Thursday, July 8, 2010

Safe Dial Part 2- The Casting

I cast the dial from Smooth Cast 325 using what they call a 'cold cast' technique, or what I call, schmooeying bronzing powder into the mold. This technique gives a metallic look to the resin. Here is how the process works.

Once I finished demolding, it was time to reassemble the mold.  The bumps and ridges formed by the cured rubber actually act as registration points for the mother mold. There are three important things to remember here. First, make sure the mold is seated well into the mother mold. The rubber should be solidly seated into the plasti-paste, without any wiggle.  The seam should be flush, and almost invisible, you don't want any leakage. Second, the mother mold should be clamped/taped/banded together- whatever it takes to get it secure and level. Leveling is very important for this casting, more so than usual because the back of the dial needs to sit flat on the safe, and the large surface area makes it harder to sand flat. Third, RELEASE RELEASE RELEASE. I used a liberal amount of Universal Mold Release in the mold before applying the bronzing powder. Release agent is important! Urethane resin is adhesive, and it will stick to all sorts of things- so I like to get some release agent pretty much anywhere I think I might get casting resin.

After the mold release was applied, I brushed bronzing powder into the mold. The idea here is that the resin will trap the powder in its surface and the finished casting will have a metallic look. Bronzing powder is another dangerous substance though, so before you use a soft brush to apply an even coat of powder to the inside of the mold, make sure to wear proper respiratory protection.




Once the bronzing powder was in place, it was time to pour the mold.  Following the directions, and wearing the proper protective equipment, I mixed the Smooth-Cast 325 and poured it slowly into the mold. It's always good to pour into the lowest point of the mold, and slowly allow the resin to rise. This will help prevent bubbles from forming in the casting. 



Once cured, I demolded the dial by gently removing the mother mold and peeling back the urethane rubber mold.  TA-DA!


 
I actually made two castings of this piece so that we could cut the center piece from the outside ring, and mount them to the safe so that the interior could spin.  To store the mold, I like to keep the mold in its mother mold, in a cool, dry place.

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