Table 6.2 and Table 6.3 give values for typical form-holding capabilities and roughness as a function of grit size for standard precision-plated and postplated conditioned wheels. Roughness values will vary somewhat depending on workpiece hardness. The values indicated are those for grinding aerospace alloys in the hardness range 30 to 50 HrC using CBN abrasive.
6.3.5 Wheel Break-In Period
The phenomenon of a break-in period associated with a high rate of wear of a new wheel is particularly important when trying to hold tolerances of <.001" (25 |jm). Table 6.2 and Table 6.3 give the break-in depth for both precision and conditioned wheels. As can be seen with conditioning
|
TABLE 6.2
Standard Precision-Plated Wheel Form Capabilities
|
|
Minimum
|
Precision
|
Precision
|
Precision
|
Precision
|
|
Grit Size
|
Grit Size
|
Radius
|
Allowance
|
Tolerances
|
Roughness
|
Break-In
|
|
FEPA
|
US Mesh
|
(mm)
|
Blank (um)
|
(±um)
|
(Ra)
|
Depth (um)
|
|
B852
|
20/30
|
2
|
920
|
100
|
|
|
|
B602
|
30/40
|
1.5
|
650
|
90
|
|
|
|
B501
|
35/40
|
1.3
|
650
|
80
|
|
|
|
B427
|
40/50
|
1
|
500
|
60
|
160
|
63
|
|
B301
|
50/60
|
0.8
|
400
|
40
|
125
|
|
|
B252
|
60/80
|
0.7
|
290
|
30
|
85
|
40
|
|
B213
|
70/80
|
0.6
|
260
|
30
|
75
|
|
|
B181
|
80/100
|
0.5
|
220
|
30
|
63
|
35
|
|
B151
|
100/120
|
0.4
|
190
|
30
|
38
|
|
|
B126
|
120/140
|
0.3
|
165
|
25
|
35
|
|
|
B107
|
140/170
|
0.26
|
140
|
25
|
32
|
|
|
B91
|
170/200
|
0.23
|
130
|
25
|
32
|
20
|
|
B76
|
200/230
|
0.2
|
100
|
25
|
28
|
|
|
B64
|
230/270
|
0.18
|
90
|
20
|
25
|
|
|
B54
|
270/325
|
0.15
|
75
|
20
|
22
|
|
|
B46
|
325/400
|
0.12
|
65
|
20
|
20
|
10
|
|
of the wheel surface to remove the tips of the grits, it is possible to virtually eliminate the break-in period. Although conditioning can double the price of the wheel when trying to hold tolerances of <.0005" (12 pm), it can be easily justified by increasing wheel life by an order of magnitude.
|
TABLE 6.3
Conditioned Plated Wheel Form Capabilities
|
|
Min Radius
|
Condition
|
Condition
|
Condition
|
Condition
|
|
Grit Size
|
Capability
|
Allowance
|
Tolerances
|
Roughness
|
Break-In
|
|
FEPA
|
US Mesh
|
(mm)
|
Blank (um)
|
(±um)
|
(Ra)
|
Depth (um)
|
|
B852
|
20/30
|
2
|
850
|
10
|
|
<5
|
|
B602
|
30/40
|
1.5
|
600
|
10
|
|
<5
|
|
B501
|
35/40
|
1.3
|
600
|
10
|
|
<5
|
|
B427
|
40/50
|
1
|
450
|
8
|
80
|
<5
|
|
B301
|
50/60
|
0.8
|
360
|
6
|
70
|
<5
|
|
B252
|
60/80
|
0.7
|
250-280
|
5
|
60
|
<5
|
|
B213
|
70/80
|
0.6
|
240-250
|
5
|
50
|
<5
|
|
B181
|
80/100
|
0.5
|
200
|
5
|
40
|
<5
|
|
B151
|
100/120
|
0.4
|
165
|
5
|
32
|
<5
|
|
B126
|
120/140
|
0.3
|
140-150
|
5
|
28
|
<5
|
|
B107
|
140/170
|
0.26
|
110
|
5
|
25
|
<5
|
|
B91
|
170/200
|
0.23
|
95
|
5
|
22
|
<5
|
|
B76
|
200/230
|
0.2
|
80
|
5
|
NA
|
<5
|
|
B64
|
230/270
|
0.18
|
70
|
4
|
NA
|
<5
|
|
B54
|
270/325
|
0.15
|
60
|
4
|
NA
|
<5
|
|
B46
|
325/400
|
0.12
|
50
|
3
|
NA
|
<5
|
|
