DSR3 Beehive Dome Completed!

The masonry heater is finished. So far, it works!

Previous threads about this project are:
Planning and Design,  https://permies.com/t/40/192518/Planning-DSR-Build-Cooktop-Questions
and
Testing and Troubleshooting https://permies.com/t/40/219558/DSR-Beehive-Dome-Build

The core is a Double Shoebox Rocket 3, designed by Peter VanDen Berg
https://donkey32.proboards.com/thread/3710/dsr1-vortex-aspects-dsr3

which shares elements with the Vortex stove
https://donkey32.proboards.com/thread/703/vortex-stove?page=22

The beehive dome is roughly based on the Hungarian "bubos kemence." But any open bell you wish to build should work.

More pics. I did clean up the finish where I had to raise the cooktop. It now lights and runs very well, without a bypass. Next year I may even replace the priming hole in the chimney with solid pipe, but I want to get through this winter first – the weather has been too warm for more than a couple of test fires.

Kettle heats nicely. Oven has barely passed 150*F, but like I said, hasn’t had continuous running yet. Black single wall exit pipe about 120*F. Some quick heat off the cooktop and glass window, but mostly absorbing into the brick, which is just barely warm to the touch about 3 hours after fire. But again, I expect there’s a significant flywheel effect.

That vortex is beautiful, epileptically mesmerizing, and slightly scary. I do hope the glass and cooktop hold up. (Yes that glass is more than 4” away. Actually, 4” to the front wall of the top box, which is soft brick, so nearly 6” to the glass.)

The first test fire was a stalled-out smoky disaster, even though all post-core restrictions had been removed by the spacious dome and by scooching the core forward to give extra space behind down to the exit. Drawing on the lessons learned from that messy driveway testing last summer, I raised the cooktop by one inch to increase top box space even more. This worked perfectly. (I told you all those annoying driveway tests would come in useful!)
The moral of the story seems to be that if you cannot source the parts to build Peter VanDenBerg’s exact design, make sure you leave your top box accessible for tweaking, and when in doubt, raise the ceiling.

(Satamax’s suggestion on the last thread about afterburner tubes, by the way, was correct: That company definitely does make them. However, like every other foundry supplier in the US, they just would not return my call. Surprise!)

Here are the final dimensions for the top box. Because of the way the dome lintel crossed, it was easier to change the front half than the back, which was left in its original position. I *can* get it out if I ever have to but it would be messy. Raising the cooktop, which is bolted on for easy access, was enough to solve the problem, and now the back part at original height serves perhaps as a crude sort of stumbling block.

Is it going to hold up to time and use? Will the afterburner fail? Will it crack to pieces? Will it fall through the floor? Set the wall on fire? Who knows? For now it seems to be working great.

SO. Suppose I should share the rest of the plans and what I learned while building, for anyone who wants to make something similar.

System size is 5.5” (140mm), which dimensions fit well with available core materials. That’s a 6” afterburner tube (110% system size) going into a 6” (150mm) chimney. Cabin to be heated is 16x20, 2 stories, well insulated. Climate is frigid.

**Unusual materials I was able to luck out and find:
2 9x24” firebrick slabs made lintels much easier!
Cordierite kiln shelf between firebox and top box.
Some softer, warped kiln shelves: extra support beneath oven, oven backing, odd corners.
Scavenged soft fire brick for insulated top box.

**What I could NOT find:
A foundry tube for the afterburner! Cobbled something together from cement fiber board and a special glue from Ceramaterials. We’ll have to see if it holds up. Okay so far.

**Did need several scraps of ceramic fiber board and blanket for odd corners throughout, but I could certainly have wrapped the core in something cheaper if I had had it to hand, since the insulative layer wound up outside of firebrick.

