I've made my burner out of 44 mm scaffold tube for the main diameter of the venturi , added three legs at one end 75 mm x 12 mm cut from same tube & welded back on to the major diameter . at the free ends I welded on a turned a 1/4 " thick walled ring x 1 inch long , big enough to easily allow a half inch galv steel pipe to slide though it for tuning the flame by 3/4 " long to slide over a halt inch galv steel water pipe & set a locking screw in a welded on nut into the side to hold the 1/2 tube in position The 1/2 " tube has had a steel plug with a 1.2 mm hole drilled in the end , TIG welded on at one end & a brass ribbed turned up hose connector brazed in the other end for the gas supply hose . The hose is gas tube crimped on at both the hose connection points . Assembled by sliding the !/2 " tube in the venturi assembly , putting the propane gas on via a variable pressure regulator & lighting it whilst the steel tube was held in the vice away from all flammable stuff inc the garage roller door . I slid the venturi assembly back & forth till I got a maximum tuned flame about 16 inches long by six inches wide , it roared like a Chieftain tank going full bore . That was all done a couple of months ago, the furnace was cast the same time & by now should have dried out considerable . I cast the refractory lining from refractory concretes around a galv 5 mm thick wire 40 x 40 mm square steel mesh former to help it stop splitting when heated & help it retain it's shape when hot .The furnace throat was made using some thick pliable plastic sheet rolled up round a Dulux 5 litre plastic paint can as it had no bottom rim to catch on when it was removed ......unlike a metal tin . Under the paint can I screwed a 1" nipple of polystyrene in tot he hole where the filler valve had been so as to allow exit of any metals should the crucible disintegrate Before doing the casting I found some tube that the 44 mm venturi would easily slip into so welded on an angled entry to the steel cylinder body so it touched through to the inner former plastic , again the steel tube has a simple welded on nut & bolt to lock the venturi into a set /known position . The former was removed a few weeks ago & I cleaned up any bits of crud with a bit of coarse glass paper Next step for me is to work out a way of placing the graphite crucible down in the furnace & still be able to lift it out when it's full of molten brass . I've also got to wait till I can afford another sack of furnace concrete to make the furnace lid as well as fabricate some form of rotating horizontally hinge mechanism as I don't fancy the idea of flipping back a red hot tank commanders hatch style lid .