Author Topic: Fire Pit Oven  (Read 2103 times)

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Offline scott123

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Re: Fire Pit Oven
« Reply #20 on: June 05, 2013, 08:26:20 PM »
I just crunched some numbers regarding firebrick weight.

According to this page here:

http://www.traditionaloven.com/articles/84/firebricks-heavy-dense-fire-clay-bricks

a typical 23% alumina split would come in at 3.5 lb. The base setup of the square concept is 14 bricks, which is 49 lb. A 10 brick ceiling would add another 35 lb. to that.  If you use bricks to cover up the sides, and add two more columns, that's 10 more bricks, 35 more lb. 

That's 120 lb., not counting the weight of the angle iron or the quarry tiles. 
« Last Edit: June 06, 2013, 03:04:04 AM by scott123 »


Offline wahoo88

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Re: Fire Pit Oven
« Reply #21 on: June 05, 2013, 08:48:52 PM »

a typical 23% aluminum split would come in at 3.5 lb.


What's that?

For the ceiling, I can't imagine that stove pipe would be able to support bricks on end.  Are you suggesting full firebrick cladding/walls to hold up a ceiling?

120 lbs is reasonable, but the cost of even 24 firebricks is a bit much.  From what I see, they run about $24 for 6 bricks, so I'd be about $100 out just for 24. Are there any other materials that sacrifice thermal properties for price?  I'm definitely using firebrick for the floor though.

To recap:

Floor: the angle irons supporting firebricks, covered with UQT.
Walls: Stovepipe, perhaps slid in between the firebrick and irons on the sides, and in between two bricks at the back.
Ceiling: Firebrick.  Not sure what is supporting firebrick.  I'm assuming there must be a support sheet under the bricks.
Covering for the side openings: Would flashing work here?  There would be direct flame contact.

Thanks

Offline scott123

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Re: Fire Pit Oven
« Reply #22 on: June 06, 2013, 03:44:22 AM »
Sorry, that was a typo.

I meant to say "23% 'alumina' split"  aka, a half width firebrick split (1.25 x 4.5 x 9) with 23% alumina content.

I haven't purchased firebricks in a while, but $4 a brick sounds really high. Are you going to a brick yard? You want to go to a place that just sells bricks- wholesale, in huge piles- not a fancy schmancy retail outlet with a brick department. Also, are you pricing splits (1.25" thick) rather than full size (2.5" thick) bricks?

Copper flashing (flame safe)- expensive. Aluminum flashing- non flame safe. Steel flashing- galvanized, pain in the butt to remove the zinc- zinc is toxic when burned. Start looking around for old non cookie sheets- such as this:

http://www.walmart.com/ip/Oneida-Large-Cookie-Sheet/10174459

I believe almost all non stick cookie sheets are teflon on steel, but I'd check the specs first, if you have them.  You can also feel if it's steel by it's heft- it will be thinner, but not that much lighter than aluminum cookie sheets.

The brick ceiling is exactly the same setup as the floor, except the angle iron is running side to side rather than back to front so that the stove pipe can support it.

Think about the force it takes to crush an aluminum can, the diameter of the can, and the gauge of the metal. Stove pipe is stronger metal, thicker gauge and the downward force is spread over a much wider circumference- 72" of it. If you made a 72" circumference 18"-ish diameter stove pipe that was only 5" high and put a piece of plywood on it, you could probably stand on it.  What we're building won't be quite as strong because it will be missing a side, but it should be plenty strong enough to handle 10 firebrick splits and the angle iron supports.

It's depends on the quarry tile (I've come across really fragile and really durable quarry tiles), but you might be able to go with a UQT ceiling.  Since it's not in contact with the food, you could also go with a glazed tile ceiling.  I've been recommend black glazed tiles for broilerless oven setups.  You could point the black tile down and gain some emissivity, but, for your target temps, you might not need it and could point it up.  If you do go with a glazed tile, try to get one that has the darkest base color possible and isn't pure white. Also, if you go with glazed tiles, you'll probably want to double them up for a bit more thermal mass.  1/2" is as small of a thickness as you want to go.

Btw, a bit unrelated, but I just figured out another way to suspend a Kettlepizza knockoff ceiling that might be the cheapest of all, depending on what you drink.  Aluminum soda cans might be tall enough to crimp together into a long wall, or, if they aren't long enough, 24 oz. aluminum cans. It's a bit more work than flashing, but, for some people, you can't beat free.

