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Read this first.
The box is made of 1/2" chip board and is 5' L 2.5' W and 4' H. I have
a
door hinged on the front as you can see and I put a scrap piece of 3/16
Plexiglas on the inside and outside attached with silicone for a "thermo
pane" window. The insulation material is 2' X 4' X 5/8" ceiling
tile from
Lowes at around $2 each and it took 8 of them. The entire inside of the box
is insulated with the exception of the floor which is the concrete floor of
my shop.
You can see that the lower section is the "furnace"
chamber. The end
opposite the Reddy, has a single sheet of aluminum, you can use flashing,
inserted in a semi circle and the rest of it is lined with aluminum sheet.
I lined it just cause I had it, but the semi circle is used to cause the
forced air to circulate. You will also see a small hole on the same end as
the heater that will allow for air flow.
Between the heating chamber and the "furnace" chamber,
I put small wood
slats that support a grate that is heavy rectangle wire fence. At first, I
thought that would all I would need and that it would allow the heat to rise
freely. It rose too freely on the left side by about 25 degrees, so I put a
sheet of aluminum over 2/3 of the left side. Then I got a rage of hot air
coming up over the right edge of that sheet, so I covered the entire grate
with aluminum sheet leaving about 2" exposed on the back and front.
I have two oven thermometers which I watch through the window.
Now the temp
rises almost the same on both sides. At around 200 deg, I turn off the
Reddy to let the temps stabilize and keep turning it on and off to raise the
temp evenly while the plastic forms itself. This entire heating process
takes less than 15 minutes. The 3/16 Plexiglas starts to form at around 200
degrees, but won't really get going until about 225 and at 250 it is really
drooping. I ran a test with some 1/8 and it really gets loose at 225.