converting a box cooker to have
round inner walls
my sbc to round inner walls was easy, here are the steps for anyone wishing to
- cut a long rectangle of smooth, flexible card (not corrugated or stiff),
its width being the height of the inside of the sbc, plus about 1/2 inch for
- mark, cut and fold tabs along both sides.
- bend it into a cylinder, overlap the ends sufficiently so that it makes
the biggest cylinder that will fit into the sbc and glue together.
- from stiff card, cut a square the same size and shape as the outside
dimensions of the top of the sbc. cut a circle out of the middle the same
diameter as the cylinder of flexible card.
- using the tabs, glue the cylinder to the card top made in step 4.
- insert cylinder into existing sbc. it should just touch the flat inner
walls and rest on the oven floor. glue it all together.
- glue aluminum foil over the insides and floor.
- make a cross out of two intersecting cardboard strips, glue them in the
centre of the floor of the oven. this makes a stand that raises the black pot
above the floor. besides raising the pot to a warmer part of the oven (small
gain), it increases the surface area of the pot which 'sees' the sun (larger
there may be significant temperature gains to be had with:
- adjusting ratio of pot size to crude focal beam width.
- making the inner sides into a section of a cone.
- using a reflective hemisphere for the inner walls and floor.
i shall probably try these all in time but as my modified sbc stands right
now it is the best one i've ever built. i would like to hear results from anyone
else who tries out this design, i feel that there is room for even greater