General Rules for Bearing Arrangement
Fixed vs. Floating Bearings
A shaft is supported at least by two bearings, which are usually arranged in different ways:
- One is designated as a “fixed” bearing
- The other is designated as a floating bearing.
Floating bearing is the one that is left unconstrained axially, to accommodate for thermal (or other) expansion of the shaft.
For non-separable bearings:
- Fixed-end: Constrain all four corners
- Free-end: Leave both sides open for inner ring or outer ring (but not both)
For separable bearings:
- Cannot be made fixed-end
- Free-end by default, so we can constrain all four corners
For angled bearings in a pair, there is no distinction between fixed and floating bearings.
Whenever appropriate, bearings are arranged with one as fixed-end and the other as free-end. Usually, the working end is fixed and the driving end is free. If the shaft is short and thick, and no significant axial load, then we may not use free-end.
If the machine requires more precision, free-end may be constrained with Bellville spring washers. Bearing still allowed axially, but with some loads. Such preloading also reduces noise and vibration.
