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# Ratio of torque required to raise versus lower screw jack2

## Ratio of torque required to raise versus lower screw jack

(OP)
Hi All

Some help please. Does anyone know how to calculate the torque required to lower a load with a screw jack? Plenty of formulas available for raising it.

Or even a formula to calculate the ratio of torque required for raising versus lowering? I think these values will not differ by much seeing as friction between screw and nut remains in both cases.

### RE: Ratio of torque required to raise versus lower screw jack

Have you ever used a car jack? Lowering is far easier than raising it. Likewise when using jacking bolts and jacking nuts, but the effect is less smaller thread pitch.

I'd say the torque required is about 50-70% less for standard trapezoidal 'screw jacks'. That torque figure is calculated based off the analogue feedback from of my highly calibrated hand.

### RE: Ratio of torque required to raise versus lower screw jack

Work = torque x angular displacement (at input shaft) = frictional torque x angular displacement (at screw & bearings) + gravity load x vertical displacement. lowering is a negative displacement

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