Tapered Cuts

[JoeT62]

A question - looking at some of the domes with taper cut bricks, I can't help but think "maybe I should..."

I was wondering if those who have done the tapered brick cuts could comment on how they measure those angles for cutting, and whether they recommend it.

[Unofornaio]

Re: Tapered Cuts

Hey Joe,
While I haven't built a dome oven (yet) I have built 2 roman style ovens and worked with fire brick for many years and I can tell you that the weak link in the building process with fire brick is the mortar joint. When I build the pizza oven here at the house I will cutting each and every brick to fit as tight as possible. the plan is to document every single cut variation.

[jahysea]

Re: Tapered Cuts

Hi Joe,

I would highly recommend tapering the sides if you have a wetsaw for the duration of the bricklaying portion of your project.

I rented one on the days I spent forming the dome & found that to be a good solution.

I cut bricks into simple trapezoids starting at about the 5th chain and realized I should have started earlier. The half bricks looked a little like this:
_
/_\

Some folks may have tried to create trapezoids that are larger on the outside to allow for less mortar use. This would provide a better dome because brick and mortar have different thermal expansion values. I deemed it too difficult and used the "simple trapezoid" approach. My trapeziods were tight on the inside of the oven but had mortar gaps on the outside.

The first chain I spent a lot of time measuring for the correct angle, cutting bricks, etc.

I eventually realized you just needed to dry place 3-4 half-bricks and estimate the amount of angle you need visually by eye and measure distance in from the corner. Then find or cut a scrap slice of brick the thickness of that distance. I started at something like 1/4 inch from memory. Place this piece of scrap on the saw under the edge of your half brick that is away from the blade, tilting the half brick toward the saw blade. Run the brick through the saw, then turn it 180 degrees and run the other side through.

Be slightly conservative with your cuts, make a couple and see if you like the fit. If they are still too wide on top, cut a steeper angle by using a thicker shim scrap.

Each chain the angles in the trapezoid get more aggressive.

When you get to your last chain or two, you will find the process easier if you use quarter bricks instead of half bricks.

[Balty Knowles]

Re: Tapered Cuts

You can use a straight edge from the center of the floor to mark the correct angle on each brick. Cut 3 or 4 & dry fit to make sure the angle is correct. You can also use this method to mark the wedge angle.

See pic this is how I started mine.

Rgds

Balty

[Hendo]

Re: Tapered Cuts

Some folks may have tried to create trapezoids that are larger on the outside to allow for less mortar use. This would provide a better dome because brick and mortar have different thermal expansion values.

Wouldn't this depend on the composition of the mortar? My mortar consists of 40% alumina and 60% silica - the same as the bricks. So I was hoping it would have an identical thermal expansion coefficient to the bricks? Yes/No???

[RTflorida]

Re: Tapered Cuts

I used a very similar approach to Balty. Measuring, cutting and installing 3 bricks at a time. I also varied the widths of my bricks to keep the mortar lines from the previous course as centered as possible....this resulted in the angles not being constant, resulting in only doing 3 at a time. Was a slow and tedious process but I achieved my goal of a very tight fit and minimal mortar.
As many have stated; if there it to be a failure (crack), it will occur along a mortar line.
In hindsight, I would do the same again....just figure out a faster way of achieving the same result.

[Unofornaio]

Re: Tapered Cuts

Wouldn't this depend on the composition of the mortar? My mortar consists of 40% alumina and 60% silica - the same as the bricks. So I was hoping it would have an identical thermal expansion coefficient to the bricks? Yes/No???

Excellent point as far as expansion properties. I guess it would be safe to assume they would react the same since they are the same material. Then again a difference I would think is the bricks are baked which I'm sure changes its properties to a degree. I have always used fire clay to lay fire brick, I don't know much about the 60-40 mix but it sounds very interesting.

[JoeT62]

Re: Tapered Cuts

You can use a straight edge from the center of the floor to mark the correct angle on each brick. Cut 3 or 4 & dry fit to make sure the angle is correct. You can also use this method to mark the wedge angle.

I love that idea. Simple enough for even me! Looking at your photos, it looks like you also tapered the soldier course as well? Also, do you make wedge cuts on all four surfaces to get the trapezoid? Or just the two lateral surfaces and one of the superior or inferior?

[JoeT62]

Re: Tapered Cuts

Hi Joe,

I would highly recommend tapering the sides if you have a wetsaw for the duration of the bricklaying portion of your project.

I rented one on the days I spent forming the dome & found that to be a good solution.

