Planning DSR2 Build With Cooktop -- Have Questions!

Yes, exactly. The thing that's got me scratching my head though is that the Vitcas Zircon stuff apparently functions BOTH as rigidizer and IR-reflection. But ITC-100 maybe not so much? And I tried to ask this of the HeatGuard people, whether it required pre-rigidizing or functioned itself as a rigidizer, but they never got back to me (going on a week now so they probably aren't going to). I worry the stuff may be a thin paint meant to be applied over a firm surface rather than a firm coating in itself. I haven't found any information clear either way.

If it's NOT firm, the procedure for longest life may be, Rigidize - cure - Satanite - cure - IR reflective - cure. Which adds up to a fair cost in separate coating materials.

But I haven't tried these yet, so I don't know. I'm just summarizing what I've read. It does seem like some sort of treated custom form would be what we'd need.

April Wickes wrote:Y I tried to ask this of the HeatGuard people, whether it required pre-rigidizing or functioned itself as a rigidizer, but they never got back to me.

Wow you have an eye for details! I didn't notice the word "rigidizer" is indeed missing from the literature on the Heat Guard product.

As for getting answers, they can ignore emails all day, but they can't ignore ebay messages or they get labeled an "unresponsive seller." I use this to my advantage sometimes.

Me: Will this (HeatGuard) act as a "rigidizer" on ceramic fiber blanket, making it hold a shape after drying?
Simond: This will not act as a rigidizer on ceramic fiber blanket. Please find below link of rigidizer: Simwool Rigidizer- Coating for Ceramic Fiber Blanket
Me: OK, so can they be used together? Would I apply the rigidizer first, let it dry, and then apply the refractory coating on top?
Simond: Yes, you can use together. Apply the rigidizer first, let it dry, and then apply the refractory coating on top.

So adding their rigidizer would bump up the cost by $35 and convolute the process a bit more, but at least we found a theoretically viable way to make this horizontal afterburner with materials available in the US.

But of course, a vacuum formed riser sleeve would be more ideal and a lot less work so I will continue to pester US suppliers until I get a quote.

In the US, Ceramaterials will apparently fabricate vacuum formed ceramic fiber for individuals and small orders. Yay, found someone.
Less yay, for a 12" length of 6" ID tube, such as would be suitable for the DSR3, they quoted me:

1 PC - 2300F MD BOARD 8”OD X 6”ID X 12” LONG - NOT RIGIDIZED AND FIRED - $382.50/EA
1 PC - 2300F MD BOARD 8”OD X 6”ID X 12” LONG - RIGIDIZED AND FIRED - $466.00/EA
$175.00 Set Up Fee
LEAD TIME: 3-4 WEEKS ARO

plus shipping, plus 3% credit card or PayPal fees.

So, all told, $700 for a one foot, 6" interior diameter tube.

That's again outside of my price range by at least a factor of ten.

There's worse news, but better to know than not. I got hold of a top notch customer service guy who was willing to discuss the nitty gritty details of rigidizers with me. Award credit to Ceramaterials for having an intelligent, no-nonsense human available to answer the phone! Here's the upshot:

They absolutely are not strong enough to support a tube by themselves. He seemed quite firm that, whether fiber blanket with a single continuous seam for a weak point or even a spiraled tube of paper with the seam spread over the whole surface, neither the rigidizer nor the colloidal silica glue would reliably hold it in tube form without an external sleeve. It would either spring apart or collapse inward.

The ITC-100 IR-reflective zirconia coating (and it sounds like HeatGuard is essentially the same stuff) can be used as a single coat, without rigidizer, to bind loose fibers, reflect heat, and maybe protect from fluxing gases, but it adds very little mechanical strength to the material. What extra mechanical strength can be had comes from a prior coat of rigidizer, cured and fired. Neither the rigidizer nor the zirconia stuff adheres well unless you pre-pre-fire the piece to burn off the organic binders. So add another curing step at the beginning. The mechanical strength of rigidizer, again, is not enough to hold soft material into a tube by itself, but if you were applying IR-reflective zirconia to a solid object, there would be no need to pre-rigidize, not even to capture fibers.

He added that the silica glue could not adhere two materials of different expansion rates -- no surprise but it's good to have that confirmed.
He also said, if it helps anyone in considering things, that the shrinkage of ceramic fiber materials at high heat, which can be as much as 5% depending on the formulation, was a one-time event. In other words, your 5 minute riser tube will shrink on first firing, but it won't continue to wither away after that. Good news for people with 5 minute risers. Y'all probably had already confirmed that through experiment, because you're smart cookies.

