Starting new 36" build

[Amac]

Re: Starting new 36" build

Looks brilliant so far DJO - very tight cuts - looks like you won't need any mortar at all In Kens vent is the opening for the flue just 4.5 ". Is there a good reason not to bite off a bit more than half a brick - or does it matter?
Aidan

[deejayoh]

Re: Starting new 36" build

In Kens vent is the opening for the flue just 4.5 ". Is there a good reason not to bite off a bit more than half a brick - or does it matter?
Aidan

Good point.

I'll probably make it 5" x 10" - giving me 50" of space - which is the same as the area of the flue I am using. Maybe 5 x 11 just to be safe!

His posts indicate that the oven draws well, and it is a 42" - so I think a 39" should be fine with the same design.

[david s]

Re: Starting new 36" build

It is a good idea to have some wooden wedges under the arch form so when you remove them it will drop 1/2" or so for easier removal. From the look of your pic you are going to have a hard time removing those bricks under it the way it is set up now. You don't want to upset your brick arch once it's laid.

[Amac]

Re: Starting new 36" build

btw DJO - on the arch geometry - it's hard to comment without knowing exactly what radius you chose for the arch curve. Maybe I missed it somewhere. The rounded part all look like the same cut from the pics (maybe not) but I would have thought that unless you go for a semicircular arch like I did, you will have trouble getting it to fit the dome as it goes up. You know this problem that the bricks need to "reach" back in which would make the arch bricks at the top appear to protrude more than the lower ones. With the bigger radius that might not be much of a problem?

I thought that Gianni had said that he would have cut the arch bricks as he arrived at them. Maybe John if you are reading you could clarify that!

[deejayoh]

Re: Starting new 36" build

Aidan -
I am going with an elipse shape for the dome - 18" height - so I am hoping the cut will be right. I expect I will have to do some trimming as I go up.

As I said, I am not planning to mortar them all into place until I get the dome up higher. I'm also planning to use my IT (once I build it...) to check all the clearances

Probably won't happen for a couple weeks - as we've got cold temps and rain forecast for the next week, and I am headed to Whistler for the weekend anyway!

[Amac]

Re: Starting new 36" build

Are you using a "lazy susan" type design for the IT to achieve the flattened top?
I think with the lazy susan IT the flattening happens naturally as you get higher up depending I guess on the offset of the pivot.

I am going with an elipse shape for the dome - 18" height - so I am hoping the cut will be right. I expect I will have to do some trimming as I go up.

Ideally the slope where the dome wall meets the arch will be exactly the thickness of the dome wall (1/2 a brick), so the inner edge should coincide with the inner radius as measured by the IT, and the outer edge with the outer radius.
With those straight sided arches I am not sure that can be achieved for the rounded part.

..and I am headed to Whistler for the weekend anyway!

I guess that means skiing - enjoy the slopes and don't forget a pint of green beer for paddy's day
regards
Aidan

[deejayoh]

Re: Starting new 36" build

Are you using a "lazy susan" type design for the IT to achieve the flattened top?
I think with the lazy susan IT the flattening happens naturally as you get higher up depending I guess on the offset of the pivot.


Ideally the slope where the dome wall meets the arch will be exactly the thickness of the dome wall (1/2 a brick), so the inner edge should coincide with the inner radius as measured by the IT, and the outer edge with the outer radius.
With those straight sided arches I am not sure that can be achieved for the rounded part.

Yes, I am using the lazy susan IT - so the vertical portion of my walls should match to the vertical portion of my dome - so that the dome meets up with the arch. If not, I've wasted a few bricks and some time cutting. I will be able to check with the IT before I lay any bricks.

It took me quite a bit of figuring and sketching up - but I think I finally have the geometry right for the dome shape I want and the offset of the IT from the center. I've attached a screen snap.

I don't even want to attempt drawing a scale model of how that interacts with the arch. Makes my head explode. I will just figure it on the real thing

[Amac]

Re: Starting new 36" build

That is an ambitious and impressive project. Excellent - may the oven gods go with you.
Aidan

[GianniFocaccia]

Re: Starting new 36" build

I don't even want to attempt drawing a scale model of how that interacts with the arch. Makes my head explode. I will just figure it on the real thing

I know exactly where you are, DJO and your approach is good. Don't kill yourself thinking about it - it will come. Consider some ideas for your gameplan. They worked for me:

1. The most important factor in arch integration is it's placement (how deep). Draw a profile of your dome and regardless of your arch size/shape, place the arch so that the top-most center brick (TDC) matches the profile of the dome. Because the angle of the dome at this level is shallowest of all arch bricks, this brick will extend the deepest into the dome. Proper placement of the TDC arch brick will also ensure consistency with the curvature of the dome (not the profile) and once the arch is complete, allow you to proceed on up in round.

If you will be following the FB plans and not angling your arch bricks, it doesn't hurt to build your arch first. If you will be angling your arch bricks, cut each of the arch base bricks first, then the TDC brick to match the dome curvature and profile. You can then cut each successive arch brick to match the front of the arch and be consistent with the inner arch curve and profile for each course.

This approach works with hemispherical as well as semi-straight-sided arches.

Hope this helps,

John

[deejayoh]

Re: Starting new 36" build

Thanks John. That is super helpful.

I am thinking I got a little ahead of myself when I cut the backs of my arch bricks, because I hadn't yet calculated what the angle should be.

But it sounds like I can use the sketchup I put together for the dome profile to figure out the angle. I just need to match the height of my arch (11" at the bottom, 15.5" at the top) to the angle of the bricks in my picture and wa-la, I have my angle.

See attached - The yellow trapezoid would be my arch brick. Does this look right? That angle carries all the way across?

Thanks!

Dennis

[deejayoh]

Re: Starting new 36" build

Another thought: Since I have to mess with my arch again, I am thinking I will raise it by a 1/4" to get a perfect 62% ratio (11.25/18).

If I do that, it seems to make more sense to have the top of the arch intersect with the next tier of brick, as pictured.

What I don't like about that approach is that there is only a 4" surface on the face that intersects the dome. I guess I could fill in the gap with mortar - but it looks messy.

Recommendations?

[GianniFocaccia]

Re: Starting new 36" build

But it sounds like I can use the sketchup I put together for the dome profile to figure out the angle.

You could, but it'll take a while and may not translate to your arch geometry unless its perfectly hemispherical. I cut all my arch bricks first, but only basic blocks. Once I had my TDC brick in place, I drew a circular line down each side to derive my final curve. As you progress upwards, will find that the inward-facing angle of each arch brick changes not only between bricks, but within each brick themselves.

See attached - The yellow trapezoid would be my arch brick. Does this look right?

Almost. You want the depth of the (TDC) brick's inside face to match the height of the courses around and above it. This will give you enough height to work with on the bricks that flank the highest bricks in the arch. Also, your arch extends too far forward. I wish I had made the face of my inner arch end up flush with the front of my oven - I would have gotten a better angle for my vent given I will have a thermal break in the entryway.

I wouldn't worry about the 4" surface bonding area. For projects the size of our ovens, the line of thrust shouldn't be an issue given the bonding strength. You may find this interesting reading (if you haven't already): Auroville Earth Institute

John

[Amac]

Re: Starting new 36" build

John

I wish I had made the face of my inner arch end up flush with the front of my oven

My arch projects just 1" from the dome all around. I feel this is slghtly too little as the dome narrows towards the inner part of the arch to just 3". If it was flush that would reduce to 2". Probably wouldn't make a lot of difference to the operation - jut 2" seems narrow from 4.5".
If I did it again I would have cut the arch bricks like I showed in my thread (see pic below) which would have made that almost 4" with almost 2" projecting. Angles would stay the same, but fewer cuts and less waste, and a bit more thermal mass.

But I agree with John DJO your projection part looks too much - just I don't think I would make it flush.
Another thing is that you will not get an even projection for the entire arch unless it is a pure semicircle in a pure hemisphere. It may be possible to match an elliptical arch with an elliptical dome, but it hurts my head just trying to imagine it.

[deejayoh]

Re: Starting new 36" build

You could, but it'll take a while and may not translate to your arch geometry unless its perfectly hemispherical. I cut all my arch bricks first, but only basic blocks. Once I had my TDC brick in place, I drew a circular line down each side to derive my final curve. As you progress upwards, will find that the inward-facing angle of each arch brick changes not only between bricks, but within each brick themselves.

with that description + the pics, I think I finally have it.

I wouldn't worry about the 4" surface bonding area. For projects the size of our ovens, the line of thrust shouldn't be an issue given the bonding strength. You may find this interesting reading (if you haven't already): Auroville Earth Institute

Thanks for the link. Looking at the dome shapes on that site is helpful. I see that mine looks a little like the one they show as being weak... I'm going to revisit the height of the vertical portion of the sides and the flat plug. I think I'm going to play around with starting the angle at the second course, and a more rounded top.

Thanks John

If I did it again I would have cut the arch bricks like I showed in my thread (see pic below) which would have made that almost 4" with almost 2" projecting. Angles would stay the same, but fewer cuts and less waste, and a bit more thermal mass.

Hoping I can figure that out! thanks Aidan

[Amac]

Re: Starting new 36" build

Hoping I can figure that out! thanks Aidan

Sorry Dennis I should have made that a bit clearer. I used the template shown to cut all the arch bricks and as you can see outside the arch projects 1" from the dome - and the inner side of the arch is 3.25" (not 3" as I said above) but still I thought it was a little narrow. If I made it flush with no projection the inner arch would be 2.25"
The lines on the brick in the previous pic show that I could have cut 2 arch bricks from one brick - using that same template just slid towards the middle of the brick.
This would have made the arch project a little more and thickened the inner side of the arch by the same amount.

I should add that that would have been varied had I chosen a different arch radius.
Sorry for cutting across the discussion you and John were having. I know how easy it is for this to be confusing, and I hope I am not adding complications.
Aidan