**Otherwise it took:
common brick in the lower parts
firebrick for core and dome
11x15 terracotta flue liner for the oven
scrap of old soapstone sink for the cap
7.5”x7.5” ceramic stove glass
terracotta chimney thimble to adapt to round, thin-walled exit pipe. (Metalbestos chimney pre-existing.)
cast griddles for cooktop and door
metalwork for airframe, hinges, attachments, and oven door.
stove gasket rope to seal glass, cooktop, oven, and chimney. Also used this as an expansion joint around the kiln shelf dividing firebox from top box. Other expansion joints in less accessible places are ceramic fiber blanket.

** Refractory cement recipe
1 pt portland
1 pt builder’s lime
1 pt fireclay
3 parts pool filter (silica) sand.

**Plaster recipe
1 pt portland
1 pt builder’s lime
1 pt fireclay
3 parts local clay thick slip
9 parts ordinary mason’s sand

Note: Our local clay is blue, silty and relatively non-expansive. So, not much shrink but not much strength either. Your mileage may vary. Maybe you don’t even need the extra binders. Test!
This plaster set up fairly slowly, taking a full day to harden. Workable about 2 hours.
2 plaster layers, with fiberglass mesh in each. Thickness between 1-3” (it had a lot of irregularities to smooth).

**Paint recipe
1 pt white stoneware clay slip dredged from the sink of a local potter
1 pt builder’s lime
1pt fine white sand
It seems this paint can be allowed to dry out and then re-wetted for future touch up.

**Mosaic was done with ordinary thin-set and grout. Didn’t take much. We’ll see how it takes the heat.

**Black pipe section of chimney comes out for yearly cleaning. Cooktop comes off for top box access. Glass can be slid out and replaced. Top cap could come off, with some annoyance, and whole oven could probably come out, with a lot of annoyance. For that matter, I could, if ever necessary, remove and rebuild the whole core. It’d just be plasterwork; the bell is self supporting.

Elevation and rough brick plan below.

What a journey ah!
Well done for persevering and getting a good job done…..

Build pics!
We started here, with the lower portion built last year.

By the way, I could probably have gotten away with building that lower portion as a double thickness box rather than cutting in all those angles, except the main opening. I believe the dome would still have lapped sufficiently.

I decided it would be much stronger to make the firebox from brick rather than fiberboard. It does slow a cold stove but seems to be fine once it gets going. It’s wrapped behind and outside with insulation. No insulation under the firebox, which I may regret, but 10” of masonry between it and the floor joists. Hopefully adequate.

Door attached, Lip for shelf made with splits set back from lower walls and lined with hardware store gasket rope. The door is pinned to a couple strips of flat steel anchored into the bricks of the bell, alongside but outside of the core, and can be unbolted from these if needed. Couple L-brackets buried in the firebox floor to secure the bottom.

Ain’t that a pretty door? Traded sugaring help for welding. What a good neighbor!

Kiln shelf with port and top box. Shelf, soft brick, and CFB afterburner tube all coated with ITC-100 for longer life. I hope.

How the top box ceiling works (except I then had to raise the cooktop portion by 1”). Exit slot is behind scrap of fiberboard.
Preparing for and setting the main lintel.

I cut the dome bricks by making lots of cardboard templates. Also, another good neighbor loaned me a heavy-duty masonry saw he wasn’t using. This would have been about impossible without it! You can cut firebrick with a diamond blade on a circle saw, and I did plenty just that way, but it’s tiresome, and the beehive made for a stupid lot of noxious little angle cuts. Much easier with a proper slidey bench and a powerful, wetwork blade!!

Cantilevering the dome out over the lintel. Prettied that weirdness up on the plaster layer.

Cantilevering in the supports for the oven

Oven set. You can see it doesn’t really get enough circulation space. No wonder it runs too cool so far.

Closing it off!

Glass window slot fronted with ordinary cement fiber board, as one would back a tile project with, mortared and plastered into place with mesh. We’ll have to see how that holds. Glass sealed with a gasket rope expansion joint all round.

Luckily I then had a plaster layer to make it all look less lopsided!

Painted. The mosaic came out a little more garish than I had hoped. My friend Allison (who helped with the wall last year) came out again for this, but neither of us had much mosaic experience, so we were just about getting it right by the time we were done.

