anybody have experience turning teflon????
we are turning a .125 diameter by .400 long teflon part on a citizen B12(.250 diameter barstock). the problems we are encountering is that the oal is not repeating. we are running dry with a constant air blast @ cutting tool. basically we are doing this. we have to hold +/-.001 on OAL but we are absorbing the entire tolerance and them some.
collet is set just tight enough to grip mat'l without slippage and GB is set with very minimal drag.
ANY HELP WOULD BE HUGE!! We always struggle with Teflon
Thanks
1-face
2-spot
3-drill thru(.050 dia)
4-re-face & turn(one cut to Z.450)
5-cutoff
Re: anybody have experience turning teflon????
Quote:
Originally Posted by
chet470
I appreciate all the suggestions. The problems seem to have stabilized to a managable level. I don't use a cutoff insert, I use a .008 wide micrograin carbide tool. The razor blade idea is interesting though, I may have to give that a try.
Thanks
I know this is an ancient thread, but I rarely see this mentioned. Teflon is a funny material, it undergoes a phase change at around 68 degrees F I believe. 1.7% change in volume because of this. If your shop were below 68F, and then when you machined it, it warmed up, then it would grow 1.7% while machining. My knowledge kind of peters out at this point, but in theory, if you took the cube root of the 1.7% you get about 1.19 which would be the linear growth in each direction. A 0.400" long part would grow almost .005" in length. Similarly (proportionally) in diameter as well.
Your part is pretty small, so it isn't a big deal, but on a 5" diameter part, it might grow many thousandths.
We are building parts for cryogenic service, so we have to deal with this phase change shrinkage, as well as normal shrinkage due to change in temperature. I'm going by memory, but a roughly 3" diameter teflon ball valve seat shrinks about 0.040" after cooling to -260F, on top of about 0.035" growth from phase change.
Here is a link to a study on this. If you are machining lots of teflon, you may want to talk to someone more knowledgeable.
https://pdfs.semanticscholar.org/5c8...e457fc4abe.pdf
Re: anybody have experience turning teflon????
I run Teflon with Super duper double dog sharp tools! It really needs water in my opinion to keep that temp constant.
For the tools, I take some diamond paste and load up some brass then make them super shiny. 500, 1500 and 4K grit I think... I forget exactly, but if you make the cutting edge super sharp you wont get any hairs.
I also have one of those lab refrigerator thermometers (50 bucks on amazon) and stick the probe in the coolant. Then you make a part, note the coolant temp, then put it in the inspection room, note the air temp. Wait 30 min, measure the part.
Then you can adjust and run them. They you have to do some kind of black magic ritual to make sure the rest come out the same. Those tolerances sound easy but are kind of tough with dealing with long skinny parts in plastic on a machine that heats up...
Re: anybody have experience turning teflon????
Great information. Super specific! I have found that the Teflon (PTFE) is super soft, and loves to move around a lot. I think your insight into the 68 degree is invaluable. Thanks.