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Mold-Casting system by DCN2049 Mold-Casting system by DCN2049
As I said I would, here's a quick documentary of the mold making and casting process. This time I was reproducing parts for a WH40K dreadnought with a two-part mold. There are numbers on the pictures, so I'll obviously be using those to guide the comments.

1.) First I assembled the parts I wanted in the mold, building a frame out of legos around them. I try and maximize the amount of parts I can fit in one mold without compromising the silicone walls in the process. This one is one of the larger ones I've made.

The bottom of the frame is filled in with clay, which is that dark blue stuff. I then press the parts half way in, or as far in as I care to depending on the complexity. After that I scoured the clay, making small trenches between the parts to act as walls. This will prevent the inevitable flash from spreading too far, and often saves resin. Final touches are placing cut pieces of plastic modeling sprue to form pouring channels, and toothpicks for air-vents.

2.) The frame is then built up to the appropriate level, and the RTV (room-temperature vulcanizing) silicone rubber, the pool of light blue stuff in the frame, is mixed and poured in. I used a 1-to-1 ratio two-part rubber, meaning that I needed equal measurements of silicone and catalyst for it to work. I also used more legos from my childhood bin to pin back the wax paper preventing the rubber from leaking through the bricks.

3.) At least four hours later, the lego frame is pulled apart, the wax paper removed, and the clay is carefully lifted away from the silicone in an attempt to prevent the parts from being removed. It's not a giant issue if the parts come out too, but it helps to keep them sealed in the rubber. This picture is after I tooled and trimmed the silicone that leaked between the cracks between the clay and the parts. I also had to reset the sprues in a few of them.

4.) I skipped a few steps before this photo here, because they're boring and basically repeats; I had to apply four coats of mold-release to my finished mold (to prevent the second half of the mold from bonding to it), then framed and filled it up again with RTV silicone. You can see both sides of the two part mold here, along with the first finished resin parts. For the resin, I used a 1-to-1 ratio Alumilite plastic, which is light, sets fast, and remains strong after cooling and curing.

If you look at the back of the top piece, the lascannon, their are large bubbles in the cooled-resin, and the optic sight is partially formed. This is natural, and easy to fix. I just trimmed off the effected area, poured in more resin, and pressed the molds back together.

5) The parts have been removed from the mold, after they were fixed. Now the excess flash is clearly visible. The lighter stuff snaps of with just a little twist, but the sprues and vents will need trimming, and the entire parts mold-lines will need to be filed down too.

6) Post-filing parts, a finished lascannon and assault cannon. All that's left is to drill out the bores and paint them.

Final picture is a collection of the molds I have made with this process so far. The yellow ones are the first ones created, using a 10-to-1 ratio silicone mold. All the molds for the Duelist and Mantis are there, along with the newly completed Dreadnought arm mold.
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Submitted on
June 7, 2009
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Make
Canon
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Canon EOS 30D
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1/60 second
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F/4.0
Focal Length
105 mm
ISO Speed
400
Date Taken
Jun 6, 2009, 12:03:10 AM
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