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lclore
10-05-2008, 05:15 PM
I am looking for a material recommendation. The requirements are for the following:
* Optically Clear Rod, 0.25" diameter
* Machinable
* Commercially Available & ideally (as always) cheap!

I have experimented with Extruded Acrylic, however it melts more than it machines. I am reading (here and elsewhere) that Cast Acrylic Machines better than Extruded Acrylic. Are there other materials I can consider? Optical clarity is a must. Thanks in advance.

Lee
Onyx Ind.

Geof
10-05-2008, 05:27 PM
Yes, extruded acrylic is not machinable, cast machines very nicely.

I think acrylic is what you need it is even clearer than glass I think.

Imancarrot might come along sometime and give an opinion; he is the optics Guru^2.

ImanCarrot
10-07-2008, 05:22 AM
Wouldn't say "expert", but thanks for the compliment :)

Cast Acrylic, optical grade is what you want. I CNC lenses all day and as Geof says it machines very nicely indeed.

Extruded Acrylic does not machine at all well and has many inclusions in the bulk material.

Polycarb doesn't give a good finish.

Zeonex machines well, but you got to use a non- hydrcarbon coolant otherwise it reacts with the material.

CR39 is quite a common polymer that's used to make lenses.

My favourite, however, is MR7- it's got quite a high refractive index for a plastic and machines crystal clear, it's not cheap though and I can only get it from Japan.

Cast Acrylic would be your best all round bet. I'm not sure if you would get an optical finish using conventional machining which Geof knows far more about than me: I use Diamond Machining (Google Diamond Machining Wiki) and make lenses for some of the strictest applications. You might get a nice polished surface using conventional machinin and flame polishing, Cerox polishing or any proprietary plastic polishing, but it will be not be anywhere near "optical" grade. And the surface profile would never be acceptable for imaging.

Here's some I made earlier.


What's your application? Is it purely a pretty thing, or an actual optical imaging component? What wavelength will you be operating at- Visible, Infrared, Ultraviolet? These factors all affect the choice of material.


Oh, I'd expect to pay around £15.85 for optical grade cast acrylic, 6mm dia, 5 metres length supplied in 1 metre lengths (5X 1 metre lengths for £15.85). It goes up to about £25.45 for 10mm diameter (same quantities).

The transmission is about 92% (visible), but this can be dramaticaly increased by anti-reflection coating.

Ask away! I'll do me best to help!