Translucent Machinable Material

Hello,
I am looking for a colorless transparent or translucent material that machines well. I can machine as thin as 0.020 inch if necessary to pass
significant light.
Delrin is often used when a machinable plastic is called for. White is one of the colors available but I don't have a sample so I have no idea how much light would make it through a 0.5mm thick sheet.
Where might I get info on transmission through various translucent plastics, especially Delrin (aka acetal and acetyl)?
A transparent plastic would be ok since the milling would leave a translucent surface. Acrylic is known to be difficult to machinge.
What colorless transparent or translucent plastics are friendly for machining?
Any other user group where I should be asking?
Tom Hubin snipped-for-privacy@earthlink.net
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We have used epoxy resin to build optical phantoms with well defined scattering and absorption properties. It machines fairly well but I don't know how it compares to for example delrin in that respect. It can be polished to reasonable standards. The resin is transparent in the visible and has a few small absorption bands in the near infrared (see M. Firbank et al. "An improved design for a stable and reproducible phantom material for use in near-infrared spectroscopy and imaging, " Phys. Med. Biol. 40 (1995) 955-961). After a few months it will develop a slight yellowish tint which indicates some absorption in the blue, but over 0.5 mm it should be negligible. It doesn't scatter light like delrin.
You have to be a bit careful when making it because if it doesn't cure properly it will become brittle and impossible to machine (like acrylic). The type we used was a solvent-free, long pot life, alifatic amine epoxy. It had to be cured at 50 degrees C for 24 hours to make it machineable.
Johannes
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Johannes Swartling wrote:

What's the problem with acrylic (methacrylate ?) ? We turn it very successfully with high rake, sharp cutters with no probs.
Steve
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Don't know, our workshop guys said it couldn't be done.
Johannes
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Steve Taylor wrote:

I agree with Steve regarding machining acrylic. You just need the right set-up.
As for translucent, machinable plastic, you might try HDPE or LDPE (high or low density polyethylene.) One is white and translucent, at least in thin slices. I just can't remember which is which. I *think* it's the LDPE. We've used it for some other stuff, but I noticed with some thin sections (~1/8") that it makes a reasonable transmissive diffuser.
Additionally, LDPE comes in sheets down to 1/16" thick, or in film from 0.004" to 0.006" thick in the McMaster-Carr catalogue.
Warning: LDPE is pretty soft. It does machine (stringy instead of chips when machined), but I wouldn't be making high tight tolerance parts with it.
Spencer
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Johannes Swartling wrote:

Do you work in tissue optics?
Perspex machines not too badly.
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Yes, or rather I did at the time.
Johannes
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Johannes Swartling wrote:

I thought so. It seemed a bit too specific to be any other application.
It was a guy (Mike Fairbank) in the group I worked in (Dept. of Medical Physics, UCL) that developed that technology for his PhD.
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A good material would be the one used for plastic eyeglasses. I don't know what is used but I bet others on this forum do.
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Helpful person wrote:

In the eyeglass business it is known as CR39. I think Pittsburgh Glass created it during World War II for bomber fuel tank lining or something equally non-optical.
I have old lenses here I can test. If it works then I just have to find a supplier for the right size stock. What I need to make is too large to start with a typical eyeglass lens blank. Diameter up to 75mm is plenty large but I may need as thick as 1 inch before machining.
Thanx for mentioning it. I'll look into it.
Tom Hubin snipped-for-privacy@earthlink.net
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Tom Hubin wrote:

Macor is a translucent machinable ceramic, if you can think outside of the plastic box.
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wrote:

Finally, a topic in the optics newsgroup I know about. Acrylic is very machineable. And is easy to machine. A tool with a lot of positive top rake works well. By positive top rake I mean the top of the tool will be like a ramp that the material slides down as it is being cut. Lots of rake means a steep ramp. It's important to keep the plastic cool while cutting, sanding, or polishing. Use only pure water for cutting and lubricating sandpaper. If polishing with plastic polish follow the directions of course. If any oil is used during cutting, or gets on a surface that is not polished, the acrylic will eventually crack. Even polished acrylic, if exposed to oil and stressed, will crack. Like a pepper mill made from acrylic. Even though the plastic is very smooth and polished the oil from the peppercorns will eventually cause cracks. I can't stress this enough. Too many times I've seen this plastic develop cracks. If I had to have a translucent surface I would use wet or dry sandpaper with water to achieve the desired surface. Good Luck! Eric R Snow, E T Precision Machine
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Tom Hubin writes:

UHMWPE and HDPE are both cheap, the former is an ideal material for machining.

rec.crafts.metalworking
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