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.


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


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.


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.


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.


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.


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!


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


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.


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


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.


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


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


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.


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


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.


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!


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.


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.


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


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


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.


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.


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


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.


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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