DSR3 With Beehive Dome Build

This is a continuation of https://permies.com/t/40/192518/Planning-DSR-Build-Cooktop-Questions, documenting the actual build.
So, I haven’t given up! There’s just been a lot of groundwork to do first. Here is a summary so far.

Also, I do need some troubleshooting help!

Last October: Gathered supplies. I mightily confused the guys at Sheffield’s Pottery Supply. (“You want to do what??”) CFB ordered from Ceramaterials online. These came well packaged and intact.

November: Beefed up the floor from below. The floor joists are now directly supported. Work done under supervision as shown.

November: Cut out CFB parts and trimmed firebricks to shape. Used “Rutland” brand firebrick splits (locally available in hardware stores) and a diamond blade on a circle saw, mostly dry except I kept pouring water over it manually. That blade cuts common brick with no trouble, but these were hard going. Also, they had a few mm variation in length and thickness, which was annoying since I intended to dry lay them in the firebox.

Cut the port in a 13x16 cordierite kiln shelf, which was *really* hard going. Spalled a good bit. Drilled a line of holes across the short cut and broke it out with a chisel, the way I would cut a pocket in a timber. Results not very neat, but it worked.

November: Fabricated the CFB afterburner tube. The CFB “adhesive” from Ceramaterials had the consistency and just about exactly as much holding power as a chewed up paper spitwad. Also it was full of hard chunks. I was not impressed. It could be made to work only by leaving very thick joints (8 mm or so) which meant I had to trim the whole thing down at the end. Very fragile. Instructions said it would dry in a couple of days, reality was more like three weeks. I set it gingerly aside for the rest of the winter.

Odd sticking out piece in picture is just a prop (the offcut from the kiln shelf) to keep the port opening from collapsing as I tensioned it. Which it was inclined to do. Accordingly, had to re-glue a broken leg. Whole thing is not as straight and even as I would like but I guess it’s okay.

Fabricated the front plate. This was 2 pieces of CFB, the outer one lapping the entire upper front, the inner one sitting on the firebox shelf, the glass to be slid between. Zero adhesion from the “adhesive” and the first time I picked it up it went to bits. Also that inner plate, although an efficient use of scraps from the afterburner tube, was too fragile. Had to cut another one with a smaller hole and rebuild. Eventually gave up and put through bolts in to hold it together. Not at ALL sure it’s going to hold long term.

Winter was now upon me. Put this project on hold and fired up the box stove for another year.

This being Vermont, heating season doesn’t actually end until May. I had to wait to remove the box stove until then.

Here is the tight corner I have to work in. As you can see, clearance from combustibles is an issue. I plan to add a layer of cob plaster (been on the to-do list for a decade). I still don’t have as much clearance as I want. (4” air gap mostly, but only 2” behind the chimney housing.)

Took up the floor so I could strengthen in between the floor joists too.

Upon accessing the floor run, everything stopped for a freak-out! Arsonist mice had stripped my electrical wires completely bare! It was exactly the sort of damage that burns buildings down. Had to re-wire my house. Aargh.

… Okay, back on track. Floor joists thoroughly blocked between. (Random pipe was part of original fresh air intake; I have now simply covered it.) Laid out a new layer of cement board in preparation for eventually tiling the hearth.

Early June: My favorite book-swap neighbor loaned me that classic masonry stove overview book from the 80s; I’m sure you’ve all seen it. I had too, but not in a couple decades. On re-reading, I promptly fell in love with the appearance of the Hungarian “bubos kemence.”  Total re-design!

Okay, so this introduces a few problems.
1) My plans for a hot plate always did seem a bit dubious. As Fox and others pointed out, it tends to be screaming hot or cold entirely, and any chunk of iron as part of the afterburner ceiling was obviously going to warp, requiring a double-layer cooktop to avoid gases in the house, thereby very possibly obviating its ability to cook at all. Also, it was going to be tiny, barely fit a teakettle. So would I give that up in exchange for a more accessible oven? Yes I would. The only way I could think of to get a good oven in the original design was to copy Fox’s cooktop oven box, or else cap the upper bell with a horizontal flue liner 13x18 and block off the open ends. I had serious doubts about the likelihood of an uninsulated ceramic flue liner surviving without cracking in the high-heat bell cap spot. Anyone tried this?