So what's that leave us with here in the US? Not much.

- Insulating castables. Certainly the most cost effective, if they can be cured properly.
- $$$$$$$, aargh.
- Moldable Mix??
- maaaybe something made of board strips mortared together? IF the mortar holds. See below. But a bit experimental as far as the negative-space resistance to exit gas flow, since it lacks the same amount of drag in the lower corners.
- a stove design that doesn't require any gosh-darn tube in the first place. See, Vortex. Or DSR2.

Addendum: I spoke again with the lovely man at CeraMaterials. He says:
- The Moldable Mix is just for patching cracks or holes in rigid board, not for forming rigid objects by itself.
- The thing about the glue is that it is formulated for adhering *fiber board to fiber board.* So he thinks Fox’s suggestion of the fiber board strips in an octagon, well glued, better yet with tongue-and-groove joints glued tight, WOULD work. (Should be easily formed and demolded reuseably with a big hose clamp, I'd think.) His objection to trying to use the glue with blanket or paper tubes is that it wasn’t formulated to bond to blanket or paper, only board. And rigidizer, again, stiffens mushy stuff up *some* but not enough to make a firm shape out of a soft material.
- Then he said, For Heaven’s sake, just go with castables. He recommended Mount Savage as a supplier thereof.

Further addendum: Looking at the Mount Savage website, they do in fact have oodles and oodles of specialty castable formulations for every possible use. What they don't have is a price list, or any immediately obvious web-based retail outlet. Again, you're gonna have to call them for a quote and then possibly argue about minimum order sizes.

A 4-pack of fiber board would leave a fair amount left over and the glue relatively cheap, so I'm tempted to try that.

Well, you officially talked me out of attempting to rigidize and refractory coat ceramic fiber blanket into a tube shape!

I like your octagon. Despite the cuts required, it still looks easier to make than a cast tube (dealing with creating casting molds and doing the whole curing process.)

One concern might be how the back of the octagon "tube" would get hit with so much more heat than the front, and that might cause an issue with differing rates of shrinking/warping from front to back, leading to gaps between the pieces of CFB. That's just my mind thinking of worst case scenarios though. Perhaps the answer there would be to burn off the binders and then apply zirconia coating.

Ye-ess, well you might be wanting to do zirconia anyway, as most affordable fiber board is only rated to 2300*F. The Ceramaterials glue is 2600* at least.

Peter's experiments with firm ceramic tubes do suggest your differential expansion concern is quite valid. Possibly one could just leave a few joints unglued ... if the thing still held together.

I can doodle a shiplap joint pattern that looks semi-feasible, but as I have learned with my (rough!) carpentry, any angled joint makes big, big differences from miniscule placement mistakes in angle cuts. But it ought to be plausible.

Straight joints would certainly be easier, but if one really needs the extra bearing surface

Another line of thought- CFB (board not blanket) donuts! Honestly not sure if this idea has merit or not, but I'll share it since we're brainstorming.
A standard 36x24x1 inch piece of CFB could yield you a dozen 8" circles. Cut 6" holes in those circles and you have a dozen rings of 6" internal diameter. Line those rings up and you have a tube.
Pros: rigid material that's easy/cheapish to procure.
Cons: rather wasteful of material and requires a LOT of circle cutting.
Unknowns: Would the rings lose integrity back where you would cut the port and compromise the ring shape?
Would gluing the pieces together cause the same warping issues between front and back?
Could you mechanically fasten the rings together with stainless threaded rod or zirconium wire instead of glue to allow for uneven expansion and contraction?

Yay, brainstorming.

It's 3 times as much material, and you'd have a lot of little bits left over to dispose of. But you saw that yourself.

If you wanted to do it this way, I'd think you'd solve the expansion issue the same way Peter has: make the tube, cut it in half lengthwise (you could even angle the cut to keep the top half from walking, since CFB cuts a lot easier than hard ceramics), then cut the top half again perpendicularly right over the high heat point (or leave that bit unglued). So if a 1" donut of CFB has structural integrity (which is a fair question), I don't see why it wouldn't work.

I'd think you'd glue everything except the 2 intentional expansion joints, to best improve integrity and cohesion, esp around the port. But I'd think adding a metal rod or wire would introduce a greater expansion problem than the material itself.

