A screw jack exchanges long circular handle travel for short axial screw travel. The calculator uses work balance to show that geometric tradeoff and then applies a declared aggregate efficiency.
Lifting Jack Interactive Calculator
Compare handle path per revolution with screw lead per revolution. The resulting ideal and efficiency-adjusted force ratios are model outputs, not rated jack capacity.
Equation Used
- Handle force is tangential and the entered handle path is total travel per revolution.
- Screw lift is axial lead per revolution.
- Efficiency is a user-entered aggregate factor and remains constant.
The calculation compares handle travel with screw lead, then applies the efficiency you enter. Its force result is a work-balance estimate; an actual jack must be used within its marked rating and instructions.
Direct rotating screw through a fixed nut
The animation follows the architecture described in US2960308A: a handle collar rotates the screw through a fixed body nut, so the screw and handle translate together. A cap journaled at the upper end carries the load without requiring the load to rotate.
The first half-cycle raises through three exact turns; the second reverses the same screw through three turns to lower continuously. There is no reset jump.
Where the screw-jack principle appears
Rotating-screw jacks are used when a long handle path must produce a short controlled axial displacement. The calculation here illustrates that work-distance trade only.
Any real lifting task must use the marked rated capacity and the manufacturer's operating instructions. The idealized calculator does not select equipment, authorize a lift or replace cribbing, stability, inspection and load-securing requirements.
Ideal work balance
Therefore ideal mechanical advantage is sin/sout. The calculator multiplies this ratio by the declared efficiency and input force. Neither result is an allowable or rated load.
Worked arithmetic example
For a 2500 mm handle path per revolution and 5 mm screw lead, ideal mechanical advantage is 500:1. With an entered aggregate efficiency of 50%, the displayed effective ratio is 250:1. An entered 30 lbf tangential handle force therefore produces 7500 lbf in the idealized work model.
That number is not a rated capacity or permission to lift a load. The model omits thread form, starting friction, buckling, bearing stress, base stability, component strength and manufacturer limits.
Model boundary and equipment selection
A smaller screw lead or longer handle path increases the ideal distance ratio but also changes turns, speed and real losses. The entered efficiency is a scenario value, not a material or lubrication lookup.
Select and operate an actual jack only from its marked rating, instructions and inspection condition. OSHA requires rated capacity to be marked, prohibits exceeding it, requires a positive stop against overtravel and requires the raised load to be secured.
Screw-jack calculator questions
Is the displayed force a safe working load?
No. It is an idealized work-balance output and does not rate any jack.
Can this calculator justify a handle extension or field adjustment?
No. It provides no guidance for extensions, relief adjustments, repairs or modifications; follow the manufacturer and applicable safety requirements.
Why include efficiency?
It lets the user apply one declared aggregate reduction to the ideal distance ratio. It does not predict efficiency from thread condition or lubrication.
Mechanism and safety references
- US2960308A, Telescopic jack: describes a threaded shaft in a nut, a cap journaled on the shaft and a handle engaging a collar to rotate the shaft.
- OSHA 1926.305, Jacks: requires marked rated capacity, prohibits exceeding it, requires a positive stop and requires the load to be secured after raising. These requirements are outside the ideal work model.
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