Pdx 42" update

[Macrinehart]

Once I finish marking all the guide lines on a course of bricks, it's time to start cutting. Using the HF wet saw with tilt blade makes this task a lot easier. I start by setting the blade tilt using a magnetic angle finder. The angle should match the side tile angle. Perfection is not required. I'm content to get within a 1/10th of a degree.

Once I have the angle set, three cuts yields 2 bricks. I line up the line with blade and cut. Do the two outside cuts first, then the middle cut. The only additional consideration is that I clean the cutting bed after each cut because the debris can destablize the bricks.



And for those wierd angles, I just prop the brick I'm cutting with wedges from remains of other cuts found in my boneyard discards, as shown below.

[Macrinehart]

There is room to get 2 dome bricks for each firebrick. To finish marking the second domebrick flip the firebrick and rotate 180 degrees so that that the inside top edge is facing you. Then use the calapers to mark the outside bottom corner on the swcond fire brick.
I label the top and bottom for reference. Notice that the top of the first dome brick is on the same face as the bottom of the second brick.

Next we mark lines 9 - 12. Keep in mind the rule of no parallel lines, lines 9 - 12 will converge and then diverg from the center line. When your finished the origin of line 9 connects to the end of line 12.

[Macrinehart]

The rest of the lines for the first brick are drawn relative to the end point of lines 1 & 2. On the top of the brick, use the side angle T-Bevel to mark lines 3 and 4 as shown. These converge to the top inside edge, the narrowest width.



Rotate to the inside face and use the side tilt T-Bevel to mark lines 5 and 6, which diverge.



Finally rotate again and mark lines 7 and 8. These also diverge and should connect to the starting points on lines 1 and 2.

[MarkJerling]

See, that's why your oven is so much tidier than mine! I just 'eyed' it all and marked my cut lines with school board chalk. But, mortar hides a multitude of sins, so all good! LOL

[Macrinehart]

The marking of the lines will come in a couple posts since the upload limit is 6 files.

First I pick a starting point, which will be the bottom outside edge, and mark my side tilt link for the back of the brick (line 1). Then I measure the width of the bottom back with the calapers, after which I I mark the other side tilt (Line 2). There are no parallel lines in the process. The first two lines should be approaching each other up the back face of the brick. If you have parallel lines at any point, then the T-bevel angle needs to be flipped.


Measuring the width of the bottom outside edge.


First to lines illustrated with the T-Bevel set for side tilt.

[Macrinehart]

First, I mark each brick with the lines I want to cut. For this job I have two adjustable T-Bevels, a woodworking protractor and digital calapers, all borrowed tools. I also printed the dome calculator spreadsheet, found elsewhere on this site, which has all of the required angles and brick dimensions for each course.
Following the guidance on that worksheet, I set one T-Bevel for side angle and the other for side tilt. The digital calapers are set to the brick width at the bottom back side, the longest dimension.



The dome caluculator file is very helpful but I recall someone saying it's not perfect, without going into the details. What I found is that my mortar joints are a little thicker than planned, which has a nominal impact on the number of bricks for each course. Furthermore, it seems like the calculator over estimated the # bof bricks required starting around course 4 or 5. Since then I've been estimating the number of bricks with each course, which is the handwritten notation on the worksheet.

The other observation, marking bricks is not like fine woodworking, the dome calculator reports angles in 1/10 of a degree, but I just get as close as I can with the protractor. There is mortar that covers any error in precision.

[Macrinehart]

I got back to work this weekend after taking a break to visit family and also to get some fall chores done. It was a beautiful day yesterday but by the time I finished my chores most of the day was gone so I spent the evening washing mortar stains off my bricks with undiluted distilled vinager. Today I put in a few more bricks between the dome and opening arch. I also cut bricks for the next course.

It's been over 1.5 years since I started my build, and one thing I learned along the way is that cutting bricks is actually a lot easier than I originally expected. When I started I spent a lot of time planning each cut and designing and building jigs to help with alignment. But after wasting a lot of time with this side projects, and a fair amount of money, I landed on my techique which is simple and low cost. I'm sure it's not original, but it can be hard to find things on this site so I thought I'd share my process in the hopes that it demystifies things for other aspiring builders. This is my technique for cutting dome bricks. Due to the limit of # of photos per post I'll spread this over several posts.

[Macrinehart]

Today I rebuilt the opening arch. While I usually with I would have followed UtahBeehiver's advice, today I decided not to adjust the height of the arch form as that task seemed like a fairly unsafe use of the tablesaw, and I figured safety first. I also measured the height of my lath strips and they are 3/8" total with 2 strips. Hopefully it is enough.

