- posted
14 years ago

I am just doing some quick back of the envelope calculations on how

much you can torque a bolt. Let's use 60kpsi as the tensile strength,

this is just approximate. if I have a 1/4" x 20tpi bolt how much can

I torque it? I've tried calculating and I think I'm making an error

area = pi*.125^2 ~= .05 in^2.

.05 in^2 * 60k lb/in^2 = 3000 lb.

sounds reasonable enough. here's where I get into trouble

pitch = 1/20 tpi = .05

lets treat the radius as 1 foot to normalize it to ft-lbs of torque.

the advantage of a screw is circumference/pitch, which gives:

pi * 24 in. / .05 in. ~- 1500

So, does that mean I can only torque it to 2 ft-lbs before I snap it?

I doubt it. Clearly I'm making a mistake somewhere.

Of course I am ignoring things like friction, shear stress, etc. just

looking at tensile strength.

Thanks,

Viktor