KEVOS® MAKEOS · Fasteners
Screw Clamp Force Check (Handle Torque, Clamping Force, Screw Stress)
For a screw clamp, vice or press screw turned by a handle, what clamping force does the handle effort produce, and is the screw stressed within limits?
Check of a hand-operated clamping screw: the torque from the handle effort and its radius, the clamping force that torque produces through the thread and the swivel pad or collar friction (the power screw torque relation solved for the load, as the power screw torque tool), the compressive stress at the screw root, and whether the screw stays put, against the clamping force you need and the allowable stress.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Handle effort | N | Force applied at the end of the handle or tommy bar. |
| Handle radius (screw axis to hand) | mm | Distance from the screw axis to where the hand pushes. |
| Mean (pitch) diameter of thread | mm | Mean diameter of the screw thread. |
| Lead | mm | Lead of the screw (pitch × starts). |
| Thread form | choice | Thread form. |
| Thread friction coefficient | Friction in the thread (dry steel about 0.15–0.2, oiled about 0.1). | |
| Mean pad (collar) diameter | mm | Mean diameter of the swivel pad or thrust collar where the screw bears. |
| Pad friction coefficient | Friction at the pad or collar. | |
| Duty | ||
| Screw root diameter | mm | Root (minor) diameter of the screw. |
| Allowable compressive stress | MPa | Allowable compressive stress in the screw. |
| Clamping force needed | N | Clamping force the job needs. |
Method and formulas
- Torque = handle effort × radius.
- Torque to raise load F = F [d_m ÷ 2 × (L + π μ d_m sec α) ÷ (π d_m − μ L sec α) + μ_c d_c ÷ 2] (as the power screw torque tool), solved for F.
- Root stress = F ÷ (π d_r² ÷ 4).
- Example: 11.25 N·m at the handle gives 6,595.5 N of clamping force and 131.21 MPa in the screw.
Limitations
- Static tightening; impact from hammering the handle multiplies the force.
- Long, slender screws can buckle; check them as columns.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check a fixture or welding clamp screw
- Find the clamping force of a vice
- Size the handle for a needed clamping force
Who it is for
- Fixture designers
- Toolmakers
- Design engineers
What you get
- Handle torque
- Clamping force and efficiency
- Screw stress and decision
Interpreting the result
- Most of the handle effort goes into friction: lubricating the thread and pad can nearly double the clamping force.
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.
WORKOS tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
Open the Screw Clamp Force Check (Handle Torque, Clamping Force, Screw Stress) calculator
