Vacuum Forming

Finding or purchasing a suitable canopy for scratch built models can be a problem. 

I managed to construct a simple vacuum forming box from scraps of chipboard and ply. 

Box size - W 230mm(9")  x L 340mm(13.5")  x D 90mm(3.5").

The sides were cut to length and  a hole drilled in one end to take the vacuum hose.

The sides were  glued and screwed. 

The frame corners were mitred  and joined

with thin ply. (Could just as easily be glued 

and pinned).

The bottom was made from ply and the top hardboard (Just happened to be lying around).

The bottom  was glued and pinned to make a good airtight seal. 

The top was perforated  with a  1/4" drill. 

My first Plug was carved from laminated balsa.

My next was laminated pine which is more difficult to carve but much smoother finish.

Both plugs were coated with yacht varnish and sanded down with 400 grain wet and dry.

A liberal coating of corn oil before placing in the oven  seemed to be the best solution to getting a good release when cooled down.  

 Technique

I wasted a couple of sheets of plastic before I could judge the right time to remove frame from the oven.

The oven temperature was set to 260C gasmark 5 and the frame placed in oven supported at either end

on 4x2 wooden blocks.

As the sheet heats up it will sag under its own weight.

The amount of sag required depends on the thickness of the sheet so experimentation  is required.

In my case the right amount of sag was almost equal to the height of the plug.

Switch on the vac and Remove frame from the oven (wearing protective Gloves).

Carefully lower the frame over the plug and box.

When the frame is in contact with the box the vacuum will take effect and suck the plastic around the plug.

         Mould just out of the oven.

               Plug is easily removed.

 Clear Plastic sheet is available from Totem Hobbies.

Sheet size 305mm x 190mm x 0.5mm costs around £1.20.