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Honing PTFE (Teflon)


May 29, 2013
Norco, Ca
We just had a drawing package dropped on us by the boss and we are looking for some help to let us know if anyone has ever done what is being asked of us on this drawing. We are looking to put a .788" +.000/-.001 hole, 12.462" long, and a second part that is looking for .250" +.000"/.001", 9.967" long, in pure PTFE. The owner is frothing at the mouth for the job, but we cannot come up with a method to achieve what the drawing is looking for. It's not like this is some existing product that has been made for years and they are just looking for a new supplier, rather it was just conceived last month. Sometimes engineers feel if they can draw it, it can be machined, but in the real world, that is not always the deal. Has anyone ever had to do something similar to this and if you have, can you give some pointers? We imagine having to hone the parts, but wouldn't impregnate foreign debris into the PTFE? Any help or suggestions would be greatly appreciated.
Anything is possible, but what they're asking might as well be impossible. I can't imagine honing something that soft. How round and straight do the holes have to be? PTFE coefficient of thermal expansion is large compared to metals, so temperature control would be a huge issue. Avoiding workholding distortion during cutting and measuring ought to be lots of fun.
Years ago I got an RFQ for a teflon part that had some stupid tight dimensions.

The one thing those engineers had going for them, is they had a table for the dimensions
right on the print.. Different dimensions for 64 degrees, 66 degrees, 68 degrees, 70 degrees,
72 degrees, 74 degrees and 76 degrees..

My quote looked something like this.
Hi xxxxxxx



If you are able to do it, make them sign a NDA and keep the process to yourself. You will be a millionaire
I have used a metal bonded diamond honing stone on other plastics, I think it was either Delrin or Nylon, and it did ok but not great. PTFE just sucks, I'll bet you can make it work, but it's going to be a trial and error type of job. Make sure the boss knows that it's not going to go smoothly.
Oh, yeah teflon ISTR has a funny dimensional bump right around room temp, or so the engineer told me when I made his crazy parts

cant make it cant measure it
Ask the customer for some upfront R&D money and work with them on a process. You both may discover and learn quite a bit with both parties comfortable with the dollars being spent.
I would be talking to gun drill manufacturers and seeing if you can skive a hole that small. They may say a drill and ream would be fine.

As others have said temperature control is not to be overlooked. You might consider dousing the OD of the part in coolant or oil so the core of the part is the same temp as the Od.

The bore might be very difficult to produce or impossible. It’s certainly a good R&D project vs a simple quote and hope you get it right.
I would suggest talking to customer and inform them that you cannot hold those tolerances. Maybe they will reconsider something more realistic. If not, no bid.
If you do end up machining any teflon, be sure to get the virgin stuff. I tried the Reprocessed/recycled stuff and had trouble with it.
More PTFE reading:

You might get lucky and hit those sizes with a reamer, but... any other tolerance like runout, concentricity, perpendicularity, etc.. you won't be able to maintain.
No quote it and save yourselves a massive headache.