2) But. Redesigning as a corbel dome means we’d be talking about a *black* oven. And I just built this core out of CFB. Maybe not so good!
… Maybe I could slide that flue liner in a few inches above the core and call it a white oven? But then we’re back to the problem of wondering if it can take the heat blast.

3) Also it makes the afterburner a lot less accessible, since I now wouldn’t be able to lift off the cooktop, and the afterburner ceiling would be buried under the oven floor. Since any possible glass replacement was designed to be done from above, that could be trouble. I might be able to think up a way around it. Still cogitating.

4) Bypass. Ugh. Chimney will run up just beside the dome, almost touching. I’m not seeing any way to make a bypass but to stick a piece of stovepipe horizontally out of the upper rings of the dome, beneath the cap. That seems A) ugly!! and B) like an awfully hot place to stick a bit of black pipe with a damper. Anybody got ideas, I’m listening.

All right. NOW. Here is where things start going wrong.
As I understand it, CFB ideally needs to have the binder burnt off BEFORE rigidizing. This meant I needed to fire the core, so might as well do a test run. I don’t have any semi-covered outdoor space to do that and it rains a lot here. I’m pretty sure soaking the stove components can’t be good for them, so I needed at least a couple of days of uninterrupted dry but not-dangerously-wildfire-dry weather to do that. Did not actually get that opportunity until the June Solstice. (This is why I don’t have an outdoor kitchen, thank you very much!)

It fit together as intended.

Attempt #1: I tried to mock up a bell by placing a chunk of flue liner on top and a cinderblock gap for exit gases at the bottom, behind the core. This bottom exit did not have a chimney stack and the whole thing was leaky. It did not work AT ALL. Would NOT light. Worse than an open campfire by far. 85% of smoke came pouring out the door instead. Mucked up the afterburner dead black. Pulled the capstone a bit clear of the flue (creating a “bypass”) and got a brief little vortex but still a ton of smoke pouring out the door (which was just a griddle laid at a tilt.)

Attempt #2: Moved the capstone off the flue liner entirely and closed up behind. So now pretty much just running the bare core, funneled into the wide flue liner. Results no better. Widened exit port to more like 4-5” (face full of smoke). No help. Yuck!

Attempt #3: Took off the flue liner entirely. Exit slot back to recommended size. Cobbed a 4 ft length of 6” stovepipe in place above the exit slot (+ 1 brick height so gases could find their way). Still fiendish and smoky to light, face full of poison. Just when I thought it *might* have been about to take off, the glass dropped out of that funky front plate array and broke. @$%*!!!

… And now I was out of daylight and very smelly and frustrated. If one’s Solstice fire is some kind of omen for the upcoming year, I’m pretty sure I’m gonna die. Luckily I ordered 2 pc stove glass.

Next morning, Attempt #4: Replaced the glass and scooched the shelf forward so it couldn’t drop out again. Built the fire more carefully and top lit. It started. It drew. It wasn’t smoking back so long as I had the "door" propped in place. So that's progress.
It was also definitely NOT rocketing. It was just an ordinary dirty fire.

Attempt #5: Although I had been very careful with my math and dimensions in the original design, I now raised the ceiling of the top box by 1”. So system size 140 mm (5.5”), CSA of top box surrounding afterburner tube 185% system size, or 44.2 in2 (96.2 in2 total area of box – 52 in2 area occupied by octagonal tube). However, the top of the tube was very nearly brushing the ceiling, which did seem like a restriction. Raising this 1 inch added an additional 11.5 in2 to CSA, bringing the total to 55.7 in2 or 232% system size.
Fire was mostly kindling, about 1/3 load, propped with bricks on the sides to keep it directly under the port.

It actually worked! It lit, it made a vortex, the smoke went transparent, and it started to clean up the soot! Hooray! …
… For all of about fifteen minutes. Remainder of the burn a sluggish, sooty mess.
I had the “door” leaned against the top of the frame, propped out about 1” at bottom, as shown. Doing any door configuration that left the *top* of the frame clear, as elsewhere suggested for the DSR3, resulted in nasty smokeback.

Attempt #6: Re-loaded. Again, about a 1/3 load. Changed position of “door” to let in quite a LOT of air on the sides, as shown. Got a nice vortex for about 20 min. Then the leaping flames died down and by 25 min smoke was puffing out the front again. Stirred the logs together and this stopped but no further vortex formed. Coaling by 45 min, which went on and on and on until I said I really am out of time today and so shoveled them into a bucket of water. Glass at the end of the burn a sooty mess. Never really cleaned, although smoke was clear during the short vortex period, and relatively clear even after.

