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UHMW vs. Nylon

F

Fellowcraft

Plastic
Joined
Oct 7, 2012
Location
Toronto, Ontario, Canada
I was wondering if you folks could provide some advice on a project. I would like to machine a large clamp ring for a quality control device that is about 24" in diameter. The clamp ring will have to be loosened so the device can be rotated, then clamped again. The surface of the device cannot be damaged, so Delrin or Teflon would have been good choices; however, they are cost prohibitive given the size of the material. My next choices are UHMW or Nylon--any opinions on either one regarding friction and machinability?

Thank you.
 
If strength matters I'd use nylon, but otherwise go with UHMW. Easier to machine (less burring), very slippery, decent strength.

Use new tools that haven't cut metals, a small corner radius on the endmill will give cleaner surfaces when milling. If everything is turning use tool bits or inserts made for Al, but again, not having been used beforehand. If drilling watch for "self feeding", clamp the part well.
 
UHMW is very slippery for sure. It machines easily, but can be hard to hold onto and is not rigid at all. Nylon is more rigid, but less slippery. UHMW will probably be less expensive.

Regards.

Mike
 
Thermal expansion at that diameter will be significant unless it is climate controlled year round. If the fixture and part are the same material then it wont be a problem.

Ive made metal assembly fixtures and lined it with adhesive backed uhmw to get the best of both worlds.

Sent from my SM-G930P using Tapatalk
 
I hate UHMW. If it was my part, I would build it out of MDS filled nylon (sometimes called nylatron). It is inexpensive if you call around, machines very well, and has a low coefficient of friction.
 
UHMW will be a lot cheaper, not as strong, lower coefficient of friction and have more thermal expansion. Virgin UHMW will be a lot better than that made from recycled material but of course, it will cost more. IME UHMW made from recycled material has many other resins in it, with a higher coefficient of friction, just depends on how much mystery plastic that is in it. Some nylons can be a real bitch to machine and Nylatron can be a little brittle so be careful not to machine too aggressively in the wrong spots.

How thick is your part?
 
Everyone has assumed that you want the lowest friction, but from your description it seems that while clamped you want things to stay in place. Since you will loosen the clamp to move the part it may be best to go with an ordinary nylon, not filled, and not UHMW poly.
 
Does the design require a monolithic ring? Or could the prohibitive cost of the clamp ring be controlled, by producing a segmented composite ring.

Along the lines of a steel band with an ID comprised of segments of whatever material you otherwise prefer to be in contact with the rotating element.
 
PVC is another plastic to consider. It is pretty cheap, easy to machine, stronger than UHMW, with a much higher coefficient of friction. It is not nearly as wear-resistant as polyethylene or nylon though.

Oh, and you can glue it together unlike any other plastics mentioned.
 
Last edited:
I really think we need more information. If you want to brake or hold the device in question you need some material with
some "grab", not something that will slide easily like teflon or UHMW both of which are pretty slippery.

How much power do you need to apply to lock the device in place? How often will you be applying the brake? Will it be
manually actuated? Or possibly hydraulic? Will the device rotating at any kind of speed? Does the brake or clamp
have to locate the device or will it be strictly used for keeping it from moving?

What about using a metal ring with a non-marking liner? There are numerous ways to tighten something like that up...
 
Be aware that most nylon's are hydroscopic and a single pc that large may change dimensions if humidity levels change. Not sure about the other resins but a factor to be aware of.
 
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