Wednesday, March 16, 2011

Reworking a Mold

Well what I suspected was going to happen...happened.  All of my molds held up and I should be able to make a few more quite easily...except for the Chest Canopy Mold.  Urethane is so hard on the molds.

One of the advantages to using a pressure pot is that the pressure forces the silicone into all the little nooks and crannies.  The back of the chest canopy has a small hole for the screw to tighten it on.  The silicone even gets into this hole and if you can believe it even molds the threads inside the hole.  Well the urethane plays murder on the mold and after 9 Clear chest canopies, the little "tit" that makes the hole, tore off.
I was a little put out and then I thought about it.  Only HALF of the mold is trashed.  Not the entire mold.  So I put the Chest canopy back into the good half of the mold and made sure it was seated properly and firmly.  Then I poured silicone over it.  It worked.  Hmmm...I have a second mold...same problem.  So I tried it again.  And again it worked.  So now I have 2 molds to use and 8 canopies left to make.  So 4 from each mold.  For the second mold however, I didn't put the head or drill back into the mold so the silicone filled up those spaces and took on their form.  It just makes for a more firm mold lock is all.  The molds with the hole in them with the little "tit" inside it are the reworked molds.  The ones on the top are still in good shape, so there was no need to remake the entire mold.  Thankfully...I am almost out of silicone.

I am only making a small amount of resin, but with 1 mold I still had lots of resin left over.  So I didn't want to waste it.  I will be making a separate post for this, but I now have quite a few sets of Clear Pharoid Wings and also some Blue Pharoid wings that will be for sale shortly.

Reworking the mold is only possible if you can reseat the original piece perfectly.  Otherwise the pressure will force the silicone into whatever airspace is there and create an extra thin layer of silicone around your piece you are using to make the mold.  This 'flap' or thin layer of silicone will play havoc on your finished cast.  If the 'flap' comes out, it will make your cast now out of true shape and it will be thicker and bigger.

8 more chest canopies to go...then full bore assembly.  :~)  YEAH!!!!


  1. That was a cool trick! You had to rebuild another entire mold box to create the replacement half, right? How were you able to build another box to the exact size of the original mold a second time? Or is it because you use Legos that the boxes are always a uniform size?

    Are you experimenting with different amounts of silicone activator? I see the mold in the upper left is much darker blue than the others.

  2. Yes. That's the beauty of Lego. You can always remake the mold frame to the exact same dimensions. It took 30 seconds to remake the frame. :~)

    I haven't been experimenting with the silicone. I have no way to explain the color difference. I have noticed it before. the color seems to vary a bit from batches to batches, but the mold is still good so while it is a wonder, I don't really question it.