I named it "Ruth" becasue the yardstick I used for the top of the box originally had "THE TRUTH" printed on it in blue, but when I cut it to fit on the box, it separated the "THE T" from "RUTH", so I glued both sides that said "RUTH" up, and named it that.
Step 1: Matherials
1 x wooden yardstick $0.3
3 x 30"x3/8"x2-1/2" wooden slats $0.15
2 x 16"x 1/16" dia. wooden dowels, or one 30" dowel, NOT balsa wood, must be hardwood. diameters up to 1/2" will work, but do not go below 1/16" $0.1
2 x about 6"-7" wooden frames. NOT paper, and must be thick wood, or metal to avoid bursting into flames. $1.5
1 x 1-1/4"x 6" pvc pipe (or whatever diameter fits over your vacuum. $1
1x sheet of thermoplastic (must melt without burning), your choice of thickness (thicker is less accurate to the actual thing, but stronger, thin is more accurate, but weaker). $0.5
1 x roll of masking tape, duct tape, or other flexible tape (not scotch or packing tape). $1
hot glue (n/a)
For those unfamiliar with vacuum forming, it is a technique of making 3D molds out of plastic which involved heating a plastic sheet until it is pliable, then stretching it over the form, and using a vacuum, or low pressure, to suck the plastic tight. Once sucked down, it takes a few seconds to cool, and can then be removed. It has been used for many well-known and even iconic objects, like the storm trooper helemts in STAR WARS, the Mythbusters "Buster V2" and much, much more. This simple mini vacuum former is good for anything smaller than about 6"x6"x6". The best part is than anyone can build it, with a budget of just $5!
Step 2: Make the Box
Once you have cut the slats, glue the two short slats to the frame opposite each other, with their tops and sides flush with the frame. Then, glue two full size slats on the remaining two sides and to the first two slats, so that you have four sides of a box, as in picute 1.
Glue the remaining three slats parallel to each other on the side opposite the frame, completing a fifth side of the box, as in picture 2.
Cut pices of the dowels to exactly the same length as the outside of the frame, in my case, 7-1/16". Insert them into the box about 1" in from either end and halfway up from the open and closed ends. Place two to each side, with one pair above the other, as shown in the third picure.
Cut the yardstick into pieces just over the length of the inside of the frame. Glue each of the pieces across the frame with a small slit between each, as in the fourth picture.
Finially, cut a 1" hole in one side of a slat, and glue the pvc tube over the hole, as in the fifth picture.
Glue over all seams except those between pieces of the yardstick, I suggest hot glue, then cover each seam with tape.
Step 3: The Plastic Sheet and Frame
Step 4: Your First Form
First, select something to form, I used a plastic cap that diffuses light inside a rubber cube. Place it on top of the yardstick top of the vac-u-form box, and attach a vacuum hose to the pvc pipe.
I use a toaster on medium and hold the frame with the plastic about 6 inches over it for about 30 seconds. When you put it on the heat, it will get wavy. After about 30 seconds, it will quickly go flat, this is when you want to start your form. If your plastic dips below the bottom of the frame, remove it from heat immediately. You want to take it off well before that.
Make sure to have the box and vacuum nearby and plugged in, as you only have a couple of seconds once you take the plastic off of the heat. When you do, place it plastic-side down over the frame in the box, and turn on the vacuum. Press down lightly along all the edges to ensure the best possible vacuum. If it is not satasfactory, then just re-heat the plastic and try again. However, after a few molds, the plastic tends to fold and warp, as it did in the pictures shown. The first form usually does not have such wrinkles and warps. If it is close, you can blow a heat gun on it while it is on the form, and the vacuum is on.
Step 5: If Something Doesn't Work...
If your plastic just smokes and burns, try lower heat, and a different plastic. Some plastics will not work for this.
If your box breaks in on itself, then make sure the inner supports (the dowels) are straight. These should prevent a collapse. If the wood slats themselves broke, make sure they are at least 3/16" thick hardwood. Thin woods and balsa wood will shatter too easily.
If the plastic doesn't suck down, test with saran wrap. If that doesn't work, check for gaps in the box or around the edges of the yardstick ends. Masking tape or duct tape will work fine, since the pressure is pulling it in, and the suction is usually not too strong to suck in the tape through the small gaps. If the saran wrap does work, then make sure your plastic is very pliable when heated, and that you use small screws to anchor it to the frame. Too big of screws will allow air to escape around them.