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:
http://www.razorlab.co.uk/. 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:
Step 1: Assemble and Glue Together
Squeeze a bead of glue around the bottom part of the box that will meet the sides parts.
Do the same to the first side. Don't forget to place glue on the box joints too. Stick in place. Repeat on the remaining 3 sides and stick in place.
Now do the same for the top and stick in place.
Wipe away any excess glue with a damp cloth.
Use bar clamps to hold the box together.
Leave to dry for 24 hours.
Step 2: Mark Top/platten for Hole Drilling
Use a long ruler to mark out a grid pattern on the top of the box for drilling. I recommend 2mm holes at 10mm intervals though 15-20mm may be okay.
Drill the holes in the top of the box. Don't worry about sawdust going into the box. This can be vacuumed out later. Once you have drilled all the holes which may take some time. Give it a light sand to remove all the raised edges.
You could laser cut the holes if you have free access to a laser cutter. If not then drilling is the best option as laser cutting the holes will take time and a cutting service usually charge for the length of time it takes to cut your design.
Step 3: Attached Hinges and Hook & Eyes.
Next you need to attach the hinges to the box and the outer sizer ring. Align the outer ring and mark and drill for screws. Be aware that with 6mm MDF you will most likely need to cut the excess screw off with pliers and file down flush with MDF.
After this we need to complete the sizer by carefully screwing in the hook and eyes. These hold the concentric rings of the sizer together. Again you will probably need to cut with pliers and file down smooth flush with the MDF. Do this for all sizer rings.
Screw on the side latches if you want to keep the sizer locked in place. This is optional.
Step 4: Add Rubber Seals
Next you need to stick the rubber seal down on each sizer ring. Make sure there are no gaps as this will not create the air-tight seal you need.
Finally drill a sizable hole in the front panel and attach and glue a piece of pipe that will allow you to connect a vacuum cleaner.
Job done. Now you are ready to test it. Good Luck.
If need help with the laser cutting. I've attached some DXF files that you can use or modify.