After working on the Aggro Crag Keychain for over five years, I designed and prototyped a six inch version. This process of building a working prototype kept getting shelved to make time for other projects and was stretched out over three years.
Creating the Pattern
In order to create a silicone mold to cast resin into, I needed to create a pattern. Patterns can be made using just about anything that is dry and oil/dirt free, including, but not limited to, clay, plastic, epoxy, wax, paper mache, plaster, etc. For the 2″ key chain replica, I used 100% wax, but in this case, I went with a combination of wax and various densities of foam.
I experimented with a few different techniques to create the texture. One attempt involved heating textured glass and pressing into the wax pattern.
Bondo was another failed attempt to create a crag-like texture.
Finally, I used an acrylic gel coat and the result was a glossy, textured surface.
I made a simple mold box with some foam board and a glue gun. To do this I scored the foam and gently cracked it down the straight edge of a table or bench. This gives you a seamless 90 angle without having to re-attach the pieces with glue or tape. This box will contain the liquid silicone as it’s curing around pattern.
I cast the silicone mold out of Hapsil 360 tin based silicone from Hapco. This is the only silicone I’ve found that does not inhibit the cure of clear urethane rubbers like the ones I plan on using to create the part.
Update 5/16: I have started prepping the mold to cast the 2nd half. I used foam and clay to form the inner cavity and then cast more silicone on over it to form the 2nd half of the mold.
I added some straws to act as the vents and gates once the silicone is cured. I sprayed the bottom half with Hapco’s Grease-It 5 release agent and build a dam with tape to contain the silicone. Normally, I would build a foam frame around the piece, but I was in a rush.
Update 6/5/14: I painted the inside of this prototype and I’m less than thrilled with the result. The clear urethane is a little too clear compared to the prop from the show and the inner core is not what I had pictured in my head.
Update 8/4/15: It’s been over a year since I made the first prototype and I decided to make a few changes and re-cast this piece.
I used the prototype mold, however I decided to make a few modifications.
With the old top half of the mold re-sculpted in clay, I joined the two mold halves and taped the mold shut. I also rubber banded two aluminum plates on the outside of the mold to keep it from warping while the urethane cures under pressure(75 PSI).I filled the mold using a Rapidshot meter-mix dispensing gun. I mixed 350 grams of Hapflex 791 part A and 52.5 grams of 791 part B and poured into an empty 400 ml cartridge. After shooting into the mold until the material came out of the vents, I placed the mold inside an X-20 pressure chamber and pressurized at 80 PSI. This was the result:
After removing the part from the mold. I removed the clay and the set the part back into the mold. I sprayed release agent onto the silicone and the part. I mixed a few hundred grams of Hapsil 360 silicone and then vacuum degassed the material. I then poured the silicone into the mold and let cure overnight.
I cast the base out of a rigid urethane that is pigmented black and used epoxy to bond the two pieces together. Unfortunately, I didn’t take any pictures during the process of making the base.
Update 8/16/15: Last week I filled the first order for a personalized 6″ Aggro Crag replica. To purchase this item, please visit my online store at: http://www.blueyestudios.com