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Caster Axle Bending Check

Treat the caster axle as a simply supported beam with the wheel load at midspan, work out the bending stress, and compare it with the axle material's yield strength at the design factor you choose.

The axle is the smallest structural member in a caster and the one that bends first. Enter the wheel load, the bearing span, the axle diameter, and the material, and the calculator returns the bending stress, the allowable stress at your design factor, and the verdict.

Stress above yield is reported rather than blocked, because showing that a chosen axle yields is the answer you asked for. A real axle also carries shear at the fork legs and sees the load millions of times, so a stress well below yield can still crack at a groove or a retaining-ring seat.

Inputs

Load and axle geometry

Range: 10–40,000 lbf

Range: 0.5–8 in

The span the axle bridges between the two fork legs, measured at the inside faces. This is the beam length in the bending calculation.

Range: 0.125–1.5 in

Material and design factor

Range: 1–5

2 is a normal design factor for a static caster axle. Use 3 where the cart takes shock or the axle is a known weak point.

Result

Actual safety factor on yield
1.77
Bending moment at midspan (lbf-in)
250
Bending stress (psi)
20,372
Verdict
Below the safety factor you asked for. The axle will not bend under a steady load, but a shock or a jammed wheel will take it into yield, which is how axles fail in practice.
Material note
Mild steel is the usual commercial caster axle material: adequate at normal loads, but it has the least margin of the options here.

What to check

  • Use the load on one wheel, not the total cart weight.
  • Measure the bearing span as installed rather than assuming the axle length.
  • Treat a passing result as a static check only, and inspect for fatigue at grooves and shoulders.

Related calculators

Pure bending only. It does not model shear, fatigue, or stress concentration at any thread, groove, or retaining-ring seat, and the yield strengths are representative values rather than certified material properties. The fork legs, welds, and raceway are not checked and are often the weaker part. Confirm the actual material certificate for a critical application.