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# Tangential Forces in a Clearance Fit

## Tangential Forces in a Clearance Fit

(OP)
I have a .508" steel shaft with a plastic bushing of size .511" (.003" clearance) and I'm trying to determine the tangential forces applied onto the shaft by the bushing. The coefficient of friction between the components is estimated 0.37.

I've found plenty of literature on pressure for interference fits, but none on clearance fits.

Essentially, I'm trying to determine a function how clearance between components affects the force applied to the shaft. F(clearance) = Force

Thank you!

### RE: Tangential Forces in a Clearance Fit

Hi kylegodwin

If I am understanding your situation correctly then as I see it the only tangential force acting will be friction between the shaft and the bushing, this will be directly related to the mass of the shaft over the two bearings, this shaft mass will also generate pressure and bearing stress on one side of the bearing, now as the shaft and bearing contact are on an infinitely thin tangential line the stress would be infinite, your best bet would be to look for Hertzian contact which hopefully deals with what you are looking for.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

### RE: Tangential Forces in a Clearance Fit

First comment is whether the .003 clearance is theoretical or actual. Next comment is what the tolerance range creates in clearances. Following cooment is the effect of thermal expansion of plastic bushing and steel pin. Contact stress is a consideration to make. Get a book and find the equations.

Here is a calculator that may shed some understanding, but without verification who knows if it is correct.

http://www.amesweb.info/HertzianContact/HertzianCo...

### RE: Tangential Forces in a Clearance Fit

when I hear tangential I think of the force that tried to make the horizontal rotating shaft climb up side of the bearing bore.
Kind of like the thing that happens in hydrodynamic bearings bot opposite.
http://gasturbinespower.asmedigitalcollection.asme...

Do you mean something else?

### RE: Tangential Forces in a Clearance Fit

The tangential force equals the radial force times the friction coefficient.

If the clearance exists all around the shaft (i.e. it's suspended by some mechanism not mentioned yet), the radial force is zero, hence the tangential force is zero.

Mike Halloran
Pembroke Pines, FL, USA

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