Before I set out to build my own vacuum former I did alot of research on various DIY sites. I found alot of helpful tips and designs. Ultimately I settled on components from several different designs. My design is by no means perfect, but it gets the job done, and was fairly cheap to build. It is capable of forming a piece 33" x 22".
Step 1: Basic Box
I started with a basic five sided wood box out of half inch particle board. This will be the infrared "oven". 24 inches deep, 35 inches long, 24 inches wide. Thats pretty straight forward.
Step 2: Heat Source (also keeps your french fries warm)
As I said, I researched many different designs before I started and found that I preferred the infrared lamp as my heat source because, well frankly, I thought I'd burn my house down if I tried to build my own heating element. I even considered buying three electric pancake griddles, bolting them side by side into a box, and placing that over the plastic sheet. I tried it with one griddle and it worked pretty well, though my wife was not pleased with me disappearing into the garage with it.
I used a total of ten infrared heat lamps that you can purchase at any hardware store. There are four 250 watt bulbs, six 125 watt bulbs, and one 1200 watt patio heater. I had the patio heater already so i incorporated it, but i'm sure I could have used 4 more 250 watt bulbs in its place. This gives me a total of nearly 3000 watts of heating.
The bulbs are mounted with ten porcelin standard 120 volt, 600 watt light fixtures. The kind you find mounted on a rafter in your attic, or in a garage, or basement. They do not have a pull string or switch built into them.
When figuring the placement of the bulbs I had to take into account the thickness of the insulated panels, which I will explain later.