Power Screw Torque & Efficiency Calculator — Lifting, Lowering and Self-Locking Validator
Calculate driving torque and efficiency using axial force, screw geometry, thread angle and friction coefficient.
Enter the known values and review the calculated result
Input parameters
Use consistent values and select the intended engineering units.
Operating mode
Screw geometry
Load
Thread type
Friction
Results
Engineering Pro Save, document and continue this calculation
Turn this result into a reusable engineering record with saving, PDF export and reporting workflows.
Method, application and limitations
Review the calculation method, intended application and engineering assumptions before using the result in a design decision.
Formula and calculation method
Calculate driving torque and efficiency using axial force, screw geometry, thread angle and friction coefficient.
When to use this calculator
When to use this calculator:
- Estimate driving torque required to raise an axial load with a sliding power screw.
- Estimate back-driving torque during lowering mode.
- Check whether the screw remains self-locking based on effective friction and lead angle.
- Compare efficiency between lifting and lowering operation for the same screw geometry.
- Evaluate how friction coefficient and thread half-angle change torque demand and efficiency.
How to interpret the result
Driving torque is defined as the torque required at the screw to move the axial load in the selected operating mode.
Efficiency is defined as the percentage result calculated from lead angle and effective friction. Higher effective friction decreases efficiency, while a larger lead angle increases efficiency in lifting mode.
- Safe — the screw is self-locking, or no non-self-locking warning condition is triggered.
- Warning — the screw is not self-locking, meaning effective friction is not greater than the tangent of the lead angle.
- Invalid — at least one input or calculation condition fails validation, such as invalid mode, invalid geometry, axial force not greater than zero, friction coefficient outside 0.02–0.4, or thread half-angle greater than 30 degrees.
The result is used to evaluate whether the selected screw geometry, load and friction model produce a feasible driving torque and whether the screw can resist back-driving through self-locking.
Calculation example
Example:
A user wants to estimate the torque needed to raise a load with a power screw.
- mode = lifting
- d — Nominal diameter = 0.04 m
- p — Pitch = 0.006 m
- F — Axial force = 5000 N
- α — Thread half-angle = 15 deg
- μ — Friction coefficient = 0.12
The calculated driving torque is approximately 15.75 N·m and the efficiency is approximately 27.4%.
Assumptions and limitations
- The screw lead is equal to the pitch.
- The mean diameter is calculated as nominal diameter minus half the pitch.
- Effective friction is calculated from friction coefficient divided by the cosine of the thread half-angle.
- Self-locking is determined only by the condition effective friction greater than tangent of lead angle.
- Efficiency is limited to the range from 0 to 100%.