by Steve » 16 Jul 2010, 15:06
Ok, I'm no offset expert, but I assume you want to use a drum a main cooking chamber and build a firebox to fit on the side.
Firstly, it's worth remembering that the steel on drums is thin. We use them for UDS but these are simple to build and have no doors or anything in them. Drums won't last a long time before they rust through, you'll get a few years out of them at best.
Secondly, heat control in offsets is considered more of a challenge, using a thin steel drum is only going to add to this, it's not going to be resistant to the wind and rain and it's not going to be stable like a proper offset - just check out the steel on John's Cactus Jack's and you'll see my point.
Third, offsets often require tuning plates welding into them, baffles etc. There's a lot of skill involved in building a good offset, not that I'm assuming you're not up to the challenge, I'm just letting you know it's not as simple as welding a fire box onto the side of a drum and letting her rip.
If I were you, I'd use the drum to make a UDS, they're cheap, stable and they cook great Q.
Now if I've not put you off building an offset, here's what I'd say about cleaning your drum. You're obviously going to be putting a door in there, so I'd cut and attach the door, open it up, scrub the inside out then burn it through with pallets. After that I'd close the door and then spot weld some flat bar around the door to get the required seal.
When cutting the door, a good way is to mark it out, cut the top and bottom edges with an angle grinder, weld on your hinges, then cut the sides, will ensure a good fit. You could also weld your flat iron rim on at this point or do it after your burn.
What are you planning to use as your flue from fire box to cooking chamber? Ar you just planning to use the bung hole or are you going to drill it out some more? You will probably need to calculate the correct size of flue, as you will with exhaust and fire box. If you hunt around on the American BBQ forums, you'll find the maths required to work out fire box and flue sizes. I've seen the formulae before but I don't remember them.
HTH