Batchrocket.eu, information site

[terry]

May 6, 2016 13:44:52 GMT -8 @yasintoda said:

Terry, information on bells is always welcomed, so please continue and please share it !
BTW, on the site there is the paragraph :

"The 'simple' bell system, as pictured above, is very effective but has a singular disadvantage, all the mass is located within the single brick skin. This makes them 'large'. There are techniques available that can counteract that. Placing the combustion unit higher within the structure as opposed to floor level results in the storage of heat at a higher temperature because the gases need to sink lower than where the combustion unit is located. Additionally, internal structures (eg, columns) can be built inside the simple brick skin that can absorb, and then release later, heat. With such measures it is possible to reduce the size of bell needed using the simple 'single skin' method."

which is a bit unclear to me. What is the physical phenomenon that makes the bell hotter when the combustion unit is placed higher ? The stream of hot gases produced by the combustion unit isn't modified so i don't see the effect here.

Peter, on the chapter "Bell heater entirely of cast parts", you write about exit temperatures but do you have some infos on how hot does the top part of the bell become ? It would be interesting to see if a refractory material is needed or not.

Thanks !

I placed my thoughts on the bell mentioned in this thread in a new thread yas, donkey32.proboards.com/thread/2005/new-bell-hidden-advantage

If the next question is asked of me I cannot answer, that was Peters addition/amplification on the matter. My thoughts are, that if the combustion chamber is at floor level, then the lowest temp the flue gases can be are 'no lower than that of the combustion chamber', as they are on the same level and so there must be temp equilibrium at that physical location. If on the other hand the combustion chamber is (half a metre say) above the floor, and there is sufficient mass in the bell to absorb the heat, then for the flue gases to fall half a metre lower than the combustion chamber they mus be *that much cooler* than the temp of the combustion chamber. It must be that way else the gases will not fall below it. (forced air, eg fans, will change that, but one based on gravity and buoyancy alone ensures that will always be the case)

You most likely grasped all of that, so (to me again) extending that thinking, AND assuming the stove has not stalled, ie we have draw and it is operating, and for the same size bell, it must therefore have a higher temperature than if the combustion was on the floor. If we kept the temperature the same (rather than the size of the bell the same) then yes, the temp would not be higher but we would have stored more heat.

Anyways, my thoughts on that and not (necessarily) Peters.

[terry]

Peter, what a lovely heater!!! What wife would 'not want that in her home'?

that will need a day or two, so bear with me.

[peterberg]

May 6, 2016 13:44:52 GMT -8 @yasintoda said:

What is the physical phenomenon that makes the bell hotter when the combustion unit is placed higher ? The stream of hot gases produced by the combustion unit isn't modified so i don't see the effect here.

I am not sure what the reason is why the gases need to loose more heat when the exhaust is lower than the firebox. I guess it has something to do with the sliding scale of no heat extraction at all when the gases are exhausted at the top of the bell on one end, and as low as possible at the other end. Probably this scale isn't linear as well, but exponentional instead. That would mean when the gases are exhausted halfway in the bell more than half of the heat is sent out to heat the birds. And the lower the exhaust, progressively more heat is extracted. But it's still a guess.

May 6, 2016 13:44:52 GMT -8 @yasintoda said:

Peter, on the chapter "Bell heater entirely of cast parts", you write about exit temperatures but do you have some infos on how hot does the top part of the bell become ? It would be interesting to see if a refractory material is needed or not.

Our heater is heavily insulated on top so it will get quite hot there. Let's put it this way: when running at full tilt the riser is spewing hot gases at temperatures as high as 900 C (1650 F). Most of the time the top gap between riser and bell ceiling is about 30 cm (1'). Normal concrete starts to break down long before that level of temp is reached, so it won't be safe to use unprotected sidewalk pavers to name just an example. Reinforced concrete isn't safe as well, the steel bars will expand more than the concrete so it will be torn apart.

[peterberg]

May 6, 2016 14:30:32 GMT -8 terry said:

Peter, what a lovely heater!!! What wife would 'not want that in her home'?

that will need a day or two, so bear with me.

Thanks, my life long girlfriend thinks it is nice so I was allowed to bring it into the house.

Take your time to scan through the text and see where corrections are necessary. Tomorrow I'll start the next article which isn't about one of my heaters so this is asking for more effort, presumably.

