A few months ago, I stumbled on Composimold-Flex. It is a re-usable mold making material that you melt in the microwave. Best of all, once it cools, it’s ready to use. That’s a huge time savings when you compare that to the silicone molds which need 24 hours to fully cure. With my limited prop building time, it seemed like a great way to make intermediate molds.

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It comes out of the package with the consistency of a slightly tacky Jell-O and has a subtle citrus scent.

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You heat it in a microwave safe bowl for 30 second intervals until it’s entirely melted. I found that 45 seconds pretty much takes care of it but it will depend on the strength of your oven.

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The pegs of my 3D-printed Mr. Potato Head eyes are slightly too long. Instead of risking messing up the masters, I used Composimold to make a working copy. I poured the melted material over the master.

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After a half-hour of cooling, I was able to de-mold the master. I only cared out the post so I didn’t make any sort or pour spot. You can see where the Composimold’s heat warped the plastic cup I used as a mold form…something to consider when you use this material.

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SmoothCast 300 is moisture sensitive so I was advised to apply baby powder to the mold to absorb any moisture. The first casting showed some reaction to the moisture in the material but since this a working piece, I didn’t care. Many resins also generate heat so it is also advisable to cool the mold before using.

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I drilled a hole through the post so that when I trimmed it down, a nail will make sure it stays aligned. This one turned out to be too short so it’s good that I didn’t modify the master!

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I poured another copy into the mold and this time got the right length to the post.

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I used the same drilling and nail technique to shorten the posts of the four masters. They should be ready to mold by next weekend.

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With the new Sakura Star Wand head master completed, I embedded it in a clay bed for molding.

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I covered most of of it with MoldMax 20. Once it cured enough to be slightly sticky, I chopped up some old molds to fill dead areas to save on silicone.

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I was able to top off the mold using just a little more silicone.

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The next day. I flipped it over, removed the foam base and removed the clay bed.

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I cleaned up the mold surface, clayed up the edges to ensure there would be no leaks and then sprayed mold release on the exposed silicone.

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Once again, I used pieces of old molds to save silicone in the second side.

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Well, it appears that I didn’t use enough mold release between the two halves so I had to carefully cut the master out of a solid block of rubber.

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I didn’t have anything to lose (except some resin, I guess) by trying a pour in this possibly ruined mold. Fortunately, the casting turned out great, with only a few easily cleaned flaws and a fine seam line. The color turned out nearly perfect as well!

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By the way, I don’t know if I’ve ever mentioned it but a running band saw or belt sander makes a great vibration table for shaking the air bubbles out of your silicone.

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In the home stretch of the Caster Gun, I glued on the barrel “eyes”. Having these as a separate part made the seam cleanup MUCH easier.

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I wrapped black vinyl around each vent band, and then glued on the metallic vinyl vents.

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The front and rear sights were glued on, completing the Caster Gun build!

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I had a base fabricated from laser-cut 1/4″ acrylic. Unfortunately, the Caster Gun is very back-heavy so it would not properly balance on the stand.

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To stabilize the prop, I needed some sort of bracket to grip the butt. I used a lump of clay to mold around the handle and roughly form the piece.

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I cleanup up the form as best I could and used Composimold to make a quick copy in resin.

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The new master will take a bit of sanding to clean up but a quick test fit shows that it functions as I need it to.

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The final master just needs a bit more cleanup before molding the final piece in resin.

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2 Responses to Progress Weekend June 10-12

  1. Shannon Brown says:

    This is great, it’s so cool you share this info, it’s a major Time & Money $aver. Thank you.

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