Looking for a Good Plastic for Some Fixturing

mayu · Sep 16, 2020

We're looking for some hard plastic for some fixturing that will support some thin wall parts during machining.

Essentially the plastic will act as plugs, but it needs to be really precise in overall length and diameter.

We want something that handles threaded and/or tapped holes nicely.

Our first thoughts are nylon.

It seems to have the desired hardness, it is decently priced, and it seems to handle temperature fluctuations comparatively well.

Any suggestions?

DavidScott · Sep 16, 2020

Nylon is a real pain in the ass to machine, especially if you are trying to hold a few tenths. Delrin is pretty much the defacto plastic for what you are looking for. Next would be PVC to save a tiny amount of money, or if you want to glue pieces together.

Delw · Sep 16, 2020

gotta agree delrin, finishing a vacuum fixture made out of delrin tomorrow. made lots of fixtures with delrin that are thread as well.
abs works but sucks and does grow with coolant I only did it cause I had 3'x6'x 2" sheets here

g-coder05 · Sep 16, 2020

Not trying to hijack your thread but when you say thin walled parts are you talking about a part with thin interior walls or profile walls? When I do thin wall stuff I use that 2 part spray foam insulation to keep the chatter and flex out. After the part is finished I just soak it in a solvent and done.

But to through in another cheap fixture plastic that holds size is ABS.

drcoelho · Sep 17, 2020

Delrin would get my vote

Milland · Sep 17, 2020

Acetal resin (Delrin) gets my vote, but as long as impact isn't an issue, acrylic can work pretty well too and may be cheaper. Just keep the sections pretty thick where possible, and avoid sharp inside corners.

Nylon would be far down my list due to hygroscopic behavior, lower stiffness, and "ehh" machinability.

mayu · Sep 17, 2020

DavidScott said:
Nylon is a real pain in the ass to machine, especially if you are trying to hold a few tenths. Delrin is pretty much the defacto plastic for what you are looking for. Next would be PVC to save a tiny amount of money, or if you want to glue pieces together.

Thanks - I've never machined it and didn't realize it was that difficult to machine.

Based on all of this great feedback I will definitely look into delrin, and the other materials mentioned too.

mayu · Sep 17, 2020

barbter said:
+1.
Nylon is rubbish. It can absorb 3% by volume.
The best material is natural acetal.

Thank you - I didn't know that nylon was so difficult to work with. I will definitely look into acetal too.

mayu · Sep 17, 2020

g-coder05 said:
When I do thin wall stuff I use that 2 part spray foam insulation to keep the chatter and flex out. After the part is finished I just soak it in a solvent and done. But to through in another cheap fixture plastic that holds size is ABS.

Awesome - thanks. I will consider these two options as well.

Rick Finsta · Sep 17, 2020

Delrin = Acetal Homopolymer

I have cut a bunch of parts out of Acetal Copolymer and we had serious issues with dimensional changes due to humidity and temperature in the shop. Parts were good coming off the machine, and then some would fit their mating part and some wouldn't as the seasons changed.

Actual Delrin is supposed to be much better but if I recall was a good bit more expensive.

plastikdreams · Sep 17, 2020

Delrin, we use it for a lot of different operations here...cuts easy, stays accurate, and is pretty wear resistant.

mayu · Sep 17, 2020

McMaster has some surprisingly well priced delrin - all the way up to 10.0" diameter.

We'll probably give that a shot.

Thank you all.

Scruffy887 · Sep 18, 2020

Delw said:
gotta agree delrin, finishing a vacuum fixture made out of delrin tomorrow. made lots of fixtures with delrin that are thread as well.
abs works but sucks and does grow with coolant I only did it cause I had 3'x6'x 2" sheets here

Those are some very $ sheets. I have some small pieces of 1" and 1.5" Acetal plate, but nothing like that. Acetal rod, I have plenty of that. Ran it in bar feed mode in the lathe all day yesterday, and will run all day today too. And all next week.

Delw · Sep 18, 2020

Scruffy887 said:
Those are some very $ sheets. I have some small pieces of 1" and 1.5" Acetal plate, but nothing like that. Acetal rod, I have plenty of that. Ran it in bar feed mode in the lathe all day yesterday, and will run all day today too. And all next week.

Yes they are, a buddy of mines work shut down about 8-10 years ago. I got a hd2500 filled to the top of the bed with ABS , Delrin,nylon and a bunch of other types of plastic from 1/16 thick to 6" thick. mostly full sheets and big blocks. cost me like 250 bucks. been making fixtures out of it for 10+ years, cause I didnt have any certs for it. 2 years ago I threw and gave away about 500lbs, didnt really want the non certed suff in shop.
we used to run lots of sheet/block delrin and 1" round teflon. The certed stuff I still have a back office filled with it.

BoscoDrummer · Sep 22, 2020

if you need a little hardness, paper phenolic might be an option and machines great.

Search

Largest Manufacturing Technology Community on the Web

Search

Looking for a Good Plastic for Some Fixturing

mayu

Plastic

DavidScott

Diamond

Delw

Stainless

g-coder05

Titanium

drcoelho

Stainless

Milland

Diamond

mayu

Plastic

mayu

Plastic

mayu

Plastic

Rick Finsta

Stainless

plastikdreams

Diamond

mayu

Plastic

Scruffy887

Titanium

Delw

Stainless

BoscoDrummer

Aluminum

Similar threads