[terry]

May 7, 2016 8:01:56 GMT -8 peterberg said:

May 6, 2016 14:30:32 GMT -8 terry said:

Peter, what a lovely heater!!! What wife would 'not want that in her home'?

that will need a day or two, so bear with me.

Thanks, my life long girlfriend thinks it is nice so I was allowed to bring it into the house.

Take your time to scan through the text and see where corrections are necessary. Tomorrow I'll start the next article which isn't about one of my heaters so this is asking for more effort, presumably.

I was going to make a stab that this heater appeared on your dutch forum, guess I got that part right. The good news is that any 'deeper' question can be answered by intimate knowledge. Well done, a beautiful final product.

It must have been fun putting that pic next to mine! You probably felt very dirty by association haha. I must at least clean mine up, sweep the floor etc just so I don't hang my head in shame and give a better pic for the site. On the to do list. I spoke with my daughter who does a lot of video editing and we will do that little video that has been spoken of, which thread it was I no longer remember. Probably this thread.



'Bell heater entirely of cast parts

This is a batch rocket variant designed and built in 2015, entirely consisting of cast refractory parts. The design is entirely geared to just a few different parts which are repeated a lot of times. In such a project, the financial investment in molds is very high, this way the positives are small in number and the rubber production molds are being used very often.'


'This is a batch rocket variant designed and built in 2015, consisting entirely of cast refractory parts. In such a project, the financial investment in molds is very high so much thought was put into devising a way to use as few unique parts as possible, thereby cutting down on the number of unique molds. As can be seen there are just a few parts repeated many times, the same few molds being used over and over as required.'



'The mantle, made of special produced terracotta-colored castable refractory, consists of 28 parts which are shaped all the same. Two parts form a block with double-sided dove tails, one on top of the other and centered by nocks. These parts are done intentionally this way in order to keep assembking of the heater a managable job. Between every block of two pieces and the next there's a horizontal crevice to assure every block rests on the dovetails only. The mantle is kept in one piece by gravity this way, without any means of securing by fasteners or such.'

Mantle, lets call it the outer skin, or visible face or any term you prefer. Mantle, tho understandable, would be very rarely used in this context. It is a bit tricky to work out exactly what is being said, so check what I write first and foremost for errors in understanding, the english is secondary right now.

Let's try 'The outer finished face is made of specially ordered castable refractory in a terracotta colour, and consists of 28 identical parts which interlock with each other (for those counting in the picture-a good way to conceptually grasp it, the last seven pieces form the rear wall behind, in other words four walls of seven pieces each). The interlocking dovetails are seen at the corners, showing how the use of the same shape placed 'up and down' alternately manage to interlock with each other. An added benefit of interlocking shapes like this is that it makes the construction easier as each piece is an easily handled and assembled part. A close look at the dovetails in the picture shows the slight, but important, angle they are cast at. This ensures that they lock together tightly, indeed force the dovetails to close. The horizontal 'seams' do not bear the load, the dovetails do. That allows gravity to do the job of holding it all together, they are not glued, mortared or fastened in any way.'     






'The door is made of steel T-profiles and hinges in a frame made of steel U-profiles with the open side left and right, top and bottom. The mantle pieces are 50 mm (2") thick and fits in the U-profile in such a way that the whole frame is kept in place by the mantle pieces. A simple tilting valve without hinges is mounted in the door which provides for the primary as well as the secondary air supply.'    How about '.... with the open side of the U profile facing outwards all around. This allows the outer skin pieces (of two inch thickness) to fit into the open U shape which then supports and locks the door into place. (this can be seen more clearly in another photo below)






'The firebox is identical to the description of "4: Cast core" in the chapter "Designs" and consists of 3 separate and different parts. The left and right halves of the combustion chamber each aren't higher than the port and form an entirety with the lower part of the riser.'              '...3 separate and different parts, the bottom left and right parts together form the port and base of the riser and the third part completes the combustion chamber when placed on the bottom pair. See assembled construction picture later. The top part locks into locating lugs as seen below.'





'The part above the port takes the shape of a simple three-sided box which centers itself with nocks on the lower parts. The core rests on a welded steel frame incorporating adjustable bolts in three directions to obtain correct and secure placement inside the bell. This frame is also holding the left and right halves together by force of gravity (again). Both halves are supported by the frame's left and right outer ridges but not in the middle. As a consequence, both parts have the tendency to fall in each others' direction so the vertical seam will be held closed at all times.'   Covered/included just now, so redundant.  The rest reads fine.