If I were doing mosaic again, I would:
*Take the time to find crockery of more subtle colors at yard sales first.
*Vary the depth of the mortar bed to bring tiles of different thickness closer to an even surface.
*Be more careful to leave the mortar joints low and empty to be filled with grout! You don’t want the thinset coming anywhere near flush with the surface; the grout is much easier to apply smooth over such irregular fissures.
*Take more time, during the initial layout, to define the edges of colorblocks with the edges of the crockery. Anyway. Here it is.

Thanks for sharing! Beautiful & functional!

Wow. Well done, April, and thank you for such a thorough documentation of how it came to be. I'm looking forward to seeing reports of how the oven performs as you get further into the cold months and the whole thing warms up.

The mosaic looks great. Not garish. I am highly sensitive to and object strongly to garish and this is not it! Love it.

Outstanding work April,
   Having built a few stoves myself, I know the hours of planning and then building really add up. but results like this, job well done.

One question, although minor I would think at the present time.   When you say, "so far the top stove box runs cool as of yet"  how cool is cool?  and if it is so, does that mean your mass at the top of the beehive is also not as hot as you would like.  I am just wondering, not critiquing in the least.  

Having never built IN a stove type box before,  how hot is ideal, and for how long is it wished for?

Again, nice job!

Scott

April - Simply stunning and so inspiring! Please let us know how it runs after a few weeks bedding in. Thank you so much for sharing the details with us.

Thank you, everyone! It has been a long job. Appreciate all your help and patience.

Scott, I think you are asking about the oven? (I have been using the term “top box” to refer to the chamber housing the afterburner.) So far I have only run single batch fires in a cold stove, and the oven has only reached 150*F. Yes, the mass isn’t getting very warm yet either. However, it is a very small firebox, and a lot of brick! I would say that my ISA (Internal Surface Area for heat harvesting) is probably near the maximum of what a core this size can power. Others have calculated this as about 33 ft2 (200 times CSA). So one batch fire at a time doesn’t count!

Once the weather turns, I expect I will burn several batches in a row to bring the bricks up to temp, and then burn two or three or four times a day to maintain them there. We’ll have to see how exactly that works when heating season starts!

I built a “white oven” (isolated from direct contact with smoke) because there are ceramic fiber products in the smoke path and these are not food safe. I *hope* the oven will get hot enough to bake bread – 400*F for an hour. I hope it won’t get all too much hotter than that because I question the durability of the flue liner, but so far not an issue. I located it high in the bell so it would be warmer, but that may mean that the bell has narrowed too much and the sides of the oven won’t have enough exposure to circulating smoke. Guess if I were doing it again I might go one brick layer down with it. We will have to see. I’ll let you know in January.

Here is the tiny firebox, and all the wood included in one batch. You can see why it would take a few rounds to heat 4000 lbs of cold mass! Firebox dimensions are 11” wide, 9” high, and 14” deep, plus another couple inches depth from the airframe.

So long as I am putting all the plans in one place, I should also describe the airframe door. Like the core, this is Peter VanDenBerg’s design, and unlike the DSR2, the outlet vents should be located at the top and upper sides. The air comes in at the front, travels through hollow tubing, pre-heating as it runs, and goes out slots at the top and upper sides, behind the closed door. It then flows along the upper walls of the firebox and ceiling shelf and concentrates right around the port into the afterburner. No secondary air is required.

People who know what they are talking about go on about “laminar flow” with this design but me, I’m just following directions! Earlier testing did show that although a vortex may form when this core is run without any door, you’re definitely going to get some smokeback. So if this is in your house, put a door on it!