Whenever I opened the “door,” I got a facefull of smoky blast. While the vortex was formed and running, it was not visibly smoking out the front, but close examination suggested there still were some fumes leaking around the sides. As soon as it slowed, it went backward. There’s no way I can live with that in my house.

And now we are back to another indefinite future period of rain.

Disassembled stove core and put it back under cover. The CFB is crumbling to the touch. Time to rigidize, I guess, which I more or less expected, but boy I sure did inhale a lot of burnt fibers fussing and cussing with this over the last few days. If I were starting over, I don’t think I’d use CFB *at all*. It’s really nasty, fragile stuff. And expensive!

Good news: the fabricated octagonal burner has held up so far. I am still treating it very gingerly, but at least it didn’t fall to bits on first firing. It even kind of looks like one piece now. I might feel better about it wrapped with stainless wire. I have no idea how long its working life will be.

CONCLUSIONS:
* It seems I can’t get a good test running a bare core in the yard. This worries me because I am talking about putting it inside brick work, which means that if it needs troubleshooting when it is in my actual house, hooked up to my actual chimney, there won’t BE any easy way to take it apart and fidget by then. Even something as minor as adding top box height would be a lot harder once that height is interacting with the rest of the array! I do believe that Peter gets fantastic results in his test set-up, but I wonder how much of that is attributable to his already having perfected the ideal balance between bell and chimney draw? Because it seems like when I’m doing funky driveway tests, I’m getting a pretty fidgety run. Would that mean that like Trevor’s original Vortex, it *does* need to be individually tuned to draw and resistance? I am well freaked out. I would really like to be able to test it, and I’m not sure how that can be done.

* I’m quite concerned about the smoke back and fumes backing up out of the primary air slots. If I get this much of it with a bare core and no resistance from any bell, what will I get when I add 32ft2 ISA heat sink? Granted I have a good chimney in the house, 18’ of metalbestos indoors and slightly larger than system size. But I can’t live with this kind of smoke. I built a tight, well-insulated house!

* It seems the exact configuration of doors and primary air must matter quite a bit. No doubt a proper airframe would help with smokeback some. (Anyone got a link to the latest DSR3 door designs?) Unfortunately, this brings us back to one of the most frustrating things for many home builders: metalworking is a hard barrier for a lot of us. And given the amount of fume that seemed to be oozing out the side slots even when it was running correctly, let alone the great ugly puffs every time it stalled, I’m still worried.

So. Is it normal to have terrible test burns with a bare core and a short length of chimney pipe? Am I just freaking out needlessly? Help??

On further reflection, I can see at least one problem I was having. Because the afterburner is an octagon and not round, and because the calculation for 185% system size around it brought it up nearly brushing the ceiling, it would have restricted the exit slot by quite a lot. Each facet was a bit more than 3” wide, which meant that instead of a continuous exit slot it would have behaved like 2 little slots to either side, restricting the exit from 110% to 80%. No wonder raising the ceiling helped.

As with the problem of loose glass, this was something I had thought up a solution to during initial design, then forgotten over the winter. My original fix was to try sending the gases not out the top, but out the back, through two wunky triangles calculated to 110% system size. Why testing matters! Why I would like to be able to get a good driveway test! Please comment if any of you know better ways to do that.

Possible fixes:
Try the back exit?
Raise the ceiling at the back at least?
Raise the whole ceiling?

Hi April, I wish I could help you but I guess you will have to wait for Peters reply.
From my own experiments with similar designs, very small changes can have big effect's

Ok what are DRS and CFB short for?
Not everybody undersatnds them.

Hello Fox,
You have done some bare core testing though, right? Can you tell me more about that process and any general advice about how best to do so/?

Are you getting a good seal between your hex-tube and your top port? That bottom side of the hex looked a bit popped up on one side.
My only other thought was that things looked rather cramped around the tube in the top box, but looks like you found a restriction and fixed it with some improved results.

Hi Matt, thanks for the note.
Yup, the afterburner is a bit wunky (see notes above regarding thick glue and broken bits). I saw a little flame going around the side but plugged it with a scrap of blankie and that seemed to fix it.

I think the close quarters are more likely to be the problem, although it definitely is 185% system size surrounding. But since the math brought that flat uppermost facet up high enough to block part of that top exit slot, that seems like a likely culprit. Waiting for another non-soggy day to try the back exit instead, see what that does (may be waiting for a while.). Also that will be a chance to cure the rigidizer.

