I built a larger 18x24 bed vacuum former first, and then decided that
I needed a mini vacuum former for smaller pieces and for the leftover scrap plastic from the big former. This was a weekend project and it makes great pulls.
• A $5 toaster oven from a second hand store. Make sure to get one with (4) elements. They are made with 2, 3, or 4 and cost the same. Prices can be higher, so check other stores.
• (3) 36" long .5"x.75" aluminum angle to form the frames
• (32) 6-32 .5" long flat head machine screws for the frames
• (32) 6-32 nuts for the frames
• (8) 1.5"x1.5" flat corner brace for the frames
• (4) 3/32" pop rivets to attach the angles inside the microwave
• plywood for the box. .5" or .75" is fine.
• binder clips to clamp the frames together
• spring clamp to handle the frames when hot
• Shop Vac. I have a 6hp, 5 gallon model
• duct tape
• Chop saw with a metal cutting blade or a hand saw and miter box to cut the aluminum angle. Aluminum is pretty easy to cut by hand
• File to clean up cuts and edges
• 5/64" bit for the screws
• 1/4" drill bit to recess the screw heads
• A drill and/or a drill press (optional)
• hole saw sized to the vacuum hose
• drum sander to enlarge the vacuum hose hole if needed
• It's a toaster oven that gets hot. Make sure you don't get burned, and don't touch the aluminum frames directly.
• Sawing/grinding the aluminum creates friction and it gets very hot.
• We're going to melt plastic. You want to be careful how you handle it, burning plastic on you will not be fun.
• Wear a respirator. Melting plastic releases fumes.
Step 1: Aluminum Frames
The frames are 10.5"x7.5" overall. It's a total length of 36" which is a stock length of the .5"x.75" aluminum angle and it also fits inside the toaster oven perfectly.
The top and bottom frames clamp the plastic. The inside clear size of the frames are 9.5"x6.5". I mitered the corners of the frames, cutting them at 45*, on a miter saw with a metal cutting blade. A miter box and hand saw would also work.
The flat corner braces are attached at each corner, (4) 6-32 machine screws for each bracket. Use a right angle to ensure the frame is square and mark the spots for the screws. You will need to make two frames.
After drilling the bolt holes in the aluminum angle for the flat corner braces, I recessed the screw heads. To recess the screw heads I took a drill bit sized to the screw head, in this case .25", and carefully created the recess. I drilled into the aluminum hole for the screw I had just created, but did NOT drill all the way through. I used a drill press to stop the drill bit which makes this easier. Test it on a scrap piece first. This way, you ensure you don't drill to deep. You only recess the one side of the frame where the two meet. This can be done by hand, but will require a lot of 'stopping to check'.
I cut aluminum angle to act as brackets for the frames in the toaster oven. I blind drilled a hole inside the oven and pop-riveted the angles in place. Be careful blind drilling, I went very slow so that I wouldn't damage components I couldn't see.
The frames need to be at least 3" from the bottom of the toaster oven so that the sagging plastic doesn't touch the bottom. Closer to the top is better than closer to the bottom.
Step 2: Vacuum Box
The vacuum box is plywood on five sides with a pegboard top. The box's overall dimensions are 9.5" x 6.5" to fit inside the aluminum frames.The sides are 3" tall to allow for the 2.25" vacuum hose. Base the height of your box on the vacuum hose. If the vacuum hose is smaller, make the height less. A larger box is more air for the vacuum to pull.
I used a hole saw to cut a hole in one side of the box, and a drum sander to enlarge the opening for the vacuum hose. I then lined the opening with duct tape to create as snug of a fit as possible on the vacuum hose. The better seal you can create, the better the pull will be.
I notched the aluminum bracket to fit around the hose. You want the top of the bottom frame even with the vacuum surface for the best definition. A wood bracket glued to the other side of the box keeps the frame level. I've got a large clamp to serve as a handle to remove the frames from the oven and onto the vacuum box. The frames will get hot, so be careful.
Step 3: Melt Plastic
I use a spring clamp as a handle to move the frames from the oven to the vacuum box. Binder clips are on the other three sides of the frame to clamp the plastic in place.
The oven door doesn't need to be shut during the heating. The oven heats the plastic up quite fast, and you may see some smoke and it will definitely smell burning plastic. A little bit of smoke is normal.
As soon as the plastic starts to sag, remove it. Switch the vacuum on and lower the frames over the vacuum box. You want to transfer the plastic quickly, because as soon as you take it out, it's going to start cooling off.
On the first pull, I let the plastic get too hot, and it ended up in a wrinkled mess.That and I was trying to form a mostly flat shape.
A vacuum former can't get fine detail. A half dome shape is the perfect buck for a former. Recesses can be a problem as well. For recesses, drill a hole in the buck so the vacuum can suck air out and pull the plastic tight. Straight vertical surfaces can make removal of the buck difficult. Optimally the vertical sides are at a slight angle.
For the second pull, I removed the plastic as soon as it started to sag. This pull came out much better. I use .020" plastic for the pulls.