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Muscats 05-13-2010 06:07 PM

Adjustable indispensable tool ellipse dome
I am trying to work out how to adjust an indispensable tool so it will make an ellipse without causing the bricks to be stepped. The tool I am planning to make will have a turnbuckle for adjustment which will reduce the length of the tool by 3 mm (1/8th inch) per turn

My calculations are as follows (I will include measurements in mm and inches)

Internal radius at floor 550mm (21.65 inches) (1100 (43.3 inches diameter)
Proposed Dome height 400mm (15.7 inches)
Required reduction in dome from standard hemisphere 150mm (5.9 inches)
Number of turns of the turnbuckle to reduce height 50
Number of courses of bricks 10
Turns per course 5
Length adjustment per course 15mm (.59 inches)

Given the above, if I angle the face of the indispensable tool that is against the brick by 15mm (.59 inches) (7.5 mm (.3 inches) top and bottom) to allow for the difference in the length of the tool will I eliminate the steps and get a smooth dome?

Alter ego 05-13-2010 07:11 PM

Re: Adjustable indispensable tool ellipse dome
1 Attachment(s)

I made a similar adjustable tool as you are talking about only mine was made from 10mm threaded rod for a 500mm internal radius oven (at the floor) and I adjusted the radius for my oven by 5mm every course of bricks.

You are welcome to have it if you are willing to pay the postage costs from Newcastle to the ACT. I can even send you another length of threaded rod if you want to start with a larger radius.

Let me know if you want it.


Muscats 05-13-2010 11:38 PM

Re: Adjustable indispensable tool ellipse dome
That tool looks perfect and it looks like it was doing a grand job with your dome.
I would be honoured to use it to make my oven.
I am still a while off starting though. I have to wait for our pergola to be build so I don't end up putting the oven where one of the posts goes and the plans for the pergola are still in with the council (been waiting over a month already).
Please let me know how much postage would be to Canberra area and your prefered method of payment send me an email with the details.
If you already have the extra rod Ill take that too but dont spend any extra on it.


p.s. As has been the tradition on this site i will endevour to pass the tool onto another WFO builder in due course.

fxpose 05-14-2010 12:29 AM

Re: Adjustable indispensable tool ellipse dome
The face angle changes with every shortening of the tool. On my build I've been ignoring the face angle of my tool with each course for the most part and simply aligning the bottom edge of the brick to the top edge of the brick beneath it. Otherwise, the tool does an excellent job of maintaining a circular plane of each course of bricks layed.
My floor radius is 17" and my dome height will be a fraction under 15".


Alter ego 05-18-2010 04:16 AM

Re: Adjustable indispensable tool ellipse dome
I did the same as you George to cope with the change in the angle of the face of the tool. The tool held the top of the brick and I just lined up the bottom of the brick with my fingers as I placed each brick and wiped the excess mortar off the brick face.


kebwi 05-18-2010 08:00 AM

Re: Adjustable indispensable tool ellipse dome
My brick placement tool is adjustable on two axes (floor arm and radial arm) to achieve any curvature with perfect brick alignment. The floor arm slides inward "across" the center of the floor such that the hinge moves toward the center of the floor, one notch (as shown) per brick level. Meanwhile, the radial arm gets steadily longer per brick level. I specified the notch locations to 1/16" accuracy although that is a matter of taste. Less precision would be fine. Here's a schematic (for my particular oven) and a few photos:

fxpose 05-18-2010 08:53 AM

Re: Adjustable indispensable tool ellipse dome
The results would pretty much be the same whether you use kebwi's method of readjusting the tool for every course or manually aligning (visually and/or by feel) the bricks as Paul and I did.

BTW, that's a pretty clever design of the tool Keith. I saw that during your dome construction.


kebwi 05-18-2010 09:11 AM

Re: Adjustable indispensable tool ellipse dome
Agreed. I'm just explaining my process. I'm certainly no advocating it. The payoff for such absurdity is probably best.

BTW, for all the precision I put into my oven, it has produced numerous cracks. I even have a wobbily keystone in one of my arches. Really makes me question the benefit of designing and shaping the oven and bricks so meticulously. What's the point if the mortar all cracks out and the oven ends up standing under its own compressive strength anyway? Oh well.

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