Or you can make nice and surprisingly sturdy plastic stuff in amazing shapes, amaze your friends with your technical prowess, and be the life of the party.
Vacuum forming is a technique for shaping sheet plastics into 3D shapes, which you can do at home, easily and cheaply. And it's fun. It's the easiest way to make an infinite variety of shapes in plastic, or to make molds for casting shapes in other materials, such as concrete.
The basic technique is to
0. clamp a sheet of plastic to a frame (such as a windowscreen-type aluminum frame)
1. heat it in an oven (such as your kitchen oven) until it's soft and rubbery
2. stretch it over a convex mold of an interesting shape (such as a life cast of your sweetie's face), and
3. suck the plastic inward onto that mold with a vacuum system (such as your household vacuum cleaner)
Once the plastic cools, you pull it off the mold and trim off the excess plastic, leaving a copy of whatever shape you sucked the plastic onto.
In this instructable, I'll show you how to make a cheap but good vacuum former, using mostly things you have around the house, or can buy very cheaply. The whole thing shouldn't cost more than about $30 to $50, maybe less depending on what shortcuts or substitutions you choose, and what materials and tools you have lying around. It also shouldn't or take more than an hour or two to make. (Plus a shopping trip to a home improvement store and an office supply store, and letting some silicone cure overnight; you can use epoxy if you're in a big hurry and want to do it all in an evening.)
Here's a movie of the vacuum former in action:
Relatively few people know about vacuum forming, or how easy it is. They're mostly radio control model builders---who use it for making thin plastic parts for airplanes, or bodies for cars or helicopters, or hulls for boats---or they're Star Wars fans who use it for making their own costume armor.
It's unfortunate that vacuum forming know-how is mostly limited to these little niches, because vacuum forming can be used for many purposes, artistic and practical. If you like making stuff in general, and especially if you like non-rectilinear stuff that doesn't look "homemade," you should know how to vacuum form.
You can use vacuum forming to make:
1. intermediate molds for modifying and combining sculptural shapes (this allows you to sculpt in whatever medium is easiest, and transfer the shapes to plastic, making one copy or many)
2. sturdy custom parts out of thick plastic to protect delicate machinery. (Using cheap homemade equipment, I've vacuum formed shells from 1/4" thick plastic that are sturdy enough to stand on.)
3. three-dimensional, internally-illuminated signs from scintillating textured plastic
4. flexible, cushiony custom liners from thermoformable foam
5. relief sculptures of various kinds
6. molds for casting chocolates, soaps, candles, or concrete relief sculptures
7. decorative architectural reliefs, or decorative shells that can be reinforced for structural purposes
8. stage props and costume parts in hard plastic or soft foam,
9. zillions of things you'll probably think of.
Industrially, vacuum forming is used for making all kinds of things, from disposable plastic cups and lids to sinks and hot tubs and McDonald's golden arches to full-sized boat hulls. (If you've never seen a 30-foot sheet of plastic sucked into a boat shape in a few seconds, trust me, it's pretty cool.)
For vacuum forming at home, the main limitation is usually space for the equipment---the size of your vacuum former is proportional to the size of plastic sheet you need to form. The $30-50 vacuum former described here doesn't take up much storage space at all, and can handle thin plastic sheets as big as will fit in your oven.
For larger stuff, you need a custom oven---not very difficult or expensive to make, but a little bigger all around than the plastic it will heat.
For thick plastics (more than about 3/32" or 1/8" thick, depending on several variables) you often need a stronger vacuum than a vacuum cleaner will provide, and again the cost and size of the equipment are roughly proportional to the size of plastic sheet you will be forming. The cost can be under $50 for a high-vacuum system for thick plastic sheets up to about 12" x 18", using a converted bike pump, or an electric air pump of some sort from a thrift store. (Such as a kitchen vacuum sealer, a tire inflator air compressor, or a "nebulizer" air pump.)
The vacuum former described here will work very well with an inexpensive high vacuum system, getting professional quality results for thick plastic, for under $100. If you want a standalone vacuum oven, so that you can use it somewhere besides your kitchen, you can make a medium-sized one (12 x 20 inches) for $30.
For now, let's make a good fast cheap vacuum former that you can do a lot with, using your kitchen oven and vacuum cleaner; it's mainly a board with a hole in it, which you can store on a shelf. You can soup it up later, if you want.
Step 1: Understand the design
(1) a board (called a "platen") with a hole in the middle of it,
(2) a vacuum cleaner that sucks air through that hole,
(3) a pair of frames we can clamp together around the edge of a sheet of plastic, and
(4) a kitchen oven.