I built the entire arch in one go with slightly higher hydration on the mortar to make minor adjustments easier. The entire process was smooth, but I'm leaving the arch support in place to allow the mortar to setup some more. I used a level to check things throughout and the front face is now smooth and perpendicular. (The picture is crooked, not the arch. )

I did have to pull it forward a little, and there is now about 5/8" gap to the inside radius of the dome. I imagine that means I'll have a little offset between the back face of the arch and dome bricks. I'm not too concerned about it.

[UtahBeehiver]

Before you start the rebuild, check how much release you have under the form, one of the pic show small wood shims (1/4"??) this "may" not enough release to drop the form after the arch is completed. In my build I started like this but soon found out 1/4" was not enough and redid form and had a release of about a 1/2".

[Macrinehart]

Today was a day of prep work for rebuilding the opening arch. I started with cleaning mortar off the arch bricks, using a hammer and cold chisel. I found the process worked best if bricks are soaked thoroughly before cleanup. It keeps the dust down and I think the mortar comes off more easily.

After that I started improvements on the arch support. My brother brought over a custom tool for bending wood, and we cut some thin mahogany plywood down to size and bent it befor attaching to the arch support. I also used some scrap wood to add a faceplate to the front of the arch support, ensuring all bricks are plumb. Borrowed this idea from one od the pros on the forum, can't remember who but I'm sure you'll recognize it - thank you!

The inside arch now ihas an extra 1/8" radius, so after dryfitting and checking measurements I went to work on the dome removing mortar and a few filler bricks to expand my opening a bit. The arch will be a little forward of it's planned position, but much better than the out of true build I had on the first pass.

As dinnertime approached, I decided rather than starting to build the arch I'd do some cleanup instead. Got out the shop vac, removed Ll the spilled mortar and dust from inside the oven, and then took out my floor protector and cleaned up around the edges. Things are looking pretty tidy and I'm ready to rebuild the arch tomorrow.

[MarkJerling]

I don't think the dome is high enough yet for you to worry about collapsing, but, of course, I'll deny all liability if it does! LOL.
No, I really don't think it should be a problem. I've seen many builds here where people get stuck into their domes before doing their door arch, while I've always considered it better to build the arch first, as you have done. Worse case scenario, a few of the closest dome bricks may loosen, but if the mortar is well set already, it should be fine.

Of course, if the first few courses are fine, then leave them be, but it is nice to have a good, straight door opening for a nice door seal, so review that as you go.

[Macrinehart]

Thanks MarkJerling! That didn't occur to me. I think the first 2 or 3 bricks are ok. Maybe just rebuild the top of the arch? Do I have to worry about the dome colapsing if I take the full arch out to rebuild it?

[MarkJerling]

While you can certainly cut it straight, considering how little it is attached to the dome, what's to stop you simply removing the arch and rebuilding it? (Making sure to keep the brick numbering and joins the same, but working over a better temporary former this time, with support wedges under, so that you can drop the former before pulling it out.)

I'd think the vibration from the cutting will loosen the mortar joints anyway, so might as well dismantle it, clean the bricks and rebuild the arch in my view.

[Macrinehart]

Hi Gang - I could use a little problem solving help with this post.

The inner arch on my oven is about 1/2" (~13mm) out of plumb, leaning forward and roughly symetrical (keystone is furthest point forward). This happenes when I was removing the arch support.

So a few lessons learned on that, first I propped the arch support on 1/8" lathe, and removed the lathe to drop the support. Right idea, but 1/8" was not enough to clear obstructions. Second, My arch support was open in the center, I just used som thing plastic binders to cover the gap but when I set my bricks the mortar pressed through the inner joint and that plastic just warped so the mortar hardened and bound between the inside and outside faces of my arch support. If I was thinking, I would have disassembed the arch support to remove it. But I was not thinking so I just horsed it out and that's that.

So, I am trying to decide how best to correct this issue, inside the dome and out. I have a couple ideas and wanted to run them past the thread.

Inside the dome, I was thinking of mortaring some excess brick material around the top inside arch to restore it to plumb before I continue with the dome. I feel like that is the right answer to prevent "the dreaded droop" form deforming my dome

Outside, I have a couple thoughts. First, I could cast a door that fits flush against the out of plumb surface, and then build the outer arch plumb and fill the gap with ceramic fiber rope. Or, I could use mortar to bring it to plumb on the front face of the arch. Or I could use my angle cutter to cut it to plumb. On this I have seen too many storys of folks injurying themselves with the angle cutter to feel comfortable with this much cutting. But with caution and a lot of blades I think it would work. The mortar solution seems a little like something that would not stand the test of time. Welcome all input!

Here are some photos of the plumb issue and outer arch prep. I paused the dome build, but there is still plenty to do!

[MarkJerling]

That's coming along nicely Mac. At this rate you'll be able to bake pizzas before the year is out!