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Step 1Understand the design
Our vacuum former consists mostly of
(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. (SETUP)
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. (HEAT)
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. (FORM)
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.)
(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. (SETUP)
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. (HEAT)
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. (FORM)
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.)
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