Saturday, 21 January 2012

Vacform box

I must thank Allan Buttrick for his inspiring work on old kits, one of his tricks is to vacform canopies, using kit ones as the former, which inspired me to give this ago. Thanks Allan for sharing your enthusiasm.

Now Allan uses a Matel Vac-u-form, which is the ideal tool for the job. I saw one on an auction site here in NZ and it was way out of my budget. So after googling around and watching a few you-tube vids to get the idea,here is my vac box,

that was build from bits and pieces that were to hand in our garage.

The box is an electronics project box from Disk Smith electronics, one of their jiffy boxes.

A piece of vero board, which is an electronics prototyping circuit board. Copper tracks on one side and lots of nice about 1mm holes in it.

A piece of vacuum cleaner hose attachment, one of the little heads that came with our Dyson vacuum cleaner.

Interior of the box, you can see the vacuum cleaner attachment which was epoxied in place.
The lid was chained drilled, to remove a large rectangluar section, where the veroboard was glued on.
The two wooden strips are to brace the veroboard, it was discovered it bowed when the suction was applied to it.
The yucky muck on the right hand side of the box, is leftover bits of foam, from when it was being used for another project years ago.

One wooden strip in profile, shaped to fit against the veroboard.

With the duct tape removed, you can see the epoxy, which was spread, then the veroboard pressed into it, cling film spread over it and weighed down until set. The cling film didn't stick to the epoxy, so was easily removed.
The sections of duct tape were put on, to reduce the area of suction, so its applied to the plastic being formed.

Now I gave some thought to how to hold the plastic, in fact one of the reasons why I haven't used it. I found you need to have a very small gap between the plastic and the top of the box, to get a good pull down on the plastic, in a light bulb moment I thought of using a jar. So the centre was cut out of a jar lid, then the plastic is trimed to fit the lid, and then the lid and plastic is screwed onto the jar. The plastic gets held nice and firm, and the jar gives you something nice to hold, while you are waving it over the electric element, to soften the plastic. You get an even pressure around all sides of the plastic too, when you push down on it. 

I've since drilled a hole in the bottom of the glass jar so it lets out the build up of air pressure as the air heats up in the jar.

In action, the canopy is a Frog/Eastern Express boxing Blenheim Mk1, tacked on a short section of wood, to give it support and lift it about 2 mm above the surface of the vac box. The canopy has had all the framing removed, and I sanded it so that it was slightly smaller than the canopy opening on the kit, to allow for the thickness of the vac formed plastic.

The plastic is just some packing, I think a little dog toy one of the toilet paper companies are giving away here.

The trickiest thing I have found, one of things to practise is telling when the plastic is soft enough to be formed. Watch it while its heating and you can see it sag, tension up and then sag again, this second sag is when its just right to quickly push over the form.
I've noticed that different plastics behave in different ways as well, so its a matter of having plenty of plastic, and just giving it a try. You can use the same piece again and again, just heat it up and the mold will disappear. I actually found it easier to see what's happening with the plastic if it had a bit of mold in it already, easier to see that tighten up.

Jar removed and the form trapped in the plastic.

A little flexing and the canopy is released.

Trim with small nail scissors and its done.

Here it is after a coat of Klear, test fitted.

Some plastic rod is cemented to the canopy edges, to give a lip for the canopy to sit against, when its cemented on. Any gaps I 'll fill with either CA or white glue or milliput, just depends on what gaps I get.

I am going to have to be more vigilant on the dust, as the dust and specks on the mold and or plastic get impressed into the molded plastic as well.