dmun's 36" geodesic oven

[dmun]

Re: dmun's 36" geodesic oven

Can't you just cut the standard square/rectangular fire brick into a wedge shape to build a dome? This way there's no need to cut or precast a triangle piece. Seems to me putting together a dome using square/rectantular pieces is more error tollerent (deviations in measurement and motar thickness).

The problem with this approach is that every level needs to have the bricks cut to a different angle, as well as being tapered. It is the traditional way of doing it, but I devised the geodesic method because it only needed two basic shapes (which could be pre-cut) to form a dome.

The most error tolerant method is to use half or third bricks and use lots of mortar.

[need2retire]

Re: dmun's 36" geodesic oven

dmun,
Thanks for your response. Quite honestly, I have no experience at all in this area. What you said about cutting bricks at different angles for each level made sense to me but
only for the sides (because the radius gets smaller as I go up in level). However, can the top/bottom (tapered ) angle be the same for all levels? Would just tapering the top/bottom sides only be enough so that the bricks will not "fall in"? This way at least the top/bottom sides of the brick can have thin motar. This way will probably have as many cuts as yours anyway

btw ... very nice work!!!

[maver]

Re: dmun's 36" geodesic oven

However, can the top/bottom (tapered ) angle be the same for all levels? Would just tapering the top/bottom sides only be enough so that the bricks will not "fall in"?

If you make a hemispheric dome, then the top/bottom sides should have the same taper. Any variation from this requires differing tapers. I built a 'neapolitan' dome using the shim method (which is discussed in the plans) and I had a different shim angle for each row.

[dmun]

Re: dmun's 36" geodesic oven

However, can the top/bottom (tapered ) angle be the same for all levels?

Yes, if you are building a hemispheric oven.

Would just tapering the top/bottom sides only be enough so that the bricks will not "fall in"? This way at least the top/bottom sides of the brick can have thin motar. This way will probably have as many cuts as yours anyway

This touches on an idea I had when I was planning a more traditional looking oven. Here's a picture:



The upright brick shows how it is cut in thirds, with a square face, and a six and a half degree angle needed to establish the dome. This is the "wedge" brick that establishes the radius of the dome. These are laid alternately with spacers, which on the first level are the chunks left over from making the wedges. On higher levels they need to be cut, or at least trimmed, to establish the trapezoid established by the tilting-in wedge bricks.

The idea of making these spacers to any degree of accuracy made my head explode, and made the geodesic plan seem more practical.

[RTflorida]

Re: dmun's 36" geodesic oven

dmun,
your latest rendering is similar to what I originally planned. After much calulation and "test" cutting, I too scrapped the idea. Too mind blowing and labor intensive. Shame, I really wanted to attempt a near mortarless build. I settled on an angle cut of the first course to get the curve started, allowing 1/4" (and 1 - 3/8") gap between the remaining courses. I did decide to eliminate the side to side gaps, with only a minimal "glue" thickness of mortar. I'm guessing that I've been doing about 50% less cutting than my original plan, and considerably less mind trauma.

I really hope someone attempts a traditional brick dome with little or no mortar, it will be a sight to see and admire.

your geodesic dome, regardless of what you say could be done better, is truely a work of art, considerable preperation, extreme patience, and most of all - skill. I've looked this over at least a dozen times.....still scratching my head and thinking 'no way".

RT

[edschmidt]

Re: dmun's 36" geodesic oven

One thought that I had about the thin mortar semi-traditional oven was to use tapered firebricks. You could run them up and cut them so that there were 4 sides and coming to a point at the top. While it would not be a true dome shape, it at least would have all sides radiating towards the center of the oven which I feel is the real advantage of the dome, as opposed to the barrelvault which has 2 flat planes radiating toward each other.

[dmun]

Re: dmun's 36" geodesic oven

Tapered firebricks would be ideal, but here in the US, they are an expensive specialty refractory item. Plain low duty firebricks are about a quarter the cost.

[RTflorida]

Re: dmun's 36" geodesic oven

Ed,

I think the tapered brick could be made to work, they could save you at least 50% of the headaches and labor in the pursuit of a tight fit thin mortar dome. I looked into it, the cost was way out of my league. The only two local suppliers that offered them wanted $4.50-$7.50 PER BRICK, depending on the size and degree of taper. I settled on the 77 cent standard duty firebricks.....and am cutting as much as I can stand (I've been able to get 2 courses done per day on the weekends, pretty time consuming). I honestly don't know how dmun did it, I just don't have that much patience.