Okay. Received my fiberboard and glue order from Ceramaterials (very solidly packaged by the way, if with a pointless addition of styrofoam peanuts, yuck). About ready to start cutting, but I’d love if someone could give a look over my not-quite-standard measurements. Specifically, since I am fabricating the upper tube, I will have to change the top box to match.

System size 140 mm, 5.5” (going into 6” chimney and just trying to come up with a close match to existing materials and bricks)
Firebox 11” wide by 9” tall by 15” deep (279x228x381mm)
Port 1.68”x6.8” (43x173mm)

AFTERBURNER An octagon of internal diameter 5.88” facet to facet (150mm), external diameter 7.88,” total internal area 28.64 in2 (18,477 mm) and external area 51.44 in2 (33,187 mm).

Because the firebox is 15” long and I don’t have a 2” airframe between it and the glass but only 1” of fiberboard, the tube needs to leave 3.31” (84mm) between its end and the front wall of the top box. So I’m looking at a top box 11” wide by 15” deep, and a tube therefore 11.69” (297mm) long.
*That’s about an inch shorter than Peter’s prototype; does it seem reasonable?

TOP BOX HEIGHT
To leave 166% CSA in negative space around this octagon, I get a total top box height of about 8.25” (209mm). Right??

And then the EXIT PORT. Peter’s prototype, as I understand it, would give me a slit all the way across the 11” width of the top box, 2.39” (61mm) deep. I could do that. My only hesitation, as I look at the way it would interact with the bell I have planned, is that it would throw a whole lot of heat on one particular area of the upper bell, which would be set back nearly to that port. That spot could very well get enough concentrated heat to crack the flue liner I’m using. I’d feel safer about that if I could run the gases straight out the back, which to keep 1.1 CSA as per Peter’s proportion of exit port would mean leaving the back almost entirely open – two wunky shapes of 7.04” open height, and just a low 1.2” high restricting wall at the bottom.

I know Trevor’s Vortex did use a back exit rather than a top exit, but A) he was using different frictional resistance in his top box than this odd-shaped negative space provides and B) his final exit port was .78 CSA, not 1.1 CSA. Would I be setting myself up for the Great Unknown here? Once the bell is built, it may be *possible* to slide out the core for modification … but it’s kinda gonna be a pain in the neck. And of course it’s hard to test before the bell is built!

Speaking of, I will probably do a bell-less mockup/ green binder burn-off/ rigidizer curing pre-fire out in my driveway fairly soon here. It probably needs some sort of chimney to test at all, right? Any ideas on getting an oddly shaped exit port, whether a long skinny top port or a wunky back port, to join a chimney? Should I just cob it?

Woohoo, just about there...

April Wickes wrote:
System size 140 mm, 5.5” (going into 6” chimney and just trying to come up with a close match to existing materials and bricks)
Firebox 11” wide by 9” tall by 15” deep (279x228x381mm)
Port 1.68”x6.8” (43x173mm)

AFTERBURNER An octagon of internal diameter 5.88” facet to facet (150mm), external diameter 7.88,” total internal area 28.64 in2 (18,477 mm) and external area 51.44 in2 (33,187 mm).

TOP BOX HEIGHT
To leave 166% CSA in negative space around this octagon, I get a total top box height of about 8.25” (209mm). Right??

Your octagon CSA calculations are correct (according to an online calculator) But I show top box height a bit different.

5.88 ID octagon tube X 166% = 47.54 square inches of negative space needed in your top box
Make your top box 9"X11" and you get a 99 square inch box. Then subtract the total external CSA of your octagon (51.44) = 47.56 square inches.
Doesn't get much closer than that.

Peter checked my math/understanding of this a couple days ago on the donkey board, but I went off of the 160% he mentioned at the time.

April Wickes wrote:
And then the EXIT PORT. Peter’s prototype, as I understand it, would give me a slit all the way across the 11” width of the top box, 2.39” (61mm) deep. I could do that. My only hesitation, as I look at the way it would interact with the bell I have planned, is that it would throw a whole lot of heat on one particular area of the upper bell, which would be set back nearly to that port. That spot could very well get enough concentrated heat to crack the flue liner I’m using. I’d feel safer about that if I could run the gases straight out the back, which to keep 1.1 CSA as per Peter’s proportion of exit port would mean leaving the back almost entirely open – two wunky shapes of 7.04” open height, and just a low 1.2” high restricting wall at the bottom.

