NTN - Precision Rolling Bearings

NTN Main Spindle Bearings
5 Internal clearance and standard preload
of duplex angular contact ball bearings
The initial internal clearance or preload for duplex
angular contact ball bearings is determined with
consideration for two factors: temperature rise during
operation and the rigidity and accuracy required after
assembly or during operation.
The internal clearance of the bearing may be
significantly affected during operation due to three
factors: the reduction in clearance caused by fits, the
temperature difference between the inner and outer
rings during operation, and the effects of centrifugal
force. Depending on the initial internal clearance, a
significantly reduced clearance may result in extreme
temperature rise, vibration, noise, and short service life.
In addition, seizure may result in some cases. For this
reason, it is important to determine the optimal initial
internal clearance and initial preload required for
operation. When using a duplex angular contact ball
bearing on the main spindle of a machine tool, the
preload is determined by considering the type, main
spindle configuration, lubrication system, drive system,
intended functions, and other factors. However, preload
can also be generalized by the dmn value (dmn: pitch
circle diameter across rolling elements [mm]
multiplied by speed [min -1 ]), as shown below:
dmn50010 3 Normal preload (GN)
50010 3 dmn65010 3 Light preload (GL)
dmn65010 3 0 to positive clearance
For detailed information, contact NTN Engineering.
Table 9.4 Radial internal clearance of duplex angular
contact ball bearings
Unit:m
Nominal bore
diameter
d
C1
C2 CN (normal)
over incl. min max min max min max
–
10
18
30
50
80
100
120
150
180
10
18
30
50
80
100
120
150
180
200
3
3
3
3
3
3
3
3
3
3
8
8
10
10
11
13
15
16
18
20
6
6
6
8
11
13
15
16
18
20
12
12
12
14
17
22
30
33
35
40
8
8
10
14
17
22
30
35
35
40
15
15
20
25
32
40
50
55
60
65
For duplex angular contact ball bearings, NTN
recommends the initial radial clearances and standard
preloads shown in Tables 9.4 through 9.19. Select the
optimal radial internal clearance and initial preload for
your application. When ordering a duplex angular ball
bearing, please specify the desired preload and
clearance. If these are not specified in the order, we will
ship a bearing with standard clearance. However, some
product types do not have a standard clearance. In this
case, we will inform you of the available clearances.
Standard preloads of angular contact ball bearings
(DB and DF arrangements)
Table 9.5 Standard angular contact ball bearings
(78C type)
Unit: N
Nominal bore
diameter
Contact angle: 15˚
78xxC
d
Light preload
(GL)
Normal preload
(GN)
Medium preload
(GM)
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
105
110
120
130
140
150
160
170
10
10
10
10
20
20
29
29
29
29
29
29
49
49
49
49
49
78
78
98
98
147
147
147
29
29
29
29
49
49
98
98
98
98
98
98
147
147
147
147
147
196
196
294
294
390
390
490
78
78
78
78
98
98
196
196
196
196
196
196
294
294
294
294
294
490
490
590
590
785
785
980
62