Ordinarily I can order PTFE rod the exact size I need to make PTFE pins. All I have to do is drill and tap it for an internal reinforcing screw. I was not able to order the exact size I needed this time around. I had to order oversize rod to turn down to size. I was wondering if you guys had any tips for getting a decent finish.
My plan is just to hand grind a medium radius tip turning tool, and hand finish the final sharpening on the fine and extra fine diamond bench stones. Diameter can be 0 to -.005 (maybe worse) with little ill affect, but smoother would be better.
I haven't done much with PTFE but have seen videos using carbide tooling, one where the guy seemed to know what he was doing and got good results, and another that is really hard to watch (looks like things are going to explode any moment, sounds like scraping instead of cutting, big dangerously arranged chuck).
Here's the 2:31 video with clean good-sounding cuts, good chip, good finish:
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(On the negative side, one of the commenters asserts "this is not teflon . it is pp/nylon...teflon chips are not like this", and poster basically replies is-so.
And the hard-to-watch 2:59 one,
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There are several inconsistent recommendations in the thread
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with several people giving detailed advice about grinding HSS, with small radius and lots of relief being a recurrent theme; and others saying modern carbides are ok; and one or two claims that PCD, polycrystalline diamond, is what to use, and if you can use Delrin instead maybe the reinforcing screw wouldn't be needed, or if you could use HDPE the material would be a lot less expensive. (Perhaps the latter have already been ruled out for whatever reason.)
I posted this same query 4 different places and received from one to several responses in all of them. In the amateur group I got a lot of the usual "You didn't provide enough information," and "You should do something else" responses I am accustomed to seeing from groups with a lot of people who are anxious to show how smart they are, but don't necessarily all have the experience. A couple did suggest cryo-grinding (my word). That was a bit exotic for me, but I can see how it might work. Many skipped right over my comment about an insert and jumped right to it being to flexible to turn. Generally not a lot of real world basic practical responses, but very entertaining.
In the mostly professional group they didn't even comment on stiffness given I had already mentioned an insert. They were pretty much split right down the middle between hand ground positive rake very sharp HSS with a radius, and high polish positive rake aluminum inserts. One guy went off on a tangent about Teflon (tm) being only a .003 coating, and when I pointed out I stock solid PTFE rod stock, he tried to say yeah, not really, but close enough, and then went off on a rant about safety, employers, and PPE. Except for him the direct replies basically all said very sharp tool, smooth polish, positive rake, and machine to dimension in one pass unless it was beyond the scope of the tool. Now some of the replies to the replies got a little bogged down in petty self measuring and one-upsmanship, but the direct replies were succinct and to the point.
Your response is a little bit of both, but much more balanced with recognition that I probably already discounted some of the "do this instead" alternatives with reason. Maybe good reason. Thank you. It was a balanced reasonable response.
Before posting I was pretty sure it would machine just fine with the approach I intended. I may switch to a carbide insert because I do have some high polish aluminum cutting inserts and that would save me the time to grind a tool. I was just checking to see if there was anything special to it that I didn't know. I have enough stock I could waste a little.
And just for fun.
Teflon(tm) is a trade name. All Teflon is PTFE, but not all PTFE is Teflon.
Radiused tool sounds optimal, but also consider collet-chucking the full-diameter rod and drilling/tapping it first, then mount on a threaded mandrel for the diameter finish. Steel threaded rod is a better approximation of 'solid' than a soft bit of PTFE.
Woodturning style tooling with circa 20 degree edges, down-bevel rubbing against the work, slanted to shear off a curl, could be worth a try.
I posted this same query 4 different places and received from one to several responses in all of them. In the amateur group I got a lot of the usual "You didn't provide enough information," and "You should do something else" responses I am accustomed to seeing from groups with a lot of people who are anxious to show how smart they are, but don't necessarily all have the experience.
Sounded like a dig or an inside joke. Figured it was 50/50 whether to go with "Cool" or "Ouch." Sometimes you take a shot and you miss.
I just cut the pins I needed. Except for the one continuous chip the stuff turns about as easy as anything I have ever turned and the finish is stellar.
I had plenty of "extra" rod to scrap, but this stuff turns about as easy as anything I have ever turned. Like a lot of plastics I couldn't get the chip to break, but the finish was perfect. I only scrapped one piece, and that's because I set it down somewhere and couldn't find it.
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