'The upper part of the riser do consist of a vacuum formed superwool circular tube which rests virtually free on the core base only held in place by a couple of short centering pins. Done in the most simple way: a couple of small holes drilled in the refractory and a couple of shortened nails inserted.'  just 'consists'. The rest is more than good enough.





'The inner walls of the entire bell are built out of two different blocks which are repeated both 24 times. The wall blocks are provided with tongue and groove, at both ends as well. Together with the red mantle the size of the whole thing is 98 x 98 x 210 cm (3.22" x 3.22" x 82.7"). and it weighs in at a little bit more than 2000 kg (2.2 US tons). One ring consisting of 4 parts is 150 mm (5.9") high and 120 mm (4.7") thick. Every ring is turned a quarter horizontally relative to the previous one, thereby locking each other in place. The sealing consists of adhesive braided glass tape of 10 mm wide and 4 mm thick (0.39"x 0.57") sticked to the tongue side and by the weight of the parts it will press down to half the original thickness.'

'The internal wall of the bell is built out of two different blocks, repeated 24 times each (naturally a slight modification to the exact duplication of these two parts occurs where the exit flue and firebox appear, other than that they are, like the outer skin, a simple repetition of parts). Note the tongue and groove seen in the picture, and careful inspection will show the tongue and groove exists at the ends of the pieces as well. The finished external dimensions of the heater are 98 x 98 x 210 cm (3.22" x 3.22" x 82.7"), and all up it weighs in at a little more than 2000 kg (2.2 US tons). One layer consists of 4 parts and is 150 mm (5.9") high and 120 mm (4.7") thick. Every layer is turned a quarter horizontally relative to the previous one, thereby locking each other in place. The layers are sealed with adhesive braided glass tape 10 mm wide and 4 mm thick (0.39"x 0.57") stuck to the tongue side. The weight of the parts will press the seal down to half the original thickness.'





'Openings have been made in the inner skin of the heater to accomodate the edges of the firebox' front. The firebox will be held in place at the front side by this, de rear side will stay centered by the adjustable support frame. The left and right sides of the inner skin's opening are chamfered at a 45 degrees angle in order to obain space for a wider door and a better view of the fire. The next photo shows how the mantle is assembled.'

'The size of the opening in the inner skin is determined by the outer dimension of the firebox/combustion unit. In this way the front of the firebox is supported by the inner wall, the rear of the firebox is supported by the adjustable metal frame pictured earlier. [is the firebox sealed with superwool where it enters the inner wall?] The left and right sides of the inner skin's opening are chamfered at a 45 degree angle in order to obtain space for a wider door and a better view of the fire. The next photo shows how the mantle is assembled.'  outer skin? whatever term you feel best. Maybe add something like 'The detail about fixing the outer skin in the U shaped steel is clearly seen in this photograph.' Just tying it back in to what was said earlier.





I'll put a break in here, will prob get back to it before you wake but if not that is the explanation.

[terry]

'The configuration of the secondary air supply which generated the best results has been found out through a lot of experiments. Twelve different combinations have been tested with several sizes of the horizontal and vertical tubes. The slits and openings are tested in a number of distinct ways also. The next photograph shows five of those combinations. All of those are affected by corrosion, some more than others. The model which will be in use in this particular heater is the second from right, the definite version sports a slightly shorter vertical tube. The vertical part of the tube in the middle is a round tube and as such is similar to the pre-port tube of Matt Walker's.'  Did you mean 'definitive' version? If so, it still does not quite fit. Do you mean that the 'final version used has a slightly shorter vertical tube'? If so, maybe just put those words in. If I missed your meaning let me know.


'Twelve different combinations have been tested with several sizes of the horizontal and vertical tubes. The slits and openings are tested in a number of distinct ways also.' Maybe 'Twelve different combinations were tested, variables such as horizontal and vertical tube sizes along with the shapes and lengths of the air outlets were investigated' or some such. Basically, no need for a separate second sentence, kinda confuses it a bit.



