Is acrylic casting resin (lucite?) machinable?
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  1. #1
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    Default Is acrylic casting resin (lucite?) machinable?

    I have machined acrylics in the past with success but I would like to try machining some of the acrylic casting resin (like they use to encapsulate rattlesnake heads in Arizona tourist shops). Anyone know if it will machine and polish like clear acrylic bar stock?

    The reason I ask, I found a complete brachiopod fossil (looks similar to a clam and is about the size of the eraser on a pencil) in some shale (Ordovician ~ 300 to 500 million years in age) rock shatter and my daughter wants me to make a pendant out of it. She's quite mad about rocks and fossils; a very healthy madness from my point of view.

    I think I'll try a sample when I get the resin of course but I thought someone here might be able to point out any potential pitfalls.

    Thanks,

    Bill

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    Bill;
    Yes, it machines and buffs up well. Be sure it is fully cured before working it. It seems softer than say plexiglass. When buffing, use a loose wheel and avoid any heat build up. If you get it hot when buffing, it will melt the surface and make a gummy mess until it hardens again. Go easy on it and it polishes beautifully. I use a white compound bar to charge the buff.

    On free hand surfaces, I go through all of the grits on a wet belt machine ending with a well worn 600 grit belt. This leaves an almost polished surface. A few seconds with the buffer and it is done.

    BTW - when machining shapes or surfaces, I spray on some windex or detergent water solution to prevent heat buildup and melting. This leaves a better finish that working dry.
    Jim

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    The following link has some good info.:

    http://users.lmi.net/drewid/resin_faq.html

    I just spent the last week machining moulds and casting resin for some prototype optical windows.This was a new experience for me so I had to do a lot of research and experimentation. I was using polyester resin.

    The main problem I had was air bubbles in the mix. I rigged up an old pressure cooker and an old 'fridge compressor to make a vacuum chamber for degassing the resin mix. That solved the problem.

    An accurate weighing scale is useful unless you are using a resin that is just mixed 50:50.


    Regards,

    Mike

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    I'll second what MikeJB said. I cast some small parts recently about the size of a pendant and found it absolutely necessary to use a vacuum chamber to deal with the air bubbles. I used a large pvc pipe coupler for a chamber and an auto ac vac pump. Good luck with your project.

    Mike

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    Good info from Magicmaker -- the MMA resin mixes that are available for casting do indeed seem to cure up a bit gummier than the typical acrylic sheet material you buy from a distributor. I have never tried any post-cure low-temp baking, but that might be a way to help harden the casting, and finalize the cure process. It seems to work well on epoxies that are alleged to cure at room temp. They always get harder when baked.
    Mix the materials very thoroughly for best cure results.
    For finishing/polishing, wet sanding with 220/400/600 grits is a good sequence. As previously noted, the 600 wet leaves a finish that requires little work on the buffer.

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    Thumbs up That's FRICKEN BRILLIANT!

    Quote Originally Posted by MikeJB View Post
    The following link has some good info.:

    http://users.lmi.net/drewid/resin_faq.html

    I just spent the last week machining moulds and casting resin for some prototype optical windows.This was a new experience for me so I had to do a lot of research and experimentation. I was using polyester resin.

    The main problem I had was air bubbles in the mix. I rigged up an old pressure cooker and an old 'fridge compressor to make a vacuum chamber for degassing the resin mix. That solved the problem.

    An accurate weighing scale is useful unless you are using a resin that is just mixed 50:50.


    Regards,

    Mike
    I've used fridge compressors in the past to pull a vacuum, they work GREAT! Not a lot of volume though, but they sure do SUCK! A pressure cooker LOL !

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    Default Thanks

    Thanks very much guys. That was really helpful. I'll experiment with the vacuum and polishing suggestions before trying it out on our fossil.

    Regards,

    Bill

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    One additional thing ... do not be tempted to add more catalyst than called for to speed up the hardening. Doing so will cause the resin to get too hot and form multiple stress cracks throughout the entire casting. These cracks are similar to what you will see if you are using a torch to polish plexiglass and get things too hot. Be patient with the whole process.
    Jim

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    Default Pressure cooker for vacuum chamber

    The pressure cooker I used was the type with a lid that has a bayonet type lockdown on the lid with a rubber seal between the lid and pot. I blocked the pressure release holes with nuts and bolts with o rings.Through drilled one of the bolts and turned down the outside to fit the plastic pipe to the compressor. I used thick wall reinforced pneumatic tubing.

    Some types of pressure cooker have a lid that is held up by the pressure; I don't think that type would be any good for a vacuum chamber.

    Regards,

    Mike.

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    Default Vacuum chamber

    I use an autoclave that a hospital scrapped because the hinges were worn and it was considered unsafe for pressure. That wasn't a problem with a vacuum. I installed a Plexiglas ( Perspex to limeys ) window sealed with an O ring and an inside light fed 6 volts through a couple of spark plugs with the side electrodes cut off and wires soldered to the center electrodes. Don't use higher voltages like 120 V because you may get a discharge through the partial vacuum. You are better off with a real vacuum pump like a Sargent Welsh 1420 and use ball valves to control the vacuum.

    Bill


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