Vacuum Forming

An oven, a common domestic one is fine. (do check with the other half first) Fortunately there is NO smell associated with the process, you can even cook tea while the oven is still warm.

Pre-heat it to 200deg C, or 390 deg F.

Arrange a metal dish or similar to support the styrene sheet and frame inside the oven.

Make sure that the dish is deep enough to allow for the sag that will occur in the plastic when it is heated. (maybe up to 30mm)

A good sucking vacuum cleaner is required. I use our Dyson.

You need some form of closed and sealed wooden box with a hole in the side to take the cleaner hose snugly, and a hole in the top over which you can place the appropriate plug  or mould. It is important to not have any leaks, you need all of the vacuum available to you.

The photo shows a rubber sealing strip which was used when I formed the Fiat front ends. Later this helped seal under other plug combinations.

I found it very important to have some way of lining up the heated support frame over the plug. With white styrene you cannot see beneath it. A tempory piece of wood screwed to the side of the box can work.

Sometimes I placed the stool and box close to a kitchen cupboard door and positioned it so that a door, and door edge, could act as a positioning guide.

The plugs are generally made from ‘MDF’ a composite board which we have here in NZ. It is very easy to work with. I have a sanding disc which I use a lot for shaping. You may have to drill small holes through the plug in places to ensure that the vacuum reaches all areas. For the Fiat fronts I made holes in the window recesses and light upstands.

The plug or mould may include an upstand of some sort to act as a seal around the edge when the vacuum is applied. In some cases this upstand has been part of the box. An old film canister glued onto a piece of wood makes a good support for very small plugs. I used this for both the Fiat roof vents, of which there are I think 21, and the SkyCab cowls. A slice off the top of a tin can makes a good dam around a plug. Having smashed the paper thin engine cowl on my Cessna, I repaired it as much as possible with sticky tape and then poured plaster of paris into it. The resulting plaster shape enabled me to make a replacement cowl out of thicker and stronger material.

A sheet of styrene plastic of appropriate thickness and size must be firmly held around all its edges.

This can be done by stapling it to a piece of thin timber with a hole cut in its centre, or clamping it in some other way. I have once used a Meccano frame to do this. If you are making a large number of a particular item (roof vents) it is worthwhile making up metal clamps to hold down all four edges. This saves on staples. 

When first put into the oven the styrene pulls tight like a drum, then with time (2-3minutes) it starts to sag in the middle. When it has sagged sufficiently, it is removed and with the vacuum cleaner already turned ON the support is lowered over the plug. This must be done carefully, yet swiftly (plastic starts cooling), to ensure proper positioning. I have had a few misalignments and disasters.😠

I have actually re heated a sheet and used it again successfully.

The actual forming process occurs incredibly fast and you very soon know whether you have a successful product.

The thickness of sheet is quite important. Too thin, I first tried 0.5mm for the Fiat ends, and the result was too springy and useless. The plastic is obviously stretched/thinned to fit around the plug. Too thick, I tried 1mm, and detail/corners are lost. 0.75mm was my final choice. Some webbing, to varying degrees can take place between raised portions. If it is no good first try, then change something, and do it again until you get it right.

The styrene is very easily trimmed with scissors or a knife to the correct size. I find curved nail scissors very good for this at times.

Larger items may need stiffening with pieces of styrene across the insides to prevent distortion.

So be prepared to experiment and give it a go!! And like me, you may be surprised how many applications you can find for this technique. I made five different parts for the Fiat construction.

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