'The air inlet in the door isn't placed directly at the fire level but instead of that quite a bit lower. All the air which is entering is icy cold as compared to the combustion chamber environment, so the air will sink down immediately. Due to this effect the secondary supply, being situated low, will be optimally fed at all times. The hotter the environment, the more air is streaming into the floor channel. The duct itself is heated up by the fire which in turn pre-heats the incoming air. The triangle shaped opening at the top of the vertical part injects the air at halfway height in the port.'                            Suggest 'The secondary air supply is fitted very low in the firebox, much lower than the level of the fire. The primary air inlet (via the flap on the door) as well as feeding the main fire also feeds air into the secondary air channel situated directly behind it. The primary air inlet too is situated low in the door (see photo). As the temperature of the air entering is very much lower than combustion chamber environment it will naturally remain low (cold air falls, in this case 'cold air stays low') and therefore the secondary air tube is fully supplied with air at all times.'  Not sure I did too good a job on that one, feel free to modify. The main point missing originally (I think) was the location of the P channel, that was what i was trying to fix. The rest should follow on, it seems clear enough.



'At the front side of the combustion chamber a steel plate is mounted which diverts the rest of the air upwards. Because of this provision the fire burns a bit more calmly and the chance to get a hefty CO-spike is reduced. See for this provision the relevant drawing in the "Designs" chapter.'        Boy, I don't recall that bit in the designs chapter, I must be going senile. EDIT, just had a look, and towards the bottom is a sketchup that looks like it might be what you are referring to? (section 5) Well maybe not going senile as it was not discussed (phew).


'For a temperate sea climate this is a large heater equipped with a surprisingly small combustion chamber. This firebox can be loaded quite compact, all the fuel is in the same direction from front to back. Na log cabin style, campfire style or criss crossing at all, just straight with very few openings between the pieces. One full load in this 150 mm (6") system size heater would weigh in at about 6 kg (13.2 lbs) bone dry medium sized birch logs. The best results with this loading style and floor channel as drawn will be obtained by a top down burn. Lit at the top of the whole batch, as far back as possible a small kindling fire will eat through the whole pile by itself.'

'This firebox can be loaded quite compact'          did you mean it can be crammed full? If so, maybe 'It does no harm to fully load the firebox with wood, all laying front to back.'

'Na log cabin style, campfire style or criss crossing at all, just straight with very few openings between the pieces.'         I presume you meant 'Not' log cabin style? Heck, I did not even know there was a log cabin style! Campfire style was readily envisaged tho. Anyways, this seems to emphasise the previous sentence, so how about 'With this design it is not needed to employ 'tricks' like crisscross sticks or 'camp fire style' wood loading (used to lessen smoke and aid burning by incorporating lots of air in normal heaters). Such methods are not only no longer needed, but lessen the load capacity. Just load the box, wood laying front to back and it will naturally have enough air'.   [that is if I got the reason right for the other loading ways, and that is if I got it right it is not needed in this design] If all of that was correct, then the previous sentence (It does no harm to fully load the firebox with wood, all laying front to back) might not be required.


'Lit at the top of the whole batch, as far back as possible a small kindling fire will eat through the whole pile by itself.''  Maybe just change 'Lit...' to 'When lit...'      and change the comma position           ' When lit on top of the whole batch as far back as possible, a small kindling fire will eat through the whole pile by itself.'



' The chimney temperature, measured in the heart of the chimney pipe won't get higher than 80 degrees Celsius (175 F) when the heater is started cold.'   centre (or center)



I think that is it, this one for some strange reason seemed quite difficult. Which has me curious I must admit. So I reserve the right to revisit it once any changes have been made, most likely things will jump out at me that I cannot see at the moment!

Let's hope not.

I would like to ask some questions of your heater later if you don't mind Peter, will leave it for now tho.

[peterberg]

Hi Terry,
This one is crammed with novel details, some of those aren't easy to explain. You've got a quite good grasp of the gravity tricks but some of the finer details can be made clear by the 3D drawing only. As long as it doesn't rain questions here we are doing a good job. Please read the whole article again, it turns out to be quite a popular item.

The flag counter is counting a fair number of new visitors every day. Yesterday 31, today is a record already, 64 new visitors up till now. The flag count is up from 37 countries yesterday to 43, 12:21 hrs middle European summer time, another 11+ hours to go. I am in front of my computer with a big grin on my face...

And thanks, you are a great help.

