Author Topic: Finally a Swedish neapolitan WFO underway (Read 7625 times)

fagilia · « **Reply #60 on:** February 11, 2013, 04:14:28 PM »

ahhhh what a mistake haha. My good i think i know what jeff means here. The joint on uppersoldiers should not be in same place in circle as in the lower soldier?
How big of a problem would this be then?

TXCraig1 · « **Reply #61 on:** February 11, 2013, 05:02:11 PM »

I don't think it is going to matter. It might even be stronger the way you built it as the weight of the dome will be completely borne by brick. If you staggered the second tier, a large part of the weight would be over the mortar columns on the back side of the soldier course. Your metal band will prevent any separation. Definitely stagger each course from this point up.

shuboyje · « **Reply #62 on:** February 11, 2013, 09:02:23 PM »

I agree with Craig, what you have done so far is no big deal, just make sure you stagger the joints in the dome.

I asked about the dome profile because of your plan for the steel harness reinforcement. A simple arched profile will put all it's outward force on the top of the soldier where you are reinforcing. A shape like Marco described would not, so it is something to consider structurally speaking.

Tscarborough · « **Reply #63 on:** February 11, 2013, 10:06:04 PM »

A flat roof would rely on adhesion, I do not recommend that. It is possible to create a lense shape and still reach the ceiling height you want. I was actually surprised that the angle required for a 42", 15-1/2" dome was 45 degrees on the sailor course, I thought it would be be more.

fagilia · « **Reply #64 on:** February 12, 2013, 11:15:26 AM »

Here are my thoghts.
I am more leaning towards the half lens half elipse version, but iam not 100% sure.
The other line in the drawings is a perfect lens even thogh i dont know exactly if i have the terminology right.
Iam leaning to half lens half elipse beacuse of ease of building it. Both versions can fit my upper soldier angle.
In both versions the total hight will be appr. diameter/3,2 with soldier hight of appr. 8,5 ".

shuboyje · « **Reply #65 on:** February 12, 2013, 11:45:46 AM »

For structural reasons I would personally build the lens shaped line you have in both versions. I don't think the compound arch makes much difference, and although probably not a fatal structural issue it isn't ideal with the way you plan to reinforce.

TXCraig1 · « **Reply #66 on:** February 12, 2013, 12:54:22 PM »

I agree with an ellipse, but not exactly how you have drawn it.

I would think the foci of the ellipse would be F1) approximately the center of the fire and F2) approximately the center of the baking pie (such that the edge of the pie is a couple inches off the wall).

Keep in mind that the foci of the ellipse are on the deck - not on the plane across the top of the soldier course. The soldier course truncates the edges of the ellipse, so you are only building the top part of the ellipse which looks somewhat like your "half lens" design.

In the drawing below, the dome height is H₁, however, arched portion of the dome is only H₂ = H₁ - soldier height.

(Illustration not to scale)

fagilia · « **Reply #67 on:** February 12, 2013, 03:52:28 PM »

Ok,

Actually Craig the so called half lens I did is more or less the same to what you did draw. I just couldnt explain my self there

When comparing craigs suggestion and jeffs and toms suggestions there seem to be only minor differences if i got it all correctly.
When i did it in right scale craigs design was more like a lens shape than i first did draw in my half lens half ellipse design.

Would this then work better you think jeff given my reinforcement strategy?

Thanks a lot by the way, this would have been a big fail without everybodys help.

fagilia · « **Reply #68 on:** February 12, 2013, 03:53:33 PM »

Comparison of lens and craigs ellipse..

kiwipete · « **Reply #69 on:** February 12, 2013, 04:14:36 PM »

Very interesting topic this, because I'm considering these things for my own oven at the moment.

So the difference between the two curves is about 7-8 millimetres..

My gut feel says that its negligible in terms of structural impact and just go with the one that you prefer / find easiest to do.

shuboyje · « **Reply #70 on:** February 12, 2013, 06:10:13 PM »

Yup, as drawn in the newest drawing I think you are fine, but am curious to hear what Tom thinks. I feel the tiny amount of force that will not be directed to the steel harness is well within the limits of what mortar can handle, but Tom is an expert on that type of thing, I'm just going by gut.

Tscarborough · « **Reply #71 on:** February 12, 2013, 06:26:13 PM »

I personally don't like the steel band, but since you are using it, you could technically make it flat and under compression by tensioning the band, so either way will be fine. I would say that a continuous curve will be easier to build than that varies, though.

TXCraig1 · « **Reply #72 on:** February 12, 2013, 06:26:55 PM »

Quote from: Tscarborough on February 12, 2013, 06:26:13 PM

I would say that a continuous curve will be easier to build than that varies, though.

Even with a sand form?

Tscarborough · « **Reply #73 on:** February 12, 2013, 07:58:21 PM »

I haven't used a sand form, but I do not think it is as simple as laying the brick upon the sand; you still have to position it correctly.

shuboyje · « **Reply #74 on:** February 12, 2013, 08:13:26 PM »

It's darn close, lol. Of course take that with a grain of salt, my oven has a very low very flat dome. Obviously the steeper you go the more positioning that will be needed.

fagilia · « **Reply #75 on:** February 13, 2013, 03:06:53 AM »

From the start i was planning to either a buttress with insulation concrete or something similar to what tom did. But, i had never worked with mortar really before and it looked to complicated so i went for a steel reinforcement. We will see how it goes but i will defenitely put som tension on the steel harness and make it fit tightly to the soldiers.

Jeff, i dont really understand why a more ellipse shape would cause more problems in the steel harness design than a lens shape would?
Is it that the forces from the dome will be more directed to the lower parts of the soldiers compared to a lens shape?

In my build i did already plan to have a metal band both in upper part of angle-soldiers and one extra at 2/3 distance up on the lower part soldiers. I dont know if it will be nessesary but i figured it would not hurt either. This second metal band will be connected to the oven door.

fagilia · « **Reply #76 on:** February 13, 2013, 05:40:00 AM »

I dont know exactly how the forces from the dome will affect the soldiers?
This is what i can think of but is it correct, and is this what you mean Jeff?
Maby this is of no big matter but iam just curious...

shuboyje · « **Reply #77 on:** February 13, 2013, 11:00:23 AM »

I made a simple drawing to explain the issue I'm mentioned earlier. Like I have said, I do not think this is an issue with your current plan. I made the arch in the drawing exaggerated to better show what I am talking about.

fagilia · « **Reply #78 on:** February 13, 2013, 12:52:25 PM »

Ok thanks, now i understad and it makes sense.
Will try to make the sandform during this weekend.

TXCraig1 · « **Reply #79 on:** February 13, 2013, 01:10:35 PM »

I agree it is not a problem with your current design. The Line of Thrust (“LT”) in an arch follows the inverted shape the corresponding catenary curve. That is, if you freely suspended a length of chain from the center points of the angled buttresses on top of your solders, the LT through the arch would follow this same (inverted) curve. The closer you keep the LT to the center of the voussoirs, the more stable the arch. As the LT moves away from the center, it creates tensile stress on the opposite side. That is what Jeff noted as “outward force” on his drawing in Response 77 – you can see that the inverted catenary curve would be well inside of that point creating tensile stress there. As long as the LT is within the center 1/3 of the thickness of the arch, you should be fine. My guess is that the truncated ellipse fairly closely approximates a catenary arch.

I think your drawing in Response 76 is incorrect in a couple ways. First, the LT, or “Force” as you called it, is independent of the shape of the dome arch. As noted above, it is a function of the corresponding catenary curve. Second, the force is not going to be directed into the solider as indicated. My guess is that the LT vector will be on the opposite side of the solider. I think this is important as it what likely necessitates a minimum of two bands (above and below the mortar line on top of the soldiers.

The solider is part of the arch. As you can see below, the LT exits the arch somewhere near the top of the solider. Clearly, this creates an extremely unstable condition. The Thrust vector is the resultant force of the Horizontal Thrust and Weight vectors. The soldiers will bear all the weight of the dome, but the direction of the Thrust vector is not orthogonal to the long axis of the brick, hence the need for reinforcement in the form of the bands or some other reinforcement.