Machinable plastic

[at6c]

I am looking for recommendations for an easy to machine plastice to be used for making a probe body. Would like a material that works well with normal machining processes, not requiring modified bits, negative rake etc. Thanks.
George

[Geof]

Delrin, it machines in a manner very similay to brass; same cutting speed same tooling with no top rake. Tooling must be sharp especially drills and taps to reduce rubbing and heating.

EDIT:

I found some threads where I had posted about Delrin;

Machinable Plastic post #9

Cutting Delrin with Taig. post #2

Is Delrin better than Nylon? post #2

[awerby]

[QUOTE=Geof;696444]Delrin, it machines in a manner very similay to brass; same cutting speed same tooling with no top rake. Tooling must be sharp especially drills and taps to reduce rubbing and heating.

[Delrin's good, but it's a brand name. If you look for Acetal, that's the generic name for the same thing, and might cost less.

Another couple of materials I've had good luck with are polycarbonate (brand name: Lexan) and ABS (Acrylonitrile Butadiene Styrene). I used regular 2-flute carbide tooling designed for metal, no special rake angles seemed necessary.]

Andrew Werby
www.computersculpture.com

[emd68]

I second the Delrin/Acetal. I have used woodworking tools to work with it.
If you are just looking for small quantities then try eBay. If you need more
then try Interstate Plastics they seem to have some of the best prices

Ed.........

[MadMax]

Acetal is a great choice for a machinable plastic. A closeish second would be nylon. Both have good stiffness (as plastics go) and higher melting temperature which reduces melting issues. For external turning, melting isn't an issue if you run coolant. For deeper hole drilling, with smaller drills especially, melting can be a problem because it'll clog the flutes.

I find polished carbides with high rake angle (typically used for aluminum hogging) can achieve high material removal rates with less part load (I've been using AK style cutters). You can also do very well with hand ground HSS form tools. I save a lot of tool changing with some of my parts with in house ground (on a bench grinder) cutters ground in 0.75" HSS rod or square.

On some of our parts, we do combined boring bar and part off tools for some of our parts which sit in a gang tool holder with a bar puller. The combo tools save use from doing any tool changing which speeds things up considerably.

Delrin is quite forgiving so you can go with very high depth of cut which makes form tools a very good way to go to speed things up a lot.

Polycarb is fairly easy to machine, but I find it has more melting issues. Deep hole drilling will require frequent pecks to clear chips and get coolant back onto the drill. Also, be very aware of what coolant you're using. Polycarb is prone to crazing (chemically induced micro cracking) when exposed to many oils or solvents. Acetal and nylon do not have many issues with most machining fluids.

Parabolic flute drills are very good for chip clearing in plastics. I often go to them if I have bad melting issues.

What's your application? That'll often determine your mat'l selection almost more than machinability.