#11  
Old 08-04-2009, 05:05 PM
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Il Pizzaiolo
 
Join Date: Oct 2006
Location: Vancouver Island
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Default Re: Problematic Pompeii Parabola Plan

"Is there a good way to draw a parabola other than freehand guessing? "

What you want is an ellipse, rather than a parabola. Dmun has a nice sketch on the post before.

As a rule of thumb, the ellipse height should be 85 to 90 % of the radius. Your 39 inch diameter has a radius of 19 1/2 and should have a height of about 17 1/2 inches.

A circle has a single focus point - the centre. An elipse has two focus points, (or in three dimensions, a ring.)

Last edited by Neil2; 08-04-2009 at 05:08 PM.
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  #12  
Old 08-04-2009, 06:14 PM
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Il Pizzaiolo
 
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Default Re: Problematic Pompeii Parabola Plan

This link has a nice explanation for drawing an ellipse with a specific radius and height:

Double Error Squaring
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  #13  
Old 08-04-2009, 09:57 PM
Peasant
 
Join Date: Mar 2009
Location: Draper, Utah
Posts: 32
Default Re: Problematic Pompeii Parabola Plan

Thanks to everyone for all the good information and help. Drawing an ellipse seems much easier than coming up with a parabola. I thought the desired shape was a parabola for two reasons: 1) stronger arch, and 2) focuses the heat to the cooking floor. However, if an ellipse works just as well, Iíll go with that design.

What I actually end up with, on the other hand, may be a different story. Iíve found that some things work on paper but in practice they donít quite work as well. Iíll be using one of the jigs I found on the forum to place the bricks. I think Iíve figured how to make the length adjustable so that I can set each course at a different length and end up with an ellipse or parabola. Iíll shoot for an elliptical shape, but when I start setting the courses I may end up going with the semicircle instead.

Dino Ė you hit the nail right on the head. I have no real experience doing anything like this, and I donít plan on moving any more, so this is my one and only chance to get it right. Iím trying to find the balance between the desired shape and dimension with my very limited skills.

I ordered the Pompeii 110 kit last week but it wonít be delivered for another week or two. This is giving me too much free time to overanalyze things.
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  #14  
Old 08-16-2009, 10:27 PM
Serf
 
Join Date: Sep 2008
Location: Saskatchewan
Posts: 4
Default Re: Problematic Pompeii Parabola Plan

There is a better wiki on making the parabola, the above doesnt give measurements for the F1 and F2 from the diameter. This one shows a scale, so that F points are well marked.
File:Constructie ellips tuinmanier.gif - Wikimedia Commons
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  #15  
Old 08-17-2009, 04:40 PM
Peasant
 
Join Date: Aug 2009
Location: WA /BC /ZH
Posts: 49
Default Re: Problematic Pompeii Parabola Plan

Quote:
Originally Posted by Freddie View Post
How are most of you building your domes – as high vaults or low vaults?
I'm a big fan of elliptical domes as well, particularly for pizza as they heat a lot more evenly than a hemispherical or parabolic dome. As most vents (doorways) should be about 63% the height of the dome for proper drafting.. that means that there is a trade off between low & high dome ovens. A low dome oven tends to be more efficient & heat evenly. That makes for great pizza & can really cut down on your wood consumption. But it also makes for low doorways and you might not be able to fit a large roast, turkey, spit or grilling rack in your oven.

A high dome leaves you lots of room for larger items like turkeys, but also means that your oven will consume more wood, is a little less ideal for pizza & probably costs a bit more up front for materials as a higher dome probably means a bigger oven overall.

There is also an issue of how much thermal capacity you want in your oven. If pizza is the main use, a thinner wall will let your oven heat up a lot quicker. If bread is more important, then thick walls hold a steady temperature better and allow the option of many batches from a single firing. Which is better depends on how you see yourself using your oven. For myself it's 90% pizza/10% baguettes, sandwiches & bread, so I'd be looking for a very low, elliptical dome.

.
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