Cutting plastic

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Mr Ron
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Cutting plastic

Post by Mr Ron » Fri Jan 18, 2019 1:57 pm

I have to cut 20 circular pucks from 3/8" thick UHMW plastic. What is the best tool to use for that. I'm thinking a hole saw, an adjustable hole saw or band saw. I need something that won't melt the plastic. If I use a band saw, I can round the rough cut blanks on the lathe.
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warmstrong1955
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Re: Cutting plastic

Post by warmstrong1955 » Fri Jan 18, 2019 2:24 pm

Edit.....

I have used hole saws. Kind of rough, but easy enough to clean up on the lathe if necessary.
Annular cutters work a lot better.
Keep it slow, and melting is not a problem.
I have made many thicker discs for linear bearings, using round-stock, and parting. Slower, but prettier.
Today's solutions are tomorrow's problems.

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SteveHGraham
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Re: Cutting plastic

Post by SteveHGraham » Fri Jan 18, 2019 2:55 pm

I made a circular insert for my vertical band saw, using the lathe. I used plexiglass. It looked beautiful when I was done. I believe I superglued it to the end of a something held in the chuck. If you use glue, you don't have to drill a hole in the plastic.
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Harold_V
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Re: Cutting plastic

Post by Harold_V » Fri Jan 18, 2019 4:25 pm

SteveHGraham wrote:
Fri Jan 18, 2019 2:55 pm
I made a circular insert for my vertical band saw, using the lathe. I used plexiglass. It looked beautiful when I was done. I believe I superglued it to the end of a something held in the chuck. If you use glue, you don't have to drill a hole in the plastic.
Much simpler to just press the piece with the tailstock, using a smaller diameter plate with a center hole drilled, and a live center. The piece to be turned is pressed against a piece of material which is faced after being chucked. To prevent movement of the chucked piece, it's a good idea to have a shoulder, which bears against the ends of the jaws. It's also a good idea to make it smaller in diameter than the target diameter, so the back edge can be deburred while still in the machine. I keep a small variety of plates near my lathe for that operation. Light cuts are required if you turn tough materials, but it works just fine. A robust lathe really helps.

This setup is quite handy when there's more than one piece to machine, as the pieces are fast and easy to install, using the slightly smaller diameter as a guide for concentricity.

H
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BadDog
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Re: Cutting plastic

Post by BadDog » Fri Jan 18, 2019 5:34 pm

My opinion, buy a piece of round and slice off the disks with a band saw.

Otherwise, probably a trepanning tool with properly ground sharp bit. Back with some particle wood or the like. That's assuming tolerance allows that to be a finish operation.

After that, I would probably choose your rough cut on bandsaw and clean up in lathe.
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jcfx
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Re: Cutting plastic

Post by jcfx » Fri Jan 18, 2019 7:26 pm

You don't mention whether the uhmw pucks have a a center hole, I agree with warmstrong about annular cutters
but they can get costly as you go up in size since you're going for the ID of the cutter rather than the OD
( not that they're any cheaper in smaller sizes ). Hole saws you'd have to take into account for the kerf, and they cut reasonably clean in
uhmw. I've done what Harold suggested with great success in a variety of materials, I gang up rough cut sheets with some heavy duty
double sided tape to keep them from slipping and do some light passes to OD, the tape works well with uhmw since it doesn't
transfer heat as well as metal.

Mr Ron
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Re: Cutting plastic

Post by Mr Ron » Fri Jan 18, 2019 8:47 pm

I should have mentioned the pucks will have a center hole and are about 4" in diameter. They will be wheels for a display model. I suspect sharp HSS turning bits in the lathe will give a nice smooth finish.
Mr.Ron from South Mississippi

RSG
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Re: Cutting plastic

Post by RSG » Sat Jan 19, 2019 7:52 am

My method agrees with BadDogs regarding disks!

Slice slightly oversized pucks and machine to the correct dia, bore the inside hole, part them off slightly oversized, make soft jaws to flip and finish the other face...done!
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John Hasler
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Re: Cutting plastic

Post by John Hasler » Sat Jan 19, 2019 8:57 am

I'd cut them out on the bandsaw, drill the center holes, stack them on a mandrel with a spacer on each end, and machine the ODs in one operation. How you clamp them together depends on what you've got for a mandrel. If it's hollow you can run a threaded rod through it and the spindle and draw them together with it.

Inspector
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Re: Cutting plastic

Post by Inspector » Sat Jan 19, 2019 2:51 pm

One thing to remember when turning it on the lathe, both metal or wood, is that the swarf doesn't break and wraps itself around the work. Fun to stop to pick and cut it off. Put a dust collector nozzle or one from a vacuum cleaner by the cutter to suck the strands away. Don't use a single stage dust collector or the strands will tangle up in the impeller. Make the cuts manually so you can pause frequently to let the swarf break. When you get to your final passes do it under power feed. It is easily cut and the surface finish is smooth. It doesn't sand well.

Pete

I forgot to mention that a radius on the tip of your HSS tool leaves a smoother surface.

Mr Ron
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Re: Cutting plastic

Post by Mr Ron » Sat Jan 19, 2019 3:34 pm

This seemed to be a simple task and to tell the truth, I didn't even think of stacking the discs and turning them down to final size in the lathe. I was going to turn each one separately. With all the discs turned down to size, I can then, with the help of soft jaws, finish each one. If it were not for the talented people on this forum, I would be running around like the proverbial chicken without a head, making mistakes and wasting time and material. When you think you know it all, you discover there are others who know more. It's the democratic process where minds from all over come together with collective wisdom. This forum is really more of an education and I am thankful for that. You learn things here that are not taught in school. Many thanks to all who contribute to this forum.

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johnfreese
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Re: Cutting plastic

Post by johnfreese » Sun Jan 20, 2019 12:24 am

I second the idea of sawing the discs, drilling, stacking for turning.

I hate turning plastic. I spent almost as much time untangling swarf as I did turning the parts.

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