Bushing material

I want to spin a nylon shaft in a plain bearing/bushing at low rpm. Is the choice of bushing material critical? Will brass or copper do?
As a matter of general principle should the shaft and bushing be made of different material? What would happen (for argument's sake) if one spun a brass shaft in a copper bushing?
Thanks,
Michael Koblic, Campbell River, BC
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On Aug 28, 8:18 pm, snipped-for-privacy@gmail.com wrote:

Sorry for the screwy units, but ............bearing material is rated by PV . The P is psi and the V is surface feet per minute. Nylon is good for about 3500. So calculate what the PV is. Assuming that it is below 3500 then most any usual bearing material will do. UHMW poly is 3000 and is the only material listed in the MSC catalog as a bearing material that is lower than nylon. It does not list copper or brass but cast bronze is listed as 75,000. So I am pretty sure copper and brass are way above the nylon shaft.
Dan
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Michael,
As a general rule of thumb, same-metal contact under pressure and motion will cause galling; the softer, the worse. Copper on copper would be a very bad bearing selections, because not only is the metal the same, it's soft.
Steel on copper works. Brass is a good bit harder than copper, but contains enough copper that I think it would smear off particles and gall.
Lloyd
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    What about the load? Low RPM may suggest high torque (but Nylon suggests otherwise) -- or is it just a clock hand's pivot. :-)

    Absolutely!
    Not different enough! I would expect galling. Brass is already part copper, and I'll bet that they would stick together over time.
    Brass in steel, fine.
    Brass in aluminum, fine -- except probably wear faster.
    Aluminum in steel, fine -- again with faster wear.
    Nylon in any of the above, fine at low forces.
    And ideally, you want to burnish the ID to make it as smooth as possible.
    Enjoy,         DoN.
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As a general principle, you want one material to be smooth and hard, and the other to be softer (but still hard enough not to deform with the pressure applied to the bearing surfaces). If both materials in a bushing have similar hardness or chemical affinity, you can get galling. Nylon will work as a bushing with most metals (unless it is glass-filled). When using nylon as a bearing material, watch out for excessive loads that deform the plastic, high temperatures, acids, and water absorption that makes nylon expand.
However, if the pressure on the bushing is low and the RPMs are low, you might be able to get away with similar materials if lubricated.
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On Tue, 28 Aug 2012 17:53:15 -0700, "anorton"

OK, thanks. The loads on this will be minimal. Did not know about nylon absorbing water.
Michael Koblic, Campbell River, BC
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