Vacuum Former

This is my first version of a vacuum former and if you skip to the last stem you see why I needed to make some changes. The new version is here Vacuum Former 2

A vacuum forming machine is used form plastic sheet into the shape of a mold. Vacuum forming is used extensively in industry to make all kinds of plastic products. For this instructable I'll so you how to make a vacuum form machine and I hope to do more instructables on things you can make with this machine. If you don't know what a vacuum former is and want to know how it works PLEASE READ THIS BEFORE CONTINUING. My machine is not be exactly like the one on the link but the principle is the same.

Step 1: Get the Parts

This is a basic list of most of the materials I used to put together the machine and a few of the tools I used.
Materials:

Oven
1. Nichrome wire
2. Hardibacker cement board
3. ceramic standoffs
4. aluminum flashing 14in. wide
5. 1x3in. Wood stud
6. wood screws assorted lengths
7. 8-32 machine screws
8. 14 gauge stranded wire
9. screw terminal block
10. crimp-on connectors
11. 1/4in. thick plywood

Control Box
1. 4 gang electrical box
2. 4 600watt dimmer switches
3. 4 dials (radio shack)
4. 14 gauge stranded wire
5. wire nuts
6. extension cord with one bare wire end

Vacuum/platen
1. 1/2x3/16in. Balsa Wood
2. 1/4in.Thick Plywood
3. Wood Glue
4. 2x4 Wood stud

Frame
1. 1x2 wood stud
2. Two Hinges
3. Two Sash Locks
4. Two 6in. Angle Brackets

Tools
1. Jig saw
2. Miter box saw
3. Hack saw
4. Utility knife
5. Wire cutter/stripper
6. Mulitmeter
7. Drill

This is the prototype machine I built before I built the real thing. It used one heated in an all aluminum oven. This is an over/under design, the oven over the platen. My machine will be a flip type machine because the oven and platen are at the same level and the frame flips between them.

Step 2: The Oven

First we will build the oven. The oven consists of a wood frame with an inner layer of hardibacker cement board and an aluminum inner lining. To build the wood frame you will need some 1x3 lumber, which you can get from Home Depot or Lowe's. For the parts of the oven I will refer to the part numbers form the .pdf file of all the parts of the oven. Parts VF-01 and VF-02 and some #8 x 1-1/4in. wood screws will be used to construct the frame. I used a miter box saw to cut my 1x3 to length but a circular saw or jig saw could do the same thing, just make your cut square. Place the wood pieces in a rectangular shape with the shorter ones(VF-02) on the outside. Drill pilot holes through the VF-02 parts and into the ends of the longer pieces(VF-01), the wood will split if you don't do this, plus it will make it easier to run the screws in. A 1/16in. dill bit is a good size to use. Screw the rest of the wood frame together in this fashion, making sure you keep everything square.

Now we need to cut the hadibacker board. Hardibacker board is basically drywall for around showers, it used because it doesn't absorb moisture. Its made with cement so its also a good heat insulator which is why its used in the oven. You can cut the hardibacker by scoring it with a utility knife and then snapping it but that can be hard to do when you need long thin pieces. I would recommend using a jig saw to cut this board. I found out the hard way that you can't use a normal jig saw blade to cut cement board, so you will need to get a masonry blade for your jig saw. When you go to the hardware store to get it, look for one that says it will cut tile, thats what you want. The blade doesn't have teeth, the cutting edge looks like a glue/sand mixture just globed on to the blade. I started with cutting the long thin pieces first, parts VF-03 and VF-04. First I cut them to the 2-1/2in. width and left them a little long. Then I went and fitted the pieces to the frame, so that every piece fit nice and snug. You want to keep the oven as tight as possible so you don't have to worry about holes or gaps for the hot air to escape.

Now you need to make the aluminum inner lining side parts, VF-07 and VF-08. This is aluminum flashing which you can get from any Lowe's or Home Depot. I got a roll that was 14in. wide because the flashing will be used on the bottom panel of the oven which is 11in. wide. Aluminum flashing is very easy to work with and can be cut with normal scissors, I'd recommend a nice sharp pair just to make it easy. Again here cut the pieces to the 2-1/2in. width and a little long, then fit the pieces to the frame. Now screw this all together through the flashing, Hardibacker, and into the wood.

I know the animation is not the best but I think it gives you a really good idea how the oven goes together. This is my first real attempt at using SolidWorks. You might be asking how does the large sheet of Hardibacker, VF-05, attach to the plywood, VF-06. That will be explained in the next two steps.

