KEVOS® MAKEOS · Mechanics
Power Screw Raise and Lower Torque
What torque raises and lowers this load with a screw jack or lead screw, including collar friction?
Torque to raise and to lower a load with a square, Acme or trapezoidal power screw, including thrust-collar friction, with efficiency and self-locking.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Axial load | N | Load to raise or lower. |
| Mean (pitch) diameter of thread | mm | Mean thread diameter = nominal − pitch ÷ 2 (approximately). |
| Lead | mm | Axial advance per turn (pitch × starts). |
| Thread form | choice | Thread profile. |
| Thread friction coefficient | Thread friction for the materials and lubrication (about 0.1–0.15 lubricated steel on bronze). | |
| Mean collar diameter (0 = thrust bearing ignored) | mm | Mean diameter of the thrust collar or washer; 0 if a rolling bearing makes collar friction negligible. |
| Collar friction coefficient | Friction coefficient at the collar. |
Method and formulas
- Raise: T = F dm/2 × (L + π μ dm sec α) ÷ (π dm − μ L sec α) + F μc dc/2.
- Lower: T = F dm/2 × (π μ dm sec α − L) ÷ (π dm + μ L sec α) + F μc dc/2.
- Efficiency = F L ÷ (2π T_raise); self-locking when the thread part of the lowering torque is positive.
- Example: 20000 N on a 30 mm, 6 mm lead trapezoidal screw needs 110.82 N·m to raise.
Limitations
- Uses the flank half-angle in the axial plane (sec α approximation).
- Starting friction is higher than running friction.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Size the handle or motor for a screw jack
- Compare collar bearings and lubrication
- Check whether a jack holds its load
Who it is for
- Design engineers
- Maintenance engineers
- Machine builders
What you get
- Torque to raise
- Torque to lower
- Efficiency raising
- Self-locking
Interpreting the result
- If the screw must hold a load reliably, add a brake; vibration can back-drive a self-locking screw.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1921–1928, 2561–2568. Topic reference; no source tables or recommended settings are reproduced.
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