[terry]

a few bits of tidying up

'. Every other horizontal 'seam' do not bear the load, the dovetails do. That allows gravity to do the job of holding it all together, they are not glued, mortared or fastened in any way.'

'The horizontal seams' (I am sure, but not certain as it is not mentioned that we do not need to worry about escaping gases as the inner construction takes care of that)




'The firebox is identical to the description of "4: Cast core" in the chapter "Designs" and consists of 3 separate and different parts. The bottom left and right parts together form the port and base of the riser and the third part completes the combustion chamber when placed on the bottom pair. See assembled construction picture later. The top part locks into locating lugs as seen below.'   Better if only 'The top part locks into the locating lugs seen below.




'The core rests on a welded steel frame incorporating adjustable bolts in three directions to obtain correct and secure placement inside the bell. This frame is also holding the left and right halves together by force of gravity (again). Both halves are supported by the frame's left and right outer ridges but not in the middle. As a consequence, both parts have the tendency to fall in each others' direction so the vertical seam will be held closed at all times.'      Possibly it might be worthwhile to add 'Note the steel frame does not support the core all of the way to the front, a small section of the core is unsupported by this frame. This will be explained later.'      Or not.


'The upper part of the riser consists of a vacuum formed superwool circular tube which rests virtually free on the core base only held in place by a couple of short centering pins.'  I think 'freely' would be better.



'The finished external dimensions of the heater are 98 x 98 x 210 cm (3.22" x 3.22" x 82.7"), and all up it weighs in at a little more than 2000 kg (2.2 US tons). One layer consists of 4 parts and is 150 mm (5.9") high and 120 mm (4.7") thick. Every layer is turned a quarter horizontally relative to the previous one, thereby locking each other in place. The layers are sealed with adhesive braided glass tape 10 mm wide and 4 mm thick (0.39"x 0.57") stuck to the tongue side. The weight of the parts will press the seal down to half the original thickness.'   

 It is not super important, but after re-reading this 'row' would probably work better than 'layer'.  Back to my earlier question above, re gas tight, we seal between with the tape, which is compressed, so we have a seal between rows/layers. What about the ends/corners, even if tape were used there they would not be compressed.

[Just while I think of it, when the modifications in the castings are done-exit holes, firebox and door needs-I am sure you did not try and cut cast refractory to accomplish this! Does that need to be made clear? OR do you think a competent handyman would know this already.]





'The size of the opening in the inner skin is determined by the inner dimension of the firebox/combustion unit. The walls of the firebox are in a rabbet of the inner skin. In this way, the front of the firebox is supported by the inner wall, the rear of the combustion core is supported by the adjustable metal frame pictured earlier. The perimeter of the firebox opening is sealed with superwool in the inner skin's rabbet/groove.'

Hmm, we jumped straight into this, think that was my fault. We need to segue into or make it clear we are talking about a new aspect, as written it just kinda 'appears out of nowhere'. How about 'In order to allow the firebox to reside within the structure, the opening for the firebox must be sized correctly and the opening is such that the front of the firebox is supported snugly all around by the inner wall. This explains the point noted above when discussing the steel frame and why it did not extend all the way to the front of the combustion core. To accommodate the usual superwool sealing, a rabbet or groove is made in the casting. That way a gas tight seal is made whilst mechanically the core is supported by the inner wall.'




'The left and right sides of the inner skin's opening are chamfered at a 45 degrees angle in order to obain space for a wider door and a better view of the fire. The next photo shows how the outer skin is assembled. The detail about fixing the outer skin in the U shaped steel is clearly seen in this photograph. There's also a superwool seal between the door frame and the inner skin, as is visible.'       Doh!  I saw the subtle details of the dovetails, missed this. Double doh.



'The configuration of the secondary air supply which generated the best results has been found out through a lot of experiments. Twelve different combinations have were tested, variables such as horizontal and vetical tube sizes along with the shapes and lengths of the air outlets were investigated. The next photograph shows five of those combinations. All of those are affected by corrosion, some more than others. The model which will be in use in this particular heater is the second from right, the final version used has a slightly shorter vertical tube. The vertical part of the tube in the middle is a round tube and as such similar to Matt Walker's pre-port tube.'    'best results was found through a lot of'           'were'           'vertical'



'The secondary air supply (the floor channel) is fitted in a recess in the firebox floor, in fact the fire is on top of it. The primary air inlet (via the flap on the door) as well as feeding the main fire also feeds air into the secondary air channel situated directly behind it. This primary air inlet too is situated low in the door (see photo). As the temperature of the air entering is very much lower than combustion chamber environment it will naturally remain low (cold air falls, in this case 'cold air stays low') and therefore the secondary air tube is fully supplied with air at all times.'   This is another detail I missed yesterday, one of the photos above (has the bike in the background, with the superwool riser) clearly shows the p channel in situ and where it is positioned in the box. Perhaps refer them to that photo if you think it helps.


