NTN - Bearing units catalog a-21000-i

APPENDICES
SHAFT DESIGN
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Develops Larger Holding Force
The ball point set screw makes a point contact with the
shaft allowing easy tightening and complete transmission
of force to the shaft.
The cup point and knurled cup point on the other hand
make a circular contact with the shaft. In those designs, a
portion of the tightening torque is used for cutting a circular
groove on the shaft, effectively reducing the holding force.
Refer to Fig. 10 for a comparison of holding force.
Can Be Used Repeatedly
The hardened steel ball does not deform when tightened.
Additionally, it only leaves a small contact print on the
shaft. The cup point set screw not only marks the shaft, but
the screw itself becomes damaged, making it difficult to
retighten if removed.
Needs No Flat On The Shaft
The ball point set screw makes a point contact and
therefore does not require a flat on the shaft. The cup point
set screw cannot make full contact unless there is a flat
machined onto the shaft.
Reduced Fretting Corrosion At The Tip Of The Set Screw
Due to the hardened steel ball of the ball point set screw,
fretting corrosion is considerably reduced. Cup point and
knurled cup point set screws can cause substantially more
fretting since they are generally not hardened.
ECCENTRIC COLLAR SYSTEM
As in the case of the set screw system, it is usual under
normal operating conditions to fit the inner ring onto the
shaft by means of a clearance fit, for ease of assembly.
Fig. 11 shows the appropriate values of dimensional
tolerances for the shaft.
100
80
Avg. 91.1 hr.
T=35 lb-in
Sample A
Sample B
T=Tightening Torque
ADAPTER SYSTEM BEARING UNITS
Since in the case of the adapter system, the bearing
unit is fastened onto the shaft by means of a sleeve, for
dimensional tolerances for the shaft, h9 is applicable under
all operating conditions. Note that it is not usable under a
loose fit ≥h9.
Time To Loosen
(Hours)
60
40
20
0
Ball Point
Avg. 12 hr.
T=48 lb-in
Cup Point
Set Screw Type
Avg. 3 hr.
T=35 lb-in
Knurled Point
dn value
d(mm)× n(min -1 )
250 000
170 000
130 000
100 000
70 000
40 000
m6
k6
j7
h7
h8
h9
On the calculation of the dn
value, apply the bore
dimension of the metric series
in the same group.
Example:
UELP205-100D1
Bore dimension 25mm
× n (min -1 )
20 15 10 753 1
Cr/ Pr
Fig. 10 Time to Loosen Test Results
Fig. 11 Dimensional tolerances for
the shaft eccentric collar system bearing units
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