The Poor Man's Vacuform Machine

I have reached a point in my Mustang model where I had to make a decision regarding the shape of the new cockpit parts. Normally when a kit includes ribs or bulkheads or any other interior structure is it shaped like a simple rectangle. This is because their molding process, of course, can't produce the actual shape of the part or it would be too thin and flimsy to work in a kit. However, if you have looked inside an airplane made of aluminum you will see the structure is made of thin metal stock with a 90 degree flange around all of or most of the surface. So the mission is to recreate this flange with a plastic part so the cockpit structure will look more realistic, even in this small scale. This is one of those details that probably won't be noticed at first, but once it is, it will blow people's minds.


So how do you make such a piece simply and cheaply? From my experience, the easiest way to do this is by vacuforming, but I don't have a 4 thousand dollar piece of machinery in my house. According to some websites you can purchase small table top vacuform machines for about $130. But knowing what I know about vacuforming (I ran the vacuform machine for Bob Violett Model Jets for 2 years) I know the elements can be recreated simply, and cheaply. All you need is some sort of box, a screen to lay the mold on, a seal to hold the plastic, a heat source, and some form of vacuum. And with a little creativity you can find all of these around the house.   

For the box, I found a small shadow box with a hinged top at Michael's which cost me $1.60 after using one of their frequent email coupons. It was the perfect size and depth and the wood was dense and should hold the vacuum well.

The top needed a little modification so it would hold the plastic to be heated and formed. I cut out the flanges holding in the little piece of glass, set that aside cause you never know when a little piece of glass will come in handy, and sanded the inside edges as best as I could.

I needed to create a good flat edge along the top of the box to create a tight seal so this little notch that was cut out for the hinge needed to be filled in. The hinge would be moved to the outside of the box anyway. A small piece of Popsicle stick worked perfectly. 

I used wide rubber bands to create the seal. These were epoxied to the top edges of the box and the bottom side of the lid. I used any extra epoxy to fill in the corners of the box and lid to prevent any vacuum from leaking out. 

To create the screen needed to hold the mold, I look far and wide for a material with small holes close together and had no luck. So I had to make my own. It needed to be easy to drill yet stuff and heat resistant. I found a lid from a microwave safe container made of thermoplastic. I epoxied it to a piece of .030" plastic to give it extra rigidity. 

The holes needed to be close together and plentiful so the vacuum will have enough pull around the small molds. After drawing a grid of 1/8" squares, I drilled over 200 1/16" holes. 

Seeing the pattern I wasn't quite satisfied, so I drilled .040" holes in the spaces between the other holes. This should provide enough pull for the vacuum to form the part. After drilling all these holes, you will need to go through most of them with an X-acto knife to clean out all the fuzzies. Sanding with medium and then fine sandpaper will remove all the burrs from the holes. 

For the source of vacuum I'm gonna try use my own lungs. This is a small box and small volume of air. If the seal is good, I should be able to inhale hard enough to pull the plastic down. If this doesn't work, I may have to resist to some sort of hand-operated pump. But for the sake of the experiment, I took a piece of 12" or so model engine fuel tubing that my dad happened to have laying around and drilled a hole for it at the bottom corner of the box. Epoxy the hose in place on both sides so it makes a good tight seal.

 

I wanted to make the vacuum screen adjustable so I could lower it in order to create tall parts in the future. Right now the parts I'm making will be about 1/16" thick, but later in the project I may need to make taller things. The depth adjustment will be made by the supports that hold the screen in place. I made them from 1/8" balsa and cut them tall enough to form my parts. In the future I can make shorter supports to create taller parts. To hold my supports in place I simple added a few more pieces of balsa at the bottom of my box. These pieces not only hold the supports in place, but they also prevent the screen from being lower than the vacuum opening.

 After a quick trial fit of my screen, I realized it needed some central support. I notched two of my support pieces and added a crossbeam. The screen must not flex or bend any during the vacuum process or the parts will come out curved.

 

 I'm going to make these parts out of .005" thick plastic, which might as well be paper, but that's the closest thickness to a scale rib. I used a piece of this plastic to find the location of my new hinge point on the outside of the box. The box came with a little latch, but this won't be adequate enough to form a tight seal, so I used more rubber bands. Again, when I actually go to try this, I might have to find another way, but for now let's go with it. The hinge was attached so that it pulls down nicely on that side when the plastic is in place.

 

 

So now my poor man's vacuform machine is complete. For the source of heat I will use a hair dryer or a heat gun on low setting. Since the plastic is real thin, I don't want to use too much heat. And it won't take that much to make it floppy.

 

I haven't yet tested the box, I'm putting it out here on faith that it will actually work. Next step would be to make the molds for the parts I need and then a proper test could be made. I only have so much .005" plastic so I can't waste it on tests. I did try out the vacuum part by squeezing the lid down over the plastic and  I could apply a very good vacuum with little effort by sucking on the tube, so I know the seals are good. However the rubber bands that I thought would hold the lid down won't be enough, so I need to think of another way to do it. It will probably be as simple as tying it down with string. But we'll see.

Oh and in case you're wondering, the total cost for this box ended up being less than $5. Not bad for an industrial piece of machinery that usually costs thousands.