Step 1 (Click the image to continue reading & for a larger picture)

This is a "Top to Bottom pouring mold. The "Parting line" of this mold remain horizontal when I cast the parts. Get some artist's "sulfur free" clay. Box the area you need and press your parts into the clay. The top of the cla

Step 2

Now start boxing the clay and your parts with foamcore. Legos also make good mold boxes and can be stacked to any height. Legos also will always give you square corners.

Step 3

With the box complete make sure all the joints are sealed. Then press the clay into the sides of the box and clean up the "trench"

Step 4

The clay is now flush with the box sides.

Step 5

Since this is a "top to bottom" pouring mold. I want to add my sprues now, I use wood or acrylic dowels here. The dowel with the clay on it is my pouring sprue/funnel. The single dowel in the forground will vent the air as I fill the mold with r

Step 6

Multiply the width x length x height, to caclulte the amount of RTV you will need to mix

Step 7

Mix up your RTV and pour the first half of the mold. Most of our RTV comes from "Tap Plastics" tapplastics.com

Step 8

After the First RTV has cured overnight, you may pull the bottom off the box and remove the clay. Once this is done you want to put a mold release on the surface of the first half. If you forget to do this your parts will be sealed in a block of silicone

Step 9

After applying the mold release, you can calculate the volume and then pour the second half of the mold.

Step 10

Because of the mold release applied earlier, the two halves come apart very nicely. If you find some areas sticking together, use a sharp x-acto knife to cut the RTV. Be sure to stretch the connection and cut close to one side.

Step 11

The left side is was the first pour. It has the sprue running out the top, The right side was originally the clay, and the second part that was poured.

Step 12

The mold is now ready to be sprayed with a little bit of mold release and then ready for use.

Step 13

You can now see the sprue holes on the left (top half) of the mold. With the clay removed a nice funnel and resin resivoir has been created. This will be filled and allowed to gravity feed the mold to create the parts.

Step 14

Mix the resin according to the instructions and pour the mold.

Step 15

15 minutes to 60 minutes later the resin has cured, and the parts can be removed. If the resin still feels soft you can wait longer. If you demold the part while the resin is soft the part may get deformed. This might be good if you are placing the parts