Can't cha' take a flat piece of delrin, steel, or SST and place a piece of
delrin on it with a bit of weight and raise one end to see which has the
lowest angle before sliding?
Makes sense to me...!
Delrin on SST, if it's polished.
If you need plastic on plastic, Valox has a lower coefficient on itself than
just about anything. It's very "delrin like" machinig wise, and very similar
mechanical properties. It is a bit more expensive though.
There are a lot of smart folks on this group (me not necessarily being
one of them) and if you give us a bigger picture of exactly what it is
you're working on (unless it's a top secret not yet patented idea), it
Not sure I'd know the answer to that one, Alex, but I can't imagine that
aluminum would be lower in friction unless you used a very hard alloy,
perhaps something like 7075-T6, or you anodized the parts first. Seems to
me the softer aluminum alloys would have a relatively high wear factor.
We always anodoze the aluminum member.
The glides are of UHMW, in a box extrusion appx 4in x 4in square, up to 24
ft long with an open side for mechanical connection to the load. The
carriage is internal, belt driven and 10in long, with 4 glides at each
end--total glide surface contact is ~appx 8" sq.
The servo is 10 amp and max velocity is ~ 2ft/sec (estimate) ---Average mass
loading on the motion plane is ~ 20lbs likely( again estimated ).
Units have been tested in the lab to simulate over 8 yrs of usage and no
failures have occured.
I cannot divulge actual customer product or give more than general info as
to design details without breaching confidentiality agreement as this is my
customer's product and design engineering.
There are available "channell" style uhmw extrusion as well as pre-made
round bushings designed just for this function--And they are quite
In retrospect, I would suggest anyone designing linear slides using plastic
bearings should investigate by consulting with the plastics suppliers,
likely they will have much data on hand as to proper selection and
engineering so that the proper choice can be made based on intended function
of the completed unit.
No one yet mentioned cleanliness. I see a ton of failures of various
Steel materials on various plastic materials materials due to dirty
shops and poor practice in cleaning before assembly. Had one (actually
many similar) occurrence where the installer did a bunch of grinding on
stainless piping above a machine and then reassembled the parts of the
machine without cleaning. The grinding dust seated into the plastic and
made a really nice honing stone for the expensive stainless steel chain.
Also....just because you go for the lowest friction by the "book"
doesn't always translate to real life. I constantly have engineers
telling me that the book says that large roller double pitch roller
chain has a friction of .1 whereas chain sliding on a plastic runner is
higher. They always forget that in practice (these applications) the
chain rollers eventually lock up and are dragging steel on steel.
The moral is, there's more to the story than just friction factor.
Remember the realities of use too.