Calculator
Formula used
This calculator models a vise as a power screw. Applied torque is converted into axial clamping force.
- T = Fh × Lh (handle mode), where T is torque.
- Lead = Pitch × Starts (pitch mode).
- Clamp Force, F = (2π × T × η) / Lead, where η is efficiency.
- Usable Force = F / Safety Factor for conservative planning.
- Jaw Pressure = Usable Force / Contact Area when area is provided.
How to use this calculator
- Select your vise type to load practical starting values.
- Choose handle mode or direct torque mode.
- Enter lead, or enter pitch and thread starts.
- Set efficiency and a safety factor for your task.
- Optionally enter jaw contact area for pressure estimates.
- Press Calculate and review force and pressure outputs.
- Use CSV or PDF to record setups for repeatability.
Example data table
| Scenario | Torque mode | Lead | Efficiency | Safety factor | Estimated clamp force | Usable force |
|---|---|---|---|---|---|---|
| Grafting jig hold | Handle: 120 N, 18 cm | 2.0 mm/rev | 35% | 1.8 | ~ 23,700 N | ~ 13,200 N |
| Stake bracket bend | Direct: 10 N·m | 4.0 mm/rev | 30% | 1.5 | ~ 4,712 N | ~ 3,141 N |
| Softwood clamp pad | Handle: 80 N, 20 cm | 3.0 mm/rev | 28% | 2.0 | ~ 9,378 N | ~ 4,689 N |
Examples are illustrative. Measure your lead and adjust efficiency to match your vise condition.
Technical article
Clamp force and garden fabrication tasks
Garden jigs, trellis brackets, and irrigation fixtures often need repeatable holding without crushing soft stock. A vise behaves like a power screw, multiplying modest hand torque into large axial force. For thin aluminum or mild steel, consistent clamping improves drilling accuracy and reduces bit chatter. For wood dowels, grafting jigs, and plant-support hardware, limit force and increase contact area using pads.
How screw lead drives mechanical advantage
Lead is jaw travel per full turn. Lower lead increases mechanical advantage, so force rises quickly for the same torque. As a rule, halving the lead roughly doubles calculated clamping force, assuming the same efficiency. Multi-start screws move faster because lead equals pitch times thread starts, but the higher lead reduces force. Measuring one-turn jaw travel is the fastest way to capture lead for your vise.
Efficiency is the real-world correction
Efficiency captures friction in threads and thrust surfaces plus small losses from jaw alignment. Dry, worn screws can run near 20–30% efficiency, while clean lubrication can push 35–45% in practical use. If your calculated force seems high, reduce efficiency and compare against how easily the handle turns. Using consistent lubrication and cleaning improves repeatability across seasonal workshop conditions.
Jaw pressure, material damage, and pads
Force alone does not predict damage; pressure equals usable force divided by the contact patch. Doubling the contact area halves pressure and helps prevent bark bruising, stem crushing, and imprinting on soft metals. When clamping coated parts, use smooth pads and avoid serrated jaws. Track pressure values to standardize delicate operations like grafting fixtures or thin-wall tubing bends.
Safety factor and practical validation
A safety factor reduces calculated force to a conservative working level. Values of 1.3–2.0 are common when the consequence is part damage or slippage. Validate by tightening to the usable-force target, then applying a controlled pull test on the workpiece. Record torque, lead, and efficiency in exported reports to build a reliable shop baseline over time.
FAQs
1) What efficiency should I use if I do not know it?
Start with 30–35% for a typical bench vise. If the handle turns very smoothly with lubrication, try 40%. If it feels gritty or stiff, use 20–25% for safer estimates.
2) How can I measure screw lead quickly?
Mark the handle position, then turn it exactly one full revolution. Measure the jaw travel using a ruler or caliper. That travel distance is the lead per revolution for the calculator.
3) Why does a higher lead reduce clamping force?
Higher lead means the screw advances farther per turn, so the same torque is spread over more travel. Mechanical advantage drops, so axial force decreases, even if your hand effort feels similar.
4) What jaw area should I enter for pressure?
Enter the estimated contact patch between jaws and workpiece, not the full jaw face. For padded jaws, use the pad imprint size. For round parts, use the flattened contact band estimate.
5) Is the usable force the maximum I should apply?
Usable force is a conservative planning value after the safety factor. You may exceed it, but risk of slipping, crushing, or tool damage rises. For delicate garden fixtures, stay near usable force.
6) Can I use this for clamp selection or only vises?
The model is for screw-driven clamping where torque produces axial force. It can approximate screw clamps if you know lead and efficiency, but quick clamps and cam clamps need different assumptions.