#1  
Old 09-01-2009, 03:30 AM
Serf
 
Join Date: Aug 2009
Location: Frankston South Victoria
Posts: 8
Default Casting a dome oven

I am casting a dome out of castable refractoy product, I am finding it hard to calculate how much to buy and what the dome will weigh ? Any suggestions on calculating it correctly ?
Reply With Quote
  #2  
Old 09-01-2009, 05:07 AM
dmun's Avatar
Moderator
 
Join Date: Jul 2005
Location: New Jersey USA
Posts: 4,216
Default Re: Casting a dome oven

The volume of the dome is roughly the volume of the exterior sphere minus the volume of the interior sphere, divided by two. The entry area roughly corrects for the door hole.

You can calculate it exactly using various cad programs, but it won't be any more accurate than the accuracy of your hand built forms.
__________________
My geodesic oven project:
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
,
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
Reply With Quote
  #3  
Old 09-01-2009, 05:18 AM
Serf
 
Join Date: Aug 2009
Location: Frankston South Victoria
Posts: 8
Default Re: Casting a dome oven

Thanks I found this web site that calculates the surface area of a sphere then divide by 2 and times by wall thickness
http://www.easycalculation.com/area/sphere.php
Reply With Quote
  #4  
Old 09-01-2009, 06:54 AM
Peasant
 
Join Date: Aug 2009
Location: WA /BC /ZH
Posts: 49
Default Re: Casting a dome oven

You might want to double check your calculation. You didn't give any numbers, but the spheres method that dmun described is more accurate and less susceptible to 'intuitive' errors.

If we ignore the vent (doorway) for the moment, it's easy to visualize that the dome is a sphere that is cut in half. So you can circumscribe half a sphere around the outside of the dome and another half sphere inside the dome. Then the entire space between the two half spheres would be filled by the dome. Ergo, subtracting the volume of the smaller dome from the larger will represent the dome wall volume.

Now contrast that against your method of calculating the area and multiplying by the thickness. Same thing, right? Well, no. If you were pouring a rectangular slab, it would be equivalent. But a dome has a curved surface. So say your dome will have an inside diameter of 100cm (radius = 50cm) & a wall thickness of 10cm. Did you use these numbers in your calculations? Or did you use the outside diameter (120cm) & radius (60cm)? Most people seem to opt for the former, but both approaches are wrong & give substantial errors of about 20%.

Since the dome wall thickness is not zero, as the diameter of the dome increases, so does the surface area. A reasonable approximation of the average dome surface area would be to take the diameter in the middle of the wall. In this case that would be 55cm. But the spheres method is still more accurate.

.
Reply With Quote
  #5  
Old 09-01-2009, 07:03 AM
Serf
 
Join Date: Aug 2009
Location: Frankston South Victoria
Posts: 8
Default Re: Casting a dome oven

Thanks, I understand what you are saying, I didnt allow for the thickness of the wall. I will add 20% to the initail calculation.
Reply With Quote
  #6  
Old 09-01-2009, 09:20 AM
Peasant
 
Join Date: Aug 2009
Location: WA /BC /ZH
Posts: 49
Default Re: Casting a dome oven

Sounds good. Just would hate to see you start the pour before realizing that you didn't have enough bags on hand.

.
Reply With Quote
  #7  
Old 09-01-2009, 06:10 PM
Lars's Avatar
Journeyman
 
Join Date: Oct 2008
Location: Omaha
Posts: 255
Default Re: Casting a dome oven

The volume of a sphere is 4/3(pi)r^3...

lets say you have a 40" inside diameter oven....
then, let's say you want your walls to be 4" thick...

so find the volume using r(outside)=24 and r(inside)=20, then subtract the inside volume from the outside volume and you get the volume of the shell.


Like this: V1= 4/3( pi) r^3=4/3(pi)(24)(24)(24) = 57905.8 cubic inches.
V2= 4/3(pi) r^3 = 4/3(pi)(20)(20)(20)= 33510.3 cubic inches.

(V1-V2)/2= 24395.5/2 = 12197.75 cubic inches.

To get cubic feet, there are 12^3 cubic inches in a cubic foot, so
(12)(12)(12)= 1728 cu.in.

The volume will be around V(shell)/1728= 12197/1728= 7.06 cubic ft.


Plug in your own numbers and do some math!

L.
__________________
This may not be my last wood oven...
Reply With Quote
  #8  
Old 09-01-2009, 07:13 PM
Peasant
 
Join Date: Aug 2009
Location: WA /BC /ZH
Posts: 49
Default Re: Casting a dome oven

Exactly right & a good exercise. But I have to admit that the online tool that the OP found also calculates spherical volume correctly.

Cheers.

.
Reply With Quote
  #9  
Old 09-01-2009, 07:19 PM
james's Avatar
Brick Oven Merchant
 
Join Date: Mar 2005
Location: Pebble Beach, CA
Posts: 4,648
Default Re: Casting a dome oven

Hey guys,
I move this to Other Oven Types. That seems like the right place.
James
__________________

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
Reply With Quote
  #10  
Old 09-01-2009, 09:02 PM
Il Pizzaiolo
 
Join Date: Jan 2007
Location: Tampa, FL
Posts: 1,446
Default Re: Casting a dome oven

OOOOHHHH... the humanity, and the MATH.
LARS, my head hurts after reading your post...I didn't realize how stupid I have become. Literally took over 5 minutes to comprehend. I think you really do lose it if you don't use it (your mind)

RT
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Why Italian Wood-Fired Ovens are Round james Newbie Forum 50 04-01-2014 09:14 PM
Oven temperature>>>barrel v dome shvuntz Heat Management 18 10-08-2010 12:55 AM
low dome clay oven jpmort Other Oven Types 15 05-16-2010 10:34 AM
All things being equal Lester Newbie Forum 13 12-21-2009 01:26 AM
Oven Dome Coskun Newbie Forum 3 08-18-2009 09:35 PM


All times are GMT -7. The time now is 12:59 PM.

Powered by vBulletin® Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Search Engine Friendly URLs by vBSEO 3.6.0
2006/10 Forno Bravo, LLC