Down Draft design issues

[wombat]

I have been playing around with various concepts for my build for a while now and have been tossing up between Reverse flow and traditional SFB. I have finally decided to take a different approach and use a down draft style made famous with the Jambo Pits range. I'm not looking to copy or clone a Jambo but to come up with something that will operate along the same principles.

I have a couple of questions I need answered before I start buying steel

1. I'm looking at a CC that's 24" X 48" X 1/4". Can I get by with a single door at 45" or do I need to run with 2 doors at around 21" each?

2. is there any reason for most people putting the door flanges on the door rather than the inside of the CC opening. It would seem like a lot less chance of welding deformation happening

3. I was going to run with Feldons calculations for the size of the FB/CC opening adding a 45o baffle to direct the heat upwards. Should I allow some extra clearance due to the restriction of the baffle eg 125%. I'm going to make the baffle a bolt on extra so I can play with tuning it.

4. I will be making the FB as a single skin (not insulated) and was going to 146% of Feldons calculations. (W24"x H22" X L 20"). Will this be a problem?

5. The  chimney will be 5" square welded directly to the end plate with an opening cut out from just below the bottom grill, full pipe width for 6". The chimney will rise 32" from the top of the CC

Am I on the right track with these numbers? Any advice will be greatly appreciated. We don't get to see too many varieties of BBQ pit in Australia and I'm keen to give one of these a go

 

[ribwizzard]

Going extra big on the firebox with out double plating or insulating it will give you more heat loss due to extra surface area.

Door flange on door instead of cc helps hide inperfections in your cutting of the door, easier to weld, more forgiving as crud builds up.

 

[daveomak]

2. is there any reason for most people putting the door flanges on the door rather than the inside of the CC opening. It would seem like a lot less chance of welding deformation happening


Skip welding using blind welding techniques solves "continuous" weld problems......

Plug and Slot welds.png

• daveomak
• Oct 24, 2015

PlugandSlotWelds.gif

• daveomak
• Oct 24, 2015

 

[daveomak]

For the door seal/flange, I would use a thinner material so it can be tweaked to fit any contour problems that arise to get a good seal on the Cook Chamber.... All you are trying to accomplish is an air tight seal... 16-20 gauge is adequate... If it overlaps the CC ~3/4" and the door the same, that should work well...