I cut bricks into simple trapezoids starting at about the 5th chain and realized I should have started earlier. The half bricks looked a little like this:
_
/_\

Some folks may have tried to create trapezoids that are larger on the outside to allow for less mortar use. This would provide a better dome because brick and mortar have different thermal expansion values. I deemed it too difficult and used the "simple trapezoid" approach. My trapeziods were tight on the inside of the oven but had mortar gaps on the outside.

The first chain I spent a lot of time measuring for the correct angle, cutting bricks, etc.

I eventually realized you just needed to dry place 3-4 half-bricks and estimate the amount of angle you need visually by eye and measure distance in from the corner. Then find or cut a scrap slice of brick the thickness of that distance. I started at something like 1/4 inch from memory. Place this piece of scrap on the saw under the edge of your half brick that is away from the blade, tilting the half brick toward the saw blade. Run the brick through the saw, then turn it 180 degrees and run the other side through.

Be slightly conservative with your cuts, make a couple and see if you like the fit. If they are still too wide on top, cut a steeper angle by using a thicker shim scrap.

Each chain the angles in the trapezoid get more aggressive.

When you get to your last chain or two, you will find the process easier if you use quarter bricks instead of half bricks.

Excellent advice! Thank you. I will indeed have a wetsaw for the whole process, so I think taking the extra time here will be worth it.

[Hendo]

Re: Tapered Cuts

I don't know much about the 60-40 mix but it sounds very interesting.

It's Shinagawa's SHIRABOND 50 airset mortar. See info sheet at http://www.shinagawa.biz/system/file...ND_50_REV1.pdf. It's a bit higher on the alumina than I thought, but I believe my firebricks are around 43% alumina in any case.

Cheers, Paul.

[Hendo]

Re: Tapered Cuts

Originally I didn?t plan to make any radial cuts (other than cutting whole bricks in half/thirds/quarters as necessary), as I?m using tapered bricks to form a natural 1100mm (43?) dome shape. I was still going to end up with triangular mortar joints between bricks on each course.

But my brickie has done one or two domes and has encouraged students (he teaches bricklaying at a TAFE college here) to cut tapers on each of the dome brick courses where the bricks butt up against each other. After he explained how to do it, and with the convenience of a wet brick saw at my disposal, I have decided to go down the same route. So I?m effectively manually tapering tapered bricks!

This is how the tapers were calculated for the first perimeter ring around the floor, which consists of normal, rather than tapered, firebricks:

External diameter = 1330mm (52.4?)
External circumference = 1330 x π = 4178mm (164.5?)
Number of (half) bricks required = Ext Circ/brick width = 4178/115 = 36.3
Internal diameter = 1100mm (43.3?)
Internal circumference = 1100 x π = 3456mm (136?)
Difference in circumference = 4178 ? 3456 = 722mm (28.5?)
Total taper for each brick = Difference in Circ/No of bricks = 722/36.3 = 19.9mm (bit over ??)
So half this (9.9mm or a tad over ⅜?) needs to be removed from the inside of each connecting face.

I set up all these calculations on a spreadsheet, and plan to do the same for subsequent courses.

When it came to cutting the (half) bricks, I marked one brick, and adjusted the stop on the brick saw table to be just under the brick width of 115mm (114.6mm as calculated). I then clamped a G-clamp to the stop to give me the desired 9.9mm of taper. Like JC, I cut one taper, then flipped the brick upside down and cut the other. It took probably an hour or so to run through the 30 half bricks for the first ring. Easy peasy! See pics below for a better explanation of the setup.

At this stage, I?m not sure how I?m going to cut tapers for the upper rings, as these can?t be laid flat on the brick saw table, but must be lifted on the outside face to simulate the angle they?d rest in when fixed in the dome. I?d like to rig up some sort of support so I can just rip through them as easily as the ?floor ring?.

One mistake I have spotted since doing the first ring is that I didn?t allow for the thickness of the 1mm or so mortar joint. Ah, the benefit of hindsight! Early days yet.

Cheers, Paul.

[Balty Knowles]

Re: Tapered Cuts

I love that idea. Simple enough for even me! Looking at your photos, it looks like you also tapered the soldier course as well? Also, do you make wedge cuts on all four surfaces to get the trapezoid? Or just the two lateral surfaces and one of the superior or inferior?

I cut just the bottom face to form the wedge shape. In this way when you line up the top face with a straight edge from the center then the face of the brick is perpendicular to the center point.

I also used this method to strike the angle to cut the soldier course. Be careful I found this seriously changes the radius of the dome & you'll need adjust the radius with each subsequent course.

Rgds

Balty

[Unofornaio]

Re: Tapered Cuts

Hendo- thanks for the link.