As I cogitate about the black oven / white oven problem, I think I have come up with a white oven design that will make it possible to access the front plate/glass slot with relatively little trouble, and theoretically possible to access or even replace the whole core if necessary. But it’s going to require a lintel to span an 18” gap and support some of the dome. Anyone have ideas on that? If I run threaded rod through core bricks is that likely to do?

DSR = Double Shoebox Rocket, a series of Peter Van der Berg’s designs
CFB = ceramic fiber board. Also sometimes ceramic fiber blanket.

You could try asking Peter on the other forum, he does say there are over 20 built and working but also mentions how critical the build must be….
https://donkey32.proboards.com/thread/4022/solution-thermal-runaway-style-stoves?page=1&scrollTo=38882

Somehow I missed this thread, sorry.
It's true that the afterburner tube (hexagon in your case) shouldn't touch the top box' ceiling. When it is doing that, raise the ceiling until there's at least 1.5" free space. A larger version (don't know what size yours is) should provide even more room. In my small development model this space is smaller, just under 1". More space around the tube won't do any harm, too cramped is not good at all.

To my eye, your first port looks overly large. This should be 50% of cross section area of the chimney pipe, W:L ratio 1:4. The end port as wide as the top box itself, cross section area 100% of the chimney again. The back exit you are sketching isn't tested, it's unsure what results it would yield.   This design is very, very tight. Changing some aspects, although seemingly unimportant, tend to render the whole thing useless. It took me a full year in order to get a properly working core.

I've never run this core by itself in the open air so I am unable to tell you how to do that. My guess: this core really do need a proper drafting chimney. You have been running it for 20 minutes with reasonable results and then it suddenly got very stubborn. For me, that's a sign the chimney should be warm by now, drafting properly so the combustion process won't be interrupted.

Hello Peter,
Thanks so much for your help! Don’t worry, you hadn’t missed me for long. I only went live here a couple days ago.

System size is 140 mm, fairly close to your development model. First port is 44 mm x 176 mm, so yes, 50% and 1:4 (or as near to the line as I could cut!). I really was careful with the math. But this octagonal afterburner with 1” thick sides just sits differently in a top box with 185% surrounding than your thinner, rounder ceramic tube does, and I guess that matters.

I see NO sunshine in the foreseeable forecast, but when I next get a chance, I will try the back exit and also the raised ceiling, and maybe a taller “chimney.” (Hope it won’t be a windy day.)

Now that I see where it was restricting, I’m less worried about the core as a whole, but it still concerns me that it smokes out the door when it stalls, at least when bare. Now I’m thinking I definitely should not try to get away with a janky casserole or griddle “door” in the house, but I really will have to build a proper airframe. Do you have results on how that differs in the DSR3 from your already published specs of the taller, narrower batchbox door?

April Wickes wrote:Now I’m thinking I definitely should not try to get away with a janky casserole or griddle “door” in the house, but I really will have to build a proper airframe. Do you have results on how that differs in the DSR3 from your already published specs of the taller, narrower batchbox door?

Yes, the DSR3 airframe is different from other air inlets. All of the air is entering in the top half of the door frame. So there's a slit left and right, and in the top lintel. The slits aren't facing the fire, but each other instead if you see what I mean. Since the core itself is the limiting factor, the total air inlet csa is quite spaciously.

Moreover, I am used to starting the fire with air inlets open and the door opened a generous crack. While the chimney temperature is coming up, I do close the door gradually, say, in two steps.

I'll have a look for the sketchup drawing of the air frame.
See https://pberg0.home.xs4all.nl/pictures/dev2021/luchtinlaat2.skp
It's just the frame, there aren't any other air inlets in the door. The glass will stay clean this way, no worries.

Peter, thanks so much, that’s fantastic. I think I have the idea from your description and have saved your file, but since internet out her is very intermittent, I have trouble accessing Sketchup. If anyone out there (Matt?) wishes to kindly open it and post a couple of screenshots that would be even better.

I have been entertaining myself during the wet weather. Painted rigidizer on the CFB – which was sending up huge nasty fiber clouds at the slightest brush. (Did I mention I don’t think this stuff can possibly be worth the hassle of working with?) The colloidal silica rigidizer had more or less exactly the texture of a $75 gallon of water. I really hope it does something useful on firing.

