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carioca 12-16-2006 06:44 PM

A question of geometry...
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Hello there!

I'm not much good at the abstract, so I laid out a sample 'section' of my planned 1 m ID dome oven on our verandah on some plywood - to get a feel for what I'm up against :-)

My supplier, Darley Refractories in Melbourne, sells a 'kit' specifying 67 firebricks that are 230 mm long and 115 mm wide and which taper across from 75 mm to 63 mm, as well as 33 bricks that taper from 75 mm down to 57 mm cross section.

There are NO instructions available, but I was told the first ring takes whole bricks, every subsequent course is built from bricks cut in half across the length (i.e. they will all be 115 mm by 75 mm on the outside, and 63 or 57 on the inside.

So I played around with some assumptions, as shown in the attached snap (more variations at Picasa Web Albums - carioca - Forno_del_gallo ).

But I'd be happier if some sharper brain could suggest a better way to build a 1 metre inner diameter dome from the quantities and shapes of the bricks listed in the 'kit' (I have a few extras of each type, plus 20 straight 230x115x75 mm bricks, just in case).

Thanks for any input! It's still raining here, and I've got plenty of time for a series of 'dry runs' before I even start on the footings :-)



maver 12-16-2006 07:29 PM

don't drop the keystone!
That first picture doesn't work unless you "push" the sides out with mortar wedges at each joint. The keystone has to wedge in from the top. The one with the keystone made of the less aggresive taper looks ok, and no matter what you will have to shape the keystone - it shouldn't end up as just a split brick for the gap. What happens if you start with the more aggressive taper on the base instead of in the top rings? I think that would give it a low vault profile. It's interesting trying to put together how the oven was designed without the instructions. Maybe someone with the brick CAD program can play with it for you. Don't forget to consider those mortar joints in the bricks of the dome, but probably not in the oven floor.

carioca 12-16-2006 10:53 PM

Hi Maver,

I'll try your suggested way with the steeper bricks in the first four rings, thanks!

I've meanwhile posted another snap to the picasa album showing how I tried a ring of STRAIGHT bricks in the top centre - I think that might work, too...

BTW: the joints are supposed to be only 1 mm but no more than 3 mm - I assume 2 mm and the dome will close up 25 mm or so sooner, i.e. the gap at the top will narrow by that much, I think!

Yes, the lack of instructions is 'challenging'! I had already worked out in my mind that the "slide-out" downward configuration for the keystone wouldn't work, that's why I tried the other ways.

Sun's out now, the geese are sleeping under a figtree outside my french door and I might amble into the shed and uncork a bottle of australian chardonnay pinot grigio (Sero, from de Bortoli)... it's nearly 6 p.m. here now.

Cheers mate, and thanks for your comments.



Marcel 12-17-2006 06:45 AM

Be sure that your dome bricks are heavy
(M) Carioca: Just in case your dome bricks are not the correct density, consider weighing one. It should be fairly heavy; between 6 and 8 Lbs. Their very light color in your thumbnail looks rather like an insulating brick. I hope that is my mis-perception.



carioca 12-17-2006 04:26 PM

Hi Marcel,

the flatter tapered brick weighs 3930 g - it feels alright to me, particularly as both my thumb joints are suffering from all the gripping already (I crashed into a cow near home one night13 years ago, and the shock went right through the steering wheel; van was a write-off but otherwise no damage).



redbricknick 12-17-2006 08:20 PM

How is the cow?

carioca 12-18-2006 01:32 AM

Shot by the cop attending the accident...
and no, I didn't get any of the meat, and neither could the owner of the straying beast be traced - so no compo!

carioca 12-18-2006 01:42 AM

Tried that, but
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Originally Posted by maver (Post 6867)
What happens if you start with the more aggressive taper on the base instead of in the top rings? I think that would give it a low vault profile. It's interesting trying to put together how the oven was designed without the instructions...

Further to this idea: I attach a new thumbnail but I don't think this would do the trick - for a start, I only have half as many steep-taper bricks as the flatter ones...

I've consulted my son, who's doing a PhD at UCLA and may be too busy before the January exams; but he's done a good job 20 years or so ago analysing my bisected shed roof for the house and drawing up angles and a materials list :-)

Meanwhile I got the gravel and slab mesh delivered, so I'll concentrate on the footings for a moment...



jengineer 12-18-2006 07:57 AM

unit conversion challenged
3930 grams = 3.9kg = 8.6 lbs

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