Wednesday, August 6, 2008

How I made the plastic parts

I have been asked to explain how I made some of the parts for Noblemen. It is not really a long story. I saw this in my local hobby store: Mini casting kit

And I thought COOL! With this you could take some small 3D trinket and make copies of it.

The process is simple:

  1. You first have to have a positive mould. This is the item you want to copy. Affix the item to something flat on the bottom like a floor tile.
  2. You use this to make a negative mould.
  3. Pour quick setting resin into the negative mould and wait 3 minutes.

It was $30. I could not justify just making something I didn't need just to play with a cool kit. BUT if I rolled the $30 in to the cost a hobby! Everyone knows that hobbies cost money.

Around this time I was thinking about making a board game where players build estates out of squares of lands and castles, palaces, and stuff. If you wanted to make copies of something new you first had to have the new thing for the positive mould. So I read stuff and started asking my friends what they knew about making clay moulds and one showed me a product called Sculpey.

Sculpey is pretty neat stuff. You shape it like clay but then bake it and you have something solid. I do not recommend the Original type. It is too pliable.

Anyway I made parts I thought I would need for the game out of Sculpey. I made two castles, two sheep, and one palace, glued them to a 6” floor tile, built cardboard walls around the sides, and used the blue clay that game with the kit to seal the seam between the cardboard and the tile. This completed my positive mould. I only made one Palace because I knew I would not need as many for the game.

The kit comes with a powder that when mixed with water makes a thick liquid that becomes this rubbery stuff. They call it RTV or room temperature vulcanizing. So you mix it and poor it over the positive mould up to the edge of your cardboard walls and wait for eight hours.

When it was done I pulled off the clay and cardboard but the rubber didn’t want to come away from the floor tile! The problem was my sculpey pieces were not completely flat on the bottom and I only glued them in the center of each one. The rubbery liquid got under them. So when I figured this I carefully had to tear away the mould from the pieces that were super-glued to the floor tile. It was a bit scary and I had to trim away the excess on the bottom but it worked. Now I had a negative mould!

The next step was the most exciting.

Plastic resin begins life as two liquids that you measure out and mix together. Once you are done mixing you have about 5 minutes total before your liquid will be rock solid. So you pour a little fast into the negative mould and wait.

Then there was a problem. It was difficult to get the pieces out. These were not glued to anything so I had no way to get a hold of them. This meant I had to flex the rubber mould and squeeze my fingers into the gaps. Ultimately this caused rubber mould to start to crack and tear. I was only able to make about three sets before the mould was becoming unusable and I needed eight sets. Then I got the idea to wrap the mould with rubber bands before pouring in the resin. The mould continued to crack but it worked long enough and I got my eight sets.

I learned along the way to slightly over pour the resin this created a bubble on the bottom of the pieces making it easier to get a hold of them and pull them out. If you under poured the resin you the opposite was true. The pieces would have a concave bottom. This meant that I had pieces that would wobble a bit and not sit flat. This was easily fixed I held each one to a belt-sander and in a couple seconds they were flat.

Quick reminder list:

  • Make your positive moulds with flat bottoms
  • Glue them to the flat surface completely not just the center
  • Over pour the resin a bit to make it easier to remove
  • Remove the pieces carefully
  • Heat the rubber mould each time to make it more pliable
  • Sand off the bottoms to make them flat
  • The rubber mould will copy everything including your fingerprints

Then I painted them and presto I had parts for my game. As my game developed more I needed more parts but luckily I didn’t need large quantities of them. So I just made them out of Sculpey.

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