Adventures in plaster casting

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jsc
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Re: Adventures in plaster casting

Post by jsc » Tue May 20, 2014 7:07 am

Apparently, oogoo (a cheap sugru substitute consisting of silicone caulk and corn starch: http://www.instructables.com/id/How-To- ... ubstitute/) will not stick to PLA after curing. May be a useful material for more mold experiments.

Toby
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Re: Adventures in plaster casting

Post by Toby » Tue May 20, 2014 6:33 pm

Worth a try. From what I've read there are two potential downsides: It shrinks about 10-12% as it cures, compared to 0.5% for a commercial brand like Aluminite. And to make it pourable you have to add a solvent like mineral spirits or white gas, which then gases off as it cures, stinking up your house.

The shrinking is the bigger problem. That would make exact reproduction and fitting parts together difficult I think.

There are other DIY techniques around the web, both for mold-making and casting material. A couple I vaguely remember involved cooking things. In once case it was (I think) milk + vinegar, and the result was something that cast as hard as stone (due to the casein protein in the milk).

If you want to do more casting, I'd recommend you get a hold of this Activa Permastone stuff. I've just used it as something I can cast, but the question of what it's good for made me take a closer look. I don't know what's in it, but I think you're right that it must contain lime plaster to be more cement-like. It's quite strong and durable. That octobox is only 5mm thick, but there's no way I can break it. It feels just like soapstone after it's been sealed with elmers. Even whacking it with a hammer won't hurt it.

jsc
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Re: Adventures in plaster casting

Post by jsc » Tue May 20, 2014 7:02 pm

After I find some way to use up this 5 lbs of Art Plaster, I will check it out.

Another thought I had was epoxy putty. It comes in high heat resistant form, too... The question is, this stuff is supposed to bond to things, so how do I avoid gluing the mold together with it?

markb
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Re: Adventures in plaster casting

Post by markb » Tue May 20, 2014 7:02 pm

I saw someone using this for casting but it looks expensive.
http://www.smooth-on.com/Urethane-Plast ... index.html

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jimc
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Re: Adventures in plaster casting

Post by jimc » Wed May 21, 2014 2:52 am

smooth-on makes alot of good products. i have used their foams, urethane casting resins and epoxy casting resins. all work great but each has different properties and each has its specific use. alot of casting resins need to be vacuum degassed otherwise you are left with may air bubbles. i have a vacuum pump and a very small chamber for this. i hardly ever use it but maybe in the future when i get some time and with all the casting going on here i but get a bug up my ass and use the m2 to make some molds.

jsc
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Re: Adventures in plaster casting

Post by jsc » Wed May 21, 2014 6:58 am

Casting: it's the wave of the future.

Look, I made a crayon.
Attachments
crayon.JPG
crayon.JPG (69.94 KiB) Viewed 3231 times

Toby
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Re: Adventures in plaster casting

Post by Toby » Wed May 21, 2014 7:38 am

Casting is the killer app for 3d printing.

Jin, could you explain what we're looking at there? Did you print a crayon mold and cast it in....what?

jsc
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Re: Adventures in plaster casting

Post by jsc » Wed May 21, 2014 7:58 am

Crayon wax. Now I can make whole crayons out of partial crayons. Kind of silly.

You can also make your own sidewalk chalk from plaster, although maybe not from that Permastone stuff.

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ednisley
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Re: Adventures in plaster casting

Post by ednisley » Wed May 21, 2014 12:09 pm

Toby wrote:Casting is the killer app for 3d printing.
Believe it!
http://softsolder.com/2014/04/09/chocol ... d-pouring/

Image

OOMOO 30 silicone rubber delivered nearly perfect results without vacuum degassing:
http://softsolder.com/2014/04/10/chocol ... -closeups/

The Tux-shaped positive molds came from height map images, similar to the lithop(h)anes you folks have been doing, glued to an acrylic sheet:
http://softsolder.com/2014/04/07/chocol ... eight-map/
http://softsolder.com/2014/04/08/chocol ... ylic-base/

I intended to make a bunch of Tuxes for after-supper chocolate treats, but the big bag of Ghirardelli chips went missing... [sigh]

Toby
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Re: Adventures in plaster casting

Post by Toby » Wed May 21, 2014 2:11 pm

You could make multi-color crayons. No need to change crayons while you're drawing.

I haven't found a way to color plaster before you pour it. I tried acrylic paint but then the plaster never set. Maybe food coloring would work.

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