What can go wrong if both ends of a thermally expanding shaft are axially locked?

LILY Bearing | 2026-10-28

Best answer

Check whether expansion is accommodated or deliberately restrained

A shaft and its support structure can change length by different amounts.

If both bearing positions prevent the required relative axial movement, the resulting restraint can alter internal loading and setting. JTEKT's arrangement guidance therefore distinguishes locating and free-side functions. It also describes paired arrangements where fixed/free positions are not separated in the same way, so “both ends located” is not automatically a defect in every design. The important question is whether the actual arrangement was designed for its thermal and loading conditions. Adding an extra shoulder or locking feature during a repair can change that arrangement even when the bearing part numbers remain unchanged.

Use free expansion to expose the required design discussion

As a purely illustrative calculation, assume a length of 1 m, a thermal-expansion coefficient of 12 × 10⁻⁶/K and a uniform temperature rise of 50 K.

Free expansion would be 0.0006 m, or 0.6 mm. The coefficient is an example assumption, not a verified property of the machine's shaft. This arithmetic does not calculate restraint force or specify a floating allowance; housing movement and bearing settings still matter. It does show why an apparently small temperature change can create a real axial accommodation question. Compare the actual materials, temperatures and restraint geometry before deciding whether the assembled support arrangement preserves the design intent.