How to machine PTFE ?

[awemawson]

I need to make a PTFE bush that seals the coolant port on my Traub lathe tool turret. I've never machined PTFE so would appreciate any advice from those who have.

I would imagine it needs very sharp tools, but that's just a guess. Fortunately I have a drawing of the bush

[Pete W.]

Hi there, Andrew,

Do you already have the PTFE you intend to use or do you still need to procure it?  I ask because there are (I believe) grades of filled PTFE that preserve the non-slip qualities but are rigid enough to stay put when the cutting tool approaches.  I can't supply chapter and verse regarding grades and specification numbers, I'm afraid.

The other thing I remember about turning PTFE is that smoking a cigarette while turning was reckoned to be a big NO-NO, exposing the PTFE swarf to high temperatures (like the end of the cigarette that's on fire) releases toxic fumes.  In any case, I hope you're a non-smoker but if you're not, don't smoke and turn at the same time.

If you're going to turn the PTFE bush on the Traub, I suppose it'd be OK to smoke while you're watching progress through the windows.

[Stilldrillin]

Andrew.
Back in 2009, I made some 5/16" dia. PTFE pistons, for a Special Mamod steam engine I had built.

The 10mm dia stick, machined just like hard soap.

Sharp, normal shaped tools. Plenty of revs. Easy to take off, a thou', if needed......

They're still doing the job. Now, in Australia. 

David D

[awemawson]

Pete: No, not got the ptfe yet - I will probably wait until I've pulled the original one out as I might get a clue as to type. Fear not I'm not a smoker. This will have to be manually turned rather than on the CNC, as getting the original out stops me turning the tool turret.

David: That's very encouraging - I had visions of it's lubricity causing all sorts of issues.

I've not totally committed to replacing it yet - the leak isn't that bad unless I'm using high pressure coolant, which is rarely necessary.

[Arbalist]

PTFE is quite soft and I've found not too dimensionally stable, although for your application it may be ok.
Ertalyte TX is pretty good stuff and machines very nicely.

http://www.theplasticshop.co.uk/ertalyte-index.html

[NormanV]

I've made PTFE for steam fittings on a loco. I just used ordinary tools. One good thing about it is that when you assemble it if you overtighten the fitting the PTFE will flow to fit and when you slacken it off a little you will find the fit has improved.
Norman

[lordedmond]

make sure you have a good length in the chuck if its to short it will pull out good by part

as other have said sharp HSS but not to much top rake or it will pull in ( dig in )

done plenty for valve seat for locos

has as been mentioned do not smoke whilst machining it the reaction to the smoke causes phosgene gas to be produced ( so I am told )


Stuart