So if you have a system CSA of 28.64, would your exit port need to be 28.64 X 1.1 = 31.5 square inches? That is roughly a third of the 99 square inch back wall of your top box, which I would not consider to be "almost entirely open." But I have no idea if you can chose to shoot those gasses out the back versus making them bend 90 degrees to exit upwards. My guess is that the final 90 degree bend is essential to the flow of the system, but I hope you get a better answer than my guess.

April Wickes wrote:
Speaking of, I will probably do a bell-less mockup/ green binder burn-off/ rigidizer curing pre-fire out in my driveway fairly soon here. It probably needs some sort of chimney to test at all, right? Any ideas on getting an oddly shaped exit port, whether a long skinny top port or a wunky back port, to join a chimney? Should I just cob it?

When I do my own core mockup burn, I know some amount of "chimney" connected to the exit port is needed so I plan on using some scrap HVAC duct and just slap some scrap tin together as needed to get the port covered.

We're looking at calculating the negative space of the top box off of *TUBE* interior CSA instead of *SYSTEM CSA*?? That would certainly account for the discrepancy!

As for calculating the exit port out the back, I'm assuming the tube backs right up against the back and is closed. So I'm calculating only the odd shapes on either side. But I'll look again.

April Wickes wrote:We're looking at calculating the negative space of the top box off of *TUBE* interior CSA instead of *SYSTEM CSA*?? That would certainly account for the discrepancy!

Yes. Because as Peter explained to me, the thickness of CFB "tube" (much thicker than his ceramic tube) calls for factoring it in since it is occupying negative space that gas would otherwise expand into.

Yes, I get that we need to remove the total exterior area of the tube, whatever that winds up being, in order to leave the right amount of space for gas flow. Just missed that that "right amount left over" would be calculated off the afterburner interior dimensions (150mm) rather than the system CSA (140mm), which surprises me. But I too read Peter's reply in the Donkey thread as seeming to concur with you.

Hi April, how is it going?
Have you made the afterburner?
Why an octagon and not a more round design using more pieces?
Ceramic fibreboard is not the easiest stuff to work if you plan to make the half laps joints that you show, I dont think that will work very well?

Hello Fox, thanks for thinking of me.
I haven’t cut quite yet, since I’ve been gathering materials. Almost there, but still hunting stove glass.
I suspect you’re right about the over-complicated lap cuts. They were the suggestion of the glue manufacturer, to give extra grip, but I was indeed planning first to try fabricating one with straight cuts and see if it held. If not, I should have enough scrap left over to try again.
--
My larger problem is that, as Matt has kindly pointed out, when I look back over Donkey’s development thread, I find a range of proportions for the top box size.
In March of 2022, Peter said there was room for play in exactly how big the afterburner tube was as compared with system size:
>By the way, there appeared not much difference between a slightly narrower or wider tube in the development model. Anything between 4.92" and 5.91" seemed to work grossly the same. Now I come to think about it, the wider ones seemed to be a bit more forgiving. [on a 5.12” system size I believe]

But the figure most often given seems to be 115% system CSA, so that’s what I’ve been going with.

In February 2022, when Matt first asked for the Sketchup file, Peter’s accompanying note was:
>To round off, not only the proportions of the parts are important, also the open spaces. In short: the port is 50% system size and proportions 1 to 4, the tube's inside is 100% system size or slightly bigger, the space around the tube is 150% of system size and the exhaust of the core is system size again in the shape of a slit.

Going by the spreadsheet extracted from that Sketchup, what I’m actually getting is a top box open space of 150% tube CSA, 170% system CSA, because the tube is 115% of system. This is in line with Peter’s comment on August 11, 2022
>The csa around the tube should be at the very least 150% of the tube's internal cross section area.

And I believe 150% tube/ 170% system were the proportions used by the Loam Freemanship build??

But then just a few days ago, October 24, Peter said 160% of tube CSA, which, if the tube is 115%, seems to give me 194% system CSA!

So now I’m well and truly confused.
I do understand that the prototypes are still in development, and that the Sketchup file represented only one point in time of that development. It could even be that these stoves seem to work over a wide range of values, or perhaps this is a dimension best tweaked to the particularities of an individual mass and chimney. Or it may be that Peter’s further testing has concluded that a roomier top box gives best results; I have high respect for his exacting mind and perseverance toward perfection. But if so, I just missed the memo that the design had changed along the way.

