converting a box cooker to have round inner walls

converting my sbc to round inner walls was easy, here are the steps for anyone wishing to try:

1. 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 tabs.
2. mark, cut and fold tabs along both sides.
3. 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.
4. 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.
5. using the tabs, glue the cylinder to the card top made in step 4.
6. insert cylinder into existing sbc. it should just touch the flat inner walls and rest on the oven floor. glue it all together.
7. glue aluminum foil over the insides and floor.
8. 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 gain).

there may be significant temperature gains to be had with:

1. adjusting ratio of pot size to crude focal beam width.
2. making the inner sides into a section of a cone.
3. 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 improvement.

regards,

richard mcmahon