Mack Upgrade

[Chuck Diesel]

I purchased the Mack plans a while ago, life happened and I didn't have the time to start a build until now. After looking over the plans I realized that my needs have changed and would like to add another shelf in the CC. Below is the change I keyed into the calculator. The opening at the end of the baffle plate is the same size in cubic inches as the throat. Also, I wanted to go with a single 12" over sized damper on the firebox door. Any feedback would be greatly appreciated to avoid measuring once and cutting three time.

Cook Chamber:25.5 x 49.75 x 32, actual size: 40596 cu

Firebox: 25 x 24 x 25, actual size: 15000 cu, recommended size: 13532 cu, differential: 110.85%

Chimney: 6 x 25.48, actual size; 720 cu, recommended size 750 cu, differential: 100%

Firebox Air Intake: 1 inlet, actual size: 113 cu, recommended size: 45 cu, differential; 261.57%

Throat: recommended size: 120 cu

[Dirtytires]

Not sure if your plan was to just add another shelf (which is no problem) or were thinking of making the cook chamber bigger. I might recommend getting Frank involved if your plan was to increase the cc as he might have some good pointers for you.

The single damper is definitely possible. My first concern is placement as intakes work best located low on the firebox. Second, I have had times when shutting down vents on one side of my firebox (and opening only the other side) has helped with unstable temps due to wind. A single air vent would mean a more complicated solution.

[Chuck Diesel]

Dirtytires,

In regards to the cook chamber size, the plan was to add another shelf with the same space between each shelf. As I looked over the plans I realized that I would have to add more volume to the cook chamber to accommodate an extra shelf. Once I figured out how much space in between shelves I needed I plugged the measurements into the calculator and adjusted my plan for a larger firebox, throat and chimney. As for the single large damper, after watching multiple videos of people using popular named brand smokers, and using my current smoker, everyone likes to open the firebox door for extra oxygen from time to time. My thinking was, keep it safe and just add a larger controllable vent. I PM'd Frank last month but haven't gotten a response. As I read through a number of similar post, most seem comfortable with firebox measurements within 115% of actual size. Your response about the cook chamber has got me worried. I thought if I modified the cook chamber, firebox, throat and chimney proportionately based on the calculator I'd get similar results close to the original Mack plans... what am I missing??

[Pete Mazz]

Nothing that I can think of.

[Chuck Diesel]

Peter,

Thanks for the feedback. I'm looking to start cutting steel the first week of December.

[Dirtytires]

As long as you make all the proper adjustments to sizes you should be fine. I was concerned you were not but sounds like you are on top of it.

The size of the fire (and therefore temperature) is regulated by the amount of air allowed to feed the fire. Opening the door will definitely allow air in but it is extremely difficult to maintain and regulate temperature with such a crude ‘valve’. Tho it will work, a more precise damper will be more efficient in the long run.

Hit frank up again....if it has been longer than a week he needs a reminder.

[Chuck Diesel]

Hi all, I just started my build and have a few questions in regards to insulating the firebox. The question is, when sealing the insulation in the walls of the firebox is it necessary to vent the walls. My thinking is, if you cap seal the walls the air inside the insulation chamber will expand and interfere with the sealing weld and lead to warping of the walls when it heats up. Is this overthinking the process or will sealing the chambers be okay? Firebox inner wall is made with 3/8" plate and outer wall is made of 1/4" plate.

Will post pictures later this weekend.

[Big T]

You need to completely seal weld the inside and outside box. You don't want any moisture getting into the insulation.

[Chuck Diesel]

I worked most of last Saturday cleaning off the rust I created and assembling the inner firebox.

[Dirtytires]

I completely sealed my insulated firebox. Absolutely no issues with warping or cracking in 4 hard years of use.

[Chuck Diesel]

Six weeks in and she's starting to look like a smoker.

[Pete Mazz]

[Big T]

[ajfoxy]

definitely coming along nicely.

[Chuck Diesel]

Thanks for the feedback everyone.

I'm looking forward to this coming weekend to get the cook chamber framed and hopefully attached. Although my decision to use 3/8" plate for the inner firebox, and baffle plate was a good idea i think, the days of quick manipulation are long over. This thing is just heavy.

[Dirtytires]

Yes....you are getting into some serious weight.

[Chuck Diesel]

Here is a few pix of my progress... getting closer. As for mounting the smoker on the trailer, I have a 3,500 pound Dexter axle, would mounting the firebox within 2.5 inches of the axle cause any issues?

[Dirtytires]

It’s not an oil filled axle like on a vehicle so I would sea absolutely no issue with the heat that close.

[Chuck Diesel]

Thanks for the response, I was hoping that it would be okay since I was using 2" Rockwool and 3/8" plate in the firebox.

[Chuck Diesel]

Baffle Plate

I'm at the point of welding in my baffle plate and would like this thing to cook at it's best. I had planned on leaving a reasonable amount of air space under the baffle plate and gap the end the same as the throat. I've read post were some have reduced the baffle plate gap smaller than the throat. Does changing the baffle plate gap help in evening out the temperature across the cook chamber?

[Pete Mazz]

Frank recommends 50 to 75% smaller gap to keep the BP hotter. Some builders make it 100% and add an extension for fine tuning

[Big T]

If you want to try some different gap sizes without a lot of work you can let your BP run long, down to say 25% of the recommended opening but weld your grease dam where 100% BP gap would be. Then when you finish your build you can season the CC, do some test fires and see how it runs, if you think you should open it up a little bit then just trim a little bit off of the end of the BP, do a few more tests and see how it does. You could open it open to 100% with 30 seconds of torch work vs having to move your grease dam every time that you change the BP gap. If you get it too big and want to close it up. you simply lay a piece of flat bar across the end of the BP and tack it in the desired location.

[Chuck Diesel]

Thanks guys, those are great ideas. Pete I like the idea of the hotter BP, I also like Big T's plan. Hmmm... Looks like I'll use Big T's Idea to get to the desired hotter BP that Frank talked about. Seems like that would take the guess work out of tuning.

[Chuck Diesel]

Now that I've gotten all the major pieces built, it's time for assembly. Connecting the cook chamber went a lot smoother than anticipated. I think only working on this on the weekends has given me the time to better approach each part when working with this much weight.

[Chuck Diesel]

This went way better than expected

Got the fenders on today.