Step 3: The Electrical Equations

Now that oven housing is done its time to move on to the part that makes it an oven, the heating coils. In the world of vacuum forming machines there are a lot different ways to create the heat, but the simple fact is that you just need a heat source that can effectively heat your entire plastic sheet. I found some Nichrome wire heating elements from a surplus store but there are many other options. You could use electric grill elements, a toaster oven, your stove, a heat gun, and I've even seen a gas heater used. Nichrome wire is the same kind of wire thats in a toaster and works off the fact that as current passes through the wire it heats up. I'm going to run through how I determined how to wire the oven so that it could be run off a normal household 120V outlet. This is specifically how I did it but these same equations and be applied to any other oven like this one.

This first equation we need to look at is commonly known as Ohm's law:

V=IR or I=V/R or R=V/I

In this equation V= voltage, I=current, R=resistance. The units for voltage is Volts, for current its Amps, and for resistance its Ohms. For this oven I want to use 120V, so that gets me one part of this equation. Now its time to measure the resistance of the nichrome wire. This can be done with a common multimeter and for each of my heating elements the resistance is about 74 Ohms. The resistance of nichrome varies depending on the diameter of the wire and the length of the wire your using. If your building your own oven with a roll of nichrome wire this where you can make changes to suit your situation.
So lets calculate the current (I), from these two values:

V=120V R=74 ohms

I=V/R I=120/74 I=1.62 A

So if I was to hook up one heating element to the wall, the current through it would be 1.62 Amps. But I want to hook up 8 heating elements not just one. There are two ways to wire the elements, in series or parallel. Each method has its benefits but we are concerned with the resistance of the entire oven. In this way we will consider each element as a single resistor. If I hooked the elements up in series they would all be wired end to end and the total resistance of the system would be the sum of the resistance's of each element. This would mean there would be 592 Ohms of resistance so the current would be:

V=120V R=592 ohms

I=V/R I=120/592 I=0.20 A

You would find that this is not enough amperage heat the wire to the desired temperature. This chart at infraredheater.com shows some common wire gauges and the amperage needed to heat them to a certain temperatures http://www.heatersplus.com/nichrome.htm To get more amps through the wire you need to hook up the elements parallel. This equation shows how to solve for the equivalent resistance in a parallel circuit:

1/Req = 1/R1 + 1/R2 + 1/R3 + ...

In this equation Req is the equivalent resistance, or the overall resistance of a parallel circuit, and R1, R2, R3 etc. are the resistances of each individual resistor. In this case I have eight individual resistors, or heating elements. So using this equation and the individual resistance of 74 Ohms, the equivalent resistance is:

1/Req = 1/74 + 1/74 + 1/74 + 1/74 + 1/74 + 1/74 + 1/74 + 1/74

Req = 9.25 ohms

So the current for a parallel circuit would be:

V=120V R=9.25 ohms

I=V/R I=120/9.25 I=12.9 A

Now this is more like the amperage we need to heat the coils up. I could wire the oven in parallel and call it a day but I would like some more control over the temperature and amperage. To do this I decided to use a regular lighting dimmer switch. A dimmer switch is basically a variable resistor, also called a potentiometer. By changing the resistance of the circuit I can control the amperage flowing through it and therefore control the temperature. I got the dimmer switches from Home Depot and they are rated at 600 Watts. A watt is a unit of power so I need some way of relating this to the voltage, amperage, and resistance. This equation does it:

P=VI or P=(I*I)R or P=(V*V)/R

To find the amperage:

P=600 W V=120 V

P=VI 600=120 * I I=5 A

So one of the dimmer switches can handle up to 5 amps at 120 V. The current calculated earlier for the parallel circuit was 12.9 amps, this is to much for a single dimmer switch. So I decided used four dimmer switches, each controlling two heating elements. You can see how it was wired in the pdf.

If you didn't understand some of this stuff that all right, because here is a calculator that can do it for you http://www.imperial-armor.com/ovencalculations.html This does not work in the same way I figured out my oven though. It asks for your final oven requirements and then tells you what you need. I started with what I had and figured out a way to make it work. I think this is way that most people would do it. The calculator also assumes that you are building a purpose built oven with coiled nichrome wire. If you decided to go that route here is a link that can really help with finding supplies, http://www.infraredheaters.com/

Step 4: The Wiring

So this is how I wired my oven. Here are some of the specifics one how I actually built it. I used a 4 gang electrical box to hold the dimmer switches and an extension cable with the female end cut off to plug into the wall. I used 14 gauge stranded wire throughout the electrical system. Four wires and a ground wire run from the box to the oven and connect to it with screw terminal. From there the wires break off into each of the four sets of heating elements. They are then connected to 8-32 machine screws which also hold the heating elements in place. On the inside of the oven, short sections of uninsulated wire are connected to the heating element mounts and then to the nichrome wire with some 4-40 machine screws.

