I Have a nice closed head barrel that was hard to find for the right price so I dont want mess it up. My plan is to cut off 2-4 " from the bung end, the cut off part will become the base with a 8" hole in the center for the burn tube . the larger part will then go back on. where the cut was made my Idea is to join the barrel back together with a male female arrangement I will have to stretch one side and or shrink the other to get a nice smoke free seal (may be 700 degree high temp silcone??) anybody try this yet. Ideas suggestions Help.
Some ideas.... I am not fully sure what you plan, so let me make some assumptions. I am assuming the burn tunnel is under the level of the bottom of the barrel. Where is the flue exit from the barrel? The hole for the riser is 8 inches... is that the size of the riser inside? or the size of the outside of the insulation (6inch system)? If it is an 8inch system, then there will be a layer insulation around the 8inchs say to 10 inches... in a 24inch barrel that leaves only room for a 7inch exhaust tube on the bottom unless the riser is offset an inch or so. Offset is not a problem... one side of the barrel may be a bit warmer... but you do have to remember to do that so the exhaust still fits as it should be the same size as the riser. Next, what is supporting the riser? If it is brick, you will want to use a "split" (1.25 inches thick) set "shiner" next to where the exhaust comes out. I am assuming for exhaust you will be using a 90degree elbow plugged into the bottom of the barrel, set as close to the edge as possible. The other option would be to have a straight exit out the side of the barrel, but that would put it above your split and make removing the barrel for cleaning problematic once the bench was in place.... I am assuming part of the reason for the split was for easy cleaning. In my design ( http://www.permies.com/permaculture-forums/10653_0/alternative-energy/yet-another-portable-rmh ) I put the split above my exit, but I have thicker steel and so they mate and I will put a cover over the join. I think the high temp silicone will be ok at that point. I am planning to use it along with high temp insulation. (the rope looking stuff used to seal iron stoves)
Note: everything above is my opinion, based on my experience with my particular setup. It is not definitive. Every installation is different.