Instructables

Step 17: Chapter 3- Helmet Molding 1: Preparation and Clay Walls

Picture of Chapter 3- Helmet Molding 1: Preparation and Clay Walls
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Tools and Materials
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We now begin the process of making the mold from which you pull a light-weight wearable cast.

The shape of your model will determine the complexity of your mold.  The simple shapes that we've made so far were easily replicated with simple, 1-part molds.  A shape as complex as your helmet would be impossible to replicate with a single mold.  You could coat the entire helmet in a thick coat of silicone but then you'd never be able to remove the model without destroying the mold and you could never pull cast from it either.  In this instance, it will require a 3-piece set that consists of a mold of the front, a mold of the back, and a mold of the bottom.  The molds are intended to join where they can part most easily from the original model and subsequent casts.  You can find many videos on Youtube that elaborate on the basics of mold making if you need more information.  I am only going to focus on the specifics of molding this particular project.

We begin by creating the parting wall that divides the front from the back and the bottom.  I determined that the ear-line and the "lower jaw" were the best places to build a dividing wall of Klean Klay.  This dividing wall prevents the silicone from leaking into the areas we want to keep free of rubber.  You'll want to create "key shapes" in your clay.  These shapes will allow the different parts of your mold to register with one another and interlock.  In this instance, I used a long, narrow strip of clay and some simple wood pegs I had lying around. 

Build up the sides of the dividing wall to keep the silicone from spilling over the edge of the dividing wall.  Now you're ready to mix and apply the silicone.