Help With Machining Delrin

[sparkymeller]

I'm using my cnc lathe to cut a large quanity of delrin bushings. I need to hold and internal dia. within plus or minus .001 . I'm using my regular Kennemetal boring bar inserts that I use for cutting stainless and alum. It's working but I'm finding that I have to change the internal dimension about ever 3 parts. I'm running it at 2000rpm. Any ideas for me out there.

Thanks
Sue

[Metalmanti]

Try using as positive of an insert you can get and make sure you are cutting the material and not smearing it. If your speeds and feeds are right your insert should last and you should be able to hold the dimensions.

[Delw]

not knowing how exactly your holding or the size, I am guessing 2 things heat and or chuck pressure. those 2 things alone will cause you problems.
I have used regualr inserts in a pinch and have no problems with tolorance issues .001 is nothing, providing the part has some stock. but all the parts would be the same not just every three so that leads me to chuck pressure and heat issue.

chucking is 90% of tolorance problems on plastic and its never the same


I preferr positive inserts, I like ccmts with a .015 rad best