Rocket BBQ

[hpmer]

Next I worked on opening the holes.


Bottom of the bbq, original 3" hole and plans for expansion.


Old baffle and new.


Go big or go home. Next up, install.


The top (actually the bottom of the barrel) was pretty rusted out so I covered it with a piece of hardware cloth and covered it in cob.


Tools of the trade.

[hpmer]

BBQ in place.


Grate to keep lava rock in place.


Lava rock used as a diffuser and cooking grate installed. Ready to cook. With the new, larger hole temps are now up to 450* so it seems I'm getting there.

[hpmer]

Matt, here's a better shot of the feed tube area to help put your mind at ease. ; ) That's a temporary insulative brick that is 6" high in the middle there for reference. I plan to cob it in for good with 6" opening all around, hopefully this weekend. Note the plastic can cover hiding in the oven. I use it to clean out the ash since I don't want to use metal against the masonry.

[matt walker]

Oh, yeah, sorry about that. That's much better than I thought. You might try building up the feed a bit, maybe mud a 4" collar or so around it, and keep it narrow. That will speed up the intake air and focus it a bit on the fuel. It may or may not help. Sorry to doubt you man, I figured you knew better since this isn't your first rodeo.

I love that barrel top technique! Very cool way of working with what you have to make a sealed top. I wonder if the hardware cloth in the port there is obstructing flow? I think maybe a bit, but I'm totally guessing. Really dig the baffle as well, nice one. That's a fun build Hpmer, lots to play with. I think you are on to a good cooker there...my thoughts on the exhaust came from playing with mine. With two 5' sections of exhaust I couldn't get my oven hot at all. Once I took one of those sections off, so my exhaust was 5' from bottom to top, I was able to heat things up. Sometimes I damper that exhaust completely if I'm going for pizza cooking temps.

[hpmer]

Good thought on the hardware cloth in the opening. Never occurred to me. Something else to fiddle with as I get it dialed in. The opening is a full 4"x 6" but by using the damper I could close it down fully if needed. So far I have to run it wide open, but I'm lovin' it. I don't like smoked foods but the clean heat I get from this thing gives the food a great flavor.

I used to use a charcoal grill and would start it up with one of those chimney things with newspaper underneath but was always amazed and disgusted with the amount of gross smoke involved to heat the charcoal enough to cook on. Not to mention the time it took, 15-20 minutes minimum to preheat the coals. And then you're dealing with a dwindling heat source and cooking for longer periods required another round of coals. What a pain. Now it's literally less than 3-5 minutes for smoke free heat and I'm ready to go and I can cook almost indefinitely. Takes a bit longer than that to get fully up to temp, but it's a lot of fun to play with. And I can literally cook an entire meal on just the twigs that fall off my big oak tree in the side yard. No sawing, splitting, and stacking, just a bit of wandering around with a bucket picking up stuff off the ground, stuff that I have to pick up before I mow anyway.

My exhaust pipe is a single 5' section of 7" pipe, but I can try dampening it down too. Also, I'm battling with the chipmunks in the exhaust area so I've got a few exit holes to patch. You're right though, it is a fun build. The only things I had to pay for were the hardware cloth, the damper plate, the exhaust pipe and another section used as the outer form for the burn tunnel and heat riser, and a small sheet of floor underlayment that I used as my form. My mix is simply clay:ash with chopped up ornamental grass leaves as a straw alternative. I'm amazed at how well it works and holds up, though my stoves don't get used every day like those of the rest of you guys. By adjusting the ratio it can be super light and insulative or heavier and more robust. I use the lighter stuff for most of the mass on the outside with a thinner skin of maybe an inch or so of the harder stuff in the flame path. The rest from the barrel to the bbq were dumpster dives (probably self evident). Still, as a prototype, I'm pretty impressed. I've learned a lot from all of the improvements and still have a few things to try. Thanks for all the input.

[mannytheseacow]

Those photos really trick the eye. I had to go back and look at them a second and third time. The coolest thing about this build, in my opinion, is the core composition. I think the stuff nutcase was doing is really awesome, and Nirkys thread likewise, but the biggest be fit these stoves have is for efficient cooking for people that might not have access, budgets, or infrastructure to support exotic materials. Just clay and ash; that's awesome.

I've followed your threads over on donkey's board for a while, too, hpmer. This is where my experiments have been going lately too. Clay/ash, soil/sawdust, different amounts of sand in the mix. They all seem to work. The biggest difference seems to be the mineral composition of the materials available as far as what ratios to use.

How is that rebar in the feed holding up? I would have expected some expansion/contraction issues there.

[hpmer]

Yeah, I might just have really great clay subsoil. Never tested it for composition. I don't add any sand or anything else to the mix, it's really simple. Dig the stuff up, soak it in a bucket, screen out the roots and rocks and go. Simple and works great. Got the idea from Donkey a while ago. Originally I made a "puck" mold out of an old tuna fish can to test mixes so I could have consistent sized pucks to measure weight, durability, etc., then I fired them in one of my original "L" rockets. Everything from 1:1 clay:ash up to 1:5 to find stuff that would work. For me, 1:1 and 1:2 or 3 seem to work best. Any higher and they're too fragile and crumbly. The "problem" with these stoves is they don't produce a lot of ash, so I have to store it up for a while. And, since I don't burn every day or even every week, it can take a long time to collect enough material.

The rebar just floats in a little cradle that I form when the core is wet, so it's not permanently connected or buried in the mix at all. I take a piece of rebar, wet the ends and squish it down and back and forth so the "cradle" is just a bit longer than the piece of rebar. I lift it off when I clean out the ashes. I don't think it gets hot enough to have a material impact on raising the temp of the wood resting against it either. And Peter and Donkey's experiments with the Peter Channel uses a big, flat piece of steel to form their channel and that seems to work pretty well for them.

But it protects the front edge of the feed from the wear and tear of longer pieces of wood banging up against it and sliding down and generally wearing it away. Plus it may have a similar function in that air can get down in between the rebar and the front of the feed since I have it stand off maybe 3/8" from the feed. It obviously doesn't stick down past the top of the burn tunnel like the P-Channel, but works really well for me, and is super simple to execute. I like simple.

Now that you guys have shown me how to use Photobucket, I went a bit crazy with the pictures. Maybe I'll go back to my maple syrup stove thread over at Donkey's board and throw in a video of that thing in action. I call it my maple syrup production facility. A bit grandiose, perhaps, since I only produce about a half gallon of syrup, but hey. I'm planning on building another smaller sap warming stove for next spring so I'll document that process, too.

[mannytheseacow]

That's a good idea with the rebar cradle. I might do that to my indoor stove.

Yeah, I saw that whole thread on the pucks on donkeys board. Thanks for posting all that, it was very helpful.

[mannytheseacow]

Any idea what your soil type is, Hpmer? You can find out at:

[hpmer]

Can you narrow it down a bit? What's the magic number/information I'm looking for after I find my location??