Fixturing for machining teflon rings

I'd like to machine a few (2 or 3) teflon gasket rings out of quarter inch sheet stock. The ID needs to be roughly 50 mm, the OD about 60 mm and thickness that of the stock. The only critical dimension is the OD, which has to be a snug fit in the groove where it'll live.

The sheet stock is what I happen to have. Likely most people would start with bar stock then turn, bore and part off.

It's been a couple decades since I last did this, and all I can remember was that fixturing was a bit of a pain. I think I turned the OD first, with the stock pinched between chuck jaw tips and tailstock, but I can't remember how I held the resulting disk to bore the ID. It's way too soft to hold in a chuck.

Everything I can think of involves making at least one faceplace fixture and probably two. Can anybody point me to simpler methods? I'm not looking to save time so much as material; I'm retired, so time is cheap but it looks like any reasonable teflon stock will cost at least $100. And, it's good mental exercise.

Thanks for reading,

bob prohaska

---------------------- Holtzapffel's lathe book suggests turning ivory rings on a custom wood plug or cup chuck. He claimed it would hold size for one day, perhaps two unless the weather changed.

The plug chuck could be a snug fitting shouldered stub with the work held on by tubing pressed against it by the tailstock, avoiding expansion. If you don't have suitable tubing or don't need to check the final fit repeatedly it could be held by screws and washers.

The outside chuck he suggests is a cup slotted into fingers and closed with a ring sliding on an external taper. A simpler version could be a shallow locating recess surrounded by screws and washers that catch the edge of the work.

Both ID and OD can be turned by screwing the blank to plywood on a faceplate. Fender washers can be bent into low profile step clamps. The lathe bit will cut its own clearance in the wood. This is simpler but provides less radial support.

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If the stock is valuable I rough cut the ring or bushing's ID with a hole saw.

If the only critical dimension is the OD, I suggest punch a hole in it, rough cut it round by any means, and then bolt it to the end of a mandrel with a support washer/cap on the outside. Turn to size. Glues won't stick to any significant degree, but they may mechanically hold it just enough to help you take light passes while holding it lightly with your cap. PTFE will distort if you reef down on the bolt.

If the only critical dimension is the OD, I suggest punch a hole in it, rough cut it round by any means, and then bolt it to the end of a mandrel with a support washer/cap on the outside. Turn to size. Glues won't stick to any significant degree, but they may mechanically hold it just enough to help you take light passes while holding it lightly with your cap. PTFE will distort if you reef down on the bolt. Bob La Londe

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A 2" pipe nipple faced square might serve for the mandrel. While the OD is larger than 60mm the threaded end is slightly smaller.

<snip>

You can buy "gasket cutters" that can work on PTFE up to 1/4 inch. See for an assortment:

This one isn't priced too bad and might do the job🤷

You can buy "gasket cutters" that can work on PTFE up to 1/4 inch. See for an assortment:

This one isn't priced too bad and might do the job🤷

Fisk

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If you've used one, how easy was it?

I haven't used one. Just know they exist🤷

I have used the "Hole Saw" which is built in a similar style:

They work pretty well in a drill press. I've cut parts from 1/4 inch steel using one. That's probably close to their limit. Using them in a hand drill is highly dependent on the operators degree of finesse and material being cut...

I haven't seen anyone suggest this . If you can cut an accurate center hole in the material (maybe screw a square piece to a wood block held in your chuck) , machine a mandrel with a stub a half inch long sized to fit that hole just snug and a cup that fits over the stub that will clamp your gasket ring in place . Cut your center hole , clamp the piece to the stub mandrel with the cup and tailstock ram , machine the OD .

I haven't seen anyone suggest this . If you can cut an accurate center hole in the material (maybe screw a square piece to a wood block held in your chuck) , machine a mandrel with a stub a half inch long sized to fit that hole just snug and a cup that fits over the stub that will clamp your gasket ring in place . Cut your center hole , clamp the piece to the stub mandrel with the cup and tailstock ram , machine the OD . Snag

------------------------ Searching in the shed I found a 1-1/2" PVC pipe cap which has an ID of about

48mm and OD about 57mm.

Wait. Are you the one that doesn't have machine tools like a mill or lathe? Might be able to use a drill press, or even a hand held drill motor, and bring it in a little at a time.

If this is the gasket for a compressor check valve, it might be that the front and back faces are the sealing surfaces. I've used PTFE to make a check valve gasket before, but it didn't last long for me. Maybe I did a bad job, but the gasket wasn't the only thing flaky with it.

