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  • MarkJerling
    replied
    Originally posted by Blairt View Post
    I still feel lost on where the arch should be. After JRPizza reviewed my cardboard mock-up I thought I had the arch pretty much properly placed but deejayoh says it should be further forward. The arch is lined up with the inner mark which is the outer edge of my floor bricks. I’m stalled until I can lock in the arch placement...

    I understand that the lowest arch brick needs to have angle cuts to then line up to the lowest level of the wall bricks (I’ll be placing this lowest course as a header brick, lying flat on the insulation - with a slight amount of firebrick/sand compound for leveling as required.
    The placement of the base of the arch is determined by where the brick at the top of the arch intersects the dome. So, you need to find that position. That can be done in various ways: You can use an IT or you can use a cardboard template, for instance. The trick is that the brick at the top of the door arch must intersect the dome because your dome courses needs to coincide with that top of door arch brick location. Put another way, that's the innermost location necessary for your door arch bricks.

    Once you know where that brick needs to be, you'll know where your arch needs to sit and consequently where you need to set the base of your door arch.

    Leave a comment:


  • JRPizza
    replied
    Originally posted by UtahBeehiver View Post
    Tapered inner arch are more work up front but saves a lot of time on the back end and makes the transition to the dome much easier and cleaner. So like the Fram oil commercial, pay me now or later. Half height soldiers or half headers will work either way. In reality you really do not gain much vertical space with half soldiers but that is up to you.
    Russell, I think Blairt was talking about leaving his bricks rectangular when looking at the arch from the front and having triangular wedges of mortar vs tapering the sides of the bricks and having a constant thickness of mortar. I think you are talking about tapering the rear of the bricks where they intersect the dome, which indeed makes incorporation into the dome easier and cleaner. Just wanted to make sure we weren't getting him too confused.

    Also Blairt if you are not sure the arch is placed right do as I suggested. Put your arch form where you think it should be, and draw a line across the front edge of your form on your cardboard. Extend the line out using a ruler. Measure from the center of the arch along that line a distance equal to the height of your door. A brick laid at the end of that line with the forward lower edge touching the line is where a tdc brick will sit on your completed arch. Make sure that brick is in the double circles like I showed in the sketches I attached. Any other method is really just "eye balling" and not guaranteed to get the arch in the right place.
    I struggled like you did and created a thread where Gulf helped me understand where my arch should go and how to use a large scale template.
    https://community.fornobravo.com/for...18-hearth-size
    Last edited by JRPizza; 03-13-2021, 08:27 PM.

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  • UtahBeehiver
    replied
    Tapered inner arch are more work up front but saves a lot of time on the back end and makes the transition to the dome much easier and cleaner. So like the Fram oil commercial, pay me now or later. Half height soldiers or half headers will work either way. In reality you really do not gain much vertical space with half soldiers but that is up to you.

    Leave a comment:


  • Blairt
    replied
    Thanks Russell!

    I'm leaning towards NOT tapering the arch bricks but rather leaving them full 4.5x2.5" width and using additional mortar to fill in the wider gaps that would result. This seems like a lot less work and cutting the full 4.5" width of the bricks would be a challenge with my saw. Would this change your recommendation?

    Also, in order to get a bit more height for larger pans etc I'm leaning towards using half bricks on edge rather than on the flat for my bottom dome course. (Half soldiers)

    Leave a comment:


  • UtahBeehiver
    replied
    IMHO, the placement looks good with the inner edge of the arch form intersecting the inner diameter of the oven as shown in post #23. The top dead center will be the longest final cut brick and the the shortest final cut at the bottom. Refer the post I had shown earlier on how the IT sets the angles.

    Click image for larger version

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  • Blairt
    replied
    I still feel lost on where the arch should be. After JRPizza reviewed my cardboard mock-up I thought I had the arch pretty much properly placed but deejayoh says it should be further forward. The arch is lined up with the inner mark which is the outer edge of my floor bricks. I’m stalled until I can lock in the arch placement...

    I understand that the lowest arch brick needs to have angle cuts to then line up to the lowest level of the wall bricks (I’ll be placing this lowest course as a header brick, lying flat on the insulation - with a slight amount of firebrick/sand compound for leveling as required.

    Leave a comment:


  • deejayoh
    replied
    That is too far back, and you need to make 2 cuts
    1) to the edge of the brick that is inside the dome, cut it to align to the inner circle
    2) to the edge of the brick that will meet the next brick in your first course - cut it to align with the angle of that brick

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  • Blairt
    replied
    My bricks arrived!

    In laying out the side arch bricks, I think I've finally got the placement correct - please advise...


    Click image for larger version

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    Question - when you put the bricks in a herringbone pattern for the oven floor, how/where do you transition from that pattern in the archway tunnel where your heat break goes? Is it just a matter of cutting straight across the herringbone to insert your heat break?

    Leave a comment:


  • JRPizza
    replied
    I probably was not as clear as I thought I was being. You can take the cardboard template you have already drawn and proceed to step 2 of of my post. It would be really simple to find the proper arch placement without using cad - just something to measure with and something to draw an 90 degree angle. Either way good luck and keep posting any questions and progress!

    Leave a comment:


  • Blairt
    replied
    Hi all - thanks for the words of advice! JR - I wish I had access and knowledge of a CAD program but my degree is in finance not engineering . I can barely draw a stick figure...

