Convertible Build - Offset to RF

[antirice]

Hi all -

I'm getting started in the design phase of a smoker I'd like to build. I figured I'd start a thread to keep track of everything and get some feedback from y'all along the way.

My intent is to make an offset that I can convert back and forth between a RF and a standard offset. I have been looking and looking, but haven't seen much in the way of other folks attempting the same thing - time will tell if that's because the idea is horrible, or just not been thought of yet. We shall see.

In regards to the odd design - the shop I work in is a bit limited in how heavy of a piece of metal we can form, so I'm designing with press brake forming in mind (the whole thing will be 1/4" plate). I just threw a model together (we use Solidworks) so I had something to look at for the time being. I've found a few calculators here that I am going to start crunching numbers on to make sure that I'm not shooting myself in the foot out of the gate, and then I'll dive into the modeling a bit more. For now, the CC is roughly 60" long and 28" deep. I want enough room for a pan of water and 4 15lb briskets. That's already way oversize for what I have ever needed at one time, so I should be good for just about anything I'd want to make.

Here's a pic of what I threw together for the time being (yes, I'm aware that it has no chimney. I didn't need one for my visual. It will be included in the final product.):

- Chris

 

[radioguy]

I'm not sure why you want to make a convertible cooker. Just go with a RF and be done with it. If you do go convertible make sure you have a good seal on the RF plate and smoke stack. Stack will have to move side to side depending upon setup.

IMHO nothing cooks as well as a good sealed RF cooker.

RG

 

[antirice]

I'm not sure why you want to make a convertible cooker.

I dont see the need for anything else or any advantage of a standard non reflow over a reflow

My reasoning for the convertible is that I would like one of each but don't have the time or space for two. There are times (ie: cooking 4 briskets at once) where the RF would be fantastic because of the fairly even cook temps throughout the CC. Other times (ie: cooking brisket, ribs, wings and mac & cheese at the same time) that the temperature gradient from a traditional offset would be nice so I don't have to fire up 4 different grills/smokers. If I can make a convertible then I can get the best of both worlds. At least that's the thought, anyway.

- Chris

 

[antirice]

I have read a few folks' posts about how to interpret the various bbq calculators that are on the internet.

Based on what I have read and the following info:

It looks like my sizing is about right. The firebox shows oversized a little, but that should be fine once you take into account that the fuel sits on a rack and not on the bottom of the box. It's currently 24" deep and 30" long.

Also, the opening between FB and CC is right around 135 sq in and the various calculators call for about 115. I can always shrink the hole size, but what I've read suggests that a RF smoker wants a bit larger (50% give or take) opening than a standard offset, but that's measured at the far end of the smoker where the opening is at the end of the RF plate, not between FB and CC.

While 135 sq in isn't 50% bigger than the calculator's 115, it is about 17% larger. I can make the RF opening at the other end of the CC as big as I need if the current FB to CC opening is big enough. Or I can enlarge the FB to CC opening if I need if bigger for the RF and just block off some of the FB to CC opening when using as a standard offset.

Thoughts on the FB to CC opening size?

- Chris

EDIT: Other calculator results:

 

[antirice]

So I have re-read some of the threads related to RF calculators here and opted to go with the 50% oversized opening. Worst case scenario, it's too much and I can block it off a bit.

On to the next hurdle - the exhaust stacks.

Seems like everyone recommends having them at or as near to grate level as possible. For the standard offset, this is no biggie since that end of the smoker is wide open. On the RF though...

Looks like the FB lid won't be able to open as-shown. I'll have to either rethink the lid (sliding to the right instead of hinging or hinging on the side instead of the top or something like that) or redo the stack. I was shooting for something like this:

Anyone out there have alternate door or exhaust ideas that might work for this application?

- Chris

 

[antirice]

Its isn't really a problem on a reflow either since the bottom of the stack opening should be right at the grate level or maybe an inch or so above while the reflow plate is far below the cooking grate with the opening to the fire box below that.

The issue I'm having is that if I run the stack into the side of the CC at grate height, the FB lid (if hinged at the top) will hit it when I try to open the lid.

I am thinking that I'll put the stack in the top/back of the smoker and put a baffle in to get me down to grate height. That'll still let me use the top of the FB as a warmer and also be able to open the lid without sacrificing having the exhaust start near grate level.

 

[hardcookin]

I think with each type of smoker your not going to have exactly even temps.
Plus you can adjust your temp end for end on the trailer models by lowering or raising your tongue on a RF.
Looking at your plans is your cooking chamber length going to be 60"? That should give you plenty of room for 4 briskets on whatever type smoker you go with.
Also with my RF my top shelf runs about 20 degrees warmer than the bottom.

 

[antirice]

I think with each type of smoker your not going to have exactly even temps.

Yep, I'd definitely agree! I have just found the gradient to be quite a bit in the standard flow offset and have been told it's no where near as bad in a RF. Perhaps in the end I still rotate the meat occasionally when running RF mode, but at least I won't be burning the pieces.

Plus you can adjust your temp end for end on the trailer models by lowering or raising your tongue on a RF.

Good to know! I may put adjustable legs on this one to try and accomplish the same thing then!

Looking at your plans is your cooking chamber length going to be 60"? That should give you plenty of room for 4 briskets on whatever type smoker you go with.

Yes, 60" is to be the ID of the CC. I figure I'll end up with around 52-54" or so of usable length on the cooking grate. I really doubt i'll need to run 4 briskets at once but hey, better to have a little more space than I need instead of a little less.

Also with my RF my top shelf runs about 20 degrees warmer than the bottom.

Noted, thanks!

Responses in red

Thanks for the input!

 

[antirice]

Design progress!

 

[antirice]

well, that didn't last long. Started pricing the materials needed for this build and happened to stumble across a few cheap 120 gallon propane tanks.

Using the tanks will save me 50%-75% vs the cost of building one from scratch, so I guess I'll head that route instead. I'll start a different thread for that build, so I guess this one's done.

 

[Berettaclayshooter]

I would advise on ditching the firebox door on the top. It's just a place to loose heat. A door on the end is plenty good and will allow you to make a plenum at grate level for a reverse flow. Also step bending 1/4" plate is a PIA especially into a octagon and then you would have to contend with fitting it and having 2 weld seams. I see you sourced some tanks (lucky little devil).