Also bricked up the initial platform and plastered the nook. I suckered my visiting friend Allison into helping. Funny how much better your funky cob sculptures come out when you involve an actual artist!
https://aestrygallery.com/

Will give it a more colorful top coat once that dries.

Don't worry, that rigidizer will make a big difference to your CFB. Looking like the beginnings of a beautiful build!
Here's that screenshot of Peters air-frame.

Bless you, Matt! Yup, that’s about how I thought it went.

Got a lone dry day. Further reports.
Attempt #7: Back exit. Low ceiling. So 185% surrounding the afterburner, 110% exit, but wunkily shaped around the octagon. An area at the back 8” high, 16” wide, and about 4” deep to funnel smoke up to a 4’ length of stovepipe. Factors which would not have helped: CFB was still a bit damp from the rigidizer, and accordingly I built a wee tiny kindling fire so as not to shock it and flash steam inside the board.
Took a solid half hour to get it lit at all. 75% smoke up the chimney, 25% out the door. No draw. No secondary combustion. Just a nasty sluggish fire. Let it burn down while I weeded my garden so as to at least dry out the rigidizer a bit. All seams smeared with thin cob to prevent leakage; this does seem to work.

Attempt #8: Raised the ceiling by 1”, so space around afterburner 232%. Kept the back exit, but moved it up by 2”. Since that meant blocking 2 small rectangles while adding 1 large one at the top, I figure the math is pretty close though I haven’t calculated exactly. If anything the exit is probably a bit more than 110%, closer to 120%. Slightly larger fire, though still small.
Lit easily, though smokily, from the warm coals of the previous fire. Smoke out the door while getting it going, mostly straightened out but still continuing to puff backwards occasionally. At 15 minutes the thick plume of white smoke briefly cleared for a weak vortex, less than 5 minutes, back to smoke. At 30 min the smoke ran relatively clear and the fire burned but peering down the afterburner I dunno as I’d call it a vortex, more an occasional flicker in a vaguely curvy direction.  I did change the door prop to let air mostly in the top instead of the sides, closer to the recommended primary air positioning, but I’m not noticing any difference, except that it seems even more prone to smokeback. Coaling at 45 min.

SO. I have now tried every driveway mock up configuration I can think of with the materials I have on hand. The “best” was the top exit slot, raised ceiling, but – and I feel this is important to reiterate – that was still *not very good*. Not at all.

I will leave this up overnight and try again tomorrow repeating the top exit, but I feel I’m back where I started. Certainly not seeing any great breakthroughs. Possibly one simply cannot get a good test in the driveway.

If you could post a video that might help folk iron out the issues.
Are you top lighting a decent amount of dry wood?

I have found that the fuel can make a huge difference, if you can try some super dry kindling you might get it working better.

Hello Fox,
Internet is too spotty here to upload or watch video, but I took your advice today about a bigger fire and it did indeed help. Wood is what I’ve been burning for years: mixed hardwoods, mostly ash, birch, and red maple. It’s been in the shed for 2 winters so certainly ought to be dry, although the 90% air humidity at present doesn’t help!

Attempt #9: The best yet. I could live with results like this!

Parameters are:
Raised ceiling so 232% system size surrounding afterburner and 1” free air space above the octagon
Top Exit at 110% of system size, full width
1 brick height continuing the shape of the exit slot
then capped with scrap brick and a whopping 7 feet of 6” stovepipe. (This was a bit alarming because they were calling for thunderstorms this afternoon and there was a breeze throughout—just enough to make such a tall unsupported pipe exciting. Extra bricks in the picture are me trying to keep the thing from flopping over. Lots of cob. Yes it’s ugly, but I was in a hurry because I wanted to get it done and disassembled before the storms hit.)
Primary air mostly over the top of the door, a little at the sides.
Went ahead and burned a full load of mixed hardwood, and if it wasn’t exactly top lit, it was at least lit within the upper third.

Here are my notes as it burned. Sorry Fox, I did at least try to snap shots of what it was doing but mostly only got glare, blur, or my own reflection off the glass. It was doing something though!

