The Dowell BBQ Pit

www.britishbarbecue.co.uk

 

 

 

 

 

 

 

 

This Pit is called an offset smoker, this type of pit is very popular in the USA.

It is of all steel contraction, and should last for fifteen to twenty years if looked after.

The pit is made from 5/16 inch thick steel pipe 16 to 20 inches  in diameter and 1/4 steel plate for the firebox, also steel angle steel strip and heavy duty expanded steel mesh are required to complete the job .

If you are handy at Mig welding, or know someone that is, and can cut the steel or know where you can get it cut, then construction should be strait forward.

My thanks to D. Dowell for his permission  to use his  materia


Click for the Building Instruction's and Plan's


 


 

This is one of the best brick pits around

Click on link Below for full building plans

LEXINGTON Web Site


 

 

Building a DOWELL Offset Horizontal Smoker

By Deryl Dowell

1.  Design considerations.  My brother-in-laws (Mel and Doug)  set out to build a smoker similar to the Oklahoma Joes/Klose bbq's that we had seen in pictures and in person.  It soon became apparent that the majority of cost in building such an appliance lay more in the labour costs than the costs of materials.  The major design decision was in the firebox construction; i.e. whether to utilise the same dimensional steel pipe for the firebox as the pit or to go with a rectangular construction out of " plate steel.  The round design requires FAR less man-hours for construction, but leaves the user without the option of an adjustable griddle, and complicates cleanup and the design/use of an ash-pan to protect the bottom of the firebox.  Accordingly, we opted for the square firebox design.  The next basic questions were; which pipe dimensions to use (16" vs. 18" vs. 20"" and what firebox dimensions to use after the pit dimensions were decided.  We chose 18" because the 16" smokers we looked at just seemed too limited, and 20" looked mighty big for our personal uses.  To maintain proportionality, we settled on an 18" by 18" square firebox, which matched the pit width and appeared adequate for the task.  We had settled on a 3' length for the pit, but the piece of pipe we had selected measured almost 10', so for 3 smokers we just divided by 3 to end up with the 40" pits that we built.

2.  Material selection.  We shopped competitively for materials for the construction; the major cost lying in the round steel and the " plate.  Since we were building in Oklahoma;  used steel and plate were readily available, and we obtained 5/16" wall 18" steel pipe for $12.00/ft.  Additionally, we were able to buy " plate steel (used) for $.15/lb, which at 10.2/LB for " plate, added up to around $1.60 per sq. ft.  The prices for new materials are at least double the prices quoted here.  For the frame construction, we utilised 1 " square steel tubing (14 gauge) since you can double the strength by sliding 1 " square tubing inside of it.

Flange material was 1/8" by 1" flat steel, which appears to be an industry standard for this purpose, and we settled on flat expanded metal ($32 for a 4'x8' sheet) for the shelves and heavy-duty (gauge unknown) expanded metal for the grate/griddle ($65 per 4'x8' sheet).  Other materials included " steel angle iron for shelf/grate/griddle supports, and 3/8" steel rod as well as " steel rod, and steel tubing to fit the steel rod.

  1. Construction sequence and details.



A.  Firebox construction.

1.  Cut steel for firebox sides.  We chose a box made with (2) 18"x18" (the end-plates),  (2) 18"x17 " (the top/bottom) and (2) 17 " x 17 " (sides).  I'm sure we had a reason, just don't remember what it was.  In retrospect, I think I would swap the end/tops, and use the 18x18 pieces on the top for purely aesthetics.  Anyway, we cut all steel, grind the edges with a 7 " hand grinder, and burnt off all old paint with a combination of propane blow torch and wire wheel.  By the way, if you decide on a detachable firebox, one of the endplate pieces must be 18"x20".

2.  Join the top/bottom pieces with the side pieces to make a four sided box. We did this to leave the end pieces for later, and allow construction of the firebox/pit mate without having to use the entire box.  All welding was done with an ancient AC arc welder at the highest setting that could be used without burning holes to ensure penetration.  All welds were both inside and outside.  The welding generates a lot of heat which can translate into significant warping;  We combated this by welding from the "middle" out to the sides, which seemed to help. Pipe clamps and magnets were a great help in this phase;  two magnets easily held the plate in position for welding the initial "90's".

