Subject: Re: making molds for cast acrylic

From: [email-masked] (Randy Gordon-Gilmore)
Date: Fri, 28 Jul 1995 21:26:56 GMT

In article <[email-masked]>, [email-masked] says...
>
>Ok.  In the infinately odd list of things that go on around my house, I
>need to manufacture a weird clear acrylic piece.  It is a 7" dia pipe,
>1/4" wall with a 1" thick flanges on both ends.  OD of each flange is 10"
>and the overall length is 36".

Mark,

Why can't you just take a piece of 7" OD x 1/4" wall acrylic tube and bond on 
the flanges?

The company for which I work makes all kinds of laboratory apparatus from 
fabricated acrylic.  Acrylic can be solvent-bonded using methylene chloride, 
liquid- and gas-tight, with all the strength of the stock plastic.

Randy

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From: [email-masked] (Mark Anderson)
Date: 27 Jul 1995 20:45:49 GMT

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The inside can have a significant taper for mold access (ie, ID = 6.5"
at one end and 6.0" at other end.)  The tube has to be clear and optically
ok (some mold marks are ok, can probably polish out).

I've built one piece out of plexi stock, but the material cost is $225
and it takes a fair amount of time to machine the tube and both flanges.
I suspect that even in "mass production" mode that I would be lucky to
make one part in under 10 hours.  No I'm not the fastest person on a
lathe.  It is almost cheaper to hire this out to a shop where they
know how to produce parts quickly.

Thing is that I'm looking to make at least 15 parts (thats $3375 and 150
hours if I don't screw up).  The cost of resin to cast these is about
$40 per part ($600 total), so if I can make a mold and cast parts fairly
quickly, I could invest a lot of time and money on a mold and be ahead.

So, does anyone have information/experience/referneces on:
    making a mold
    casting acrylic
    not welding the mold parts together with acrylic resin
    controlling bubbles in the resin (vacuum???)

Thanks in advance
--mark anderson
The trouble that I'm getting into is all my own and not the trouble
of my employer.

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From: [email-masked] (Jon Gellman)
Date: Sun, 30 Jul 1995 19:07:43 GMT

>liquid- and gas-tight, with all the strength of the stock plastic.

Randy is absolutely right. Casting this piece would be an unbelievable 
bear and expensive in mold rubber. You can fabricate it as Randy says with 
methylene chloride, or with dental acrylic, which fills and doesn't require 
the same level of perfect join as the solvent method. both methods also works 
with polycarbonate (lexan) making it virtually indestructable.

Jon

Jon Gellman Effects
[email-masked]
NYC, NY