Airframe dimensions:
*Bottom member custom welded of flat stock, 2.5” deep by 4.25” tall by 16” wide (exterior dimensions). Interior dimensions are 2x4, or 30% CSA
*Sides are 2.5” square stock, exterior, a bit more than 2x2 interior. 15% CSA each (15 + 15 = 30% CSA)
*Total outside height 13.5” x 16”. Open door measures 7” high x 11” wide. You could increase the height by 2” if you had designed your brick platform to sit the whole door frame down correspondingly, but I didn’t. Oh well. Small door.
*Air inlet centrally located on bottom member, 1.75” high x 7” wide. 50% CSA
*2 Side outlet slots 0.75” x 5”, located high.
*2 Top outlet slots 0.75” x 4”. Add these 4 slots together for 50% CSA as air outlets.
*Air inlet closure is just a piece of flat stock with magnets. In theory, closing snugly at this point will keep the heat inside the bell without an after damper (known to cause CO problems in the house when misused). Leave it open when the stove is not in use, though, and your mild household air will likely circulate right through the bell and up the chimney, cooling the brick and pretty well defeating the purpose.

An important note for those more accustomed to box stoves: While the fire is burning, you are NOT supposed to fool with the air vent. Leave it wide open. You want a quick, clean, super-hot fire; this is why you go to such hassle to source an afterburner of refractory material! You can close it once you're down to a bed of coals.

Once you have the airframe, you attach any door you can make close tightly. I used a cast iron griddle, which my handy neighbor drilled through to bolt on hinges and latch of his own design. (Cast cannot be welded.) Seems pretty snug but if I notice too much air leakage I may later add gasket rope. Any hardware store should carry this, along with the appropriate adhesive. Or at least, any hardware store in Vermont.

It does help, I think, that since Vermont has such a lively sugaring (maple syrup) industry, building supply stores with a good masonry department often do carry refractory materials for the care and repair of evaporator arches. Not sure that would be true in other parts of the country. Shout out to WW in Newfane! Otherwise source parts from pottery supply or discontinued kilns.

Airframe pic taken lying on the floor looking up inside.

And a last summary of the most important design parameters I learned along the way:
Here is the scaleable spreadsheet for DSR3 core dimensions. Don’t try to change the public copy on Docs there, but make your own copy to play with.
https://docs.google.com/spreadsheets/d/1kG219Qu3fmGGtTDFo4IfJOhCPk1RR8Z8/edit?usp=sharing&ouid=114630257550685626397&rtpof=true&sd=true

This was a 5.5” system (the number at which the firebricks and afterburner all came out nice and even). 5.5 is thought of as the diameter of a cross-sectional circle, which means the System CSA (Cross-Sectional Area, your all-important number for calculating proportional dimensions) is pi x r^2, or about 24 in2.

Chimney can be any regular chimney with good draw (ideally insulated). It must be System CSA or slightly larger, so this is often the starting point. I’m getting away with a 5.5” system on a 6” chimney, but you probably could not run a 6.5” system on a 6” chimney! People with bigger houses in the North often seem to like 8”, which (pi x r^2) is nearly twice as large. If your chimney is square, the gas is not traveling in the corners much, so pretend it’s a circle of equal diameter when calculating CSA.

Core proportions matter so get as close as reasonable. Your afterburner tube needs to be able to handle at least 1200*F.

Once you have your core, you then put it inside any heat harvesting bell of equal to or less than the recommended ISA for your system size. Your bell design should have no channels tighter than 5 times System CSA -- and that is for one-way flow. Right above the core, where the gases first expand and swirl around, up, down, and sideways, it is better to have 10 times System CSA or even more.

Do support your floor! Even a little heater like mine is probably 4000 lbs!
Masonry heater standards: Double-walled brick takes an awfully long time for the heat to soak through, so bear that in mind with smaller stoves. Double wall should be built with an expansion joint between to stop propagating cracks. (You can use scraps of cardboard; it’ll burn out.) It needs a minimum 4” air gap from combustibles. Single wall should have more. Single wall should also have reinforced plaster to minimize gases escaping through brick cracks. If hot brick is anywhere in direct contact with wood, I believe code says it should be 12” thick. The front of your firebox and any radiative metal surfaces should have the usual 36”.

Finally you run the exit gases out the bottom and into the chimney. Make sure your exit slot is at least 1 CSA, as low in the bell as possible, and ideally wider than tall, because of gas flow behavior. More is better; you don’t want a restriction there. Do make a cleanout of some kind. In my case I plan to once a year remove the section of black single-wall pipe and snake the tube of a vacuum cleaner down into the exit slot, and also brush out the chimney. Hope that works.