    So what everyone has said makes sense. I'm at a stage where I need to have actual bricks to play with and put into place on the arch to see where things should go. I had expected my materials to be delivered by the beginning of the week but the supplier didn't get them on a truck to the store until today. Now I'm hoping that they might arrive tomorrow so that I can work on things over the weekend.

    I shortened the width of my forward arch template to 6". Hopefully that is near a sweet spot where it still has strength but won't get in the way of brick placement where the arch meets the dome. If it needs adjustment it won't take much to alter again...

    Leave a comment:


  • JRPizza
    replied
    I have always recommended using CAD to help properly locate fore/aft placement of the inner arch, but if you are building a hemispherical dome oven with a hemispherical arch there is a simple way to determine location using any surface large enough to draw your dome inner and outer diameters in full scale. A large carpenter's square comes in very handy when using this method.
    1. Using a marker with string, a large compass (bought mine at Harbor Freight) or your IT, draw two concentric circles representing inner and outer diameter of your brick dome.
    2. Draw a line from the center of the circles out past the circle representing the outside diameter, which in my drawing is the lower horizontal line running to the left. This line represents the center of your vent/landing
    3. Draw a line above and perpendicular to this line at a distance representing the height of your opening. This is a set dimension. In my drawing the line is at 12.25" representing the height for a 39" oven.
    4. Now you can place a full size brick lying flat with the lower edge resting on this line, and move it fore/aft making sure it still lies in the area bounded by the dome ID and OD. If it does not properly intersect the dome you will have to go "out of round" to integrate the arch into the dome. The first and second picture show the extremes of fore aft placement. In the first picture the brick is in a more forward position, which provides for the largest interior cooking space, largest protrusion at the top of the arch to build your vent either on or over with a heat break, but also makes for a slightly longer vent landing. The second picture has the brick at a very rearward position. This can give the shortest landing, but cuts down some on the inner space in the oven and does not provide any protrusion for incorporation into the vent arches.
    5. When you are happy with the fore/aft positioning of the brick, draw a line downward at 90 degrees to the horizontal line you measured your arch height from. Measure the distance from that line to the center of the oven, and you have the distance from the center to the front edge of your arch form. Build and shim your arch form so that the forward face is straight up and down (perpendicular to horizon) and if you index your arch bricks flush with the face the arch bricks will all be in the same plane and a door will have a good even surface to seal against.
    6. With the distance from the center to the front of the arch set, you can now draw a similar perpendicular line at a distance equal to half the width of your door. I did this in the third figure at 9.75", representing half the width of my 19.5" opening. There are 2 bricks shown representing the most forward and most aft arch placements I looked at in the steps above. Lay the inner edge of a full size brick at the door width and position the forward edge at your arch forward distance. The the inner diameter circle now shows you the arc you need to cut on the bottom arch brick and will help you determine how deep you need to make the arch form. You can kind of see how wide to make the arch form. You should be able to index both the front and rear inner edges of the bottom brick (after trimming) against the arch form to keep the bricks in proper orientation fore aft and perpendicular to the centerline of the landing. This is what I was trying to show in the first picture of post #22 above.
    Last edited by JRPizza; 03-09-2021, 08:09 AM.

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  • JRPizza
    replied
    From my experience, the only important "datums" (control surfaces) on the arch form are the forward edge for indexing the arch bricks fore/aft (the rear edge is useless as brick length varies) and the front and back edges of the radius that sets the arch height and makes the bricks perpendicular to the vent arch. That said, the placement of the arch form should not be looked at relative to the inner rear edge.

    I just figured out a way to use your cardboard template which I will try to explain when I get done with a few chores. It will help you locate your arch.
    Last edited by JRPizza; 03-08-2021, 05:58 PM.

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  • UtahBeehiver
    replied
    Click image for larger version

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ID:	436104 I disagree with Mark. The placement of the bottom inside is correct for a tapered inner arch. I do agree with JR that the form is too wide. For a tapered inner arch, a full length brick is used and cut back with the longest being the top dead center brick. See attached on how the IT is used to determine the various angles.

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  • MarkJerling
    replied
    Originally posted by Blairt View Post
    Thanks - you're right. I only had the outer circumference shown. I've drawn in the inner circumference now - is this the correct placement for the arch?

    I do intend to use half bricks for the soldier course - is there a preference to half headers over half soldiers?

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    Your arch needs to be further "in" as the arc of the dome needs to intersect the top of your door arch.

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  • JRPizza
    replied
    Blairt a couple of things. You might want to consider making your arch forms narrower front to back, as arch bricks for most builds are shorter at the bottom (not full length) and longer at the top. having a shorter form with parallel arches front and back will give you the best chance of indexing the bricks at the proper location and angle. This worked for my arch and if you look at the first link below you can see how a deeper form would not have allowed me to use the rear part to locate my bricks.
    Secondly, the arch needs to intersect the dome both at the bottom and the top, so at this point in the build some folks already have an IT built and are using it to make sure a brick sitting on top of the arch will mate properly. I verified mine both using a cad program (see capture in second link). I also included two pics to show the arch form locating shorter arch bricks and how I used my IT, arch form, and a couple of bricks to make sure the arch placement was correct.

    https://community.fornobravo.com/for...899#post380899
    https://community.fornobravo.com/for...319#post380319

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