I know there are a few vacuum formers already available on Instructables. Well here is my version. It is slightly different from the others.
All the MDF parts are laser cut. Though this is not necessary for a vacuum former generally, but is very useful for the sizer. The sizer on top is hinged and can be removed with the sprung hinges.
In many of the Instructables I've seen, the frame cannot be resized. This hinged sizer allows for you to use even the small pieces of plastic you have left over, so nothing goes to waste.
The dimensions of this vacuum former are 400mm x 400mm x 100mm. However you could make it bigger or smaller.
6mm MDF will probably be best suited to this project.
Hinges and screws
Side hook and eye catches x 4 (x how many sizer rings you build in)
2 x toggle catch/latch + screws (optional)
single sided rubber seal/draught excluder.
Piece of pipe.
If you don't have access to a laser cutter you could use a laser cutting service like this:
. I have used Razorlab and found their service very good and quite reasonable. They are based in South London, UK.
DON'T FORGET LASERS ARE EXTREMELY DANGERS TO LOOK AT. ALWAYS PROTECT YOUR EYES. DO NOT LOOK DIRECTLY AT THE BEAM. USE PROTECTIVE EYEWEAR
Alternatively you could cut square and rectangular pieces with a band saw and glue and screw.
Or you can try and win one with the instructables contest: