#21  
Old 05-31-2013, 08:21 PM
Peasant
 
Join Date: May 2013
Location: Brisbane, Australia
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Default Re: Brooky Tom's 900mm build Brisbane

Time to start above the bench slab. Bought firebricks yesterday (230x115x75) and a have also obtained hearth slabs 450x300x50. I have more than I need for the hearth so may also use them on the bench outside of the oven. I assume I will need to allow expansion jointing if they run up against or near to the hearth bricks. Does the vermiculite perlite mix act like an expansion joint?
After much deliberation I've decided to stick with the 900mm build on my 1500x1750 slab. I plan to allow for the following outside of the inner circle: 115 for brick, 75 for blanket, 25 for a vermiculite/perlite "smoothing layer", 25 for render and 25 for contingency -so that makes 265mm from outside of the slab at back and sides.
I'm writing this so the good advices from forum folk I've had before can correct me at any obvious errors.
If I base the circle from the back (as above) that leaves me 1035 to the front lip of my slab.
For the inner arch position, with a 475mm width, I assume I find where 475 width meets the inner circle and that will be the back of my inner arch? Inner arch to be 115 wide. That line seems to be about 390 from the centre, and hence 645 from the front. My big question then is that too far back to allow easy use of the oven? I've never used such an oven so appreciate advice as to how far one can stretch back easily to move the food and fire etc.
I can easily bring the oven forward, so the balance is between space at the front (in the oven landing and the vent landing) versus whatever problem there might be as queried above.
I plan to take up the advices to date re the water sealing; and extending the hearth bricks out under the first row of oven bricks (floating).
So next step is to mix and set the verm/perlite "leveling/sealing" area; then the calsil. Also have to make the forms for the inner circle and dome, and arch supports once I work out the arch configuration with the bricks I have. I am aware of the good advices on the arch form piece construction.
My brotherinlaw's brick saw is available but don't think it will have the fancy cut facility some have employed but can do an angle in one plane.
Lots to do. Will start on the forms while I wait and see any help with the question whether 645mm is too far back for the back of the inner arch? Thanks

Last edited by Brooky Tom; 06-04-2013 at 05:19 AM.
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  #22  
Old 05-31-2013, 08:23 PM
Peasant
 
Join Date: May 2013
Location: Brisbane, Australia
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Default Re: Brooky Tom's 900mm build Brisbane

That second time I wrote 475 came out as 4475. Since edited (thanks Chip)

Last edited by Brooky Tom; 06-04-2013 at 05:20 AM.
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  #23  
Old 05-31-2013, 09:10 PM
cobblerdave's Avatar
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Default Re: Brooky Tom's 900mm build Brisbane

Gudday
My own oven is 500 ml deep to the oven entry. That's about 2 1/2 bricks. The entranceway is 600mm wide and 500 high. A lot of folk would consider it a deep but because it is both wide and high I don't suffer from a tunnel effect.
I like it because I use it as a mini fireplace.
In saying this most folk it seem work on about 1 1/2 bricks 340 mm . Remember also in setting out the dome entrance bisects the circle footprint of you dome so the ovens set a little bit more forward than you would think. Also plan for the hearth and entrance brick to be at the one level right through to the edge you'll find this important when clearing ash.
Yor ovens a 900 mm so the dome entrance is lower than mine for example. I would go higher and wider at the entrance way to reduce "tunnel" effect regardless of the setback.
Hope something in here helps
Regards dave
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  #24  
Old 06-01-2013, 04:45 PM
Peasant
 
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Location: Brisbane, Australia
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Default Re: Brooky Tom's 900mm build Brisbane

Thanks Dave. Steve (Redlands build) kindly showed me his stage of building yesterday and so I got a better feel of the distances to the oven in practice and that dome entrance interface. I will go with what I have, probably stretch the 900Mm to 940mm since I have the width, and that will bring it a little forward. At his suggestion, I may also use slightly longer bricks in the arch to enable a taper at the top to sit the dome arches on (not that I'm anywhere near confident I will actually be able to master that interface).
I looked at my IT device last night and realized that using a castor with threaded rod means it does not construct a pure hemisphere. Circle is ok but the offset of the castor changes the radius as the dome height increases. I plotted that out and see how I can adjust at each course to get the right radius.
It seems to me as well that the important point to get the radius set is at the top of the brick being laid (or near the top). Is that correct? The top of the previous brick determines the bottom of the new one, and if I get the top of the new one right it is the angle of the brick in the vertical plane that will change to suit.
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  #25  
Old 06-01-2013, 06:03 PM
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Default Re: Brooky Tom's 900mm build Brisbane

Hey BT - I agree about the threaded rod and castor given that the pivot point is not perfectly centred. The difference is about 10mm and over the whole dome comes to about 1mm per course. That is a very fine adjustment.

I used the castor and threaded rod at the same setting from start to the course before the keystones as I didn't use a form and the result works fine. I expect that the use of various forms would involve similar variations. I suppose it depends on what tolerances you are willing to wear. I figure that the physics of the thing will tolerate that and probably some more. I have a good eye for detail but I try to avoid getting bogged down in the minutiae. Diminishes the pleasure of it and makes my head hurt.

Just my humble opinion.

Looks like you are about to launch into it, good luck.

