New Project: Vacuform machine

My quest for a decent plastic-producing technique has not been successful so far, and damnit, I've tried! (Just search for "plastic" on this blog)

During my research, I came across the vacuforming process. A sheet of plastic is heated untill it becomes elastic, and then it's stretched over a mold. The air between the mold and the plastic is sucked away and the plastic fits on the mold like a glove. This is the exact procedure that is used to package all kinds of products (especially toys). A couple video's about this process can be found here:

Since the process of vacuforming is so simple (it doesn't even involve weird chemical formulas or strangely-named, unhealthy-vapor-releasing solvents), it should be no problem to build a vacuform machine at home.

Jim Egner from linked above, is a StarWars fan who hosts an older site (After his StarWars designation) and who has built a vacuform machine.

My goal is to create one of those machines aswell. It will be one of the projects for the summer of 2007.

[Update 23.00]
I went down to the hardwarestore to write down some prices for things like PS, MDF, several types of wood and aluminum sheets. Here's the list (all prices in euro):

PS transparent 100cmx200cmx2mm29.04
PS transparent 100cmx200cmx5mm67.67
PS white 100cmx200cmx2.5mm35.42
PS transparent 100cmx100cmx2mm11.34
PS white 100cmx100cmx2.5mm15.33
MDF 244cmx122cmx12mm23.31
MDF 122cmx61cmx12mm10.55
MDF 122cmx61cmx18mm13.75
OSB wood 122cmx61cmx11mm8.21
OSB wood 122cmx61cmx18mm13.95
AGGLO wood 250cmx125cmx18mm15.67
AGGLO wood 125cmx62cmx12mm4.91
AGGLO wood 125cmx62cmx18mm6.89
wood 240cmx5mmx20mm2.98
wood 240cmx5mmx10mm1.30
aluminum sheet 50cmx50cmx0.5mm12.59
metal perforated L profile 200cmx27mmx27mm11.59

I've been reading a lot about making a vacuform machine on the tk560 forum. While I wait for the registration process to finish so I can ask some questions on the forum, let me lay them out here first.

The first part of the vacuform machine is the forming surface. So far, I've seen only 1 approach: 2 MDF panels with a small "sandwich" in between (a couple mm), then a metal sheet on the top and perforated through the metal and the first panel. Also, a hole in the bottom panel for the vacuum cleaner.

This thread hints about a better way to create this forming table. Instead of a sandwich and a bunch of small holes, only a single hole is used. This should allow for a better seal (not sure why at this point). BUt more importantly, I believe this design can make it possible to use different sized plastic sheets to vacuform. That would be really interesting, since I don't want to use a huge sheet every time I vacuform something small.

So what would a vacuform look like that allowed different sized sheets ?

Another question on my mind is: what is the metal sheet for on top of the forming surface ?

And: how is the vacuum tank supposed to work ? Pump all the air out of it with a vacuum pump, attach it to the vacuform and open the valve ? This could save me from having to buy a powerful vacuumcleaner...

some pictures of polystyrene sheets and their prices