Well I guess there is only one man on this earth who can really help with that!.

Just bare in mind that when you work with CFB is very soon becomes unstable and the fibres can loosed up around the cuts, so it is not easy to get tight accurate joints.
You could use a form, 150mm pipe, and build the tube over the form, then clinch the components together with stainless wire and pull out the form.
You could, as has been suggested, cut out rings and try to glue the rings together but from my own experience with glue it will form a rock hard joint that only really glues the first mm of fibres and can be easily split away from the main body.
You could make rings and send some stainless wire dont the length at 50mm spacings and bend over the ends.
Maybe a cardboard form could be coated with zircon or similar and the pieces fitted on top while wet, then the cardboard could be burnt out.

April Wickes wrote:So now I’m well and truly confused.

Sorry for the confusion, I tend to forget how I formulated my former comments exactly.
The reference figure for the csa is the chimney size, nothing else. My development model happens to be a 130 mm system, which is a little bit more than a 5" one. The csa of that particular chimney size is the starting point for the whole of the core. So, when you are building a 6" core, the cross section area of that one would be 28.27 sq. in. The firebox is tailored to that number, as is the port. In my case the exact size tube wasn't available so I used one that was slightly larger. The csa of the back fold (or negative space) around the tube happened to be 150% of tube csa, but at the same time about 160% of system csa.
The Loam Freemanship (liking my translation of De Vrijlemerij, a lot) built a 200 mm system, equivalent to 8", with the correct proportions throughout. It worked as intended so this is what they are building as standard size and proportions today.

In short: the 160% csa phrase is referring to the original system size, being 5", 6", 8" or whatever, nothing else. Just to let one know there is plus leeway in the size of the tube but the back fold should be also larger, accordingly.

Peter, thank you so much. That makes it all clear.

Since Permies doesn't host spreadsheets, I am attempting to make a scalable version of the DSR3 specs, as best as I understand them, public on Google Drive. I am an unrepentant Luddite, so please let me know if this does not work, or if something ought to be fixed.

Credit goes to Matt for extracting the original dimensions.

https://docs.google.com/spreadsheets/d/1kG219Qu3fmGGtTDFo4IfJOhCPk1RR8Z8/edit?usp=sharing&ouid=114630257550685626397&rtpof=true&sd=true

** I do note that changing that proportion to 160% of system CSA makes the top box almost exactly the same size as the exterior diameter of the 1" thick tube. This might present a challenge for some configurations.

April Wickes wrote:** I do note that changing that proportion to 160% of system CSA makes the top box almost exactly the same size as the exterior diameter of the 1" thick tube. This might present a challenge for some configurations.

That 160% of system csa should be around the tube, not including it. The top box would be much larger than the outside of the tube as a consequence.

The idea is that at the very moment the gases are coming out of the tube, room to expand is available. Shortly after that expansion has happened, the whole kaboozle need to exit through a slit that's system size again. That won't be a restriction during most of the burn, only at the point that a thermal runaway is imminent it will be. As such, it's an automatic self-regulating system that won't kick into an overfuel situation that easily. And beleive me, a full-scale overfuel situation (or thermal runaway, same thing) is as scary as a chimney fire.

Right. The issue arises when the tube available is much thicker than the one you are using.

So on a 140mm system with a tube of *exterior* diameter 200 mm (interior 150, 115% of system size), a top box with 160% system CSA negative space, minus the complete tube, would be 280 wide by 201 high -- just the height of the thicker tube.

It works out at this scale, but as it scales up according to present proportions, then somewhere around a 200 mm system, if someone could only find or fabricate a 25mm thick tube rather than your thinner walled pre-made tubes, they would reach a point where the tube exterior diameter is taller than a 160% space top box would be. It might not matter. It was just something I noticed.

April Wickes wrote:So on a 140mm system with a tube of *exterior* diameter 200 mm (interior 150, 115% of system size), a top box with 160% system CSA negative space, minus the complete tube, would be 280 wide by 201 high -- just the height of the thicker tube.

Hmmm... your calculation seems to be correct, I think I spotted a mistake in mine, I'm terribly sorry. According to the drawing of the 150 mm system there's 185% csa around the tube. What's more, the lower horizontal side of the tube is sank in the floor of the top box or so it looks like.

To solve this, you could cut off some of the tube in such a way there's a flat side where it lays on the box' floor. The Loam Freemanship did it this way in order to stabilize it. The opening shown in the picture being as wide as the port, in their case.

