In article ,
says...
In article , Ned Simmons
says...


One thing that I worry about on my machines is the fact
that once grit or a particle gets imbedded in the plastic
it'll likely get dragged back and forth for a long time. My
mill has bellows way covers so is pretty well protected,
but the lathe has a dovetail bed with a nice wide flat
surface to catch anything that falls on it.

But isn't the ability of softer way sliders a plus? Then
the abrasive particle will simply embed deeper as time
goes on, whereas in cast iron/cast iron systems, it
will embed in something *hard* and keep on wearing
the bed ways?

I've heard this claim for many different bearing materials
over the years, and while it makes sense to me that if the
offending particle is hard enough to wear a bearing surface
it's likely to be hard enough to embed in the mating
surface. And it makes sense if you're going to have an
embedded particle, it's better to have it stuck in a softer
rather than harder matrix. Nevertheless, it always troubles
me.

Quite a few years ago I was in the marine hardware
manufacturing business. One of our product lines was
stuffing boxes and stern bearings. We used a composite
plastic bearing rather the traditional rubber cutless
bearings in our stern bearings. Initially, most of these
were installed in lobster boats here in Maine where deep
water and muddy bottom is typical. When we started selling
more into southern New England, where shallower water is
the norm and sandy bottom more common, we started getting
complaints about excessive shaft wear. I never got a
definitive answer, but always assumed that the sand was
embedding in the plastic bearing, rather than flushing thru
like the rubber bearings. I realize this isn't a very good
analogy, but it's always made me leary of this sort of
claim.

It looks like the company now offers a composition
specifically for conditions where sand is suspended in the
water.
http://www.thordonbearings.com/3bii1.htm


Has anyone created bed sliders out if, say, brass or bronze?
If not, the reason probably is that they get charged as
a lap does, and will wear the harder bed rapidly.

I'm quite sure my old Rathbone chucker had bronze bushings
running on round ways, but that was a pretty unique
machine. It was a clone of a Hardinge chucker in that it
used the same turret and spindle tooling, but looked more
like the Monarch chuckers. In any case, having round ways
made it easier to exclude crud from the way bushings, so
the bronze didn't seem to be a problem. It was 40 years old
when I sold it, and it could easily work to a few tenths.

Ned Simmons