Think that is all the housekeeping for the moment.  A couple of questions about the build itself that occurred to me. Firstly, as said before, congrats, very beautiful indeed. The cast colour is a really nice touch, something that I would not have thought of probably. But a good trick to remember.

Ok, why all of castable??  Dunno in your neck of the woods, but the price difference between castable and concrete has gotta be four times or so??  Sure, use castable where needed, by why all??

Another point that occurred to me, this will radiate heat 360 degrees, whilst what would be optimum would be 180, well what I mean is the rear wall is 'wasted' as it is against the house wall. Did you feel it not necessary or it would not be beneficial to change it in some way to optimise the radiation pattern of the heater? Conceivably it might have saved some money so that makes me curious about why you did not do so. Maybe it 'just does not work' trying to favour one direction over another.

[peterberg]

Will do the housekeeping tasks tomorrow so this is to answer the questions.

All the same castable is to save time, a lot of time in fact. The tools for casting, like the through and the paddlemixer need to be cleaned after each casting session. In case the casting guy used two different types of concrete on the same day which shouldn't mix he should have done the cleaning twice every day. Which means 26 times of cleaning is taken out of the equasion now by using the same material.

Apart from that, this castable refractory can be de-molded in 8 up to 12 hours, depending on environment temperature. Normal concrete need a few days in the mold otherwise it is too vulnerable to abrasion, so this saves waiting time again. Eighty-five percent of the heater's cost is plain and dusty work, only fifteen percent is material.

And last but not least: properly mixed, vibrated and cured refractory is very nice material, smooth, hard and not dusty at all.

The rear wall isn't wasted in terms of heating. There's a 10 cm gap between the heater and the wall, and lots of insulation in the special plaster board wall as well. In the gap a convection current starts to rise which is contributing to the heating of the house. Not as efficient as radiation as you found out yourself, but heating nevertheless. It would be better to have the heater in the middle of the room but my GF didn't agree to that so it is placed along a wall as the alternative.

[peterberg]

Hi Terry,
I added "The straight sides of the parts are locked relative to each other with two "ball and dimple" locating pins." because in my view it wasn't clear how this was achieved.

About the tongue and groove construction I added earlier: "Note the tongue and groove seen in the picture, and careful inspection will show the tongue and groove exists at the ends of the pieces as well."
And in the part about the tape I added now:"The same goes for the vertical ends, tape on the tongue and pressure to compress the tape and to lower the part into place as the photograph shows. Note the groove is 2 mm deeper than the tongue is high to provide space for the tape, each block is resting on the sides, not on the tongue."
This should be adequate to make things clear.

About the seal between firebox and inner skin I changed some sentences slightly and added:"This seems complicated but the supplied SketchUp drawing will make this clear no doubt."
This heater has a lot of small design details which aren't obvious but still important to the construction. In order to avoid confusion I tend to point to the drawing when things aren't clear.

The sentence about the seal between steel door frame and inner skin wasn't there before, I added it for clarity.

Same goes for the placement of the floor channel, I felt you hadn't the right picture. I added a pointer to the core as well.

[terry]

' Every other horizontal 'seam' do not bear the load, the dovetails do.'  'Every other..' does not work. I am not sure part you want to stress here, why you kept that wording? (if I knew which part you felt needed to stay I could re-write it to suit)  Would 'The horizontal faces do not take the load, the dovetails do.' suit you?


'The firebox is identical to the description of "4: Cast core" in the chapter "Designs" and consists of 3 separate and different parts. The bottom left and right parts together form the port and base of the riser and the third part completes the combustion chamber when placed on the bottom pair. See assembled construction picture later. The top part locks into locating locating lugs as seen below.'        I do feel 'The top part locks into the locating lugs seen below'    no 'as'      works much better.  Double word.