Btw, the more I think about it, if you were really careful about how high your fire goes, you might be able to pull a Kenji and use aluminum- on the walls, where, hopefully, they won't get much direct flame.

Hmmm. I'm wondering if you could run bolts up through the angle iron and use those to thread the ribbon of stove pipe through, kind of like the rollers in a film projector. That would give you more stability.

Lastly, I mention metal recyclers before- if you have a large one near you, go. It's amazing how much metal gets recycle.  I went a few months ago to one near me and there was a load of stuff being tossed- perfectly good rebar, angle iron, some sheet.  No promises, but you might find something that suits your needs.  You won't be baking on it, so it doesn't need to be pristine clean, or if you do want it pristine, there's always naval jelly.
« Last Edit: June 06, 2013, 04:16:52 AM by scott123 »

Offline JD

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Re: Fire Pit Oven
« Reply #23 on: June 06, 2013, 09:46:57 AM »
Not to completely undo what Scott has suggested, but you could make a foundation to drop a Mighty Pizza Oven on :) http://www.pizzamaking.com/forum/index.php/topic,25065.msg256449.html#msg256449

Josh

Offline wahoo88

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Re: Fire Pit Oven
« Reply #24 on: June 06, 2013, 06:33:36 PM »
Ok, the setup is beginning to crystallize for me.

Only real question:  I don't really see any 18'' stovepipe/chimneypipe.  I believe you mentioned that if the pipe is snap-to-lock, then I should just be able to get, say, 8'' pipe and snap it together.  And 5'' is a good height (length of pipe) to get?

I'm going to make a good drawing of the whole setup, take a bunch of screenshots, and post them by the weekend.
Google isn't great for brickyards/scrapmetal, as they probably get their business mainly from contractors, but my dad probably knows some good places.  I'll be calling around for split firebricks and scrap steel.

Thanks Scott.

Offline wahoo88

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Re: Fire Pit Oven
« Reply #25 on: June 06, 2013, 09:00:58 PM »
Ok, I've drawn out what may be the final product.  The right stovepipe wall is cutaway for easy viewing.

Materials are as follows:
Tan/Gold: fire bricks, split
Red: Unglazed quarry tile
Wavy silver: steel (angle irons)
Dark grey: miscellaneous metal, not aluminum
Orange: shows where the oven is open to the fire below
Black: Stovepipe

Scott, is this exactly what you had in mind?
I may change the roof to UQT to cut down on costs.

Thanks.

Offline scott123

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Re: Fire Pit Oven
« Reply #26 on: June 07, 2013, 02:39:46 AM »
18" diameter x 5" high stove pipe doesn't exist.   If it did, this would be WAY easier.  That's for the most part, what you're creating- what you're piecing your small strips of cut stove pipe into. The only difference is that your finished 'pipe' won't be a full circle, but, rather, a U shape with an opening in the front where you launch the pizza.

5" high stove pipe doesn't exist either.  You might find some sort of 5" adapter or extender, but I wouldn't waste your time looking for it.  Here's what you want:

http://www.homedepot.com/p/t/202907227?productId=202907227#.UbFdEmoub0k

This is 6", you may want 8".  It depends on the wall height you go with.  Earlier you spoke about tucking the wall between the brick and angle iron, but now I see that you have the wall sitting on the brick in your diagram.

If you sit the wall on the brick, and go with 5" walls, with .5" quarry tiles, that's 4.5" to the ceiling. It's tight, but think that's what I'd go with.  You don't want to cramp the launch, but, at the same time, in bottom heat scenarios, the ceiling, for proper heat balance, should be as close to the hearth as possible.

If you tuck the wall between the firebrick and angle iron, that means you have to add the 1.25" thickness of the bricks to get the same 4.5" dome height making for a wall height of 6.25". There's one consideration with a tuck, though.  If you're at angle iron level on the sides when it comes time to run the wall across the back the two angle iron pieces in the middle will block it.  What I'm think you can do, though, is terminate each wall run at the back middle.

