Locating the arch????

[Cheesesteak]

I'm laying out the floor on my oven - and am marking where I think the arch / opening should be located. I've seen pics of folks that have the arch too far our - and the dome has to "reach" out to the arch.

Is there a rule of thumb for locating the opening / arch? If I'm building a 42" oven with a 20" opening - do I just locate the opening where the 20" intersects the 42" diameter oven wall?

Here's a plan I found where the 20" opening is still set back a bit into the oven:



Here, in Dino's oven - the 20" opening seems to be set outside of the 42" oven diameter:



is there a preferred location? Has anyone seen any pitfalls associated with locating it in a particular place?

Feedback is greatly appreciated.

[david s]

Re: Locating the arch????

You are right. If the entry is fairly deep you have way more trouble in working the oven. I believe that if you have decent funneling to the flue pipe then you can make the entry not very deep at all. In my case I made the entry only 5" deep, but my oven is only 21" diam with a 5" flue pipe.I also made the oven mouth quite wide to make it easier to work The disadvantage is probably that more heat is lost through the door. I also placed the entry actually inside the oven diameter too. Works ok. every design change is a compromise. It's like boat design.

[brickie in oz]

Re: Locating the arch????

Im sure its all about dome to arch height that determines where the arch goes? But I could be wrong.

I did a rough drawing about it for another thread, Ill see if I can find it.

The other thread is here. http://www.fornobravo.com/forum/f8/teardrop-15579.html

[fxpose]

Re: Locating the arch????

Im sure its all about dome to arch height that determines where the arch goes?

I think that would be the main determining factor.

By sketching out the dome profile you will more clearly be able to see where the arch top meets the dome and perhaps place the arch there, although this approach may not give you the exact opening width you want to end up with, but close.

[Mike D]

Re: Locating the arch????

If you are going by the plans, than you want to draw it all out to see how your dome will intersect with the arch.

You should read the Teardrop thread, This is what I didn't know. Or check out my build Round shape to see how I am working with my arch being too far out (I was using the plans as my guidelines for the size of the opening).

Mike

[Cheesesteak]

Re: Locating the arch????

one would think, though, that there would be a good, approximate location for the arch. Given the relatively standard oven opening (for the 42" Pompeii) - the intersecting point should be pretty standard. At least it would get you in the ball park.

okay - I haven't messed with SketchUp in a while - I just downloaded it and threw this together. Does this look right? 42" radius dome, 20" dome height, 12" arch height. The inside edge of the arch should be 4 1/2" inside of the inside wall of the oven. That would make the top of the arch meet the inside edge of the dome where they intersect.

Is it more difficult than that?

[brickie in oz]

Re: Locating the arch????

Is it more difficult than that?

Nah thats it.

Underside of arch to intersect the underside of the dome no matter the size of oven or arch.
If you mess with 1 dimension you have to mess with the other.

I cant see opening width being a factor, height yes.

[david s]

Re: Locating the arch????

The wider the arch the greater the heat loss, but the access to the oven is improved.

[Paul in Rockwall TX]

Re: Locating the arch????

For what it's worth, my dome is 39.5"W at the bottom, dome Height 19.5", opening width 19" and opening height 12". As you may be able to see from the attached, I used a dome template made of plywood. It allowed me to radiate from the center point of the floor to see how the dome would progress from any angle. I just set the inner arch where I wanted it to intersect with the dome, if that makes sense.

PhotoPlog - Dome and Floor

[GianniFocaccia]

Re: Locating the arch????

I cant see opening width being a factor, height yes.

Within limits, I agree, depending on arch geometry. One can see in the diagram below that a hemispherical arch that is moderately wider than a vertical-sided arch would still retain more upper-dome heat. I would not define smoke/hot-gas exhaust as heat loss, rather a function of the normal aspiration of an oven based on its inner-arch geometry.

Further, the frontal profile of the hemispherical-entryway suggests that it may create an easier task to merge the dome to the inner-arch. Granted, per the FB plans, the vertical-sided inner arch is less daunting in its initial construction requirements, but IMHO, I believe the hemi-arch solves many transition problems (including arch location) and results in a stronger, symmetrical arch that requires no buttressing.

John

[david s]

Re: Locating the arch????

The wider the arch the greater the heat loss, but the access to the oven is improved.

Generally the wider your arch is the greater will be the area that is presented to the outside, given that the height is fixed. It will be the frontal area of the arch that will lose heat through radiation and the fact that doors don't insulate as well as the insulated floor and dome. In my case of a small oven the doorway is a larger percentage of the oven area. This is one of the main disadvantages of smaller ovens.

[Neil2]

Re: Locating the arch????

Buy some cast angle iron and make a rectangular opening.

Arched openings offer no practical advantage and several disadvantages (such as increased complexity in fabricating a door and the spreading of the arch over time).

[mrchipster]

Re: Locating the arch????

Arched openings offer no practical advantage and several disadvantages (such as increased complexity in fabricating a door and the spreading of the arch over time).

Neil I am not sure why you say arched openings will "spread" if the opening is a true hemisphere it should be self supporting and free standing. No spread should occur. Unless you are considering the weight of the chimney to be a significant stress factor on the arch which it may be.

I still cannot in my mind come up with a stronger brick built design than an true hemisphere.

Chip

[Sharkey]

Re: Locating the arch????

I still cannot in my mind come up with a stronger brick built design than an true hemisphere.

Chip

I load tested my arch with a bit over 100kg (220 pounds). No problems.

Other than a hemispherical arch being inherently strong I think the arch being tied into the dome well prevents spreading too.

[GianniFocaccia]

Re: Locating the arch????

Arched openings offer no practical advantage and several disadvantages (such as increased complexity in fabricating a door and the spreading of the arch over time

The advantage for me was the straightforward transition construction. I feel it was much easier than making and tying in the complicated frontal dome brick cuts required to fit a rectangular 'arch' or the traditional straight-sided shallow inner arch as called for in the FB plans.

Neil I am not sure why you say arched openings will "spread"

This is because true arches inherently exert side thrust. Practically speaking, I can't see an oven's inner arch spreading (ever) as long as it is properly tied into the mass of the dome. To me, the hemispherical arch has centuries of proven strength, clean symmetry, and was fun to build. Much more work than dropping in a piece of angle iron, but well worth it.