So... Are we shooting for 160% system CSA then? Or 185%? Which number do you like best?

April Wickes wrote:So... Are we shooting for 160% system CSA then? Or 185%? Which number do you like best?

Best go for 185% or more, just because it's the tested configuration. Originally I've had just the port cut out, one of my experiments was done with a 1"-walled ceramic fibre tube. Later on, I kept the same top box and flattened the bottom of the tube so more space became available. Later again, I tried the ceramic thinner-walled tube so I ended up with even more space.

Actually, I let it slip from the point where I used 150% csa onwards.

Okay. I have corrected the spreadsheet, and tweaked the other dimensions which were close but not exact to your recommendations (the port came out 48% instead of 50%, the exit port came out 110% instead of 100%. They are 50%, 100%, and 185% now.)

Anyone can feel free to use or copy or post this anywhere helpful.

https://docs.google.com/spreadsheets/d/1NtSG8JYFwjceHdosV2u81YJz48gw78qr8_DaigujjMo/edit?usp=sharing

April, your contributions on this subject are amazing. Do you have any results yet from your attempts at building an afterburner? I hope you haven't given up, would be great if you have succeeded, but if not I have an idea for procuring them that I could float. Craig

Thank you, Craig. I haven't given up, but I am waiting for spring, because I am not about to take apart my present stove in the middle of winter!

Fabrication of a tube from CFB has been ... sort of successful? The glue seems to have somewhat less adhesive power than a chewed up paper spitball and took weeks to dry. I haven't test fired it yet. Once the snow melts I thought I'd start a new thread on the build itself. But meanwhile, don't be coy about your idea! What have you got?

There is a guy over on proboards who managed to get a ceramic tube in the States.
I think April knows about him?

I have three half-baked ideas. Maybe tenth-baked.

The first was to circle back with either Ceramaterials or Danser, and ask what they would charge for a bulk order of 6" and 8" tubes. I want an 8"  It seems like there is enough interest/frustration/demand here and at proboards that we might be able to divvy up at least 5, maybe 10 at a time of each size, at a price that doesn't make people choke. I was thinking of taking a poll on interest. Shipping could be an issue, IDK, but if that were solvable I could buy the bulk order and then distribute. I'd probably give you a big discount in thanks for all your efforts, and charge a little extra to everyone else.

My second idea was to ask why we can't get the European supplier to ship here. Too fragile, import issues, price too high?

My third idea is to throw in the towel on CFB and learn how to make refractory castings. Maybe start a business for my son.

Anyway, hope I'm not wasting your time here, and good luck with your project.

Like I say, ceramic tube is available in the States, I dont have the complete address (i live 4500 miles away) but apparently they can be bought from Zartech in Portland.

Fox James wrote:Like I say, ceramic tube is available in the States

Yes, just at a silly high cost. Which is why I bounced the idea of square tube off of Peter and he encouraged me to try it. And Fox, your work with vermiculite board and zirconium coatings (and just recently those chamfer edge cuts in your Vortex afterburner) have further encouraged me to try square in the DSR3!

Unfortunately finding the time to work on it is the issue. Maddening since I have all the materials on hand now!

Well if you are prepared to try vermiculite, it would be easy to form a multi sided circular shape.
If you have a table saw you could cut the angles very easily and just use two big stainless screw clips to hold them together or just some stainless wire.
Skamo Vip 12 HT is the best vermiculite I have used, it is a full one inch thick and rated for 1200c.
One sheet cost me £50 and that would make loads of 10” x 6” tubes.

April Wickes wrote:

Fabrication of a tube from CFB has been ... sort of successful? The glue seems to have somewhat less adhesive power than a chewed up paper spitball and took weeks to dry. I haven't test fired it yet. Once the snow melts I thought I'd start a new thread on the build itself. But meanwhile, don't be coy about your idea! What have you got?

April, not to be nit picky, but may I propose, and perhaps I could go back far enough, for the answer. but...

1) So, if I am reading this correctly, CFB for the riser? and if so, what does "sort of successful" mean?
2) what density of CFB did you use?  as there is a huge range, it seems and does make a difference in the building of various configurations
3) Glue type? this really goes back to #2, as bonding low density vs High density can be uniquely different
4) And this is for all, but using bands on the exterior of a riser, work well if done carefully, but unfortunately are never seen again with the riser deep within the stove. with these on the exterior they are or should not be exposed to the extreme temps (I don't know if the heat eventually soaks through the CFB?

