This Unfortunately isn't going to be the best instructable ever. It's more of a show and tell.
So here we go.

I loosely based my machine on this one http://formech.com/Manual/508FS/Images/508FS.gif

First off, for those of you who don't know what a Vacuum former is, I will give you the super simplified answer.
Its a machine that heats up a sheet of plastic until its pliable then the plastic is put over a form of your choice and vacuumed down tightly onto the form. The plastic then cools until it is no longer pliable leaving an impression of the form in it.

caution: please be careful when working with high heat , and high voltage.

Step 1:

To build A vacuum former you need a frame to clamp the plastic into, a heat source, a platform for the molds to be put on (platen) and a vacuum source.

on mine I have 2- 4 square ft aluminum frames to put the plastic in between I made it 2ft by 2ft so that I would be able to get 8 pieces of plastic out of a 4'x8' sheet.

the platen is made out of mdf and 2x4's and 400 little holes I had to drill.

the vacuum comes from a vacuum pump and a air tank (that is vacuumed down).

I made the oven using nichrome wire and ceramic insulators and using the oven calculator on www.tk560.com in the discussion
section under vacuum forming (this was a key part of me building this), by the way my name is gadgetman on that site. Mine runs on 220v.

Here are a couple pictures of the platen.
a picture of the underside of the oven.
And a picture I found on the net of how my plumbing works.

Step 2:

if your looking at this, odds are you have seen other home built vacuum formers
but I just wanted to show you one that is just a little different.

Here is A picture of final products and a video of the process.

In the video I explain a good bit about the machine.

Keep in mind this is ONLY the SECOND time I ever used this machine and it is not 100% yet.

I still need toggle clamps to hold the metal frame around the plastic tight and I need to insulate the top of the oven to keep people from getting burned or shocked by accident and it would be nice to be able to control the heat better than just tuning it on and off.

Again I'm sorry this isnt the best instructable ever but I started this 2 years ago, then wasn't able to continue working on it until just recently.