A wise man once said "Many fortunes, and at least twice as many eyebrows have been lost by those experimenting in the field of gas combustion"
This site may be useful:-
http://www.backyardmetalcasting.com/oliverburner1.html
I made a setup capable of producing castings in aluminium and brass just using a Sievert propane blowtorch with a large burner. I forget the rating of the burner now, but it is about 1-1/2" diameter.
A simple stand with a 'U' clip around the neck the torch supports it in alignment with a hole in the side of the 'furnace'. Adjust the gap between the burner and the furnace simply by moving the stand. Usually about two or three inches gives the best results.
The 'furnace' is a ring of firebricks stood on end, with the bottom corner trimmed off one of them to admit the blowtorch flame so it spirals round the crucible. A couple of bands of black iron hold the bricks together like a barrel. I grouted the open joints between the bricks with a mix of brick dust and fire cement.
Four half bricks serve as a lid, simply resting on top and moved in and out with the crucible tongs like a camera lens iris to regulate the exhaust or charge the crucible.
I did consider adding insulation and prettying it up with a sheet steel wrapper, but it works as it is, and I never got around to it.
'Foundrywork for the Amateur' and 'The Back Yard Foundry', both by B Terry Aspin is another source of information, but I think his furnaces were solid fuelled.
http://www.amazon.co.uk/exec/obidos...ss&index=books-uk&field-author=B. Terry Aspin