3.  Top door construction  (See figure a since construction is same as side door.)  We had a hard time settling on the top door dimensions.  Considerations were access vs. structural strength.  Details follow:

(1)  Cut square hole cut  in the top,  14"x14", which leaves 2" steel around the perimeter.
 
(2)  Grind sides of the hole.

(3)  Weld 1/8" x 1" flange vertically with the bottom of the flange flush with the bottom of the " steel (leaving " above the top).  The steel is welded only along the bottom edge, and the corners only on the inside ( the outside was left alone to ensure a proper fit with the lid frame.  The flashing is not aggressively clamped;  only clamped tight enough to keep in place so as to not disturb the straight edge of the flange. Note:  Do not weld the inside corners until the flange is inspected and adjusted judiciously with a small sledge to insure that it tapers towards the inside of the hole; otherwise, the door fitting will be extremely frustrating.  As matter of fact, would be good headwork to leave these welds  until the very last.

(4) Cut a frame of 1" steel square tubing was made to fit the flanged opening.  The frame is "picture framed" with 45 degree angles on the corners, using flat washers (or you could use Tin) as spacers between the frame and flange to prevent too tight a fit (we learned this the hard way;  they seem to shrink after all the welding that follows). We laid out the frames right on top the box using C-clamps to hold everything in place, and then tack welded the frame, pulled it off, and finished the welding.

(5)  Grind all welds nearly flush, and then insert the 14"x 14" piece of " steel that had been cut out of the top, and  using 1"x4" wood pieces underneath to hold it flush with the top of the frame, weld (again, from the middles out to prevent warping).  We only welded the top side, to leave a clean inside edge to mate with the flange.
 
(6)  A lot of grinding now follows, to match the frame top with the " plate.  You now have a lid that has exactly " clearance inside to match the " flange sticking out of the top. 

(7)  Make hinges using 3/8" steel rod ground to mate with  " steel tubing.  We simply laid the " tubing on the middle of the outside edge of the frame, welded it, and then welded matching pieces of " tubing onto the top of the box, after welding bases of " steel (1"x3") to the top of the firebox to match the height of the tubing.  Insert pins drilled for cotter pins into hinges, and voila, a door!  One of the hardest things to find is round tubing that fits with 3/8" or " steel rod.  We used " tubing, which required us to grind down 3/8" rod a little to fit inside.  This was done by inserting one end of the steel into a drill and then grinding on a bench grinder (the spinning from the drill helped even out the grinding.
 
(8)  A handle was made from two pieces of " steel (1"x3") and about 5" of  3/8" round rod, with steel spring coils robbed from a field cultivator as a grip.  The handle was cantered on the front of the door, 2" in from the edge and welded solid.  We did drill the " steel "posts" with a 3/8" bit and inserted the rod before welding for looks. 


4.  Firebox door construction (see figure (a).

Basic construction essentially same as the top door described above.  Here we chose to leave 2" of steel at the top and 1" around the sides and the bottom with the following
rationale: (1) you need an edge to latch the door onto, (2) if you omit the 1" on the bottom (like I think Tejas does with their smokers) and just flange it, you are betting your bottom dollar that the bottom is perfectly square (this would be a cool thing and make cleanup much more of a breeze; but we decided it was risky).
 
Latch construction.  We thought about this quite a bit, and decided on a simple latch made by welding a stop on the end of steel rod, which passes through a collar and is  threaded on the outside end to permit adjusting the depth of the latch.  A picture is worth a thousand words here;  see the figure of the latch system we used.  Lesson learned was that using " steel instead of the 3/8" we used would have been a better idea.  The 3/8" works; you just don't want to yank on it too hard.  Construction steps were;
 
(1)  Layout hole for collar (basically cantered on the door and around 2" in from edge.

(2) Drill  3/8" hole.
 
(3)  Position collar carefully to extend 7/8" from the inside edge.  Weld collar.

