Creating molds for my characters

By | July 21, 2015

So I didn’t just make these prints to look good. I wanted to make molds and cast a lot of them in plastic resin for a small side project. So I ordered a bunch of material from siliconesandmore.nl. Silicone, resin, plasticine and filling powder…. that kind of stuff.

Unfortunately, to date it didn’t work as well as I’d hoped. I made a bunch of molds, but ran out of silicone and most of the resin ends up being to brittle to actually be useful. So I adjusted a few models. The model of the shark pendant (made the fins thicker and removed the pectoral fins) and the eggcup model.

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Making multiple molds at the same time.

Well technically, for the 3D print, I didn’t have to change the model at all. The egg cup had no support on the feet, so I was worried it might snap. However, I tried making a single-cast mold for that one (which means I put the whole thing in silicone and then try and cut the model out) and while that didn’t really work well for the mold, it did show me just how strong that plastic print was.  I was really pulling and bending HARD at that print to get it out of the mold, and I was expecting it to break so many times, but it never did.

"Come on, pull us out!"

“Come on, pull us out!”

YAY! free again, and in mint condition. This is one strong egg cup!

YAY! free again, and in mint condition. This is one strong egg cup!

Unfortunately, again, not all models were so lucky. I tried the same with the sword wielding stickman, and while pulling it loose, it’s head came off… but that might also be due to me accidentally cutting into it.

The first victim of the mold making process...

The first victim of the mold making process…

Now for the molds themselves, the ones that came out right were the ones I did in 2 parts. I built a box made out of lego, laid a bottom of plasticine and pressed my prints into them. Filled up any holes or odd angles with plasticine as well. As I also pushed a pencil in the plasticine to make some slots for the 2 halves of the mold to catch, so they would not slide around against each other later.

Using Lego to build molds

Using Lego to build molds.

Cleaning off the plasticine from one side to cast the next side.

Cleaning off the plasticine from one side to cast the next side.

Both sides cast, original print can come out again.

Both sides cast, original print can come out again.

By the way, using lego has some advantages and some disadvantages. The main advantage is that it’s really flexible. You can make a very solid and precise case relatively easily. The main disadvantage is that it does not seal as well as you might expect. A lot of silicone drips in all the gaps and not only does it take a lot of time to clean, it also wastes a lot of useful silicone.

Once both sides of the mold were completed I did a little bit of editing. I cut out a few sections where air could get trapped, so I knew plastic would be able to get everywhere. I still had a lot of trouble to cast resin, for various reasons.

  1. The resin dries too fast.
  2. There are always at least a few air bubbles which get stuck at inconvenient places.
  3. When creating the molds, both ends of the silicone mold AND the original print tend to stick together

Things I learned from this:

  1. Use injection needles to forcibly push the resin into the model. Works faster, but still not perfect.
  2. Carefully stir the 2 components of the resin. REALLY carefully…
  3. Use Vaseline to coat both the original print, the plasticine/half of the cast to prevent the other half from sticking to it.

There will be an update for this at some point… For now, some more pictures.

Copy head and copy body next to the original print... Cause: airbubbles.

Copy head and copy body next to the original print… Cause: airbubbles.

Sword wielding copy came out as pin wielding pieces.

Sword wielding copy came out as pin wielding pieces.

the original next to one of the copies. The first successful copy in fact, until its tail broke off.

the original next to one of the copies. The first successful copy in fact, until its tail broke off.

Some initial casts. All very brittle. I have to find how to solve this.

Some initial casts. All very brittle. I have to find how to solve this.

Failed mold. Plastic doesn't go in fast enough before it dries.

Failed mold. Plastic doesn’t go in fast enough before it dries.

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