Calculator Inputs
Use 0° included angle for square threads. Typical trapezoidal or Acme forms use a positive included angle.
Example Data Table
| Case | Load | Mean Diameter | Pitch | Starts | Thread μ | Collar μ | Included Angle |
|---|---|---|---|---|---|---|---|
| Machine Jack | 15,000 N | 32 mm | 6 mm | 1 | 0.12 | 0.08 | 0° |
| Lift Table | 8 kN | 28 mm | 5 mm | 2 | 0.10 | 0.06 | 30° |
| Positioning Actuator | 2,500 lbf | 1.25 in | 0.2 in | 1 | 0.15 | 0.05 | 29° |
Formula Used
Lead: L = pitch × starts
Helix angle: tan(λ) = L / (π × dm)
Equivalent friction for thread angle: μ′ = μ / cos(α), where α is the half-angle.
Thread torque to raise: Traise,thread = W(dm/2)[(μ′ + tanλ)/(1 − μ′tanλ)]
Thread torque to lower: Tlower,thread = W(dm/2)[(μ′ − tanλ)/(1 + μ′tanλ)]
Collar torque: Tcollar = W μc(dc/2)
Total torque: Ttotal = Tthread + Tcollar
Raising efficiency: η = [W × L] / [2π × Traise,total]
These equations are commonly used for screw jacks, feed screws, vertical lifting screws, and actuators where thread friction and collar friction both affect drive torque.
How to Use This Calculator
- Enter the axial load and choose the matching force unit.
- Provide the mean screw diameter and collar mean diameter.
- Enter pitch and number of starts to establish lead.
- Set thread and collar friction coefficients from material data.
- Use 0° for square threads or the actual included angle for trapezoidal forms.
- Enter screw speed to estimate travel rate and power demand.
- Press Calculate Torque to display results above the form.
- Use the CSV or PDF buttons to export the calculated summary.
Frequently Asked Questions
1. What does this calculator estimate?
It estimates thread torque, collar torque, total lifting torque, lowering torque, efficiency, travel rate, power demand, self-locking behavior, and possible overhauling risk.
2. Why is mean diameter required?
Torque depends on the radius where the axial load acts through the thread. Mean diameter gives that effective radius and directly affects helix angle.
3. How does thread angle change the result?
Non-square thread forms increase the effective friction term. That usually raises required torque and can improve resistance to back-driving.
4. What is self-locking?
A self-locking screw resists reverse motion under load without external braking. It generally occurs when friction exceeds the helix tendency to back-drive.
5. What does overhauling risk mean?
It means the load may help drive the screw downward. In that case, braking or control measures may be needed for safe lowering.
6. Should collar friction be included?
Yes, when the load passes through a thrust collar or bearing surface. Ignoring collar friction can noticeably understate the motor torque requirement.
7. Can I use inches and pounds-force?
Yes. Select lbf for load and in for length. The calculator converts everything internally and still reports torque in standard engineering outputs.
8. Is this suitable for final component sizing?
It is useful for preliminary engineering checks. Final sizing should also consider buckling, stress, thread wear, duty cycle, lubrication, and bearing details.