(4)  Make stop and attach to rod. 

(5)  Thread rod (or use all-thread).  Insert latch.  Double nut outside end.   

(6)  Check for operation and proper adjustment (make sure the sucker will work).  Once you're sure you're okay, then weld a handle onto the shaft (point of no return).


Vent construction

We debated between the "butterfly" system and the "horizontal
sliding panel" designs, and opted for the sliding panel because the air inlets are all
below the "wood level"  (as opposed to the butterfly vent which opens at both the bottom and top).  The butterfly would have been much easier, and is more easily adjusted.

Figure (a) gives all details;  dimensions were selected because (3) 1.5"x2.5" openings exceed the square area of the 4 " pipe used as the smokestack (theory here is that as long as inlet = output, you're good to go).  The slides were constructed from " angle iron with " cut off one side (we used a sawz-all with bi-metallic blades) and then welded to the door (using those washers as spacers again) after the vent holes were cut in the door and the sliding vent put in place.  A 2" piece of 1" steel rod was welded to the vent as a "kick-handle".  Our biggest problem in this phase was warping of the door as result of cutting the vents.  Heat and a 16 lb. Sledge were committed to use on
occasion.

By now you've probably got the idea that the firebox is the major part of this smoker.


5. 
Grate/griddle supports.

These were made by using " angle iron welded along the sides with the flat side "up".  We only made two griddle heights, 11" and 13" above the bottom.  Reason here was we couldn't find enough room to adjust the grate with more than two (it would bind).  We decided that if we needed another griddle height above the highest one, we could lay a couple pieces of 1" tubing on the 13" supports to raise the griddle another inch.


B.  Pit/firebox plate joint. 

We used two designs;  one, a detachable firebox, and the other a "permanent" firebox/pit construction.


Detachable firebox plate construction (figure b.).
 
(1)  Cut 18" circle from plate steel. Grind edges.
 
(2)  Stand pit on end and clamp cap onto end.
 
(3)  Find centre, and lay out perpendiculars.  We decided to hang the firebox 2" below
centre, which seemed to maximise the trade-off between the dimensions of the opening
and vertical "drop" of the pit for draft. 

(4)  The opening was laid out on the steel, and cut with the torch (see figure c.) 

(5)  Cut firebox endplate, basically a 20"x18" piece of steel, with notches cut out of the
top corners as shown in the figure.  Three holes at the top, and one below the opening
were laid out on the plate, and drilled with " bit. 

(6)  Clamp endplate  to the pit cap, and transcribe the holes from the firebox plate to the
pit cap, and transcribe  the pit opening onto the box-plate. 

(7)  Drill appropriate holes and cut the firebox's opening to mate with the pit opening.

(8)  Flange opening the same way as the door construction described above. Fit-check.  (9)  Weld  pit "cap" into place, and the firebox endplate left bolted to the pit. 

 

Permanent firebox plate construction (figure c). 

(1) Cut 18" circle from plate steel.  Grind edges. 

(2) Stand pit on end and clamp cap onto end.
 
(3) Find centre, and lay out perpendiculars.  Mark line 2" below centre
 
(4) Unclamp, and cut along line.  Grind edge.
 
(5) Clamp cap back to pit and weld. 

(6) Clamp 18"x18" endplate to pit mated with edge of cap.  Lay out opening onto endplate, leaving 1 " steel along the top (for structural strength), and close to where the inside edge of the pit is at the bottom (we left " for slop, cut the opening, and then used our eyeballs to carefully cut the bottom of the endplate opening flush with the inside of the pit for a good, weldable mate).  Endplate is now ready to be welded either onto the pit or the firebox (we welded it to the pit so we could use it for the framing.


C. Framing detail.  (figure d)  General.

The frame was constructed of 14 gauge, 1 " steel tubing. (Figure e.)  Construction: 

(1)  Cut (4) 13" pieces of tubing as accurately as possible. 

(2)  Cut (2) pieces exactly 3"  inches shorter (width of the two 1 " legs) than the length of the pit + end-cap you have constructed.  These are the side rails, which in my case measured 37".

