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.