RT

[edschmidt]

Re: dmun's 36" geodesic oven

I actually bought 6 pallets of tapered, and large radius firebricks which are used to build a cylender for a blast furnace. Some tapers are high duty others are super high duty (90%aluminum silicate 3000deg.) for about .20 each. I might lay this up to see what it looks like with no mortar.(though its still impractical at full price ).
The guy I bought them from said they came in the building when he bought it, they ordered the materias and never built the furnace. He said that If I hadnt bought them he was going to use them for landscaping. What a waste that would have been.

[dmun]

Re: dmun's 36" geodesic oven

I actually bought 6 pallets of tapered, and large radius firebricks which are used to build a cylender for a blast furnace. Some tapers are high duty others are super high duty (90%aluminum silicate 3000deg.) for about .20 each.

Wow! You hit a home run! I felt lucky to buy plain used brick pavers for $.20, which I used for my exterior enclosure. If you measure one of the bricks I'll tell you what the angle is.

[maver]

Re: dmun's 36" geodesic oven

You have to be careful in planning to be clear why we would want to reduce mortar in dome construction. David has expressly indicated his reason was due to the cost of mortar used. With his excellent planning he was able to engineer a dome that had low material costs - and probably not a big difference in labor from my dome (or any other made from splits). I tried to reduce mortar (primarily in the oven face) by alternating half bricks with trapezoidal cut bricks - didn't measure, just pieced them together with some good estimates of the angles needed. Usually any miscuts were incorporated into the dome for upper rings as the angles constantly changed. While an oven built with less mortar is theoretically more stable, with modern refractory mortars or even the pompeii home mix mortar with fireclay I doubt it is likely to become an issue for a home oven.

I like David's design for the thinness of the dome - I'm anxious for weather to improve in the Northeast enough for David to cure his oven and report back on heat up times (probably the sixth full firing before the oven will hit it's stride). How's the weather David?

[edschmidt]

Re: dmun's 36" geodesic oven

The reason I would prefer to reduce the mortar is because the refractory sales people I have talked to have expressly stated that large areas of mortar are inharently unstable. He told me that the maximum I would want to any mortar is 1/8" thick and the thinner the better. Granted he is selling refractory products for use in kilns, blast furnaces, etc. But with that said the firebrick is a pressed and fired ceramic and therefore very stable structure. Mixtures of fireclay,sand,cement are not (cement degrades, fireclay increases strength as heated but not fully until cone 5, approx 2000deg.)He also didnt give have alot of faith in heatstop. I know the real world experience is that in our applications these products work, but the 2500deg pre-mixed airdry mortar he sells is .50cents a pound so why not try for an oven that could double as a blast furnace if the need came up.

One more thought since im obsecing about the tapered oven, I would start the base as a square, and the corners could be alternately overlapped like normal brickwork right? that way I would only have to cut 2 bricks per course, plus gain the stability inharent in an overlapping structure right? Am I missing something or would this work smoothly?

[edschmidt]

Re: dmun's 36" geodesic oven

One more thing, durring the brief thaw here in MI, I did a little more work to the oven exterior. I went back and forth alot on the roof materials and decided I just wanted get something more permanent than the Ice and water shield which has graced it for over a year and bent up a standing seam aluminum roof. My wife wasnt impressed, until I told her I can paint it. Im also contemplating using granite on the face (now white).

[RTflorida]

Re: dmun's 36" geodesic oven

very nice. personally, I love the "tin" roof. As for a granite front, it would really dress it up, upscale - yet keeping with your stone theme. very nice

[need2retire]

Re: dmun's 36" geodesic oven

I've been reading this thread and forum over and over again, so I'm starting to understand a little more (I think ). I'm still sticking to the "traditional" way of building the oven because I think it will be more forgiving for a beginner like myself

I've also convinced myself that cutting wedges on the two sides are easier (as apposed to my previous post) than doing the top/bottom sides. I "THINK" I have a way of cutting wedges without the need of calculating the wedge angle and/or radius for each level. I've already test that, but only on a two-dimensional plane.

I think I can figure out the cut for wedges on the top/bottom side as I progress on each level. However, the bottom side get harder because I need an additional "curve" shaped cut to fit the curvature of the ring ... to eliminate any space between bricks. Anyone tried this?

So, I do have 1 crazy question. Does anyone know where I can get styrelfome block for cheap? I'm thinking of building a dome out of styrelfoam block 1st. Why you may ask?

1) For me, building from foam block is a good way to practice ... and mistakes are very easy to fix.
2) When I'm done, I can take the foam pieces apart and use it as a templet to cut my real brick. Hopefully this way I can get a near perfect fit. I guess if you're building oven professionally, you'd have a permanent templet to use over and over again.
3) I can slice the foam dome to pieces and use it as a form to do castable brick.