Power Screw Calculator
Analyze power screws (lead screws, jack screws). Calculate raising and lowering torque, efficiency, and self-locking condition.
Inputs
lb
in
in
in
Results
Raising Torque
1,517.6 in·lb
Lowering Torque
1,110.7 in·lb
Self-Locking
1
Screw Efficiency13.1%
Lead Angle3.04°
How to Use This Calculator
- Enter the Axial Load (W) in lb — the weight or force the screw must raise or lower.
- Enter the Mean Thread Diameter (dm) in inches — the average of major and minor diameters.
- Enter the Lead (l) in inches — the axial travel per revolution. For single-start threads, lead equals pitch.
- Set Thread Friction (f) and Collar Friction (fc): dry steel ≈ 0.15–0.25, lubricated ≈ 0.08–0.12.
- Enter the Mean Collar Diameter (dc) in inches where the thrust load is transferred.
- Review Raising Torque and Lowering Torque in in·lb, Screw Efficiency %, and whether the screw is Self-Locking — a non-self-locking screw requires a brake to hold load.
How the result changes with Axial Load (W)
| Axial Load (W) | Raising Torque | Lowering Torque | Self-Locking |
|---|---|---|---|
| 100,009 | 30,353.8 in·lb | 22,215.7 in·lb | 1 |
| 350,007 | 106,230.7 in·lb | 77,749.6 in·lb | 1 |
| 650,004 | 197,282.9 in·lb | 144,390.1 in·lb | 1 |
| 900,001 | 273,159.6 in·lb | 199,923.7 in·lb | 1 |
What each input means
- Axial Load (W)
- Axial load to be raised or lowered by the screw.
- Mean Thread Diameter (dm)
- Mean diameter of the screw thread. Average of major and minor diameters.
- Lead (l)
- Axial distance the nut travels per revolution. For single-start threads, lead = pitch.
- Thread Friction (f)
- Coefficient of friction between screw threads and nut. Dry steel ≈ 0.15-0.25; lubricated ≈ 0.08-0.12.
- Collar Friction (fc)
- Friction coefficient at the thrust collar or bearing surface. Ball bearing ≈ 0.01-0.02; sliding ≈ 0.08-0.15.
- Mean Collar Diameter (dc)
- Mean diameter of the thrust collar or bearing surface where the load is transferred.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersAxial Load (W) = 5000, Mean Thread Diameter (dm) = 1.5, Lead (l) = 0.25, Thread Friction (f) = 0.15 = 6 input(s) provided
- Calculate Raising TorqueRaising Torque1517.6 = 1517.6
- Calculate Lowering TorqueLowering Torque1110.7 = 1110.7
- Calculate Self-LockingSelf-Locking1 = 1
- Calculate Screw EfficiencyScrew Efficiency13.1 = 13.1
- Calculate Lead Angle3.04 = 3.04
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