My Dumb Projects
Monday, July 31, 2006
  TOKAMAK: Vacuum Forming Machine
I've had quite a few projects where a vacuum forming machine would have been a huge help. It wasn't until I found a great site with a step-by-step tutorial on how to make one from scratch.


I also HIGHLY recommend reading the posts in his discussion board before and DURING your build. You'll find great information and advice from people who have already built one.

Discussion Board

And if your math skills are like mine, be sure to check out the oven calculator when it comes time to do the wiring.

Oven Calculator

Unfortunately I neglected to take photos during the early stages of this project. But as I followed Jim's tutorial closely I'll hit the high points and show where I deviated.

Due to limited space, I decided to build my machine where the oven would hang upside down over the forming surface. I built the supporting table high to alleviate too much stooping over. The vacuum surface is 21.5" x 21.5", made with MDF and covered in aluminum.

Since I can't weld I made my plastic-holding frames from canvas stretcher bars (like painters use). Inside I applied no-slip tread for a firmer grip. The lower frame is attached to a pillow block bushing that allows the frame to slide on steel rods up and down from the oven to the vacuum surface.

To allow for a tight grip on various thicknesses of plastic, I used window sash locks on each side.

I cut a hole in the bottom of the table and made a flange out of one of my shop vac's attachments.

The oven surface was made with concrete board and the ceramic posts were attached accoring to the tutorial.

The sides were cut from leftover concrete board, attached with scrap aluminum and sealed with furnace caulk.

The NiChrome heating element wire was a bear to figure out. Each segment had to have equal resistence for even heating. With the help of the oven calculator, and much advice from friends and the TK560 board, I was able to get the segments exact!

I built a supporting wooden structure to hold the oven. Please excuse my crap carpentry!

The completed oven in its frame.

Up until this point I had not yet decided how to support the oven over the table. Just in time, my friend Jeff gave me some Gorilla Racks and I happened to have some parts left over!

I attached a shelf support to either side of the wooden oven box, and then attached the vertical rack posts to the table. This also allowed me the freedom to change the height of the oven if I needed to.

So I didn't waste any expensive wire, I did a "dry run" with string. It gave me a better idea of how much wire I would need and helped me understand what I would eventually have to do.

The wires were attached to the segment posts and run out a hole to the switch.

The wires attched to a 20 amp switch.

All the parts assembled. I eventually moved the oven up to the top rung to make more room under the oven. I had to get new steel rails for the added distance but was able to find a set of 4 at a scrap yard for $6!

For my first test "pull", I wanted to experiment with different types of objects: A large smooth-sided unsanded MDF dome, A small unsanded MDF dome, a small flat-sided sanded shape and to fill the space a pocket knife and wrench. All pieces a placed on plywood risers placed on washers as not to disrupt the airflow.

The first test pull may not be considered a success my experience formersa but I was just giddy that it actually worked! The "tenting" between shapes can be corrected by adding more space between the forms. I expect a big shape like the large dome would have to be pulled by itself.

After the first pull, I saw some areas to improve. I flipped the sash locks so the frame could get closer to the oven. I also added a flip-up support half way up the rails to hold the frame for loading. Once the plastic is loaded the frame continues upward to be held in place by the two wooden "L" clamps"

I made an oven door with the last of the leftover concrete board and embedded a oven thermometer in the center. The door slides into aluminum U-channel attached to the bottom of the oven. Closed up the oven can get to 375ºF.

Now I guess I need to make something with this beast!

MUCH, MUCH thanks to:

Jim and the guys at
My high school chum Jerry for the wiring advice
The overly generous Ron for the technical assistance, bushings, rails, multimeter and other goodies
Jeff for the Gorilla Racks (They make great shelves, too!)

Thanks guys!

Many months to build, cost $250-300 (visit your local scrap yard and cull-lumber bin!)
You did a great job with your vacuumformer! You can pull the large bowl with the others and won't get ribbing if you use a "pusher." It's usually a wooden tool used after you bring the plastic down over the mold. You push down the ribbing before turning on the vacuum. It works great!
That's a great tip, thanks!
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These are all the dumb things I find myself obsessed with building when I SHOULD be doing something more productive.

As a kid I built lots of plastic model kits, never knowing that one day those skills would actually be of use.

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