Starting new 36" build

[deejayoh]

Re: Starting new 36" build

After reading through the link that John provided, I realized that the arch profile that one gets with the "lazy susan" style IT is probably more rounded than is ideal. It looks like the "thrust line" that the article refers to would probably cut through the inside third of the arch.

I'm sure that for all practical purposes - the design would be strong enough - but I figure I am only building this thing once, and I'm not so far along that the changes will really cost me any time. So I have reworked both my dome profile and my arch profile and guess what? They look remarkably like what John and Aidan have done. Just took me a while to tumble to the logic...

Anyway, the only remaining bit of confusion that I have is what to do for the IT. I have a 19.5" radius on the floor, and am targeting an 18" internal dome height. It turns out that the way the math works, when the radius of your dome is greater than the height of your dome (in my case, the radius is 20") - so the center point for the arch is below the surface of your cooking floor. I can see no practical way to use a single length arm keep everything all nice and even.

John, I am guessing this is why you went with the plywood form instead of the IT? How did that work for you? I was thinking of rigging up some sort of off-axis jig - but not sure it is worth the time.

[GianniFocaccia]

Re: Starting new 36" build

It looks like the "thrust line" that the article refers to would probably cut through the inside third of the arch.

I have several thoughts on this. The application of the ideal dome shape as it relates to stability is noble from the educated engineer's viewpoint as well as the dome's potential for longevity. However, when I first saw your lower, flatter dome profile I was envious, not just because that shape is sexy, but because in all practicality, now that I've built my dome, I don't think the forces at work here (line of thrust) would overcome competent construction skills and modern materials and cause your dome to fail in your lifetime. Of course, this is total conjecture, but lastly, does a flatter dome and the potential for a perfect pizza outweigh the benefit of a slightly higher dome ideal for roasts etc?

John, I am guessing this is why you went with the plywood form instead of the IT?

Exactly. My original dome shape was slightly flatter as well (19.5" radius and 18.5" ceiling) and was based on a freehand template drawing that allowed for a slightly taller 'shoulder' than a true hemisphere. My plan was to build an adjustable IT and use the dome template too but decided to go with just the template. As I progressed upwards through courses 3 & 4 I discovered that I only had to use the template two or three times per course to stay 'on profile'. Merely cutting the bricks consistently and careful alignment kept the dome true and the sticky homebrew meant I didn't have to prop the bricks up at all. The only error I made was getting about 1/4" outside the template at the shoulder which left me with a 19" ceiling, 1/2" higher than planned.

John

[deejayoh]

Re: Starting new 36" build

Of course, this is total conjecture, but lastly, does a flatter dome and the potential for a perfect pizza outweigh the benefit of a slightly higher dome ideal for roasts etc?

John

I think I am still going to have a flatter dome. Targeting 18" high with a 39" diameter. I think the only real change I am making is that the dome will be a continuous arc of 21.25" from shoulder to shoulder, instead of two quarter circles @ ~18.5" joined by a flat top.

I did rework it one more time since my last post - in order to incorporate two sailor courses (instead of the one in my last sketchup version) so that I'll have slightly more height at the edges - and I am pretty happy with that. That is what brings the dome radius in at 21.25 inches - which I am going to cut out on a plywood form in order to ensure the shape stays on track. I have a vague idea about building some sort of slider for a bracket along the edge of the form so that I can consistently manage the height - which may or may not happen. (see drawing)

If I could build this thing in sketchup I'd be golden, but I think the weather is finally going to cooperate this weekend so I can get started on mortaring!

[deejayoh]

Re: Starting new 36" build

Made progress today, and not just in sketchup! I got the bottom three courses in. Ran out of daylight just as I was getting to tie the top course in the second side of the arch.

After a day of working with bricks and mortar, I am certain I did not miss my calling in terms of being a mason. It's a lot harder than I thought - but what I laid up seems to be sturdy enough, so I am hoping I'm ok!

[deejayoh]

Re: Starting new 36" build

Next course, the dome starts taking shape

I need to angle the shoulder by a few degrees. I guess I could have done this with soldiers, but I didn't

Does anyone see any problems with a course of angled bricks like these?

[Les]

Re: Starting new 36" build

I would think that the thin edge will spall easier. But after a point it will stop - where that point is I have no clue. Why are you tapering them so much? If you are willing to cut the angle why not do it to a full size brick.

[Amac]

Re: Starting new 36" build

I would think that the thin edge will spall easier.

I think the thin edge dennis is making will be invisible to the inside of the dome - so maybe spalling shouldn't be a problem.
On the other hand if he used the full brick and the same angle it would show a very narrow edge to the inside, which could be problematic.
So I think it will be OK.
I have seen builds where some people fill what would be large mortar joints with wedges of brick, and haven't seen problems reported.

