#11  
Old 06-28-2010, 10:09 PM
mklingles's Avatar
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Join Date: May 2010
Location: Portland, OR
Posts: 93
Default Re: Michael's 42" in Portland

I'll get my bricks from Mutual Materials too. Curiously they make the concrete blocks that Home Depot sells in town, but Home Depot retails them for half the price Mutual Materials charges. Very strange.
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  #12  
Old 06-28-2010, 11:08 PM
Banned
 
Join Date: Feb 2010
Location: Bend, Oregon
Posts: 131
Default Re: Michael's 42" in Portland

I paid 1.13 a brick at Mutual Materials in Bend oregon
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  #13  
Old 07-03-2010, 10:55 PM
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Location: Portland, OR
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Default Re: Michael's 42" in Portland

I got my bricks, I picked up a saw, the hearth pour went well and today I took the side forms off and started on the floor.

I uploaded more pictures to my album. I did my plans on a drafting board (I get to work on a computer all day long), so I took some pictures didn't come out great, but they work:







Here's the insulation board cut and ready. It doesn't seem like finish work, but getting the front edge square and placed correctly will matter. I'm having a hearth stone cut to fit around my arch, so it all has to be in the right spot.
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  #14  
Old 07-03-2010, 11:04 PM
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Default Re: Michael's 42" in Portland

On friday I did a bunch of geometry. My oven will be 42" wide and 18" tall. I plan for arch of the dome to be hemispherical. Given the height of the dome is lower then the radius of the floor, the indispensable tool will not be at the center of the sphere. I think I've got it all worked out. Distance from the base of the tool to the face of each course of bricks. Once I got started I also worked out the length of the 4 edges of the trapezoid for each course of bricks. I'm going to wait to test my math on the build before I post it.

I plan to cut my bricks into trapezoids with a single cut. The piece cut off will be rotated and mortared onto the opposite side of the brick. I will only angle the side edges. I'll leave the brick at 2 1/2" front to back. Since the dome is hemispherical the angle between every course (moving from bottom to top) is the same, and that creates a gap at the back of about 1/2".
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  #15  
Old 07-05-2010, 09:19 PM
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Location: Portland, OR
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Default Re: Michael's 42" in Portland

I got my floor in. It's set in sand. You can see the 4 thermocouple connectors in the front corner of the picture. I put 4 in the floor: 1 about 1" from the surface (crappy drill bit didn't want to go any further), 1 about 2" from the surface, 1 at the interface between the brick and the insulation, and 1 at the interface between the insulation and the concrete. These are the "standard" ones from Omega - they are only rated to 900 deg F working temp. They might hold up and they might not. I've got some special order ones from Omega coming to go in the dome. They are rated to 1600 deg F.

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  #16  
Old 07-05-2010, 09:26 PM
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Default Re: Michael's 42" in Portland

Below you can see my indispensable tool. For hardware I used a lazy suzan bearing and a hinge. A turnbuckle will allow me to adjust the distance to each course. I'm planning for a hemispherical dome with a height of 18", so the center of my tool is not at the center of the dome.

Unfortunately turnbuckles have a left handed thread on one side. I need to find some left handed nuts (and washers )

The 3 legs are attached with carriage bolds and wing nuts. I slotted the plywood so I can adjust the distance and alignment of the legs. The wing nuts will allow me to remove the legs to get the tool out of the finished oven.


Last edited by mklingles; 07-05-2010 at 09:31 PM.
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  #17  
Old 07-05-2010, 10:22 PM
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Join Date: May 2010
Location: Albany, NY
Posts: 16
Default Re: Michael's 42" in Portland

I like the Tool. It is similar to the one I am making. Not actually ready to start building, but since I've been reading these threads I felt the need to build a tool. Must have WFO on the brain. Looking forward to watching your build.

Jon
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  #18  
Old 07-05-2010, 11:40 PM
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Join Date: May 2010
Location: gloucester ma
Posts: 24
Default Re: Michael's 42" in Portland

Mike-Like your drawings & tool. I am also using a turnbuckle for lenght adjustment and found that a pair of nuts helps lock the adjustment. Looking forward to more of your pictures. I am struggling with how much to tip the rings to acheive the arch and the fourth, fifth & sixth chain intersection with the 20 x 12 inch arched access tunnel. Good Luck Glosta
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  #19  
Old 07-06-2010, 12:04 PM
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Join Date: Oct 2006
Location: Vancouver Island
Posts: 1,374
Default Re: Michael's 42" in Portland

Since you have an adjustable tool, have you considered an elliptical shape rather that a truncated hemisphere ?
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  #20  
Old 07-06-2010, 07:44 PM
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Location: Portland, OR
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Default Re: Michael's 42" in Portland

@Glosta: I assume by “how much to tip the rings” you want to know the length to adjust your tool to for each course. I have created a spreadsheet to answer that question for my design. I am not ready to post it yet, because I want to test it on my build first (not tested = broken). If you are into excel, I can send you what I have. It is only useful if your oven is designed to have a hemispherical dome.

The other solution is to do a construction like in high school geometry. Draw a cross sectional picture of your dome shape to scale, and then measure the distance to each course from the point of the pivot of your tool.

@Neil2: I did consider an elliptical shape, but decided that the geometry would be easier to work out for a hemisphere. At first I was thinking heat was reflected like light on a mirror, and that optics would provide insight into the “correct” shape for the dome surface to “focus” the heat onto the cooking surface. I decided that the majority of the heat is actually absorbed and re-radiated by the brick. I assume the radiation from the surface of a hot brick is uniform in all directions. So, I conclude that the exact shape of the dome does not greatly affect the heat distribution in the oven.
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