Importance of Shaft & Housing Tolerances
Machined parts and components all have tolerance standards when manufactured. These standards produce a consistent, uniform product.
Bearings have tolerance standards for the inner diameter (ID) and the outer diameter (OD). Machined shaft and housings also have tolerance standards on their parts that range around 10µm.
It’s important to know about tolerances because, during operation, temperatures rise causing the bearings, shaft and housing to expand, along with their respective tolerances. Be prepared for these changes when machining a shaft and housing unit so that you are choosing the correct bearing and fit for your application.
Resultant Fits
Finding the right shaft OD to match the inner ring (or ID) of the bearing and the correct housing ID to match the outer ring (or OD) of the bearing, produces a resultant fit.
In rotating shaft applications, we recommend a press-fit between the shaft and the inner ring (ID) of the bearing and a slip-fit between the housing and the outer ring (OD) of the bearing, when in use.
Using our thermal range calculator, you can manipulate the shaft and housing tolerances to automatically find the best tolerance for the resultant fit.
Slip Fits & Press Fits
On applications where the shaft is rotating, using a press fit will prevent the bearing’s inner ring from rotating, relative to the shaft. If the inner ring rotates separately from the shaft, then micro-fretting and premature bearing failure could occur.
For high-speed applications, the centrifugal force could cause the inner ring to expand and lift off the shaft which could lead to drastic machine malfunctions and a decrease in bearing life. Increasing the press-fit on the bearing and shaft would help counteract this scenario.
Slip Fit
We recommend using a slip fit on the housing so bearings can move axially for spring preloads or to absorb thermal expansion.
However, if the slip fit is too large then micro-fretting between the bearing outer ring (OD) and the housing could occur. In extreme cases, the bearing orbiting geometric center could also result.
Web-Based Bearing Analysis Calculators
Reduce your chances of a premature bearing failure or machine malfunction by using our quick-and-easy proprietary tolerancing calculators:
Automatic Tolerance Calculator: Ensures your shaft and housing are (or will be) machined within the recommended tolerances.
Thermal Range Calculator: Calculates the thermal expansion effects due to operating temperatures to find the right shaft and housing tolerances for the application.
Using our free web-based automatic tolerance calculators should give you the tolerance analysis you’ll need for your machined shaft and housing.
GMN Precision Bearing Products
Our ABEC 7, P4+ precision class of bearings allow for tighter resultant fits for those doing final grinding / lapping just before assembly. We provide the exact bearing inner diameter (ID), outer diameter (OD) and width (W) value deviation from nominal for each specific bearing which will also give you a tighter resultant fit.
Other tolerance recommendations such as shaft and housing concentricity, surface roughness and runout and are located on pages 70-72 of the GMN Bearing catalog.
If you’d like a custom bearing performance analysis or tolerance analysis fill out our contact form or give us a call today at 800.323.5725 for more information.
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