UHMW or Acetal material choice

Making some stabilizers for a customer, basically a 6" OD, 4 inch ID tube that tapers down to a 4 inch OD 3 inch ID, 8" long that gets split in 2 lengthwise and screwed back together once it goes over his product. Has lots of windows and slots in it , nothing close tolerance, but a lot of machining. My question, which material will be more stable (less twist / bow) and more rigid after splitting them apart? Or is there a better choice of material? Non marking, non conductive, light weight are the only real characteristics needed. Customer looking for a recommendation from me. My thoughts are whichever will have less residual stress will probably be better. I know acetal will machine better, but that isn't the only consideration.

UHMW is more wear resistant, if that means anything. Acetal is cheaper and less prone to post Machining movement. UHMW is notoriously bad about not staying the shape you Machined.

R

IMHO Polypropylene, machining and stability wise is sort of in between Acetal and UHMWPE

Acetal would be my pick for ease of machining AND part stability after machining. Maybe start with plate, profile,drill and tap them, then lathe to what you want.
PVC would be in there as well, but not as good as acetal in any way but price.

Another vote for delrin...uhmwpe is a bastid...not as bad as tefzel though

+1 for Acetal. You also could look at HDPE which is reasonably tough and low friction, machines OK, is affordable and is the most recyclable of the bunch. Unless for some reason the thing needs to be autoclaved in which case polypropylene. I just made some lids from PP and in terms of machining it doesn't flatter the not-pro machinist as much as Delrin or HDPE. And we're about to find out if it distorts a lot after autoclave!

Another vote against UHMW. Doesn’t machine well, hard to get good surface finish, doesn’t hold shape. UHMW has great chemical resistance but doesn’t sound like that’s a factor.


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We don't really have enough information. You say nothing close tolerance, but are worried about stability. With plastic parts of this size, we need to know tolerances even if generally open, because there can be a LOT of movement.

You mention, "non marking" which makes me think they are rubbing on something sometimes. Of the two options given and limited application knowledge, I would go with acetal copolymer as it is a bit more stable than acetal homopolymer (ie Delrin). UHMW PE is not really a nice material to pocket the hell out of and screw together.