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Homemade Torso Mold


By Mike Joyce

This page describes the process of forming a six piece mold from the plug which was constructed earlier. 

I'm planning the seams as follows. 
Part 1 will be mouth area. 
Part 2 will be the chest and programming area. 
Part 3 will be the top dome. 
Part 4 will be the bottom dome. 
Parts 5&6 will be the left and right tube sections. 

Preparing The Plug
The first step is to prepare the plug to allow release of our mold.  First apply and polished 3 separate coats of release wax.  Then after waiting 6-8 hours apply and polish two more coats. 

Here's the polished plug

Another shot of the polished plug

Note how the pole allows access to all sides of the torso without touching the ground. 

After waxing we apply a coat of PVA release agent.  This stuff is best sprayed on in three thin coats.  It forms a very thin sheet that separates the plug from the mold.  Once the plug is released from the mold the PVA can be washed off.  Let the PVA dry between coats. 

Planning The Mold Seams
We must create seam lines so that each separate mold piece can be pulled.  I will align my seams on the raised trim areas, this will allow any flashing on the final piece to be easily sanded off. I will start with the moutharea.  Then the chest and programming area.  Domes and finally the two tube sections. 
We use clay to create a "dam" around the area to be done.  Once done the clay is removed and release agent is again applied.  We will make "keys" or small indentations in the clay dam.  These will ensure good alignment of the separate mold sections when we reassemble it. 

Step by Step For The Mouth Area 
I'll show step by step how to do the first portion, the other portions will be similar.
I created a dam around the mouth portion using clay.  Note the small "key" holes in the clay.  The clay has been given a coating of PVA release agent. 

Mouth area picture

Mouth area picture

Next step is too apply the tooling gel coat.  This should give our mold a smooth, hard and durable surface.  The tooling coat will be 20-25 mils thick.  The first mat layer should be added with 1.5 - 5 hours to stabilize the tooling gel coat.  After that cools, we'll build up using 8-10 layers of 1.5oz mat. 

Here the black tooling gelcoat has been applied.  Also note that a fillet of resin, cabosil (thickener) and 1/4" chop strand has been used to round out the sharp corners.  This will allow use to lay up mat without trapping air bubbles in the corners. 

Tooling coat and fillet

Now we can lay-up the mat.  I'll do only two layers for now.  After all sections have two layers I'll go back and add more. 

Remove the clay and we're ready to start the next portion. 

Note how this area will mate up against the first area.  We continue this process until all the areas are done (two layers of mat). 

Two layers of mat

Here's a shot of chest area dam

Here we've covered all areas except the bottom dome 

Here's a shot of the finished mold, plug still in it

OK, we've covered all portions of the mold.  Next we use 8-10 layers to build up the mold thickness to ~3/8 - 1/2 inch thick.  This makes a very strong mold. 

Then we drill holes for the bolts that will hold the portions together when we are ready to cast a torso.  Finally we trim the edges. 

Now for the moment of truth, will the mold come off the plug? It does!  I am amazed how easily.  The mold surface is a high gloss too!  If you look close at the following pictures you can see the very thin mold release film.  (It's on the dull looking areas.) 

Here are the parts as they come off the plug 

Another shot

Another shot

Another shot

The release agent washes right off.  Here the mold family sit and watch their favorite Lost In Space episode, "Wreck of the Robot". 

The Mold Family

The Mold Family

Here's a shot of all the pieces reassembled, except for the bottom portion

The mold is finished!  Next step is to give this baby about six coats of wax, then it'll finally be time to cast our torso! 


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