ChrisAtUpw@....... wrote:
 > In a message dated 06/11/05, jpopelish@........ writes:
 >
 >> All this discussion of using parts from ball bearings as hinge
 >> bearings, and it finally dawns on me that people are talking about
 >> everything except the surfaces that are made precisely as low friction
 >> bearing surfaces.
 >>

 >> I sawed a small (3/4 inch O.D.) ball bearing outer race in half with a
 >> moto cut off wheel and used the two halves as one side of the each of
 >> the hinge bearings.  I dimpled a piece of aluminum and epoxied a ball
 >> from the same bearing into the dimple as the other bearing surface.

 >       If these are ordinary bearings and not stainless steel, you will
 > need to put a drop of light oil on the contact point (clock oil?) and
 > make an overlapped paper screen around the joint to prevent the oil from
 > collecting dust.
 >       Chris Chapman

Hi Chris

There are several materials that I would consider if I were using a ball 
bearing for a pivot.   Ultra High Density Polyethylene for one bearing 
surface and a stainless steel, sapphire or ruby ball for bearing.

Using this chart on Coefficient for Static Friction 
http://www.carbidedepot.com/formulas-frictioncoefficient.htm a sapphire of 
tungsten carbide ball on a polyethylene seat look petty good.

The UHDPET would need to be pretty thin and backed by a rigid surface so 
the ball didn't creep into it and make a round socket that increased the 
friction. To over come the creep problem using a tungsten carbide tool 
insert with a screw hole in it as a socket 
http://www.jjjtrain.com/vms/Media/glossary_c/carbide.jpg and a sapphire 
ball may make a better bearing but the sharp edge of the hole in the 
tungsten carbide tool much be lapped smooth.

Gordon Couger
Stillwater, OK
www.couger.com/gcouger

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