To use it, we'll do three basic things:
(1) heat the plastic in the oven until it's soft and rubbery and stretchable
(2) stretch it over the shape we want to copy, and
(3) suck it down around that thing, and let it cool in that shape
In more detail, we'll
0.a. Support the board on something near the oven. The support(s) can be pretty much anything, or any convenient pair of things that is reasonably sturdy, allows us to route the hose to the vacuum cleaner without kinking it, and can be put very near the oven we're using.
0.b Put some things in the oven which we can support the plastic-holding frames on. (Glasses made of actual glass, for instance.)
0.c. Preheat the oven. This usually gives us more even heat.
0.d Position some object that we want to shape plastic over on the board, over the hole, but with some spacers under it, so that air can flow from around the the object, under it, and to the hole in the board.
1.a Clamp a sheet plastic between the pair of frames and support it on three or four things in the oven (such as glasses made of actual glass)
1.b Wait a few minutes for the plastic to get hot and rubbery and stretchable. For most plastics, we can tell how stretchable it is by how much it sags under its own weight. When it sags about the right amount, we know it's ready.
2.a. (Turn on the vacuum cleaner, open the oven, and) QUICKLY but carefully remove the plastic from the oven with gloved hands...
2.b. ...stretch the plastic down over the shape we're copying, until the frame meets the board, creating a kind of "tent" of hot rubbery plastic over our form and stretching down to the board, and...
2.c. ...let the vacuum cleaner suck air out from under the "tent," by sucking air from under the form, and in turn from around it. This will suck the stretched, rubbery plastic inward into the desired shape, in about one second, and the plastic will cool enough to solidify in the new shape in about 10 to 20 seconds.
To make this work well, and flexibly, we'll add a few basic enhancements:
1) We'll put a foam rubber gasket on the board, the size and shape of our plastic-clamping frames. That way, when we stretch the plastic over our mold, we can press the frame against the gasket to make a seal. When the vacuum cleaner sucks air from around the mold, it will do a better job because it's not sucking air through any little gaps between the frame and the board.
2) We'll make the gasket removable, so that we can use different-sized gaskets (and plastic-clamping frames) for different-sized sheets of plastic. The obvious benefit of this is you can waste less plastic if you make different-sized things. A less obvious benefit is that it helps you use odd-sized scraps that you get from cutting the larger size out of a sheet of plastic. A much less obvious benefit is that you often get better results for certain difficult-to-form shapes, by using plastic that is somewhat bigger than the thing you're making, but not a whole lot bigger.
(I won't explain that here, but if you're interested you can check out this thread on www.rcuniverse.com, about "webbing" problems and ways to avoid them: http://www.rcuniverse.com/forum/m_5086453/anchors_5086453/mpage_1/key_/anchor/tm.htm#5086453 One of the best ways is to use plastic sheets about the right size for your project.)
Making the gasket removable is easy. Instead of sticking the self-stick foam rubber directly to the platen (board), well stick it to a slightly oversized sheet of something flexible---such as thin plastic, and tape that down to the board.
3) We'll make our frames out of pieces of aluminum windowscreen frame material, with internal aluminum corner braces. That will let us mix and match a few side lengths to make frames of different sizes and proportions for different projects.
4) We'll use a 3/4" galvanized floor flange (plumbing fitting) under the hole in the platen, as part of our connection to the vacuum cleaner hose. This will let us replace the vacuum cleaner with a more powerful---but surprisingly cheap---vacuum system later, if we want. A more powerful vacuum system lets you form thicker plastic and still get good detail. (If you know you'll never need to do that this, you could just make the platen hole the size of your vacuum cleaner hose, or some attachment that fits it, and glue the hose or the attachment permanently to the hole. That would be cheap and easy, but you would lose flexibility for later upgrades.)
If you've seen other homemade vacuum formers, you've likely seen "vacuum boxes" several inches thick covered with pegboard. Don't make one of those. You don't need a bunch of holes in your platen; One big one works at least as well if you're only forming one object at a time, and if you want to distribute the vacuum across several smaller molds, there are other ways of doing it. (Many industrial vacuum formers use one-big-hole platens.)
Thick "vacuum forming boxes" are likely to collapse if you ever add a powerful vacuum system---and to reduce the vacuum system's effectiveness, because the air inside the box has to be pulled out.
(If you decide later that you really want a many-hole platen, you should make a thin "sandwich construction" platen; you can use your one-hole platen as the bottom layer of the "sandwich," so starting with a one-hole platen is a good way to go.)