Well I finished the vacuform table. The materials, all purchased from your local hardware store: hardboard, pegboard, wooden slats, wood glue, vinyl foam weatherseal, some screw hooks, duct tape (of course), some wooden dowel, and metal clips (of the office supply variety). Tools used: hacksaw, miter box, drill press.
I got the store to cut the big pieces of board into more manageable chunks, which I then attacked with my hacksaw. (Yes… a hacksaw. I never said it was pretty. I live in a 1-bedroom apartment, what can I say.) I made three similar frames out of the wood and wood glue, big enough that a one-foot-square sheet of plastic can be used as the thermoplastic (which becomes the mold). One of the frames was made with a gap in one corner, which is where I would later attach the vacuum cleaner.
I wood-glued a stack of solid hardboard (like pegboard but with no holes in it), one of the wooden frames (as a spacer of sorts), and a sheet of pegboard on top. This leaves a gap between the hardboard on bottom and the pegboard on top, which allows the air to flow through the holes in the pegboard when the vacuum is turned on. (I also glued some wood scraps as support spacers underneath the pegboard to prevent it from buckling under the vacuum and weight of the part.) Then, a simple border of weatherstripping makes the seal, and duct tape connects it to the nozzle of the vacuum cleaner. I then drilled out a couple of holes and glued in some lengths of dowel. This helps to steady your hands and ensure that you align your frames correctly (it’s easy to mess up that melted plastic!).
For the molding frame, I simply clip the two remaining wooden frames together with a sheet of thermoplastic in between (I’ve been using styrene from the hobby shop — thinner stuff takes on more details, thicker stuff will smooth over nicely and is stronger). Holes were drilled in the top frames to match the bottom frames (they were drilled at the same time actually, and then widened to make an easy fit).
After testing the vacuform frame once, I noticed that the thickness of the weatherstripping and the bottom half of the molding frame were separating the plastic from the pegboard, and this was causing a fair amount of slack to be taken up needlessly around the edges. I then added a smaller piece of pegboard on top, and that should give me a little more slack to use to capture a deeper mold.
The final touch was to screw in three metal screw hooks. This way I can hang the molding frame in the oven underneath one of the racks, and watch through the door. When I see the thermoplastic sagging sufficiently under its weight, I whip it out of the oven, turn on the vacuum cleaner, and lower the molding frame.