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-   -   Full hemisphere arch? (http://www.fornobravo.com/forum/f28/full-hemisphere-arch-8064.html)

kebwi 09-30-2009 08:02 AM

Full hemisphere arch?
 
I've seen a few (two?) ovens in the gallery that have full hemisphere arches. I highly prefer that look. I'm trying to determine if this design is functionally less desirable however. In particular does it constrain the smoke from exiting the dome into the vent area?...or does it cause any trouble and is perfectly acceptable?

Could I make such a design with the top of the arch a little higher than 63%, assuming that the lower corners would average out the smoke's exit-path, or would such compensation not really help the smoke exit and still let too much heat out?

I would love for the people who built full hemispheres to pipe in and say whether their ovens work optimally and whether they have any regrets about the design.

Thanks.

papavino 09-30-2009 09:35 AM

Re: Full hemisphere arch?
 
Check this thread:
http://www.fornobravo.com/forum/f8/v...vice-6698.html

There are probably others you can find by searching a bit.

kebwi 09-30-2009 09:45 AM

Re: Full hemisphere arch?
 
Thanks for the ref. FB's forum search is a little weak. It won't accept close-quoted multi-word phrases for one thing.

Thanks again.

GianniFocaccia 09-30-2009 10:09 AM

Re: Full hemisphere arch?
 
All you have to do is Google Forno Bravo vent arch advice and you go here:

http://www.fornobravo.com/forum/f8/v...vice-6698.html

sjmeff 09-30-2009 10:13 AM

Re: Full hemisphere arch?
 
I went the full hemisphere route on my oven mostly because I liked the look of it. Also, since I'm building an igloo, I thought it would be stronger and preferable to having some kind of brace on the sides.

I created three full hemisphere arches--interior, exterior, and finally a decorative arch. I haven't had any problems with smoke coming out the front and don't have any discoloration on my decorative arch. I don't do anything special to warm up the flue, either, it just works great as-is.

I think the transition and chimney size (I have a 8" x 36" Duratech) are much more critical to it drawing well. I don't think the hemispherical arch has much of an impact at all in this regard.

If I had to do it over, I'd still go this route. Cutting and assembling the arches was one of my favorite parts of the build.

If you can find tapered bricks in your area, you could create this kind of arch very easily. I couldn't find them so I cut them with the HF saw.

-Stephen

p.s. Here's a search trick. I always use this method rather than the forum search. Type this into google: vent arch site:fornobravo.com/forum

kebwi 09-30-2009 10:16 AM

Re: Full hemisphere arch?
 
@Gianni: thanks. I had noticed that if I do general Google searches on these topics, sometimes FB forum results pop up in the results, but I admit, it never occurred to me to put "Forno Bravo" in the google search query along with the terms of interest.

Sorry for the trouble, I appreciate the tip.

kebwi 09-30-2009 10:17 AM

Re: Full hemisphere arch?
 
By the way sjmeff, how did you taper across the wide face of the bricks? Did you make every taper with two cuts, turning the brick over between cuts? I don't think my HF 10" will cut 4.5".

GianniFocaccia 09-30-2009 10:23 AM

Re: Full hemisphere arch?
 
I too like the looks of the rounded arch and have noticed that most commercial ovens have a more eliptical-shaped entry to them. It appears this proportion provides a wider entry for access in and out of the oven and a lower arch height for heat retention.

Regarding Pompeii oven design, do most builders construct their entryways so the front arch is slightly (1"?) lower than the vent arch to help prevent smoke from exiting the front of the oven?

Thanks,

John

sjmeff 09-30-2009 10:36 AM

Re: Full hemisphere arch?
 
Quote:

how did you taper across the wide face of the bricks? Did you make every taper with two cuts, turning the brick over between cuts? I don't think my HF 10" will cut 4.5".
For my inner arch, I cut full-sized bricks in half and then tapered the sides by raising the saw so that the brick would just fit under it (careful, the saw sometimes "catches" on the brick since it's not cutting all the way through). I then had to make two passes for each taper, turning the brick upside down and around for the second pass. The inner arch had 19 bricks and it probably took me 90 minutes to cut them all.

For the outer arch, I lopped off an inch of the brick so that it would fit under the saw. I created a jig to tilt the brick, then cut all of the bricks. This was much faster and they were by far more exact than the ones I cut for the inner arch. Since I left a 1" reveal for the door, the inner and outer arches both lined up on top (the side where the chimney plate sits).

Quote:

do most builders construct their entryways so the front arch is slightly (1"?) lower than the vent arch to help prevent smoke from exiting the front of the oven?
I agonized over this, thinking that having the decorative arch lower would prevent smoke from discoloring the arch, but I thought it would restrict the opening too much, so I put the decorative arch flush with the outer arch. Fortunately smoke coming out the front hasn't been a problem.

Dino_Pizza 09-30-2009 02:31 PM

Re: Full hemisphere arch?
 
You have a few things to consider here. 1st do a forum search on “parabola” & “ ellipse” and “squished ellipse.” I don’t recall your future ovens size but a 42” diameter oven that is half spherical can be quite big depending on how high your soldier course will be. A half sphere is beautiful and strong but a parabola will transfer the loads from the weight at the top better. However, no one ever had a dome collapse over these dome shape preferences.

Also, for pizza or flat bread, you want the heat lowered in the center of the dome closer to the floor, not up at the peak of the half-sphere. The flatter the top, the more heat reflected down. The taller the top, the more brick and the farther away the heat and the more wood to burn. This is all incremental though. I think a half-sphere is easier to build with half bricks without tapering much. You could build a lower dome (squished ellipse) but then build up the insulation on top into a half-sphere and by the time you stucco the outside, it’s the shape you want with an efficient lower dome within.

Some have found that lowering the front arch can make putting in the oven door a more careful process as you have to tilt it in. Remember, you can always use the decorative tile or brick you put on the outside of your finished outer arch to drop down a 1/2" to hold some smoke back if that became an issue (ie: you did not have enough front landing or tall enough vent chamber to have made a sufficiently drawing oven).

BTW: if I'm way off about any of this stuff, please don't hesitate to say so :).
-Dino


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