Machining clear plastic and keeping it that way



Use an exceptionally sharp tool with a large nose radius and a material removal rate that produces a continuous chip.

Flame polish the edge while it's still spinning in the lathe.
Or use Mcguire's.

Polycarbonate (lexan) is much "tougher" and behaves a lot more more like a metallic alloy than acrylic (plexiglas) which has mehanical properties that're more similar to a glass.
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Modern acrylics have almost the same durability as polycarbonate (lexan), so, unless you're going to be torturing this, I'd go with the acrylic.
Flame polishing works, but you may have to practice to get it right.
Another option is to sand with grades of emery paper, then do a final polish with jeweler's rouge. You can get small quantites of that in a liquid suspension by buying the liquid CD polishing medium.
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This is _almost_ a silly conversation, except that it's not commonly known that contact lenses and eyeglasses are turned from cast resin on lathes.
It doesn't 'come out' clear. It's ground with successively finer abrasives with mechanized laps... just like any other form of mechanical lense polishing.
I used to grind telescope mirrors by hand. They don't 'come out' clear, either... the initial curve is ground with abrasives so coarse you can't even see through the glass afterwards. Then finer, then finer, and over again with at least five grades before doing the 'rough' polishing with something aggressive like Barnesite, followed by 'fine' polishing with washed rouge.
You can cut any piece of plastic you can successfully cut, and eventually get it back to clear that way... but it takes a LOT of labor and time.
LLoyd
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"Lloyd E. Sponenburgh" wrote:

This is why the flame polishing or solvent dip polishing are preferred when you don't need optically perfect surfaces.
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Hogwash.
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I'm not positive what plastics i used to machine. Getting old and stupid. I remember machining (i think acrylic)blocks for gas manifords for medical devices. I had to keep the speed down, to keep the heat down. Have to use o il, not water as I was once told by a boss I had. I did try that that time and it didn't work. Water just beads up. You have to make sure you always h ave oil on it or else. I've machined plastic at several shops, different material and always used oil for lathe, mill and thread. It was crystal clear.
On Tuesday, November 5, 2013 12:26:16 PM UTC-6, Tim Wescott wrote:

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On Tue, 05 Nov 2013 12:26:16 -0600, Tim Wescott

I've gotten pretty good finishes on acrylic (Lucite, Plexiglas, etc.) using Hangsterfer S-500 coolant mixed about 1:10 with water, eitther flood or mist. A squeeze bottle or aspirator (like window cleaner bottles) would probably work pretty well, too.
Here's the result from one of my earliest trials:
http://memweb.newsguy.com/~mphenry/DiskFinished-2.JPG
Sharp tooling helps and you want a fairly fast feed to avoid melting the chips to each other or the milled surface.
Mike
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