Molding and Casting

This week we are learning molding and casting, which has a few more steps than you might expect:

  1. Design a 3d model with “registration” and a “pour hole.”
  2. Mill the part out of a wax block.
  3. Create a silicone negative from the wax block.
  4. Fill the silicone negative with a casting material to form the final part.

Designing the part

I wanted to make something that would prevent the ends of cables from falling off of my desk. There are a few subtleties in modeling a mold part:

  • We are using a 2.5 axis machine, so all cuts have to be vertical. You can divide the piece into multiple sections to achieve this.
  • Include “registration” ports so that the parts can fit together cleanly.
  • Include a hole that is exposed to the outside where liquid can be poured.

Here is a work in progress of my model that shows these features:


I milled the part on the ShopBot and had a great time learning the MasterCam software.

ShopBot doing its thing!
ShopBot doing its thing!


Creating the mold is the easiest part. I mixed some OOMOO 25 as the mold:

And then filled the wax cavity:

Tada! It comes out really easily, even without anti-stick spray:


I used SmoothCast 256 with black dye as my casting material. It’s pretty straightforward to use, just follow the instructions on the box.

The final part: ready to hold cables!
The final part: ready to hold cables!