heat the plastic until it softens enough to bend into
the shape of the mould.
To this end, I drilled a large
number of small holes through the deepest part of the mould.
I then flipped it over and
built up a thin frame of stand-offs to make a "plenum"
behind the mould.
I then glued a sheet of
1/2" plywood across the back to finish the plenum chamber. A
hole in the back of this later will allow a vacuum pump to evacuate
the mould.
The plastic sheet needs to
be held in place and a reasonable seal needs to be made between it
and the mould. So I put caulking around the rim and smeared a layer
around the edge of the mould.
The hinged frame closes
with catches and holds the plastic in place.
I built a stand for the
mould, with a dowel pivot on the mould so it can be easily rotated.
The mould is quite heavy and I didn't want to be heaving it up and
down countless times.
Here it is with one of my many early failures
(this time due to not having an adequate heat source).
I later added a couple of handles to the sides of
the stand to make it easier to carry around.
I drilled a 2 1/4"
hole in a piece of 2x4 to take the hose of the shop vacuum. It's not a
very tight fit, but the suction holds it in place well enough.
I drilled a smaller hold in the back of the plenum
so the vacuum hose doesn't get pulled in and block the plenum.
