Jeremy Harris wrote:Marty,
The box was made using the "lost foam" method. I hot glued two bits of 60mm thick extruded polystyrene foam insulation together (the pink or blue stuff used as house insulation) and just carved it to shape (the outside of the foam becomes the inside of the box).
I covered the foam with brown plastic parcel tape (the 2" wide stuff) then laid up woven glass cloth with epoxy resin over the lower half, leaving the top face uncovered (you have to use epoxy as polyester attacks the foam). Once this had gone hard, I trimmed the edges so they were flush with the uncovered top face and then parcel taped over the newly laid up glass fibre. I then laid epoxy glass over the top and sides (to about half way down the sides) and let that cure.
Once it was all hard, I drilled a hole on the lower half (at the end where the wires come out) and poured petrol (gasoline) in. This melts the foam and the pretty horrible sticky mess runs out (it takes three or four goes to melt all the foam). The two halves of the case then pop apart, with a reasonably good internal finish, due to the shiny surface of the parcel tape.
The last thing to do is to trim the top part edges, fill and sand the outer surface and give it a coat of paint. The top is a tight sliding fit over the bottom, as it was moulded on top of it, with just a thickness of parcel tape as clearance. This makes it fairly watertight, but to be sure I put a wrap of PVC tape around the joint as well.
The longest job was filling, sanding and painting the outside, the actual carving and laminating is pretty quick. I did this because I wanted a box that would fit exactly into the limited space I had. You can use this technique to make pretty much any shape box you like. I've made odd shaped fairings, aircraft fuel tanks and even an inlet manifold for an experimental fual injection system using this technique. You can make the shape as complex as you like, as long as you can get the glass cloth to drape over it OK.
Ypedal wrote:Will tin snips cut thru the stuff ? or a blade knife ? *( prior to epoxy )
Ypedal wrote:If epoxying the fibers, it will no longer breath and allow gas to pass... just a thought.
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