Cheers ........... Steve
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  #26  
Old 06-02-2013, 05:20 AM
Peasant
 
Join Date: May 2013
Location: Brisbane, Australia
Posts: 38
Default Re: Brooky Tom's 900mm build Brisbane

Thanks Steve (of Bundaberg-can't get those crab photos out of my mind). But I agree there is a balance of wills between wanting to start the build but worrying about making an irrevocable error on the way that could have been corrected by the wise advice of the forum.
I hope that the other thing that's valuable from our deliberations as a newbie is that other newbies have the same deliberations and questions and benefit from our standard queries.
I've sketched up my outcomes from people's advice in terms of a design - it will be different from others - but in due course I will scan and load and hopefully of some use to future newbies as a starter.
On your response re the IT and my use of the castor in it, I am going to start with using my calculated adjustment of the radius length for each new course rather than a dome template. The IT should confirm.
I have another query for advice.
The arch opening. For a 36 inch I see general advice for 19inch wide and 12 inch high. That's 475mm and 300mm in my language. Seeing that most designs I see have some form of arch, it is not clear to me whether the height of 12inches (or300mm) is the height at the side "vertical sides of the opening" or the height at the peak of the arch? Any advices?
Meanwhile I can understand both camps re 1 a vertical start on the sides and an arch over the top (adv-simplicity of build, height at sides for operation, minimum width of oven landing: disadvantage - arch strength, need for buttress? Or 2 arch overall (eg Colin) - adv arch strength, aesthetics? , width for access at lowest level, Disadvantage build complication, height of access at sides, more arch bricks). I'm still open (for a day or two) but am favoring the vertical sides as a more standard way to get the job done.
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  #27  
Old 06-02-2013, 04:32 PM
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Default Re: Brooky Tom's 900mm build Brisbane

There are a couple of schools of thought on the opening size. There is a thread discussing this at http://www.fornobravo.com/forum/f8/o...-size-692.html (Oven opening size) .

My oven is 36" with an 18" dome the oven opening size is 19" wide 10" high at the sides and 12" high in the middle of the arch.

I built with the straight sides and brick arch for the entry. It seems to do everything required. That is plenty of room to get things in and out and the vast majority of the smoke goes up the flue (I would say all of it when things are warmed up).

The 'Golden Ratio' (1.618) comes into the equation and if that is applied to the dimensions that I used comes very close.

I used the numbers on the FB plans pretty much.

Like you say, both straight sides and the full arch have their pros and cons. If I was doing it again I would do the full arch if I was making an igloo again but would use straight sides if I was going to enclose it.

The pic is what is keeping the crabs company in the river.

Cheers .......... Steve
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  #28  
Old 06-03-2013, 03:16 PM
Peasant
 
Join Date: May 2013
Location: Brisbane, Australia
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Default Re: Brooky Tom's 900mm build Brisbane

Thanks Green(prawn)man-more envy from here as prawns my favorite food!!
Can you say why you'd change to an arch side for an igloo? Strength? Aesthetics? Construction?
I mucked about with different possibilities. My bricks are 115 x 75. I'm aiming for approx 19inchx12 inch (480 x 300).
For straight sides and no tapers on arch, I finished with 4 bricks in the side with the 4th cut to support the first of 6 bricks in the arch. Would Need another cut brick to complete the side/arch interface. Mortar gap looks like it would be 15mm on the top of the arch.
If I tapered the arch bricks to reduce the mortar gaps, it looks like I'd target a taper down to 64mm and use 7 bricks in the arch.
If I went for a whole arch, it looks like I'd target a 55m taper approx. (do i remember seeing someone (Colin?) work out he would target a 53mm?). I also remember seeing advice that there is no need to cut both sides of the brick. My rough sketches suggest I could get three different arches with a 55mm taper by doing one of: 1 cutting both sides on all but the bottom brick on each side- and finish with an opening about 510 x 290 using a total of 15 bricks; 2 cut all bricks only one side and lay with the right angle (uncut) side on the bottom side. And finish with an opening about 480x300 using a total of 15 bricks (probably double side cut the top arch brick for symmetry) or 3 use the same single side cut bricks with the cut side on the bottom and finish with an opening about 500x250 using 14 bricks.
This has probably been discussed heaps before so does this variation make sense?
Because it all gets covered in blanket, it is not seen except maybe the outer arch face. I assume a decorative arch facing can be cut and faced to look like anything one wants?
On this basis, I'm tempted to go with option 2 above but will appreciate any and all comments and advices. Thanks.
Also appreciate advice as to whose thread to look at who might have already done a 36 inch oven with a full arch opening using bricks of the size I'm intending ( 115x75 on the face or 4.5x3 inches). I would probably get good info on the interface issues. Thanks.
Tom
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  #29  
Old 06-03-2013, 06:53 PM
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Default Re: Brooky Tom's 900mm build Brisbane

Gudday
I would myself go for an arch with straight sides for no other reason than you get more room on the sides for putting things in the oven and a better view into the oven.
Regards dave
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  #30  
Old 06-04-2013, 03:51 AM
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Default Re: Brooky Tom's 900mm build Brisbane

Tom - My idea of a full arch on an igloo oven was about both the structural integrity of the full arch and the low profile with the igloo. It just strikes me that the streamlined look is completed that way. All that said, some of the larger structures built around some of the ovens seen on this forum are little short of works of art.

The setting you are building in provides an excellent environment for a WFO. The stone walls look a treat and speak of many hours of careful work.

Cheers ............ Steve
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