Torque holding ability of a press fit bushing 1

[trallee]

After researching a while on the internet, thru Mark's, and Roark's I thought I would ask here if my logic is correct. I need to know the torque holding ability of a bushing press fitted into a bore. I can calculate the implied force from the equation Deflection = (P*L)/(A*E), where deflection is equal to my interference fit. P would be my implied force. If I multiply this force by the coefficient of friction for my two materials and resolving it at the OD of the bushing I should have my theoretical holding torque? Or am I totally out there on this one? Thanks for any help on this one.

Trallee

 

[CanEngJohn]

You need to resolve it at both OD and ID looking at the frictional coefficients at both points (unless either is keyed). The weaker joint will lose its grip first. (Either the bushing will spin on the shaft or the bushing will spin in the housing.)

Basically though you are correct with the following twist - static vs dynamic frictional coefficients. Once you start to spin the amount of torque you can hold usually drops.

As an aside I have never even heard of someone relying on a press fit bushing to transmit a torque. Once torque transfer needs to occur usually a key or dowel is designed into the joint.

 

[trallee]

Thank you for the verification. The reasoning behind the torque calculation is the bearing had spun in the bore and now I am trying to get an understanding of what happened so I can size my dowels and new fit. Thanks again.

 

[desertfox]

Hi trallee

Take alook at thread404-45029 it gives all the formula you require for torque capacity of press fits.

regards desertfox

 

[trallee]

Thanks for the info.

 

[desertfox]

Hi trallee

Your welcome glad I could help


regards desertfox

 

[trallee]

Hello desertfox,
I was redoing this equation in the other post (javascript:gothread(404,45029)) and noticed I had substituted for Ui with Uo in the last part of the equation. I do not remember if this a typo or something I did because I thought it would look better. I am writing a standard for our guys to calculate the best fit for bushings we use here. We have always used the 0.0005"/" of diameter and then double checked the hoop stresses but since we are getting bigger we need a better method that our draftsmen can use for our simpler stuff.

I was going to write a TK sheet and publish it to excel for our guys to use when I noticed the typo that I had made. Is it a error I made or should it be Uo/Eo?

Guess I could trace out the logic but it will save me a lot of time if you could verify it.

Thanks,
Troy

 

[desertfox]

Hi trallee

It is an error on my part it should be Uo/Eo however if the
materials your putting together are the same ie steel on steel you won't notice any difference.
By the way well spotted.

regards desertfox

 

[Cockroach]

You can use thick wall pressure vessel equations to double check your original work.

There is a nice presentation on Interference Fits, Lecture 15 (Engineering 473 - Machine Design) from the University of Tennessee at Martin, School of Engineering. Looks like the professor quoted Shigley for the most part, possible the course textbook or reference.

At any rate, Lame's Equations are discussed, developed and put to use through an example.

I think you're all over this problem like white on rice. It never hurts to have a backup calculation to proove your work.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[unclesyd]

Here is the website mentioned by Cockroach

http://www.utm.edu/departments/engin/lemaster/machine_design.htm