(3)  Cut (4) 29" pieces of tubing, and eyeball the angle required at the attachment point, transcribe to the tubing, and cut this "arc" out with a torch.

(4)  Using pipe clamps (it takes 4 or some other creative measure) clamp the frame together.  We found using both the 13" pieces on the ends worked best for the initial fit, and then moving the two lower side braces to the inside of the side beams later when it was time for welding.

(5)  Lay pit on flat surface, and position the firebox plate truly vertical using a level.  Block the pit carefully. 

(6)  Set the frame onto the pit, align with the firebox for vertical, and eyeball the fit of the legs to the pit.  Tap the "top" 13" crossbars down to rest on the pit.  Once you're happy with the square and vertical, start welding, starting with the legs attaching to the pit and then the frame welds.  Don't weld the other 13" pieces until you've slid them up between the sides as in figure (e).  These are your supports for the shelf, as well as being framing supports.  If you're really ballsey, you'll go ahead and drill the " holes in the rear legs for the axle before the welding if you have a drill press; otherwise,

(7)  stand this puppy up on its new frame now, and check again for level to see if you need to trim any legs off.

(8)  Mark your axle holes (depending on what wheels you've decided on) and drill out axle holes.  We slid 12" pieces of 1 " tubing into the bottom legs for added strength,  welded them in on the bottom, and drilled them out as well. 

(9)  Make 1 " square caps (we used square tubing cut with a sawz-all) and weld onto legs to seal the bottoms.

(10)  Slide in axle shaft (1/2 steel rod threaded on both ends) and attach wheels.

(11) cut a piece of expanded metal approx. 16" by 35" and weld onto the frame as the bottom shelf.



D. 
Pit door construction.

Everything we heard was to "make the door as large as
possible".  We decided on a 28" wide opening for the door, which left 6" on either end; we figured we can work with 6".  The pits we examined all seemed to have an opening more than the of the perimeter we had anticipated;  after some thought we decided that this would improve accessibility  a little bit so we decided to copy it.  Details:

(1)  Clamp other endplate onto pit to assist layout. 

(2)  Find centre, and using a level, mark the "top of the pit" on both ends (the pit must be sitting level before you attempt this.  Next, mark the 90 degree position at both ends, and draw a line for the bottom of the door. 

(3)  Mark  a point 1 " from the top of pit marks to widen door a bit, and draw line.

(4)  Using a good edge on some moderately wide material to wrap around the pit (we used a piece of roofing felt, mark the verticals 6" in from the edges.

(5)  Fire up the torch and cut the sucker.  Don't forget which end is the top!

(6)  Grind edges of door and opening.

(7) Cut 1/8" x 1" steel flange to fit around perimeter of door and weld in flashing " from the sides around the sides and bottom only (leave the top open because of hinges).

(8)  Fit the door to the opening, and  make hinges.  We welded 4" lengths of " tubing to the pit, bent 8" lengths of 3/8" rod to a perfect 90 degrees, inserted the rod into the hinge, and then bent the rod to mate with the lid and welded it in.

(9)  Cut and weld in the top flange (3 pieces).

(10) Make a handle similar to the one on the top of the firebox and weld in.



E. Pit shelf construction.

(1)  Cut " angle iron to fit within 1 " of each end (38" in our case). 

(2) We decided on placing the pit shelf 1 " below the "90 degree" point. We were Going to rim the expanded metal with angle iron for extra strength; but unless you're cooking a small cow, that stuff ain't gonna bend much, so we left it alone. 

(3)   Once the supports are welded in, the end cap to the pit can be clamped on and
welded.



F.  Finish details.

General "to scale" is figure (e).  Couple passes with a 4" grinder and wire-wheels; and a wipe down with rags and mineral spirits to clean the metal and
remove dust/rust.  Paint away with the best high temperature paint you can find ( I used some 1300 degree paint (derusto©) on the firebox, and some 1000 degree paint (rustoleum ©) on the pit/bottom shelf/frame).


Drawings

Figure A
Figure B
Figure C
Figure D
Figure E


 

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