For selected handle radius L, hand force F, screw pitch p and lumped efficiency η, handle torque is FL and the conditional axial force is Faxial = 2πFLη/p. The ideal screw advances one pitch per revolution.
Ideal Screw-Clamp Work Model
Explore ideal screw-clamp work balance, handle travel, torque and selected-efficiency axial force.
Equation Used
- Hand force is tangential at the selected effective radius.
- Pitch is axial advance per revolution for a single-start equivalent screw.
- Efficiency is a selected lumped value applied to input work.
- Thread, collar, pad and frame stresses, deflection, wear and ratings are excluded.
The former undocumented 8 kN frame comparison is removed; use manufacturer ratings for real clamps.
Connected clamp topology
The animation shows a rigid C-frame, fixed threaded boss, translating screw, connected swivel pad, workpiece and fixed jaw. A projected end view of the tommy bar rotates with the screw while the screw advances one selected pitch per turn.
The force result is a selected-efficiency work model; the animation does not simulate thread contact, pad swivel dynamics or frame deflection.
What the calculator determines
Select effective handle radius, thread pitch, tangential hand force and lumped efficiency. Outputs are ideal geometric mechanical advantage 2Ï€L/p, handle travel per turn 2Ï€L, conditional axial force and handle torque FL.
It does not calculate thread stress, stripping, buckling, pad pressure, frame bending, proof load, safe working load or manufacturer rating.
Work balance with selected efficiency
Handle work per turn is F(2πL). Conditional axial work is Faxialp, so Faxial = 2πFLη/p. Mechanical advantage is 2πL/p, handle travel is 2πL, and torque is FL.
Selected-input example
For L = 120 mm, p = 3 mm/rev, F = 50 N and η = 48%, geometric mechanical advantage is about 251:1, handle travel is about 754 mm/rev, torque is 6 N·m and conditional axial force is about 6.0 kN.
Scope and design boundary
The former page compared force with an undocumented 8 kN frame value; that pseudo-rating is removed. Real efficiency depends on thread geometry, friction, lubrication, collar friction and load, while safe clamp force is limited by every component.
Use manufacturer ratings and appropriate engineering verification for real hardware. Do not infer a safe force from this idealized work model.
Questions
Is 2Ï€L/p the actual force multiplication?
It is the ideal geometric ratio; the selected η scales the conditional force for lumped losses.
Why does lower pitch increase force?
The same input work is spread over less ideal axial travel per turn.
Is handle torque a clamp rating?
No. It is only FL for the selected tangential force and radius.
Can this size a clamp?
No.
References & Further Reading
- Wikipedia contributors. Clamp (tool). Wikipedia
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