Interference Fit Pressure & Torque Calculator
Estimate interface pressure and friction-driven transmittable torque for a solid shaft pressed into a same-material hub, from the diametral interference.
Interference Fit Pressure & Torque Calculator
Estimates interface pressure and friction-driven transmittable torque for a solid shaft pressed into a same-material hub, from the diametral interference.
Assumptions & Limitations
- Assumes shaft and hub are the same material — dissimilar materials (e.g. steel shaft in aluminum hub) require the general two-material Lamé formula, not implemented here.
- Assumes a solid shaft (no bore); a hollow shaft reduces the achievable pressure for the same interference.
- Does not check whether the resulting pressure exceeds either material’s yield strength — always verify against your material’s yield/allowable stress.
- Does not account for thermal effects during shrink-fit assembly, or stress concentration at the hub’s edge.
Reference: ISO 286-1 IT Grade Tolerance Widths
Precomputed values from the exact formula used above — useful as a quick lookup without re-entering inputs.
| Nominal Size Range | IT6 | IT7 | IT8 |
|---|---|---|---|
| 18–30 mm | 13.1 μm | 20.9 μm | 32.7 μm |
| 30–50 mm | 15.6 μm | 25.0 μm | 39.0 μm |
| 50–80 mm | 18.6 μm | 29.7 μm | 46.4 μm |
Computed from the ISO 286-1 standard-tolerance-unit formula i = 0.45·D^(1/3) + 0.001·D (D = geometric mean of the size range, in mm). This gives the tolerance width only — fundamental deviation letters (H, g, k, p, s…) that set where the zone sits are not covered by this reference table.
Pressing a Bushing onto a 0.75″ Shaft
A steel bushing (1.5″ OD) is pressed onto a 0.75″ steel shaft with 0.001″ diametral interference, 1″ engagement length.
- p = Δ·E·(Do²−d²) / (2·d·Do²) = 0.001 × 30×10⁶ × (2.25−0.5625) / (2 × 0.75 × 2.25) ≈ 15,000 psi interface pressure.
- Transmittable torque (f=0.15): T = f·p·π·d²·L/2 ≈ 1,988 in-lbf (165.7 ft-lbf).
- Before finalizing, verify 15,000 psi is comfortably below both parts’ yield strength — this tool does not check that automatically.
- Assembly method matters: a hydraulic press assembly (f≈0.10–0.15) vs. a dry force-fit (f≈0.15–0.20) changes the achievable torque capacity even at the same interference.
Related reading: Metallurgy & Quality Control →
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