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Posted by Dave Baker on April 28, 2008, 5:00 pm
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> What sort of surfaces are best for steel/bronze bearings?
>
> I thought to polish the steel shaft as high as I can (shiny!), but leave
> the bronze bearings as-bored, ie a little groovy. The bearings compress,
> so after wearing in I can adjust them back.
>
> They are 22 mm and 18 mm dia, will run at up to maybe 10,000 rpm,
> lubricated, sideways loads only (it's the mill main shaft, with an
> integral ER20 chuck on the end, for a BCA).
>
> Is this a good idea? Any ideas what kind of lubrication to use? Any
> suggestions? Looking for better-than-a-tenth (~1.5 microns) tir.
In an engine you'd have a number of similar situations.
1) The crankshaft pins and bearings would be pressure fed with oil and
surface finish on both would be as fine as possible. Lubrication would be
entirely by hydrodynamic wedge separating the running surfaces.
2) In the little end of a fully floating conrod the only lubrication would
be from whatever got splashed up there. The pin would have an ultra fine
finish and the bearing would be either honed to a cross hatch finish or
roller burnished.
3) The finish in the gudgeon pin bore of a splash lubricated aluminium
piston is normally roller burnished. I've also seen honed finishes but only
in aftermarket pistons where perhaps the manufacturer didn't have the ideal
equipment.
In other words lubrication, or the absence of large amounts of it, doesn't
seem to impose a requirement for the bearing to have an oil retaining
surface if that's what you're concerned about and I'd recommend a fine honed
finish. I suggest that leaving it as bored wouldn't be ideal and the bearing
contact area would be much reduced. The shaft would always be fine polished.
--
Dave Baker
Puma Race Engines
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>
> I thought to polish the steel shaft as high as I can (shiny!), but leave
> the bronze bearings as-bored, ie a little groovy. The bearings compress,
> so after wearing in I can adjust them back.
>
> They are 22 mm and 18 mm dia, will run at up to maybe 10,000 rpm,
> lubricated, sideways loads only (it's the mill main shaft, with an
> integral ER20 chuck on the end, for a BCA).
>
> Is this a good idea? Any ideas what kind of lubrication to use? Any
> suggestions? Looking for better-than-a-tenth (~1.5 microns) tir.