Clamp Bushing Torque Capacity Calculator

How to use

1. No mode selection is required; this calculator represents one uniform-pressure cylindrical clamp interface.
2. Enter shaft diameter d and actual engagement length L in millimetres. L is the length over which the bushing overlaps the shaft and is approximately half the overall coupling length in the illustrated two-sided arrangement.
3. Enter combined clamping force Fᵢ in kilonewtons. Use the total effect of the two clamp screws combined, not the force from one screw.
4. Enter a defensible interface friction coefficient μ. Surface finish, coatings, contamination, and lubrication can change μ substantially.
5. Select Calculate, or edit a field for an immediate update. Select Reset to restore the 14 mm, 14 mm, 2 kN, and 0.2 example.
6. Read torque capacity as the canonical result; pressure, friction force, and area explain the load path. Displayed outputs are rounded to two decimals.
7. Correct any input warning and independently check material contact pressure, screw preload, slip safety factor, and service loads.
8. Do not use this model for taper-angle preload conversion, keyed torque sharing, nonuniform contact, shock, fatigue, plasticity, fretting life, or safety-critical final design.

Worked example

1. Use d = 14 mm, L = 14 mm, Fᵢ = 2 kN, and μ = 0.2. 2. The interface area is 615.75 mm² and mean pressure is 20.41 MPa. 3. Friction force is 2.51 kN and maximum transmissible torque is 17.59 N·m. 4. The result is a nominal slip threshold; select a lower allowable working torque after pressure, preload scatter, friction uncertainty, and safety-factor checks.

Equations used

Mean contact pressure: p = 2Fᵢ/(dL)

Cylindrical contact area: A = πdL

Available friction force: Ff = μpA

Maximum transmissible torque: T = Ffd/2

Here d is shaft/interface diameter, L is axial engagement length, Fᵢ is the positive combined radial clamping-force magnitude, μ is the dimensionless friction coefficient, p is mean pressure, A is cylindrical contact area, Ff is circumferential friction force, and T is torque capacity. The calculation converts mm, kN, and N to SI units before reporting MPa, mm², kN, and N·m. Positive magnitudes are used; torque direction is not signed.

Theory and method

The model distributes the combined clamp force over the projected bearing measure dL, with the factor 2 representing opposed radial loading. It then applies Coulomb friction over cylindrical area πdL and a moment arm d/2. Algebraically, Ff = 2πμFᵢ and T = πμFᵢd; engagement length cancels from nominal torque but remains essential to mean pressure.

Assumptions and limits: concentric cylindrical shaft and bushing, uniform mean pressure, full engagement, constant Coulomb friction, quasi-static loading, no key contribution, and no local yielding. The entered Fᵢ must already be a known radial clamp force; screw torque, thread friction, taper angle, cone action, split-ring stiffness, and preload loss are not calculated. Verify hub and shaft pressure limits, screw ratings, tolerances, thermal effects, fretting, fatigue, vibration, and load spectra separately.

Reference: A. van Beek, Advanced Engineering Design: Lifetime Performance and Reliability, shaft–hub connection calculation collection; the implemented equations are listed above. Apply manufacturer data for the actual bushing, fasteners, surface condition, and allowable loads.

Continue in TriboSolver to refine contact pressure, friction uncertainty, material response, and service loading with a higher-fidelity engineering workflow.

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