No mill or drill press. I do have a lathe, old South Bend 10k and some limited tooling (3&4 jaw chucks, drill chuck for tailstock, faceplates, boring tools, bits and random small extras like a steadyrest. Oh, and a pedestal grinder the shaping bits.

My problem (at least the one I recognize) is holding the workpiece while finishing the ID. No problem making it spin 8-)

This is a group gasket for an old espresso machine, an Olympia Maximatic. It seals on the faces, or one face and the OD depending on how tight it fits in the groove. The face that seals against the basket needs to be flat. For that reason a molded o-ring isn't satisfactory (I tried it).

The dimensions are rather odd. The groove ID is very close to 1.875", but the OD is 2.293", which isn't anything I recognize as a common size. The depth is about 5 mm, but the gasket normally sticks out another two or 3 mm, there's quite a bit of freedom. I've been using a thin o-ring to shim the gasket thickness, and that's worked surprisingly well. The first gasket of this type that I made lasted close to twenty years, thus my lack of recall in how I made it.

Thanks for reading and replying!

bob prohaska

Robert's your mother's brother ... so all he has to do is machine the stub arbor .

I'd be tempted to make the arbor section that the O-ring ID rests on slightly undersize and machine the O-ring OD to the claimed dimension, using a very sharp HSS cutting bit. Finding the right angle may require some experimentation.

Then, when the new O-ring is installed, the ID part will force the ring to expand against the OD component, sealing it.

This may be helpful:

.

Joe Gwinn

Mount a wood block in your 4 jaw chuck (and face it off) . Tack or screw a square piece of your material to the wood block . Machine the ID . See my other posts in this thread to proceed from there .

Wood block with a fender washer or similar large cap would work for turning the outside. Then a large ring on the outside with screws, and trepan and/or bore the ID.

Mount a wood block in your 4 jaw chuck (and face it off) . Tack or screw a square piece of your material to the wood block . Machine the ID . See my other posts in this thread to proceed from there . Snag

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Parting parallel to the spindle is called "trepanning". The tool is like a

1-tooth hole saw, or a parting tool with circular side relief, or enough angular relief on the OD side to not drag.

I would have the ID-bored square clamped onto the centering stub as well as screwed in the corners so it doesn't jump and tear when the OD cutter breaks through and frees it.

My problem (at least the one I recognize) is holding the workpiece while finishing the ID. No problem making it spin 8-)

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The proper chuck is a "pot collet" bored slightly larger than the work OD with pins or shims in the slots to hold it open. When tightened the collet clamps the work in place with full support all around.

This shows one with the chucked work being indicated, and empty, and also compares and gives advantages of 5C vs ER such as square and hex collets, which I have and use.

This is the new URL for Metal Lathe Accessories, the collet chuck is MLA-21. The quick and dirty substitute is the wooden cup chuck I mentioned. If you need to turn only the ID and not the face of the ring it can be clamped with screws and washers.

and ER collets as I have both and have encountered some of those limitations. For short items I have some 5C emergency collets machined to suit and they work great except the Chinese makers substituted the wrong sized pins, like 3.5mm instead of 1/8" but drilled the holes to

1/8" near enough. For the collet chuck I had considered buying a Bison of that style which in my experience would have been top notch kit but went for the Kalamazoo. I watched this video the other day about such 5C closers and very little runout but not built to last, but in the comments indications that other similar 5C closers are better made at not that much extra price, research required.

lathe in recent years was to acquire a 2nd tailstock and modify it for lever operation which I find I prefer for what I do over the standard screw feed tailstock.

and ER collets as I have both and have encountered some of those limitations.

--------------------- My lathe has the spindle adapter sleeve for 5C. Other than gripping range what have you found for advantages of ER collets?

I use 6-jaw chucks for odd sizes, with the disadvantages of not being precisely centered and the danger of the spinning jaws. Advantages over collets are the jaw grooves that hold washers and thin rings and being able to clamp an ID without using up part of an expanding arbor. A 3-jaw would grab the washers too, one of the 6-jaws is usually on the lathe from the last task. I haven't needed to thread thin tubing but if I did it could be done concentrically at the right end, supported by a pipe center.

The gas filler hose on my 91 Ranger has a steel insert sleeve at the tank with one end rolled outward into a press fit in the rubber tube. The edge contacting the rubber was uneven and excessively large, and the rubber eventually split there and leaked during filling. To fix it I turned the rolled end smooth and a little smaller to fit the new hose more easily. This was a good use for the 6-jaw and a contribution to paying back its cost.