Remember you might need to tweak to your mass by adding extra room to the top box, especially if you couldn’t source one of those sleek and slender ceramic foundry tube afterburners, so design accordingly!

Think that’s all anyone needs to know, right? Happy building!

Very nice stove, different to what is usually seen. Thanks. The concept of "bubos kemence" is new to me. I'll look more into it.


I've built some curved stoves myself, and i find this kind of geometries prone to slight/very fine crack marks apperaring. Have you find any on this stove?

Pablo, that is a good and important question. I will not be able to answer it until January. However, I did make sure the plaster was reinforced with 2 layers of fiberglass mesh.

April,

This is beautiful! I'd love to see a video of it with a fire going.

April Wickes wrote:Pablo, that is a good and important question. I will not be able to answer it until January. However, I did make sure the plaster was reinforced with 2 layers of fiberglass mesh.

Great. I have experience with the same material. And the same application in round shapes. And let me tell you that i've found that thermal expansion forces are irrepressible.
But there's great joy and happiness in making round stoves.

Let me share with you some my stoves in this line of work:

Danesa6 hornero 2023




Danesa6 hornero 2021




Danesa6 hornero 2020

Pablo Kulbaba wrote:Great. I have experience with the same material. And the same application in round shapes. And let me tell you that i've found that thermal expansion forces are irrepressible.
But there's great joy and happiness in making round stoves.

Pablo,
Could you expand (no pun intended) on the expansion forces? I saw several examples of Búbos Kemence while living in Hungary. It has a long, long history, and they must have a way to deal with those forces. What have you done to mitigate them in your projects?

Pablo,
Could you expand (no pun intended) on the expansion forces? I saw several examples of Búbos Kemence while living in Hungary. It has a long, long history, and they must have a way to deal with those forces. What have you done to mitigate them in your projects?

Ok.
Danesa6 hornero 2020 was lower half made of bricks and upper half in 6mm diam rebar meridians and parallels,
then metal expanded mesh,
then mud+sand+straw

=CRACKS. Clients still in love with the result.

Danesa6 hornero 2021 the same as 2020
+1 layer sand+mud in fiberglass mesh 1cm sided hole
+1º jabelga (lime + sand in a thick paintable consistence) layer with fiberglass mesh 1cm sided hole

=CRACKS (more slight but i see them and that's enough). Clients still in love with the result.

Danesa6 hornero 2023 same as 2021:
+2º layer of jabelga with fiberglass mesh 1cm sided hole in certain areas.

=CRACKS (more slight but i see them and that's enough). Clients still in love with the result. I'm not satisfied and feel exposed to a geometry that doesn't allow me to give certainty to my clients.

My guess is the radius of curvature chosen where to tight and the pieces tended to get too small, and the masonry work didnt get so resistent as when the bricks are bigger, or uncut. The second geometrical disturbance was the profile thinning designed (my fault), because the slope was too tight in certain areas, and the resulting corbel  imposed a displacement of the bricks of more than the maximum 1/3rd of thickness that's rule of thumb.

Those are beautiful, Pablo. Thanks for the info and warning. Have you found any way to patch cracks?

April Wickes wrote:Those are beautiful, Pablo. Thanks for the info and warning. Have you found any way to patch cracks?

I believe that cracks due to thermal expansion in masonry stoves are not patchable, because thermal expansion forces are uncontainable, irrepressible.

The only thing to be done (in my experience) with thermal expansion cracks is avoid them via several strategies:
-Use the biggest possible pieces of bricks.
-Thin mortar layer, less than 1 cm.
-Always lay bricks ¿interlaced? sorry, my english is not good. I mean the bricks in the next row are displaced from the current row.
-Metal has aprox the double of thermal expansion coefficient than bricks and mud, so always place ceramic wool between those two materials.

Beautiful work April. Now you'll get to enjoy the warmth of your considerable planning and labor. Bravo!

