J. SHEET METAL MODIFICATIONS
The following represents some possible modifications that you may wish to do to your grill. The end result is a grill that is more efficient in most cases and can over time substantially lower your cost per pound on coffee, and extend the life of your components. These mods are entirely optional but I don’t regret for one second the decisions.
As an example, after completing my first 6Lb assembly, I noticed that I had to run the burners at 100% to maintain 550 degrees. With a 4 pound roast you will want to run about 545 F at least through first crack and then perhaps back off just a bit.
Well imagine the savings I experienced after modifying the rear vent and capping off the dome. As a result, I was able to maintain temperature at only 40% gas. That translates to 60% more roasts on each tank. That is HUGE.
Similarly, on this model, used for illustrations. 100% gas netted 550 F, and after this rear vent mod, We achieved 600F at 33% gas. So the efficiency increase is, well, astronomical.
Granted, everyone has a different way of doing things, someone out there will tell you that not venting the heat/smoke/moisture as quickly will change your roast. Perhaps, do what you like, that’s why coffee is such an art, a million ways to do anything.
However, my costs have dropped tremendously and not one complaint from one customer.
So these are the mods we have done, others will have other mods. Share yours in the forum! Try these if you want to! With that aside, lets get on to
“Fun with Sheet Metal”.
WARNING: Sheet Metal will cut you open in a flat second. Use gloves and be aware that it will get you. I know better, I’ve done it many times, I’m experienced in Aircraft repair and construction with sheet metal, aluminum. I told myself, “Be careful, you could get cut”. Guess what, yep, I got cut….during the assembly of this nice machine. Be careful, don’t work aggressively with this stuff, you push or shove and slip, you’ll be getting stitches. Be firm, gentle, careful, plan your actions and movements and don’t swing or hammer wildly at this stuff, you slip and it gets you.
Step 14. Rear Vent Blocking.
During our roast this is where the vast majority of your heat will escape off to. If we seal this off, then a great deal of our heat will remain trapped in the grill case and we can effectively lower our burners substantially. This and the dome capping represent the greatest efficiency increases you can make. (Figure 98).
This is a piece of Zinc Plated Aluminum picked up at Home Depot, I think it was $7 as of early 2009. This is enough sheet metal for the rear vent and the motor shield, but not for the dome cap. Get an extra piece if you need to cap the dome. We’ll get to that later. (Figure 99).
Here’s the details for those who want to know exactly what I’m using. (Figure 100).
I’ll go ahead and measure my rear vent. (Figure 101).
A bit hard to see in this picture but it looks like 26.5 inches. (Figure 102).
As a rough rule of thumb, I like to block off 80% or 90% of my rear vent. In this example, I’ll use 80%. 80% of 26.5 is 21.2 inches. I’ll just round off to 21 inches (close enough). (Figure 103).
This part gets a little interesting, you need to think about how your grill hood or base works. This one is not a one size fits all mod. For example, on one grill, the hood hinged up nicely, so I was able to attach the sheet metal to the hood and when you closed the lid, the sheet metal presses itself against the base and seals off 80% of the vent. In this grill design the hood works differently. I will attach the sheet metal to the base of the grill and when the lid is closed, the lid will press up against the sheet metal sealing it off. You will have to study your grill and see how best to do it.
So the plan here is, we need approx. 4 inches of sheet metal, we will drill 4 holes in the base to screw the metal to the outside, bend a flange in the top rearward so that when the grill closes the lid pushes up against the sheet metal blocking our vent. We’ll take a better look at that as we move forward.
For this example, you see my measurement of 4″ will completely close off this vent (vertically). So we need a 21″ X 4″ piece of sheet metal (Figure 104).
Wow, do I need to find my square…..ok, so 21″ and we’ll use this piece of metal as a straight edge. (Figure 105).
Mark your line at 21″ (Figure 106).
There’s my line at 21″. (Figure 107).
Measure down 4″ square it up and draw another line. (Figure 108 & 109).
Wish I had some sheet metal cutters. Oh well, tin snips it is. See we can do all of this at home, without professional equipment. (Figure 110)
Here’s my 4 X 21 sheet and the 4 screws/nuts I’m going to use to mount it to the grill. (Figure 111)
I’m going to use my metal sheet and a piece of wood to bend the metal cleanly to create my flange that will press up against the hood when closed. (Figure 112)
Here we are after the bend. (Figure 113)
Here we’ll mark 4 equidistant points for our screw holes. (Figure 115)
Hey! Who stole my center punch??? A big nail will have to do. We’ll mark four points for our drill bit . (Figure 116)
And to the drill. (Figure 117)
Here is my 4 holes, one of those is where I accidentally center punched. (Figure 118)
Visually, center the shield on the back of the grill, I used finer widths at the sides. You see we will now have a relatively small area for heat escape. Use a pencil to mark the spots for the drill holes. (Figure 119)
Center punch your marked circles. (Figure 120)
Here, I’m going to just make a mark with my drill and verify that everything lines up (Figure 118)
After all 4 holes are started inthe grill, I hold my sheet metal up to the grill and verify that I can indeed see my mark through each of the 4 holes. (Figure 119)
Here are my 4 holes, ready for assembly. (Figure 120)
Screws in the back…. (Figure 121)
Nuts on the front… (almost sounds like a joke, doesn’t it) (Figure 122)
Tighten everything down, here is what it looks like. You can clean up some of these bends with vise grips on the bend, and a file if you choose. (Figure 123)
Here’s a view from the inside with the door closed. (Figure 124)
And one more, see how it pretty well seals off the back? It will do a little better when fully closed, how do you think I took the picture? (Figure 125)
