I'm interested in this too. Last week I purchased the Vacuum Press Kit from veneersupplies.com and have been planning to do the modifications to make it work for a vacuum clamping system for my CNC as well. In the back of my mind I also had the idea of using it for a vacuum forming table.
Here are some of my thoughts:
1) I like the heater in the unit the way the video had it. You want the heater elements above the plastic. I know warm air rises, but hot plastic sags down. You don't want it to get closer to the heat as it sags.
2) Don't build the frame to an oddball dimension. Check out common material dimensions available from your preferred suppliers and build to that. You don't want to have to buy oversized stock and then trim it down.
3) A vacuum tank does work faster than a ShopVac, but only for a limited volume of air. What I saw in the video was the air under the plastic evacuating quickly and then I heard the vacuum pump running continuously attempting to draw a vacuum on the combined system of the tank and vacuum table. This means for a minute or two early in the process, the vacuum was much less than it could have been.
A better system is to have a GOOD vacuum motor such as the LH7123-13 for $119 (http://www.centralvacuummotor.com/shopbot.htm
) evacuate the air under the plastic and then have the system switch to a vacuum pump after a certain level of vacuum has been achieved. Both the high volume and high pressure systems can run continuosly. A check valve allows the vacuum motor to be isolated when the vacuum pump is able to take over. Under any loss of pressure the system instantly switches back to the vacuum motor to maintain vacuum.
4) I think it would be good if the work holding frame could be divided in half or even in fourths. A vacuum manifold under the table would let you isolate vacuum only to the area being used. That way we can do smaller parts and not worry about wasting a big sheet.
5) Pneumatic cylinders are nice, but a manual pulldown system with pulleys and counterweights might work just as well.
6) Add a good box fan to aid in cooling the formed plastic.
7) Consider using heat lamps to heat the plastic. This may give you better control of the heat distribution and could be easier to repair.
Anyway that's my two cents for now.