All right, two week update.

My biggest problem is this: The burn is not stable.

It consistently draws well. It is usually not difficult to light. I am doing top-lit fires with dry wood, mostly red maple and ash. So that’s a couple of big pieces on the bottom, a couple medium on the sides, and (since the firebox is so small) a hollow V of kindling in the middle (birch bark, a twist of paper, pine or maple splinters). I try to make sure all logs have a bit of air between them.

Some days it burns fantastically, start to finish, just as designed.

Some – most – days it stalls out. The afterburner flame goes dull red and sooty, and the door must be cracked by ¾” to get any vortex at all. It does not smoke back. I can still feel the draw whooshing by my hand. Sometimes adding lots of exta air around the door will return it to a reasonable burn. Sometimes I can fix it by adjusting the logs in the load, moving one closer to the center after the center burns out. Often it seems a one-stick reload corrects the problem and then it all burns merrily until reasonably well consumed.

Occasionally – and so far as I know I have changed nothing! – it takes off with a roar and comes gushing out the front of the afterburner to bounce off the glass. I have been trying to correct this by restricting the air some. I am not sure if that is the best way to deal with it. Seems like Trevor’s Vortex advised actually the opposite??

Today is one of those, overexcited at start up. About 30 minutes into the burn, it settled down and started burbling along contentedly at the back of the CFB afterburner, which was glowing dull red. It is presently running with the recommended air, but now, about an hour into the burn, it’s slowing and I’m wondering if it needs more air again. No soot, anyway. For once.

So what’s up? Is it that picky about exactly how it is loaded? Is it that sensitive to exterior weather changing the chimney draw? It’s seeming finicky, all round. Would definitely appreciate advice!!

Other updates:
Yes, Pablo, I’m getting cracks. I don’t know whether or not they are serious. There are none in the main dome yet. They’re mostly at places where one type of material meets another, so, bottom edge of dome where it sits on the square of double-thick common brick; around the firebox where insulation meets the brick; in front of the glass where I cobbled together a holding slot out of ordinary cement board and plaster (I am not at all surprised that moves!) They are visible during the burn and close back to invisibility after it cools. I do worry about the lintel, but otherwise, I think the only real risk is carbon monoxide. (Which could possibly leak around the cooktop too.) I have bought a CO meter and set it next to the couch. So far it’s not whining at me, which is good. Unfortunately it isn’t a constant meter, but will only display the CO reading when something is wrong.

Chimney temp still 120*F.
House air temp today raised only 2*F during the 2 hr burn, although radiant near the front of the stove was plenty. +2* more over the next 2 hrs, +4* over the following 2 hours, and probably will continue to rising for a few hours yet. There remains some sense of heat, perhaps a bit nebulous, about 12 hrs on. Enough to turn your head as you walk by, wonder where that’s coming from.

Back of the oven after one load + one stick for 2 hours is 200*F. Not enough to do much with beyond a slow roast or drying something. Still hasn’t been cold enough to keep the stove running for more than that per day. Winter Is Coming and all, but so far just light frosts.

It all sounds promising and I suspect that as the mass dries out things will continue to improve. I am very familiar with the symptom of a fire that seems to be going well, then mysteriously stalls and reverses. It happens with my little J-tube RMH in the greenhouse from time to time, and is most prevalent in the shoulder seasons when I haven't burned it in a while (I often have weeks go by where I don't bother because it's not getting that cold at night and it's only there for frost protection).

What I think happens with mine is that long periods of no fire allows the mass to soak up ambient moisture (it is a greenhouse, after all) even though the cob is not directly in contact with the ground. As a burn progresses, it reaches a point where the burn is going well but the mass is still pulling a lot of heat out of the flue and the chimney temperature is low enough that water starts to condense in the stack. When this happens, a cold plug forms and shuts down the draw.

That's my hypothesis, anyway. In your case, with a new build indoors, once the mass is fully dried out I suspect things will get dramatically better. I assume you're using dry firewood...you might play around with the mix and see if that changes anything. Super dry wood will help limit the amount of water vapour in the exhaust, but it's always going to be there.

