KEVOS® MAKEOS · Power Transmission
Bearing Fit and Operating Internal Clearance
How much radial internal clearance will this bearing have once it is pressed on and running warm, and could it go into preload?
Operating radial internal clearance of a rolling bearing: the initial clearance range, the reduction from the inner ring expanding on an interference shaft fit and the outer ring contracting in an interference housing fit (as shares of the effective interference), the reduction from the inner ring running hotter than the outer, and the resulting operating clearance range with a preload check.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Initial radial clearance, minimum | µm | Lower limit of the bearing’s radial internal clearance group (from the bearing maker for the size and group). |
| Initial radial clearance, maximum | µm | Upper limit of the clearance group. |
| Bore diameter | mm | Bore diameter. |
| Outside diameter | mm | Outside diameter. |
| Effective shaft interference | µm | Effective interference of the inner ring fit (measured interference less surface smoothing). |
| Share of shaft interference reaching the raceway | Share of the inner ring interference that expands the raceway (about 0.7–0.9 for solid steel shafts). | |
| Effective housing interference | µm | Effective interference of the outer ring in the housing (0 for a clearance fit). |
| Share of housing interference reaching the raceway | Share of the outer ring interference that contracts the raceway (about 0.6–0.8 for steel housings). | |
| Inner ring hotter than outer ring by | K | Temperature difference between inner and outer ring when running. |
| Bearing steel expansion coefficient | µm/m·K | Expansion coefficient of bearing steel. |
| Smallest operating clearance acceptable | µm | Least operating clearance you accept (0 = just no preload; negative values allow a small preload). |
Method and formulas
- Fit reduction = f_i × I_i + f_o × I_o.
- Thermal reduction = α ΔT d_m, with d_m = (d + D) ÷ 2 the mean raceway diameter.
- Operating clearance = initial clearance − fit reduction − thermal reduction (for both limits).
- Example: 25–40 µm initial clearance runs at 4.8–19.8 µm after the fit and a 5 K difference.
Limitations
- Approximate shares; the bearing maker’s method uses ring and shaft geometry.
- Thin-walled housings and hollow shafts change the shares.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Choose a clearance group (normal, C3, C4) for a fit and temperature
- Check that a tight shaft fit will not preload the bearing
- Explain bearing overheating after a fit change
Who it is for
- Design engineers
- Maintenance engineers
- Power transmission engineers
What you get
- Clearance reduction from the fits
- Clearance reduction from temperature
- Operating clearance range and preload check
Interpreting the result
- If the minimum goes negative, choose the next larger clearance group (C3, C4) or a looser fit.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2365–2416. Topic reference; no source tables or recommended settings are reproduced.
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Open the Bearing Fit and Operating Internal Clearance calculator
