Hello, I could use a little help with a calculation that I've been struggling with.

I wish to mount a pulley to the end of a 20mm shaft whereby a M8 cap screw will secure it, there won't be a keyway or any other method of preventing the pulley from slipping, only friction. So this is where I need a little help, I want to calculate the torque required to make the joint fail so the pulley slips on the shaft. The pulley won't actually be under massive load but I'd like to be certain it's not going to fail.

Here's a few pictures of it.

Cheers, Tom

Sorry for large images.

 

Is the pulley an interference fit with the shaft? How much interference?
Or is it a sliding fit?
What are the materials of the shaft and pulley?

Will the pulley rotate in one direction only? Or will it go both directions?

If it goes both directions you will have great difficulty keeping the screw tight.

What happens if it slips? Do people die or become injured? Does high dollar equipment get damaged?

Answers to first four questions are required to know what analysis method is required.

Other questions go to deciding if the design is a good or prudent one.

 

Thanks for your response Erich.

The pulley will be a sliding fit on the shaft.

Shaft will most likely be 1050 carbon steel and the pulley 6082 T6 Aluminium.

The pulley will be used in both directions, I intended to use loctite threadlocking compound to help prevent the screw from loosening.

It'll be used in a non critical application, no people or expensive equipment will be harmed if it slips.

Also the mating surfaces will be suitably machined for good contact.

Thanks for helping!

Tom

 

You can probably get a rough calculation easily enough, but what with the loctite and a few other mitigating factors, as well as the basicness of the system, I think a practical test is the way to go. Mock it up, grab a torque screwdriver, and loosen the screw. Whatever torque it takes is the torque you're looking for.