james requested that i post some specs on the preformed archway bricks i am using for my doorway header, and for the top of my dome.
these numbers are an industry standard, so one should be able to find these from different manufacturers. unfortunately, the supplier i got mine from (HWR---you can find their distribution centers all over the U.S.. check on hwr.com) only had archway bricks in a superduty grade (the "clipper" grade, 52.6% silica, 42.2% alumina), so they were more expensive. however, the price of the arch bricks in the clipper was not that much more expensive than the straight 2.5"x4.5"x9" bricks. nonetheless, here's what i used, and what i paid:
#1 "clipper" ARCH BRICK in a 2.5" series---tapering from 2 1/2" to 2 1/8"---$2.95
#2 "clipper" ARCH BRICK in a 2.5" series---tapering from 2 1/2" to 1 3/4"---$2.95
#4 "clipper" ARCH BRICK in a 3" series---tapering from 3" to 1"---$3.27
my entire 18" tunnel from the oven doorway to the actual exposed entrance cost me $80.
the 2.5"x4.5"x9" straight clipper sells for around $2.75, so the arch bricks are not really that much more, relatively speaking.
so...if someone could just find a supplier with low or intermediate duty archway bricks, the price should be comparable to a straight brick, and the entire dome could be made much stronger. good luck.
I did the calculations for cutting regular bricks to the proper shape to eliminate all mortar joints but it wastes most of the brick and although I *know* it works in one of the dimensions (e.g. around the circumference or arched up and down) because that's how I cut my doorway arch bricks, I only *think* they work in what is effectively a compound miter scenario.
The trouble with most standard arch bricks is that they're targeted to the kiln or forge industry where the higher alumina content is desirable but for us it leads to brittleness and too much conductivity (less thermal mass).
But, if anyone found a low/med duty arch brick set (20-30% alumina), it'd make a beautiful oven. One of the design goals for the oven was to make sure the materials were readily available just about everywhere so it would also be helpful if we could find one with a national distribution channel (our international builders would have to make do with the standard design).
At least for the vent arch
I've been looking around town, and custom brick arches, where the seams line up perfectly, are definitely the norm for the "best" buildings. It would be great to put a plan in place to make it easy to assemble a custom arch for the vent opening, and perhaps for the oven opening.
yeah, i know what you're saying jim, about readily available materials. in my case, they were right along side the other bricks i was buying, so it was no big deal. if money wasn't an issue, i still woudn't have used the super duty bricks for the dome, precisely the reasons you mentioned. using them only at the door shouldn't be any problem. i am told that they are indeed made in lower grades though.
i thought a lot about the concept of how the arch would work in a dome with, as you said, a four way miter needed. i think it would work well structurally, that is it would hold the bricks in tighter vertically, but you'd still have mortar gaps in between each brick in the same course, which would really only matter in terms of thermal properties, because their sideways wiggle still wouldn't let them fall through.
please don't think any of my suggestions or experiments are trying to undermine the wonderful work you guys did designing this oven. i just can't stop thinking about different ways of doing something when doing it.
i believe hwr does carry arch bricks in low duty, they just didn't have any at the portland distribution center.
The first set of cuts results in the arch brick shape you've used and the second set tapers the other sides. In thinking about it, I was doing it based on using the 2 1/4" x 4 1/2" face inward (with a 4 1/2" depth) to start the cuts on. Perhaps doing it the other way with a 4 1/2" x 4 1/2" inward face to start the cuts would reduce the waste I was getting. The face should be narrowed sufficiently by the taper cuts to maintain a smoothly curving arch & circle.
'Course I'd need to buy a 10" wet saw.... :)
I'm going to noodle this some more. I think it would be an incredibly aesthetically satisfying project to build an oven with no mortar joints at all.
BTW, no worries on the thoughts you've got for changing things. I built a Scott oven first, wasn't 100% satisfied so I started thinking of changes. The only real difference between my Pompeii design & one the Romans built 2000 years ago is the uniformity & consistency of the source materials...kind of an ancient form updated for today's materials, tools and technology. (Alan tried to do the same thing with his update of the bread ovens of Quebec but lost the connection to the regular guy who just wanted to cook in their backyard.)
those preformed archbricks are 9"x6", so if you could figure out the arch in the vertical direction, you would only have to cut bits out if the brick laterally (i guess that's what you are saying anyway, but the archbricks would make for fewer cuts.) i'm told by professional bricklayers that 1/8" or less is a standard mortar joint in refractory. if you could get a dome that tight it would be incredible indeed!
I really want to try a "no joint" where there's not even an eigth of an inch but I think that would be okay and still not need any mortar.
Of course I need a 10" wet tile saw and somewhere to put the next oven but my wife requires that to be at either a new house or someone else's house and I'm running out of friends who want to play brick layer before I'm running out of new ideas. (For some reason, not everyone wants a brick oven in their backyard...)
I think Buckminster Fuller was misunderstood at home too.
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