To make the electrical connections easier to accomplish with the least amount of wire running inside the oven, aluminum flashing was used as a conductor. Pieces where cut in such a way to allow power to come in at four different places and then have a common ground for the entire system. The four small pieces on the sides are the power connections and the large piece in the middle is the ground. This idea short of works like traces on a PCB and was based off that idea.

You might be asking, Why did you use the aluminum? The heating elements emit infrared waves which is basically heat. The infrared reflects off the aluminum and on to the plastic sheet. This type of heating is known radiation. You may have heard of convection ovens which is basically this same set up but a fan is added to move the air around inside oven. This moving hot air helps to heat the items inside the oven quicker. I am considering adding a fan inside the oven later to see if I can get better results.

Step 5: The Platen

The Platen is the surface on which the molds are placed and on which the plastic forms a seal for the vacuum. There are many different platen designs but most are designed with many small holes that the air is pulled through to create the vacuum. My platen follows this design. To make the platen I used two sheets of 1/4in. plywood cut to 23in. long and 11in. wide. In the bottom piece I cut about a 1in. hole in the middle so that I could put the PVC fitting in to it. The PVC parts were chosen so that I connect the Shopvac to the platen, and of course this will create the vacuum. In the top piece I drilled a bunch of 11/64in. holes in a pattern. The pattern and size of holes is up to you, just be reasonable. These two pieces are separated by the balsa wood strips. The balsa wood is 1/2x3/16in. and cut to fit around the perimeter of the top and bottom platen parts. Then the whole thing was glued together. The idea here is to keep the volume inside the platen as small as possible. That way when you flip on the shopvac you don't have to pull a bunch of air out of the platen and then out from under the plastic.

Step 6: The Frame

The purpose of the frame is to hold the plastic sheet while it is being heated and during forming. I made the frame out of 1x2in. wood. The inside dimensions of the frame need to be the same as the platen and the oven, so mine was 11x23. To clamp the plastic I used sash locks which you can get from Home Depot, and the hinges make is easy change sheet. When building the frame and the whole machine for that matter you need to consider the size of plastic sheet you want to use. In my case I wanted to use a 12x24in. piece of plastic so the frame, oven and platen need to be slightly small. I choose 1/2in. smaller that's why everything is 11x23in. This size also determines how large of objects you can form. You also need to consider you plastic supplier. Where will you get the sheet from and what size can you get it in. I know you can get 4x8ft. sheets but I believe a standard size at many places is 72x40in. You don't want to waste part of the sheet because your former size and sheet don't match up.

As far as plastic suppliers go, a sign store could be a good local source. Online you could try http://www.mcmaster.com or http://www.professionalplastics.com

Step 7: The Base

The base on my machine is very simple. A sheet of plywood with 1x2's screwed around the perimeter to add support. For the first test run of my machine the oven just sat on the base with spacers and the platen was duct taped in place. I made the angle brackets but similar brackets can be bought from any hardware store. The oven and platen are lined up with the frame when its flipped over on both sides. For my platen there is no seal around the edges, its made so that the hot plastic forms the seal when it is forced lower than the top edge of the platen.

Step 8: The First Test

Now is its time to test. I got a sheet of .020in. thick Polystyrene from a hobby store. This is a little on the thin side for vacuum forming, but it all depends what you are making. A normal thickness would be between .040 and .080. A thinner material can be formed with more detail but needs to be watched closely while heating. This is the problem I had with my first test. I turned of the oven and let it preheat for a little bit. I cut out another piece of hardibacker to be a cover for the oven while it was heating. Then I put the plastic in the frame placed it over the oven and put the cover on top. When the plastic starts to heat up it will start to warp, then it will start to sag. Usually you can determine when to form the plastic by the amount of sag there is in it. But this learning has to come from experience, your first couple of times might not turn out so well. Due to my lack of experience the first time I used the machine the plastic heated up a lot quicker than I expected, saged to low, touched the coils and caught on fire. As you can see from the pictures it melted all over the oven. This ruined the oven but I can be cleaned up and used again. I don't the time to do it though. I'm living away from home for the summer and won't be able to work on it for a couple of months.

So at least for now I learned a lot about how a vacuum forming machine works and how it could be put together. I might try to change some parts of the machine to make it a little more solid and heat the plastic more evenly. If there is one thing I can tell you about build a vacuum forming machine here it is, when you are testing for the first couple of times have a fire extinguisher ready to go.