'The size of the opening in the inner skin is determined by the inner dimension of the firebox/combustion unit.'   I still feel this is very abrupt. Maybe a slight modification is the easiest (rather than my clumsy attempt yesterday)     'The size of the opening for the combustion chamber in the inner skin is determined by the inner dimension of the firebox/combustion unit.'



'The secondary air supply (the floor channel) is fitted in a recess in the firebox floor, in fact the fire is on top of it. See the photo of the completed core when you're unsure about where the floor channel is situated.'             Just 'if'


 

[peterberg]

I'll do the house keeping work tomorrow, for now I'll try to explain something important about the dovetail outer skin blocks.

When you see the picture, the horizontal lines between every two blocks are not the same. There's a straight line where two of the blocks are joined to form an assembly which has on both sides double sided dovetails. This two blocks, forming a twin, are just resting on top of each other, there's no space between them. In order to avoid the risk of sliding off there's a pair of ball and dimples to keep them from sliding apart. This moving relative to each other is very real, caused by the expanding and retracting of the different parts. They can literally "walk apart", which is prevented by the locating balls and dimples.

The other line or seam on the top and bottom of the twin pair is intentionally open by as much as 1 or 2 mm. This is done to make sure the twin pair of blocks is resting exclusively on the dove tails. So it is correct to say that every other seam the dovetails will bare the load, the other one the horizontal face take the load. So, the load is alternating between the dovetails and the face. The problem is now how to explain that in a couple of sentences in plain English, because I suspect you didn't understand what was meant with this.

Hope it is clear now, otherwise I need to take a picture of a spare part and post that to clarify.

Also, I presume you don't understand exactly how the edges of the firebox are supported by the inner skin. This groove or rabbet, whatever it is called is perfectly visable in this picture below, derived from the drawing.

[terry]

Forgot to thank you for the answers to my questions, yes you are right, (nowadays at least) labour is usually the biggest cost in a job, the extra cost of the refractory is more than offset by the saving in labour...even if it is your own I might add.

Yes, we (or I) are very definitely hitting an explanation barrier at the moment, probably partly caused by language. Firstly, pretty sure I am up to speed with the inner skin and firebox. I understand that the inner blocks rest on each other, NOT on the insulating tape between. That compresses only slightly-or 'enough'- in the 'groove' between the blocks, the load is taken by direct contact between the blocks.

(just talking thru this out loud, that way we can converge). I note that the outer skin does not have these grooves. I wonder if we are having trouble with 'horizontal lines'? I see only one horizontal line, you seem to be talking about two.

So lets talk about layers. There are seven layers, each layer made up of four interlocking blocks. These four lock together at the dovetail (which I suspect was your second horizontal line). That is the reason for the very slight angle of the dovetail, gravity forces them together due to that wedge action.

These layers are naturally stacked on each other to go upwards. The gap between these layers is the single horizontal line that I see. They lock together with the ball and socket method, no glue or other fixings.

I'll stop here for now to see if we are now on the same page. If we are, and I suspect we are, yes it will be tricky to explain in a few sentences.

Boy, I can see accurate repeatable work is required here!

A quick query to end on here, and I kinda got my own heater in mind whilst I ask this, no provision for ash removal after the riser, or indeed flue cleaning? That must have entered your mind, and was ruled out, can you explain the thinking on that one?

[peterberg]

May 9, 2016 13:55:16 GMT -8 terry said:

Yes, we (or I) are very definitely hitting an explanation barrier at the moment, probably partly caused by language. Firstly, pretty sure I am up to speed with the inner skin and firebox. I understand that the inner blocks rest on each other, NOT on the insulating tape between. That compresses only slightly-or 'enough'- in the 'groove' between the blocks, the load is taken by direct contact between the blocks.

Excellent! Nail on its head.

May 9, 2016 13:55:16 GMT -8 terry said:

I note that the outer skin does not have these grooves. I wonder if we are having trouble with 'horizontal lines'? I see only one horizontal line, you seem to be talking about two. So lets talk about layers. There are seven layers, each layer made up of four interlocking blocks. These four lock together at the dovetail (which I suspect was your second horizontal line). That is the reason for the very slight angle of the dovetail, gravity forces them together due to that wedge action. These layers are naturally stacked on each other to go upwards. The gap between these layers is the single horizontal line that I see. They lock together with the ball and socket method, no glue or other fixings.