12:16 Lit it. Went up easy, good draw. Whew.
12:25 the wood is well started but plenty of smoke. Not so much out the door.
12:36 A lively vortex, clear smoke! Mild roar. First time I’ve gotten that at all.
12:39 Vortex stuttering and intermittent, glass still dead black sooty (most of that from previous failures)
12:40 Something dull red and steady happening in the afterburner, seems promising
12:45 Turning orange, finally beginning to clear glass
12:50 Vortex still present but weaker, more a flickering tongue back and forth with occasional curls. Still seeing some smokeback out the door, but certainly less that previous attempts. Some flame in the firebox trying to move toward door instead of up.
12:53 Fire has corrected its direction, still vortexing or at least flickering around in the afterburner. Got a spot of glass clean anyway.
12:55 “Vortex” just looking like stray tongues of flame from below. Smoke still clear though.
12:58 Whoops, no, light smoke coming out the chimney now.
1:04 Vortex re-forms and smoke cleans right up
1:14 Still churning along though kinda back to flickering tongues
1:22 Fire itself slowing, occasional tongue in afterburner but pretty much done. Smoke still clear
1:34 Mostly coaling, but the big chunks to either side sending up live flame, poorly placed relative to port. Light smoke. Succumbed to temptation to rake chunks back to the middle.
1:40 Got about 5 minutes more clean flame, some entering afterburner, then it went quite smoky. Fair enough; I asked for that by stirring it. Just coaling now, and not too cleanly. Quenched remaining coals in a bucket of water so I could start the stove cooling.
3:00 Was able to disassemble and get under cover, except for the brick splits that lined the firebox, which were still too hot to bring indoors. That’s okay, I’m a lot less worried about them undergoing the thermal shock of a sudden drench than I was, say, my last piece of stove glass!

So. It pretty much worked, at last. Very glad I did this testing because I have arrived at a few conclusions, if anyone else plans to try this in the future.
1) If you are able to source that nice ceramic afterburner tube and follow Peter’s design exactly, by all means, you should do that! If you just cannot get the part, it does in fact work to fabricate something similar out of CFB but you may wind up tweaking your design on the fly just as much as people building Trevor’s original Vortex stove seem to do. Peter’s note above is correct (of course it is): Adequate circulation space in the top box is more important than following the 185% proportion exactly. I’m getting away with 1” clearance between ceiling and afterburner, but it’s a 140mm system, or 5.5”, so pretty small. If you’re building bigger, scale up accordingly. (I might get better results by raising the ceiling further too, but those were the CFB scraps I had hanging around.)
2) Just stick with the top exit. To be fair, I never tested the back exit under exactly the same conditions, but the top exit definitely did seem like better draw, even in less ideal circumstance.
3) 7’ of test pipe is better than 4’ – if the wind isn’t knocking it over! And the implication of that: Unlike the original J-tube-in-barrel, this core might possibly *not work* on a low-draw mass, like a hypocaust or a long horizontal run. It does not “push,” and it is dependent on “pull.” I’d guess its ISA for heat exchange will prove out a good bit lower than other cores. You know you’ve got a problem if it won’t light right off; might as well save yourself the rest of the burn right there. Will keep you posted how it works with the bell once I get that built.
4) It does still like to stall. It does seem like a bit of a fidgety core. It is, I would say, *not idiot-proof!* If you want idiot-proof and a simpler build, give serious thought to just sticking with the DSR2. If I were starting over, I think I might have done better to just have gone with that. (Also, the DSR2 is easier to lay out with only firebrick, never mind the CFB.)
5) Eew, CFB. The rigidizer has helped a little bit, but it’s still dusty. Although the afterburner apparently got hot enough on this last firing to start making an interesting clink when tapped. Suppose that’s progress?

So all in all, I feel better. I hope this is helpful to anyone else trying this experiment. I'm probably going to stop with the driveway testing now because ... MORE RAIN. (We got 12.7" of rain in the month of June alone, and if that sounds crazy, it is, but it's less crazy than a couple years back when it was 20". This is the new abnormal, I guess.) And also it is now high busy summer, and I have no hay yet (rain), plus I have to get the rest of the box built!

Well getting better, hopefully Peter might have some advice now that we can see some pictures of it working.
Personally I would hope for a much faster start up time, I would defenatily try to refine the wood loading.
Even if it is just just for experimental purposes I would load smaller logs at the bottom and much more kindling at the top.  
I use a couple of fire lighter on top of very dry kindling with the wood getting bigger nearer the bottom.

Watching the pictures, I think I spotted a restriction. The rear top exit slot is going in one brick high to 6" round, or so it lookes like. This works like a severe pinched spot, sorry to say. The tendency to come up to speed a bit and being on the verge of stalling the next minute is a sure sign.

