How To Repair Bushings & Pulley Bores

If you compare the area of surface between inside and out you will find the inside to be much smaller, less friction. That's why bushings are stationary relative to the shafts inside them.
 
Thanks. I was thinking that because of the increase in surface area that the normal force would be decreased and area of lubrication would be increased, so friction would be reduced.


Steve Shannon
 
After considering this more and some Google research, I remember that the calculation for friction force is only affected by normal force and coefficient of, not area. So I believe my question is still unanswered.


Steve Shannon
 
JPMacG said:
Rob, Do you ream the new bushing by hand? Or do you fixture the part and ream it on a machine?
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Mostly by hand and with a sharp reamer and minimum turns of the reamer. If I do it in the lathe I still turn it by hand if possible.
 
Steve,

I don't see any particular physical reason why the bushings couldn't be a press fit on the shaft and turn in the bore. But there is probably a sound financial reason not to do it. In practically all cases, the cost of a replacement shaft is much less than the cost of the housing.
 
Steve Shannon said:
After considering this more and some Google research, I remember that the calculation for friction force is only affected by normal force and coefficient of, not area. So I believe my question is still unanswered.


Steve Shannon
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Cor that stirred the old grey matter in the bone dome..


IIRC ............................ ro x mu x surface area = coefficient of of friction ( aka drag resistance ) ... so I suspect that yes surface area will have some effect .
The other thing that makes a big difference is the viscosity of the lubricant and its rate of decline as a lubricant etc , get it right in the correct tolerance fit and the shaft actually rotates / floats inside the bearing on a film of oil .
 
In the likely event of a lubricant film failure, the probability of survival is much greater using a steel shaft in a fixed bushing vs a bronze shaft (essentially) running in a cast iron piece.
 
That equation is not familiar to me. mu is typically used to represent the coefficient of friction (empirically determined as I recall) or a drag coefficient in aerodynamics related to shape. Rho is typically used in fluid dynamics to denote fluid density. Do you have more info about how your equation is used? Thanks!



Steve Shannon, P.E.
 
Tony Wells said:
In the likely event of a lubricant film failure, the probability of survival is much greater using a steel shaft in a fixed bushing vs a bronze shaft (essentially) running in a cast iron piece.
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What about a steel sleeve, pressed onto the steel shaft, which would run inside the cast iron piece? The actual application is the shaft within a backgear for a lathe. The replacement backgear has a bore that is 50 thousandths of an inch larger than the existing eccentric shaft.


Steve Shannon, P.E.
 
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