Step 5: The Platen
The Platen is the surface on which the molds are placed and on which the plastic forms a seal for the vacuum. There are many different platen designs but most are designed with many small holes that the air is pulled through to create the vacuum. My platen follows this design. To make the platen I used two sheets of 1/4in. plywood cut to 23in. long and 11in. wide. In the bottom piece I cut about a 1in. hole in the middle so that I could put the PVC fitting in to it. The PVC parts were chosen so that I connect the Shopvac to the platen, and of course this will create the vacuum. In the top piece I drilled a bunch of 11/64in. holes in a pattern. The pattern and size of holes is up to you, just be reasonable. These two pieces are separated by the balsa wood strips. The balsa wood is 1/2x3/16in. and cut to fit around the perimeter of the top and bottom platen parts. Then the whole thing was glued together. The idea here is to keep the volume inside the platen as small as possible. That way when you flip on the shopvac you don't have to pull a bunch of air out of the platen and then out from under the plastic.