeding.
Grinding Allowances
From 0.005 to 0.040 in (0.13 to 1 mm) is
generally removed from the diameter in rough grinding in a cylindrical
machine. For finishing, 0.002 to 0.010 in (0.05 to 0.25 mm) is common.
Workpieces can be finished by grinding to a tolerance of 0.0002 in
(0.005 mm) and a surface roughness of 50
m
in R
q
(1.2 
m
m).
In situations where grinding leaves unfavorable surface