Nearly there. The layers have alternatingly front+rear and left+right balls and sockets to keep them in place, these horizontal faces are resting on each other.



Where those ball and sockets are NOT, there's a small gap of 2 mm between the layers so all the load is on the dovetails. This is done to be able to have the same shape throughout the whole thing and maintain a stable construction. This open gap is a crucial point, otherwise the thing won't be stable at all. See the picture below. 

May 9, 2016 13:55:16 GMT -8 terry said:

A quick query to end on here, and I kinda got my own heater in mind whilst I ask this, no provision for ash removal after the riser, or indeed flue cleaning? That must have entered your mind, and was ruled out, can you explain the thinking on that one?

There's no such thing as an ash door or sweep door in this design. Sweeping the chimney is carried out by removing a piece of stove pipe complete with elbow so the chimney stack will be attainable. All the fly ash will accumulate on the bell's floor, it can be removed through the exhaust hole.

[terry]

Aaaah, bingo. 'Houston, we have lift off' methinks.  Peter, there is a saying in english, presumably something similar in dutch, that goes 'A picture is worth a thousand words.' I think that even if this is the first you have heard of it, it is pretty self explanatory. Funnily enough I DID notice the rather odd alternating slight gap that came and went, really only noticeable when viewed directly head on (in other words the gap is slight enough that it disappears if viewed 'from above or below') but did not give it much of a second thought.

I can now see why you insisted on 'every other'...meaning the dimples do not appear on every piece, but alternately, every other. But trust me, as written it does not make sense. At least I now know where you want to go!

The best solution would be to include that sketchup illustration, BUT (I think) I know why that is not the way to go. To my way of thinking, that would be delving too deeply into a single example, one that I might add or wager will never be built by anyone else. To my way of thinking (again) it is merely another example of how far, or how versatile the finished heaters can be, limited only by experience, skills and imagination.

I mean, I can tell you right now I would balk at building something that complex, and I do consider myself pretty handy. At the very least I would be doing many many trials with plain old concrete to work out the bugs in putting it together!

So to add much more to this section seems to be overkill or misdirection.

BUT, we do need to clean this bit up.

I tried downloading the sketchup file, but I don't have the required version so could not view it. Can I ask, is that detail you posted readily seen in the sketchup, or did you specifically have to 'make it happen' for the post? If that detail is readily available in the download, we can take advantage of that to help clean this up.




'An added benefit of interlocking shapes like this is that it makes the construction easier as each piece is an easily handled and assembled part. A close look at the dovetails in the picture shows the slight, but important, angle they are cast at. This ensures that they lock together tightly, indeed force the dovetails to close. Every other horizontal 'seam' do not bear the load, the dovetails do. The straight sides of the parts are locked relative to each other with two "ball and dimple" locating pins. All this allows gravity to do the job of holding it all together, they are not glued, mortared or fastened in any way.'

Lets use the fact that it is complex and can only be fully understood by studying the sketchup file in the following manner, or similar.  'An added benefit of interlocking shapes like this is that it makes the construction easier as each piece is an easily handled and assembled part. A close look at the dovetails in the picture shows the slight, but important, angle they are cast at. This ensures that they lock together tightly, indeed force the dovetails to close. Not seen are 'ball and dimple' locating pins that locate and secure each layer to the other layer. Knowing that, and referring to the picture it is clear that each layer is locked together as a unit by the wedge action of the dovetails, and each separate layer is locked to the next by the 'ball and dimple' pins. All this allows gravity to do the job of holding it all together, they are not glued, mortared or fastened in any way.  For full and complete details see the sketchup file located here blah blah'

I think something like that cleans it up nicely.

The other housekeeping mentioned still applies.



Funny how we are limited by our own experiences, my flue has no option but to be hidden behind the mass. So a simple expedient like simply removing the elbow to clean did not occur to me! Thanks. Another question. As this is (presumably) your 'best, most preferred' expression of all you have learned about rocket stoves is it fair to conclude that this is the most efficient design? I ask because you have had quite a few explorations paths, including the siphon from way back when. One would presume if the siphon provided better performance you would have built it, so what were/are you final conclusions about the relative merits of this 'style' versus any of the others you have threads about?