Normally, this exit slot would open into a bell-like structure so there would be much more space directly above the exit. All the heaters done by The Loam Freemanship in the north of the Netherlands are done this way, very succesfully I might add. On top of that, all of those are equipped with a chimney bypass.

At first sight, a solution could be the placement of a small barrel, like a grease bucket, on top of the exit covering it completely. A hole in the top for connecting the chimney pipe would be sufficient. The bucket would act as a funnel, providing a proper transition from the narrow slot to the circular stove pipe. A real funnel from rectangular to circular would work as well.

By the way, you would experience the same problems when building a DSR2 since that one exits through a narrow slot as well. Just once, I built a DSR2 bare core outside for demonstration purposes. The core was a 130 mm system, the 1.5 meter chimney pipe 180 mm round, covering the exit slot completely. It ran just like that, no door or whatever.

So, y’all are telling me it could still be better, which I think is probably true. I had tried complete unrestriction on my first couple attempts, running it into the flue liner instead of the chimney, but clearly it needs some chimney in order to draw. I might see a way to cob together both … if ever the rain stops. (Again, the only clear day coming up in the foreseeable is one I’m working a double shift. And I really don’t want that glass shocked by rain while it’s hot!)

Peter, I was considering knocking together a bare core DSR2 demonstration for our local energy fair coming up in the autumn. When you say “It ran just like that,” I didn’t quite understand. Did you mean, “It ran well just like that,” or “I had the same problem running it like that”?

Appreciate the input! Guess we’ll get this thing running sooner or later.

April Wickes wrote:Peter, I was considering knocking together a bare core DSR2 demonstration for our local energy fair coming up in the autumn. When you say “It ran just like that,” I didn’t quite understand. Did you mean, “It ran well just like that,” or “I had the same problem running it like that”?

Sorry. I meant it ran well just like that. Out of the box so to speak.

All right. Almost caught up with the summer’s harvest and thinking about the stove again. Also, just about out of time, as we are nearing frost and my house is getting chilly. I wasn’t sure how much harder to push this year until I realized if I got stuck, I could still shove the old Fisher in place of the core all the way up until I started the dome. So I decided to go ahead and build the lower half, then call it good for the year.

Pics: Smoke channel and exit, 5”x8”. Closed over that. Dropped a round flue liner on top of it. Realized I might be able to get away with a priming cap instead of a bypass, which would save me having to puncture the dome. Hope it works. Brick brick brick, etc.

Mortar is 1:1:1:3 of Portland : lime : fireclay : mason’s sand. Yes I did realize, a bit late, that I should have gotten silica sand. Will use silica for the top half, for sure. Hoping the bottom half will be cool enough to get away with it. Also plan to plaster. Still wish I could just insulate that annoying little air gap beside the wall!

Inspiration struck: now that I have the lower core set up, I could place that 12x18 chimney liner on top and get an actual test under more or less the actual conditions of the finished stove, except that the liner bell would be smaller than the eventual dome. Set up the core. Nice big unrestricted space around the exit slot.

Placed the liner and capped with a kiln shelf. (I got to salvage several kiln shelves, and also a few soft brick and a couple of 9x24” firebrick slabs, which was a nice find, even if it did include poison ivy!)

So, the test. No bypass but priming the chimney with a twist of paper. What I want to find out:
Does it draw and light, or does it smoke up my house??
Does it burn better with the real chimney in place?

6:47 to 6:59 aaah, I hate top lighting!!
Draws reasonably well. No smokeback! Does not light nearly so easily as the Fisher. Still, it’s definitely going the right direction
7:04 Nice activity in the afterburner. That was fast
7:34 This is great! Multicolored vortex flicking back and forth steady and lively and mesmerizing. Insert all the oohs and aahs of enthusiasm everyone else had said before. Pics are all coming out terrible, sorry, I don’t know how to photograph fire.
It’s running well with just the propped grill as a door, BUT, there are still creepy little tendrils of smoke and I’m getting a minor sore throat from that. It’s running. It’s running just the way it’s supposed to. But for indoor use, build a real door, full stop.
7:40 Still flames flicking in the afterburner but slowing down. More smoke, though still clean in the afterburner. Not coaling yet. I would like to understand the end of the burn better. Anyone have a good thread link for dummies on that one?
7:50 Coaling.

Yay! It works! You may officially tag this thread for the soothing of other worrywarts.