Just tossing out the question on the #4, as these are all 45 degree cuts and all the same size  in width, it will produce the size of ID (internal dimension) you desire based on the width of each piece,  in this case 7" with very little waste to the CFB, bands can be a lot wider and can make it easier

Hello Craig,
By all means, call and ask Ceramaterials or Danser what they would charge for a "bulk" order of 10 each, but my experience with them was that the price was prohibitive for smaller orders. In the range of $250-$300 apiece. I think when these people say "bulk" they mean more than 10, but I could be wrong. Good luck. The other thread following this topic is
https://permies.com/t/177125/rocket-mass-heater-riser-precast

Frankly, your third idea probably makes a lot of sense.

Scott,
Yes, the higher grade of CFB from Ceramaterials for the riser ( https://www.ceramaterials.com/product/ceramic-fiber-board-high-density/ ), and the only "glue" they had available (https://www.ceramaterials.com/product/ceramic-fiberboard-glue/ ). I followed their directions, which were to wet the board with water, then apply, then clamp. The instructions seemed to suggest it would be dry within 48 hours but it was more like two weeks and the water seemed to weaken the board itself. "Sort of successful" means it is no longer falling to pieces when I pick it up gently, but it certainly was at first and I have not yet test fired it. It doesn't seem very sturdy.

Your diagram is more or less exactly what I did, using a stainless hose clamp to hold it together. Since any exterior band must still be in the path of exit gases and temps, I'm dubious about it holding up. I have been able to remove the clamp from the tube without the tube falling apart but I'm not sure the tube alone will hold up either. Maybe it's sturdier after firing? I certainly hope so.

If a square afterburner works, that would save everyone a whole lot of trouble! I have no idea.

April Wickes wrote:

Scott,
Yes, the higher grade of CFB from Ceramaterials for the riser ( https://www.ceramaterials.com/product/ceramic-fiber-board-high-density/ ), and the only "glue" they had available (https://www.ceramaterials.com/product/ceramic-fiberboard-glue/ ). I followed their directions, which were to wet the board with water, then apply, then clamp. The instructions seemed to suggest it would be dry within 48 hours but it was more like two weeks and the water seemed to weaken the board itself. "Sort of successful" means it is no longer falling to pieces when I pick it up gently, but it certainly was at first and I have not yet test fired it. It doesn't seem very sturdy.

Your diagram is more or less exactly what I did, using a stainless hose clamp to hold it together. Since any exterior band must still be in the path of exit gases and temps, I'm dubious about it holding up. I have been able to remove the clamp from the tube without the tube falling apart but I'm not sure the tube alone will hold up either. Maybe it's sturdier after firing? I certainly hope so.

April, that helps a lot, clearly this an area that many have run into with little " It works well" being shouted. It does seem that we get to hear the good and the bad of various ways.  And if the good is Proven with hard runs as well as every day runs, that gives a far better warm and fuzzy feeling.  I will continue to test each of my steps.. reserving the final outcome for when things are run hard and with hopefully a known results.  Time will tell.

Thank you for your reports as you go along.
Scott

Hello April, and other US-based permies,

I've received a quote from Belgium for pallets of 10 afterburners, of the same type being used by the Loam Freemanship, who have worked with Peter van den Berg.

Sizes and prices (without shipping) were quoted as follows:

177mm ID x 305mm long, 30 mm thickness (approx. 7x12x1.2", good for a 6" system), 10 for 663 euros or about $71 each

240mm ID x 416mm long, 30 mm thickness (approx. 9.4x16.3x1.2", good for an 8" system), 10 for 838 euros or about $90 each.

I am looking into what it will take to get them delivered to my address near Reading PA. From there I could potentially ship them individually to others in the US, or hold them for pickup. I would provide them to you at my cost, I'm not looking to make a profit. Even if shipping triples the price to you, it still beats the best quote anyone has got from a US provider for vacuum-formed ceramic fiber tubes. And these tubes have a track record in Europe, with clay mixed in for added structural integrity, which as far as I know the US suppliers are not offering.

Please let me know what size and quantity you are interested in.

Also, if anyone has any pointers on arranging shipping across the pond, please let me know.

I'm going to create a new thread for this as I'm guessing there may be wider interest.

Can anyone tell me if Matts sketch up file on page one, is the latest and best diagram with dimensions we have available?
Thanks ….