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Mold Making and Resin Casting

The Basic Single over the top mold

This is the easiest mold to make. We use this type of mold for simple parts that have a front and sides, but no exposed detail on the back or bottom, such as turret hatches for instance; or cylindrical parts with no undercuts such as a figure torso that can stand upright in a mold box. An undercut is detail on a part that would prevent it from being removed easily from a single part mold. For example, a torso with arms attached could never be done with a single part mold because the arms would prevent the piece from being removed. You would literally have to cut the mold open to remove the piece being molded, thus, in most cases, ruining your mold.

For this tutorial, we will make molds for multiple small parts at once. (Fig 1) This allows flexibility in that when you are ready to cast parts, you can cast all of them in one pour, or just the ones you need. Here we have an ammo box and wood crate.

For this mold, we can make a mold box (see 2 part mold section) but because of the small size of these parts, we will use a piece of acrylic for the base, and hot glue a small cut-off section of PVC tubing for our walls (Fig 2). With this method, you have a mold box created in about 10 seconds. Small food storage containers also work well for makeshift mold boxes.
You want to make sure that your subject sits relatively flat in relation to the bottom of the container or base you are using. . You want about a half an inch of clear space on each side of the part for stability (Fig 3).

Now, depending on the material your subject is made from, it might have a tendency to float when you pour the silicone into the mold box. . If you think it may, you can secure it to the bottom of the container with a drop of super glue.

Now that our subject(s) is in the mold box, we are ready to mix and pour some silicone.