April,

You did such beautiful work, and I really appreciate all the pictures and descriptions. This summer I became interested in batch box rocket stoves and built one in my back yard. I am thrilled with how it works, but all I have currently is a core firebox and riser. All my parts are just compressed earth blocks of clay, sand, and perlite--they are holding up great so far, but I have only fired my stove for about 7 hours total.

After learning about the DSR design, I thought about doing that, but with a little oven over the burn tunnel. For simplicity I want to just modify my current stove in the manner shown in the drawing. Since it is just one more box on top of the second, I'm wondering if I should call it a triple shoe box?

UPDATE 12/6/24:
Well, the news is mixed. The stove continued to behave erratically, working well about 2/3 of the time, overfueling sootily about a third of the time, and occasionally bolting into a rather terrifying runaway. This behavior was frustratingly unpredictable and seemed to depend on tiny variations in the stacking of the fuel load, or maybe just the weather. I never found a clear correlation.

My conclusion is that the octagon made of 1” wide materials (rather than the round, thin-walled foundry tube that the design calls for but I just could not source), simply did not provide the same restriction in the gas path and stabilization of the burn that the DSR3 proper is supposed to provide. Because my afterburner was a different shape than Peter’s exact design, in order to achieve a good draw and prevent smokeback, I had to add too much extra room in the top box and this made it prone to overfuel. Nevertheless, it was heating my home reasonably well, and I was enjoying the house being less frigid in the mornings, as a good brick bell offers.

Then, barely two months into use, this happened:

So: that expensive ceramic fiber glue from Ceramaterials may be fit for some purpose, but obviously not this one. It burned right out. I no longer have an afterburner tube. Yes, I could probably try holding the pieces together with some sort of stainless steel band, but at this point, it seemed I should cut my losses and rebuild the afterburner as a Vortex, which can be made of much more easily sourced – rectangular! – pieces.

This meant:
*Vortex firebox can be a bit taller but essentially the same, so no changes.
*Kiln shelf between firebox and afterburner, with its port, is identical.
*I restricted the final exit from the core into the bell with a chunk of brick so that it is 80% System CSA (2.4” x 8” on this 5.5” system) instead of the full width slot of the DSR3.
*I removed the wrecked tube and built a different afterburner with scraps of CFB. It is 4.2” high and 8.5” wide (150% CSA and proportions matter). A shelf covers the top, 12” deep (4” from the front wall and glass window).
*Just like the DSR3, the gases combust in the afterburner, pass forward toward the viewing window and then turn 180* back. They pass over the afterburner shelf through a wide shallow slot – which should come out to roughly 100% CSA; mine is a bit too big at present, given the scraps I had to hand – and then go out the final exit (80% CSA).
*In my case, since the front half of my upper box is 1” taller than the back half, I added a 1” stumbling block to slow the gases down through there.

Later, I may try taking that extra height addition right off and lowering the cooktop back to my original design (9.5” top box height all the way), but for today, this is good enough. One disaster at a time please!

Initial firing as a Vortex core burned okay – good draw, fairly lively activity in the afterburner, a little sluggish but certainly not overfueling. Second firing did overfuel messily for about the first hour and then, by a judicious fiddling of extra fresh wood and restricted air, I was finally able to bring it to a good burn. Reloads thereafter were fine. So I’m still having the same pattern of problems as I did with the previous configuration.

I know the Vortex design likes to be “tuned to its mass,” which is to say I may be futzing with it for a while until I find exactly the right balance between exit resistance, air intake, and chimney draw. Anyone knows more about troubleshooting these, I’m listening.

Is the kind of weak vortex seen in the picture below what you get when there is too LITTLE restriction in the core? Counterintuitive but maybe?

And picture of a reasonable burn … eventually.

Oh no that is not the best result considering all the effort you put into your stove!
You may find my latest videos of some interest to you, it has taken me several years but I have managed to get my 4” vortex working on song.
However there are some details you may not be able to adapt and your 6” may behave differently anyway.