There's a lot to be said though for the straightforward hemispherical dome.
BTW dennis it looks like there are no wedges under the arch form. Make sure it is removable easily after the arch is complete.
Aidan

[deejayoh]

Re: Starting new 36" build

Yeah, the idea is that the edge won't show inside the oven at all - so there should be no opportunity for spalling. I agree that the straight forward dome is probably a lot easier, but I guess I just have to things difficult for myself

As for the arch - actually that is my "IT", not my arch form. I had to use a plywood form because the shape of the dome precludes a lever-type tool. So I am going to be shimming that with cardboard or something as I lay up the dome so that there will be room for it to spin inside the dome.

One thing I did with the form for the dome which may be of interest to others is that I made the radius adjustable. As shown it works all the way to the edge, but if I remove the part that is screwed on with the block, I can use it to gauge the angle of the bricks around the arch too.

The arch is sitting on a couple of pieces of 2X6 that I can easily knock sideways to get them out once the arch is in place

[Amac]

Re: Starting new 36" build

Of course Dennis - my bad - I see what it is now.

if I remove the part that is screwed on with the block, I can use it to gauge the angle of the bricks around the arch too.

When you say "the angle of the bricks around the arch" you don't mean the arch bricks? The way I see it is that will allow you only to get the correct angle on the arch keystone brick, and the only reason for removing the added section is so it can rotate without disturbing the arch form - no?
I actually used the IT to help build the arch in advance - without needing to change the radius.

[deejayoh]

Re: Starting new 36" build

When you say "the angle of the bricks around the arch" you don't mean the arch bricks? The way I see it is that will allow you only to get the correct angle on the arch keystone brick, and the only reason for removing the added section is so it can rotate without disturbing the arch form - no?
I actually used the IT to help build the arch in advance - without needing to change the radius.

Yeah, I probably wasn't exactly clear. I was referring to using it to set the bottom/back angle of the brick - which I want to contour so it matches the dome. The top angle will be set on the keystone brick to match the course of bricks to which it aligns. And yes, removing the added section lets the guide clear the arch form

[deejayoh]

Re: Starting new 36" build

Finally had some decent weather, and I got the Arch done this weekend. Man, that thing caused me some headaches. I figured out that since my dome was not a constant radius, I had to reflect that in the transition.

I knew that the arch stuck out 1.5 inches at the bottom, and from my sketchup, I knew the same measure was 3 inches for the keystone. so I laid all the bricks out side by side on a table, and drew a line from the keystone to the bottom brick - and cut all them according to that line. Seems to have worked out ok.

I had to hack at the back of the bricks with a grinder blade after I got them in, because I had that measurement wrong. But no one will ever see that...

This was the first sunny weekend we've had since I started this thing. Hoping the pace will pick up a bit now.

My new mantra: When I get something wrong, if fixing it won't make the pizza any better (or get here any faster), forget about it!


The picture is from saturday. I pulled the form this morning and finished off the transition row. The arch is still standing...

Edit: it was still light enough out that I snapped a new pic showing the arch standing on it's own.
Also, check out the little stool I snagged at the Harbor Freight sale today!

[Amac]

Re: Starting new 36" build

Well done Dennis looking good now. You won't have to worry about those angled cuts when you are doing the front (vent area?) arch. Very good tapers and you managed to get a decent size keystone.
Couldn't open the first pic for some reason btw?
Aidan

[gmchm]

Re: Starting new 36" build

Your good-looking build, and the improvement in the weather, is inspiring me to get going again on my own project.

[deejayoh]

Re: Starting new 36" build

Had some good weather this weekend, so got one day of work in. I finished up the 5th course and got most of the cuts done on 6th. Then I ran out of HS50 mortar. Grr..

I think instead of ponying up another $100 for a bag of mortar, I am going to go with homebrew. Does anyone see any issues with changing mortar type halfway through the build?

Planning to pick up the sand/cement/lime today. I already have a bag of fireclay

[deejayoh]

Re: Starting new 36" build

Got some unexpected good weather this afternoon, so I was able to start working with the homebrew mortar. My first reaction was that it wasn't at all sticky. Then I figured out it needs to be a bit looser/wetter than the HeatStop and it was ok. I do think the sand I have may be a little coarse - but I can't seem to find the superfine sand. I got it at the local cement and masonry supplier.

I got about half a course in using the homebrew. Seems to work, and what a cost savings!

Happy to report that I seem to have done ok on the arch to dome transition using my high school geometry skills. I am pretty happy with how well it seems to be lining up.

Here are some progress shots. I am off work this week and hoping to get the dome closed in!