Been doing some CNC lathe work for a local shop that doesn't have one. Working out for both of us. But this latest job I looked at, I'm not so sure I want to jump into. About 50 pcs of Vespel, bloody expensive stuff! Part is essentially a collet. What's expected of me is to turn the profile of the part and bore. The bore is .089 +.000/-.001 I looked up guidelines for machining and according to DuPont, holding .0005 is doable but they really recommend PCD tooling. Dunno about getting a PCD boring bar that small.
One of my concerns is how this material responds to temp with respect to dimensional change. I don't have a temp controlled shop and can easily see this part shrinking out of tolerance in an air conditioned inspection room. And then there's the 4 side holes and slots to be machined that make it into a collet. Now technically if I deliver them in tolerance and they deform from this work, it's the other guy's problem, but I don't like that approach. If I were doing the whole part, with these questions, I'd walk a couple parts all the way through, and make any needed changes early in the process to insure good parts at the end.
I also have never even seen this stuff, let alone machined it. Material cost is about $30 each before anything is even done to it. Stuff is kinda expensive and it could get real expensive if there's any significant learning curve. I'm not so hard up for work that I need this job, but if it runs smoothly, it could pay well.
So, what's it like to machine? Given I've never messed with it, and won't have a whole lot of material for experimenting, what kind of luck might I have holding that bore tolerance with carbide?
Thanks,
Jon