PSN-L Email List Message
From: Gordon Couger gcouger@..........
Date: Sun, 06 Nov 2005 12:51:50 -0600
> 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
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.
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