1 inch lead screw

[Ed Williams]

I have a one inch lead screw with a very good nut it is 3 feet long. I want to use it on a 3 ft table will it require a larger stepper to move it than a 1/2. With both having the same pitch.
Thanks

[vacpress]

Ed,

One could definiately assume the large load of a 3 foot long, 1 inch steel rod is going to require more force than a rod half the size. I think, actually the calculations are rather easy to do on this one.

If i wasnt about to goto bed I would dig out machinery's handbook and find the formula for you...

you want to find 'the energy required to rotate a given load', i beleive.

[Climatepro]

Ed,
The calculation to determine which one will require more torque depends on the thread geometry, as the geometry influences how much friction you have.

So I worked an example assuming a 29 deg ACME thread, 10 lb load, friction coeff 0.1
One case with a diameter of 1in, pitch diameter of 0.9in, lead 0.1in.
One case with a diameter of 0.5in, pitch diamter of 0.4in, lead 0.1in.

1in =>0.63 in.lbf torque
1/2in =>0.37 in.lbf torque

Friction really is very important with a power screw, and the bigger screw gives the frictional force more of a moment arm.

Of course torque and frictional losses can't be your only concern when selecting which screw to use. Another major consideration is the tendency of a screw to buckle in compression, and the stiffness of the screw which will affect how fast you can spin it with a given load without buckling. Larger screws also have the advantage of lower bearing pressure on the nut and screw, so longer life.

Hope this helps,
Climatepro