| RECOMMENDED FITS |
| The following table shows recommended shaft and housing sizes and tolerances for different applications. It is assumed that bearings used are ABEC 5 tolerance (+0 -.0002 inch) for bore and O.D. If a different grade of bearing is used, this will affect recommended dimensions of mating components. |
ROTATING RING |
INNER RING |
OUTER RING |
APPLICATION |
DESIRED FIT TYPE |
DESIRED FIT
(inches) |
USE SHAFT
DIAMETER |
USE HOUSING DIAMETER |
Preloaded assemblies (see pgs 31-36) |
Bonding (no adhesive grooves) |
.0004L to .0008L |
d - .0006
d - .0008 |
D + .0004
D + .0006 |
Low speed, or spring preload. |
Loose |
.0001L to .0005L |
d - .0003
d - .0005 |
D + .0001
D + .0003 |
Medium speed |
Transition |
.0002L to .0002T |
d - .0000
d - .0002 |
D - .0000
D - .0002 |
High speed |
Light press* |
.0000 to .0004T |
d +.0002
d - .0000 |
D - .0002
D - .0004 |
High speed, high load |
Tight press* |
.0002T to .0006T |
d - .0002
d - .0004 |
D - .0004
D - .0006 |
|
STATIONARY RING |
INNER RING |
OUTER RING |
Most applications
(see pgs 31 & 36) |
Line - line to loose |
.0000 to .0004L |
d - .0002
d - .0004 |
D - .0000
D +.0002 |
|
L = Loose fit
T = Tight fit
d = Bearing bore from table
D = Bearing O.D. from table |
*Notes for press fits: |
1. Interference factor may affect final radial play
2. Allow for relative thermal expansion
3. MC5 radial play bearing (.0005 to .0008 in) recommended for tight press
4. Tight press not recommended for bearing with ring thickness <.030 in. |
|
|
| |
INTERFERENCE FITS |
Where interference fits are achieved by pressing a shaft into a bearing or a bearing into a housing, particular care must be taken in dimensioning and tolerancing mating parts. Radial play values of will be reduced by an amount proportional to the interference.
∆rf = ∆r-fp • I where: ∆rf = final radial play after pressing part
∆r = initial radial play
fp = interference factor
I = interference between bearing and mating part
The interference factor fp is dependent on the thickness of the bearing ring and the material and geometry of the mating part. It is suggested that the following empirically determined values are used: |
Values for Interference Factor fp
|
BEARING RING THINKNESS Inches |
MATING MATERIAL |
STEEL |
BRASS/ALUMINUM |
PLASTIC (filled) |
<0.015 |
0.8 |
0.6 |
0.3 |
0.015 - 0.030 |
0.7 |
0.4 |
0.2 |
>0.030 |
0.6 |
0.2 |
0 |
|
*Bearing ring thickness is calculated as follows:
Inner ring thickness = li - d where: d = bearing bore 2 D = bearing O.D.
Outer ring thickness = D - lo li = inner ring land diameter*
2 lo = outer ring land Diameter*
(*Land diameters are given in the individual bearing specification tables.) |
| Note that the above fp values are intended as a guideline only. If the mating part itself has a thin section, then the above factors will be reduced slightly. The important point is that interference can significantly reduce radial play and must be accounted for in a design to arrive at the final desired radial play. For this reason it is recommended that a higher radial play (e.g. MC5 - 0.0005" to 0.0008") be used where interference fit is needed. |
| SHOULDER DESIGN |
Shoulder diameter
When a bearing is located against a shoulder in the mating part, care must be taken that the rim of the shoulder clears the opposing ring. This is achieved when the diameter of the shoulder has clearance over the opposing race land diameter.
Clearance should be > .010 inch (.25 mm) to allow for normal tolerances.
Maximum shaft shoulder diameter = Outer ring land diameter* - clearance
Minimum housing shoulder diameter = Inner ring land diameter* + clearance
(*Land diameters are given in the individual bearing.) |
Shoulder corner radius
The corner radius of the shoulder (ra) should be less than the fillet radius (r) of the mating bearing to allow the bearing to fully seat against the shoulder. The maximum shoulder corner fillet radii for bearings are given in the individual bearing tables. |
|
| RELATIVE THERMAL EXPANSION |
The effects of relative thermal expansions of different mating materials must also be taken into account when
calculating final radial play values for an interference-fit assembly that will be used over an extended temperature range. Thermal effects must also be considered in a preloaded bearing assembly (see preload section on pages 31-32). |
MATERIAL |
LINEAR EXPANSION COEFFICIENT |
ppm/oC |
ppm/oF |
Bearing Materials |
DR/ES1 |
10 |
6 |
400 series stainless |
10 |
6 |
52100 chrome steel |
12 |
7 |
Other Materials |
300 series stainless |
16 |
9 |
Aluminum |
23 |
13 |
Brass |
19 |
11 |
Bronze |
18 |
10 |
Copper |
16 |
9 |
Invar |
1 |
0.6 |
Iron |
12 |
7 |
Lead |
29 |
16 |
Nickel |
13 |
7 |
Magnesium |
8 |
4 |
Titanium |
9 |
5 |
|
|
|
ABS |
72 |
40 |
ABS (glass reinforced) |
31 |
17 |
Delrin / Acetal |
85 |
48 |
Epoxy |
54 |
30 |
Epoxy (glass reinforced) |
36 |
20 |
Nylon |
81 |
45 |
Nylon (glass reinforced) |
23 |
13 |
Polycarbonate |
65 |
36 |
Polycarbonate (glass reinforced) |
22 |
12 |
|
Example: |
SR144 bearing pressed on .125 inch aluminum shaft is used at 200°F
Initial interference at 70°F = .0004
Relative expansion of shaft at 200°F = .125 x (13 - 6) x 130 x 10-6 = .0001
Interference at 200°F = .0005
SR144 inner ring thickness .018 inch, therefore interference factor fp = .4
Reduction of radial play at 200°F = .0005 x fp = .0002 |
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