( Also a safety tip. The vents in the grill are designed to keep the grill at a safe operating temperature, thus, if you do choose to restrict the vent, then operating the grill for extended periods of time at highest heat, could overtemp the entire rig. Please do not forget that you have left your burners on high and go and do something else. We don’t want any fires)
**END OF SECTION**
We’ll start the motor shield by taking the remaining section of sheet metal we have left from the original single piece. Let’s make sure that it will be wide enough to shield the motor assembly from any escaping heat. You see the metal is at least as wide as the motor assembly. That should do just fine. While I have it here, I’m going to mark to the left and right side of the rotisserie, about 1/2″ on both sides. Making a slot so to speak, 1 inch wide, 3″ or 4″ high, doesn’t really matter much at this point. (Figure 126)
Lets do a rough cutout, that top section is a bit tough, no problem, we’ll file it later. (Figure 127)
Let’s hold it up on the grill, make sure we’re in the ballpark. (Figure 128)
Go ahead and just cut the corners off, this will allow opening and closing without interference. (Figure 129)
And we’ll trim off the top, we’ll be a little flexible, and go longer than necessary, we can always cut off, but we can’t put it back together! (Figure 130)
And lets just check again, now look at the front of the grill, where we have that big obnoxious corner just waiting to cut someone. (Figure 131)
Let’s use the tin snips and rough that out, just like scissors, round it off. (Figure 132)
Looking a little nicer. Went ahead and trimmed up the other corners too, just to avoid any accidental injuries. (Figure 133)
Using my pencil I am going to find 4 spots, preferably in each corner. Look behind the sheet metal and look for 4 spots that, are in relatively flat spots on the grill hood. Try to keep the marks in the corners to offer the most support and keep the shield from accidentally getting bent. We are getting ready to drill holes where the marks are, and insert bolts and nuts. NOTE: Also remember the shield should stay with the hood, so keep the holes/marks on the hood and not the grill base. (Figure 134)
Using my center-nail (I mean center punch), lets dent the metal under each mark, so the drill bit doesn’t walk around. (Figure 135)
There is where I’ll drill. (Figure 136)
And the drill again. (Figure 137)
Looking better!. (Figure 138)
OK, hold it up, now it’s important here we get this right, hold it perfectly in position, exactly where you want it to be. Make sure your rod, clears your shield. Take your pencil and mark the position on the grill, in the holes. This is where we will drill on the grill. (Figure 139)
Center Punch your 4 marks. (Figure 140)
And Drill….. (Figure 141)
Here’s my four bolt holes, now were ready to clean up the shield. (Figure 142)
Just to be sure make sure our holes lines up correctly. NOTE: At this point before we put it on, use a metal file and file any sharp points or edges, get it cleaned up so you can’t get cut on it and we’re ready to mount it. If you don’t have a metal file, I’ve actually used the concrete driveway in times past to file it down if you find yourself without one :).(Figure 143)
Here’s the hardware I will use. 4 two inch bolts or so, and 12 nuts, three per bolt. You’ll see why that many are necessary. (Figure 144)
Insert the bolts into each hole, (the threads towards the grill) run a nut all the way to the metal and tighten, we want this part solid. (Figure 145)
Here’s all 4 bolts with 1 nut each. (Figure 146)
Now, lets run another nut onto the end of each bolt, say about 3/8″ onto the bolt (like shown). (Figure 147)
Here’s where we should be now. (Figure 148)
Mount your shield up on the grill. See if your bolts line up. The beauty with the threaded bolts are that you can adjust the height of each bolt based on the contour of the grill. Adjust the nuts until the shield sits nice and even. (Figure 149)
Here’s the inside view, some bolts will be longer than others, this is OK. (Figure 150)
Tighten the shield down to the grill. (Figure 151)
There you have it, opened…….. (Figure 152)
And closed…….make sure there is no interference. (Figure 153)
Look closely, if there is a problem this is where it will be. (Figure 154)
Another view. (Figure 155)
Finished…… (Figure 156)
Finished…… (Figure 157)
And…..finished…… (Figure 158)
This triple burner beauty is done, it has an included thermometer and no need for a dome cap, so we won’t do anymore to this roaster. (This roaster was built for Craig Jensen of Hammond, LA-Thanks Craig) (Figure 159)
This grill has a high dome and there is a cavernous space above the drum. All your heat concentrates here. You are basically paying to heat an area that your drum and coffee see no benefit from. Capping this area off will increase efficiency, decrease heat up times and lower gas consumption. It focuses heat on the coffee and not just heating empty space. (Figure 160)
Here I basically cut this sheet metal to size, crammed it up in there and we are going to simply use a screw and a nut to hold it in place. (Figure 161)
Picture is worth 1000 words…. (Figure 162)
And the outside. That’s it, pretty simple, this whole mod took less than 15 minutes to complete. (Figure 163)
Here is the normal thermometer installation. Notice that the probe is completely exposed. On some grills, with a horizontal diffuser (Figure 165),the heat column from the burner rises straight up the internal front face of the grill and hits the temperature probe head on. This causes wild, uncontrollable fluctuations in temperature. If your probe is already shielded by your diffuser, then you need not worry about this section. This is just for grills where the heat rises up and hits the temp probe head on. (Figure 164)
You see when you push up the gas, a massive quantity of heat immediately rises and strikes the probe within seconds, and causes wild needle/temperature swings, it makes it hard to control your roast. We will make a quick shield to shield the probe from the heat blast, giving us a better idea of actual internal temperature. (Figure 165)
This is simply a piece of sheet metal, with tabs cut in the top, the tabs folded over and three screws run through the front of the grill. Now the heat column is directed around the probe and the probe now measures internal temp, and fluctuations are mitigated significantly. Note the sheet metal is taller then the probe, completely shielding it from the heat blast. (Figure 166)
Here is the view with the lid open. (Figure 167)
That concludes the sheet metal mods.