Step 3: Make a platen

Picture of Make a platen
The heart of your vacuum former is the platen, which is just a piece of MDF (medium-density fiberboard) a little bigger than your kitchen oven---about an inch bigger all the way around. The extra inch will be useful for taping down a sheet holding the frame gasket.

Measure the inside dimensions of your oven, side to side and front to back, and add two inches to each measurement. That's how big your platen board should be. (A little bigger isn't a problem, unless it makes it hard to fit your board and yourself near your oven in your kitchen.)

The easy way to make a board that size is to buy the next larger size sheet of MDF at your local home improvement store, and have them cut it to size for you. They usually make the first two cuts for free, if you buy the board, so it shouldn't cost anything and will save you a little hassle. (They don't do "precision cuts," but we don't need precision for this.)

Now make a hole 1 1/2" in diameter in the middle of the board. I used a hole saw attachment on my drill to make a neat hole, but it doesn't actually matter. If you have a drill and a portable jigsaw, you can drill a starter hole with the drill to get the jigsaw blade through the board, and cut out the 1 1/2" hole with the jigsaw.

(Don't make the common mistake of making the hole the same size as the diameter of your pipe. That creates an air flow bottleneck right around the hole, where the air must squeeze under the mold to get into the hole. You want a hole with a larger circumference than your pipe.)

Rather than cutting out a 1 1/2" hole, you could just drill a bunch of 1/4" holes in the middle of the board. (If you don't have a jigsaw or a hole saw, this is the way to go.) Start with a circle 1 1/4" in diameter, and drill 1/4" holes spaced about 1/4" or so apart, i.e., with centers about every half-inch around the circle. (Again, make pilot holes so your holes don't wander into each other.) Then drill a few more holes scattered in the middle of that. (You need 10 or 12 quarter-inch holes to avoid creating a bottleneck, with 7 or 8 in the outer circle; for a platen bigger than kitchen oven-sized, you'd need more.)

The platen shown is actually 1/2" MDF, because that's what I had around. 3/4" MDF is nicer; it's more than three times as rigid.

feyr6 years ago
I am looking into making this but I want to use my 5hp 12 gallon shopvac that is in the garage since I only have an upright vacuum for the house. It has a large 2.5" hose on it and I was wondering what size I should drill my hole into the platen? Based off your statement of using a larger hole than your hose I was thinking of a 3" hole. Bringing some pipe down and using one of those rubber reducers with hose clamps on it to create the seal between the two parts. Also on a vacuum like that how thick do you think I can work with and would it be too powerful for thinner pieces? Thanks for this awesome writeup! I am looking into using 1/16th, 1/4 or possibly 3/16 thick acrylic sheets to make an automotive headlight trim.