I've been thinking a lot about my bolt post/film projector idea. First off, I'm renaming it my wicker approach.  The angle iron lip that the firebrick sits on has enough room for thin bolts to run up through it while still allowing enough space for the brick to sit on. Beyond putting bolts at the termination points, you can put bolts every few inches (maybe 4") along the path of the wall and just zig and zag the wall through them like a wicker basket.  At the end, you can loop the wall around the post and fold it back and slide it into the previous post.

One of the strengths of a wicker approach is that, should the seam of the stove pipe be either riveted or spot welded (a distinct possibility), rather than clasped, and can't easily be reclasped, you can leave the wall sections separate as you thread them through the posts, overlapping them at the ends.  You might even position your bolts/posts so that those are where the ceiling angle iron crosses/sits on, allowing the posts to take the brunt of the ceiling weight rather than the sheet metal from the pipe. The bolts will be the weight bearers, while the pipe strips are just air entrapment.

The only potential tricky part to this is the flexibility of the stove pipe.  Flashing would probably wend it's way through the posts and double back beautifully, but stove pipe might not be quite as flexible- at least maybe not for the double back part.

Other than the decision as to how to approach the wall, your diagram looks right. The only things I would change would be, if you are going to sit the u shaped wall on firebrick, without posts either in the middle or at the end, then you'll need to add right angles at the top of the U/front of the oven and corresponding bricks for the lateral pieces to sit on (see my original drawing).  You could, in theory, fold the walls inward, but then you'd lose precious lateral real estate on the pizza size you can make. Right now, you can do an 18" pie. You might not do that all the time, but you want to try it at least once.

Speaking of real estate. The diagram has your quarry tiles arrange in a rectangle that looks about 12 x 22.  They don't need to extend all the way to the front of the bricks, but you definitely want them as close as possible to each wall. The center pieces of 1/8" angle iron, when back to back, will give you 1/4" in the middle, so your quarry tiles should be 18.25" x 18.25"- a nice big target for 16" pies and just enough to squeeze an 18 in there.

I think you're clear on how to cut the stove pipe with tin snips, but, just in case you're not, here's a picture.  Btw, tin snips can make very sharp edges.  Use leather gloves and sand all your edges down. Oh, and I think this is obvious, but don't use the crimped area.
« Last Edit: June 07, 2013, 02:46:48 AM by scott123 »

Offline scott123

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Re: Fire Pit Oven
« Reply #27 on: June 07, 2013, 02:58:15 AM »
I just noticed one other thing.  Beyond the wall, in the back of the oven, you want only one pair of bricks, not two. The angle iron should extend as if you had a second set of bricks, though, so you can slide the bricks out to add wood (remember the arrows?).  You can always add wood on the sides, depending on what metal you use to cover them, but, since you want the fire as far back as possible, feeding it from the back might not be a bad idea. Besides, moving a piece of metal might be more sketching than sliding a brick a few inches along an angle iron track. 

Offline wahoo88

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Re: Fire Pit Oven
« Reply #28 on: June 07, 2013, 10:39:11 AM »
Alright.  The stovepipe should just be able to snap securely together at the seams?  I'm worried that those joints might not be strong/flexible enough to 'weave' back and forth, especially if a seam happened to end up right at a turning point.

I just got lazy with the drawing in not covering the floor completely in UQT, but I'll put as much baking space as possible in.

I guess I should try to flatten the pipe sections before trying to weave them in by putting weights on it.

The outward stovepipe bend at the top/front of the oven is primarily to add rigidity; it isn't directly holding an angle iron and bricks, is it (and only applies if I rest the stovepipe on top of the bricks)?

Now most of the work is in sourcing the materials.  It may take a while for me to get out to all these places.

Thanks.

Offline scott123

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Re: Fire Pit Oven
« Reply #29 on: June 07, 2013, 11:03:37 AM »
An 8" pipe will give you 25" long strips.  Depending on where you put your posts, you should be able to weave them in and out without connecting them.  The stove pipe seam also might be just a folded over edge that hooks another folded over edge. If that's the case, you might be able to squeeze the two lips together with a pliers for a sturdier joint.

I think we'll have a better idea of how to proceed once you obtain the stove pipe and see how it's connected, how rigid it is, and how well it flattens.

The outward stovepipe bend isn't holding bricks. It's just there to keep the wall stable.  If you weave, though, that bend isn't necessary.