Adventures in plaster casting

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jsc
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Re: Adventures in plaster casting

Post by jsc » Wed May 21, 2014 4:42 pm

Funny you should mention food coloring:
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It works, not brilliantly. Google "plaster sidewalk chalk" and you will see people having good success with tempera paints.

jsc
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Re: Adventures in plaster casting

Post by jsc » Fri May 30, 2014 4:58 am

More casting attempts. Got some "high heat" epoxy putty and threw together a quick proof of concept mold. The paste wax worked as a mold release well enough, and the resin is very sturdy. Sadly, it doesn't work. I tried it first with the application of a heated print nozzle, then when that failed, with a direct flame from a grill lighter. It stood up to the heat, but there was no sign of melting in the plastic.
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jimc
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Re: Adventures in plaster casting

Post by jimc » Fri May 30, 2014 5:01 am

jin were you looking for your epoxy part to melt?

jsc
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Re: Adventures in plaster casting

Post by jsc » Fri May 30, 2014 5:05 am

No, this was another stab at trying to get a filament welder. The channel is for two pieces of filament. I clamped the epoxy pieces over the filament, then heated up the conical depression, first with a 240C hot end, then with an open flame.

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jimc
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Re: Adventures in plaster casting

Post by jimc » Fri May 30, 2014 5:07 am

oh yes haha, i forgot that is where this thread all started.

Toby
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Re: Adventures in plaster casting

Post by Toby » Fri May 30, 2014 5:45 am

I also had a couple of failed experiments. I used a blow torch on a mold made of air dried clay... very exciting as the heat makes the clay expand so fast it goes spraying off in all directions. But the filament just didn't fuse.

I've come to the conclusion that three elements are necessary to make this work:

1. Heat to melt the filament.
2. A mold to contain it in the right shape.
3. And the missing ingredient is... pressure applied to the hot plastic

When I pushed down on the filament with anything that was hot enough, it fused. But then I lost the cylindrical shape of the filament. If I didn't put pressure on it it didn't seem to matter how hot it got. I suspect it was melting but not mixing together. The idea that they two sides of the filament will sort of merge into each other when they melt appears to be false.

jsc
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Re: Adventures in plaster casting

Post by jsc » Sat May 31, 2014 4:12 am

Does anyone have any experience with ultrasonic welding or heat staking? I was shopping around for ultrasonic transducers, but the only easily available ones I could find are for doing things like range detection, in open air. 250 mW maximum. I was wondering if that would be enough power to induce melting, given a suitable horn/sonotrode. Don't know how one might couple it to the horn, either. There is something on thingiverse exploring ultrasonic welding, but it uses a scavenged transducer from some consumer device, and it looks to be very fragile and difficult to work with.

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