dmun's 36" geodesic oven

[brillwills]

Re: dmun's 36" geodesic oven

thanks for the reply ,
like the look of your project using the triangle technique which should equate to an extremely strong design, Im building mine using a ply rib shutter as a former and plain old half brick laid in a lime mortar backing no internal joints or beds backed off with a 50mm Vermiculite concrete render shaped with a dolly and final face brick course topped of with a twisted stack (Decorative only) im going to rely on convection to vent the smoke out of the front opening , trying to source materials at fair prices here in the Uk is pretty difficult $3 a brick makes for a pretty hefty bill $1100 build cost ! I could buy a Neff Oven for 1/2 that

[Rojaws]

Re: dmun's 36" geodesic oven

Hi Dmun,

Quick question for you regarding the dimensions of the individual triangles...

How did you work out the angle at which you bevelled each triangle so that they form the correct curve for the diameter of the dome?... I *think* I have worked it out, but I would like to know if there is a specific formula!

I have plans to build a geodesic myself, but rather than hiding the form away, plan to cast some thin triangles out of castable, then have a multi layered design on top consisting of clay tiles with vermiculite/sand/clay in between layers to provide mass and insulation..

Main reason being I love geodesics and dont want to hid the design away underneath!

Brilliant series of posts.. I am truly inspired!

[dmun]

Re: dmun's 36" geodesic oven

I am currently discouraging anyone from building as thin a dome as I did. Four inches seems to be the minimal thermal mass to assure strength and longevity. There is nothing wrong with the geodesic system per se, but a two and a quarter inch dome is just too thin. I used proper refractory mortar, and I have major structural cracking in my dome.

If for any reason you need a dome that thin, you need to get a modular oven.

I'm not a fan of refractory concrete. Unless you have a lot of experience with the stuff, it's much more difficult to work with than portland based concretes.

As far as the geometry, I used a CAD program to design the pieces. It's pretty thoroughly described in the threads.

Oh, and one final thing, vermiculite is an insulator, and a good one, but sand and clay certainly are not. Keep those out of your insulation layer.

[edschmidt]

Re: dmun's 36" geodesic oven

I have only worked with one brand of refractory, I forget the name but its a 3000 deg high aluminum, and found that it worked no differently than regular concrete, other than it heated up a bit more. If you have a form setup you add water, use a paddle bit and drill, get to the right consistencey, pour into form and vibrate. I guess it could get tricky without forms, but with forms its straight foreward.
Eddie

[brillwills]

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.

just been looking at a few threads, I used this method of ribs to create an accurate dome and its reusable and cost effective, although the geodesic cut bricks are an excellent engineering feat the work involved in my oppinion is just too much, keeping joints to a minimum on the face I use a lime mortar for backing , I have cracking externally although nothing too major, happy to help with any problems there are pics on youtube under brillwills (woodoven)

[kwiebe]

Re: dmun's 36" geodesic oven

Hi DMUN,

I recently built a Rumford fireplace very similar to yours. Luckily I was able to fire it before I fully enclosed it. I didn't survive. I had major cracking in the firebox mortar joints. To the point that most of the firebricks in "hot zone" on the back wall were very loose. I will be rebuilding it so obviously I'd like to figure out what went wrong.

One thing I noticed was how much the back wall expanded when hot. It grew about a 1/4? over it?s 4? height. I build the throat similar to yours but poured a concrete lintel over the top of it. It is tied together as you can see in my pictures. When the fireplace was hot the lintel would actually be pushed forward slightly. Which would make sense as the back wall was 1/4" taller than front (compared to when cold).

Another issue was at the back where the smoke chamber sits on the supporting backer wall (concrete blocks). As the firebox grew in height it would lift off the backer wall and the smoke chamber and chimney would be completely supported on the firewall and not at all on the backer wall.

I noticed that you poured the floor of your oven around the throat of the fireplace. Did you have any cracking or movement issues with your fireplace?

Do you have any ideas why my mortar may have cracked? I used Heatstop 50 (bag form). It is possible that I mixed it a bit too wet but not excessively. I didn't soak the bricks but I did wet them with a mister as I laid them.

Any advice would be greatly appreciated.

[dmun]

Re: dmun's 36" geodesic oven

Gosh, I don't know. Two things with my fireplace: I had a year between when I built it and when I fired it up, because of the construction of the chimney. It was really, really dry. Second, I completely enclosed the fireplace in vermiculite concrete, maybe that gave it a little give in expansion situations.

A quarter of an inch movement is really major. I wonder if there's something I'm not getting...

[kwiebe]

Re: dmun's 36" geodesic oven

Maybe I got a bad batch of firebrick. Any idea what normal expansion should be? Can I assume you haven't noticed any expansion?

[Tscarborough]

Re: dmun's 36" geodesic oven

The fire brick are not normally laid on edge in a fireplace, even more-so if they are splits, and it looks like your joints are pretty wide for a fireplace. Firebrick do not really have much heat expansion, but mortar does.

[eatingmorefood]

Re: cutting the triangle blanks

WOW !
How much did the saw set you back ?
Eatingmorefood

[eatingmorefood]

Re: brick triangles

How much was that Chinese Saw ? Do you know how big the blade is on it ?
Thinking about a purchase.

[RTflorida]

Re: dmun's 36" geodesic oven

That is the Harbor Freight 10" tile saw. Do a search and you will find several threads and many posts about the saw. Current pricing is $249, but it can be had for less - Harbor Freight always has coupons and sales going on. I paid $199 for mine 3 1/2 yrs ago.

RT

[dmun]

Re: dmun's 36" geodesic oven

Mine was $199., but that was a long time ago, when the USD was still worth something.

Here's the current link:

2.5 Horsepower 10" Industrial Tile/Brick Saw

That doesn't include the stand, or the ten inch diamond blade.

If there's a HF branch near you, you can usually get hold of a coupon to get the same price as the web price.

[bricks]

Re: dmun's 36" geodesic oven

Hi dmum
I have just viewed your dome and think that the design plans are great.The only thing that would be of concern to me would be the fine points of the cuts.In firework we never have any cuts to small or fine to a sharp point as they can be very suseptable to thermal shock and crumbling or breaking off.Eg when building over an arch instead of having a pointed cut we turn the brick on edge and mark/cut.

[brickie in oz]

Re: dmun's 36" geodesic oven

Hi dmum
I have just viewed your dome and think that the design plans are great.The only thing that would be of concern to me would be the fine points of the cuts.In firework we never have any cuts to small or fine to a sharp point as they can be very suseptable to thermal shock and crumbling or breaking off.Eg when building over an arch instead of having a pointed cut we turn the brick on edge and mark/cut.

Bricks, it was built back in 2006, if there had of been a problem Im sure we would have heard about it by now..