Plastics

[JohnS]

I am hoping you guys can help me out here - I am planning to build David Kerzel's Mini V2 http://www.floridaame.org/GalleryPages/g1Non0132.htm and I am attracted to the idea of machining the pistons from a suitable plastic material - my local supplier in the UK can come up with PTFE, Tufnol, Acetal/Delryn. Do any of you have experience with these materials and their ease of machinability ? I will be running the engine on compressed air so high temperatures will not be a problem. Any guidance would be much appreciated.

John

 

[BobWarfield]

PTFE is the generic name for Teflon, so you don't want that.

Acetal/Delryn are trade names for plastics impregnated with Teflon. They may be a good bet. I've not machined them, but have heard good things. Another thought is a lot of folks are making CNC ways using plastic and rod. I'd check out some of those threads on CNCZone. Widigitmaster, in particular, does this for his minirouters. He is very approachable and would tell you a lot about machining plastic and which plastic he uses.

The plastics machining I've done has been quite enjoyable. So much so that I regularly buy white poly cutting boards when I see them really cheap. It makes a great material for a lot of projects and is easily machined. I've also worked with UHMW, which machines well too.

Best,

BW

 

[gary55ford]

Hi John I've been machining either black or white Delrin for 23 years building PC Board testers, I drill & install spring probes in it. Some of the holes are as small as .015 dia.. Delrin is easy to machine-self lubricating and has an excellent finish.It has excellent wear factors We have machines wiyh Delrin moving parts that have been running for over 20 years with very little wear. Hope this helps

 

[AllThumbs]

Delrin

 

[Circlip]

Hi JohnS, I think you'll find that there isn't enough "meat" round the holes in the piston to use any of the engineering plastics in this application. The "nail" on the top of the piston is probably going to be driven deeper into it by the impact on the ball which of coarse is going to affect the timing. As everyone else says, Delrin has superb machining qualities and in its molded states is self lubricating and can also be made into springs and gears. Good luck if you're going to try it for the pistons, but i'd make a couple of spares from drill rod (silver steel).
Regards from our side of the pond, Ian

 

[JohnS]

Thanks guys - much to consider there. I may well give Delrin a try knowing I can always resort to other methods if I'm not too happy with the results.
JohnS