Replies

1. 
   Framer | Jul 18, 2008 04:04am | #1

   Do you have a Construction Master calculator?

   Here's one way with any calculator.

    (1/2 Chord x² / H) + H (/ 2) = Radius

   Joe Carola

   
   

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   Edited 7/17/2008 9:10 pm ET by Framer

2. 
   DougU | Jul 18, 2008 05:19am | #2

   ((1/2C)² + h²)/2h

   Sorry, I see Joe already posted it

   
   

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   Edited 7/17/2008 10:21 pm ET by DougU

3. 
   HammerHarry | Jul 18, 2008 05:48am | #3

   It depends on if you want a true semi-circle, as implied by the 'radius' term, or if you're looking for an eliptical arch, which may look better, depending on the style you're looking for.

   I think there have been several threads dealing with elipses and arches.

4. 
   JoeBartok | Jul 18, 2008 06:51pm | #4

   Circle Calculators ... that's probably more than you ever wanted to know about circles. :)

   If your arch is an ellipse (probably not, since you are looking for a radius):

   Elliptical Arch ... known: Major or Minor Axis

   Elliptical Arch ... known: Two Arch Dimensions

   Elliptical Arch ... known: Two Points on the Ellipse

   If the curve is some other conic section (or any other known curve), holler ...

   Joe Bartok

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   Edited 7/18/2008 11:58 am ET by JoeBartok

   
   

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   Edited 7/18/2008 11:59 am ET by JoeBartok

1. 
   silvertip | Jul 19, 2008 02:30am | #5

   Thanks, will give it a shot. 

1. 
   Framer | Jul 19, 2008 02:34am | #6

   What are some of the widths if you don't mind me asking?

   Do you have a Construction Master Calculator?

    

    Joe Carola

1. 
   silvertip | Jul 19, 2008 07:25pm | #11

   I did one with a witdh of 128 3/4" and the radius was 25' 9" which almost work perfect.  I think the middle was off by a 1/4" which was  easy  to fudged.  Will post a few pics when I get back to work on Monday.

   Edited 7/19/2008 12:29 pm ET by silvertip

1. 
   Framer | Jul 19, 2008 09:22pm | #14

   I did one with a witdh of 128 3/4" and the radius was 25' 9" which almost work perfect. 

   Those measurements would give you a 6-3/4" rise.

   128-3/4" [Run]

   25' 9" [Conv] [Diag]

   [Rise] = 6-3/4" or 6.780114"

   Watch how a few changed numbers in the decimals gives you a different radius by taking the 6.780114" and using that compared to the 6-3/4" number.

   6.780114" [Rise]

   128-3/4" [Run]

   [Conv] [Diag] = 25' 9" = Radius

   Now using 6-3/4"

   6 -3/4" [Rise]

   128-3/4" [Run]

   [Conv] [Diag] = 310-3/8" or 25' 10-3/8" = Radius

   If you have to use 7" as your rise for all the openings like I thought you did in your first post.

   128-3/4" [Run]

   7" [Rise]

   [Conv] [Diag] = 299-1/2" or 24'11-1/2" = Radius

    Joe Carola

2. 
   mathewson | Jul 19, 2008 05:06am | #7

   Joe,I have to lay out and elliptical stair well Monday. This webpages of yours will help.Thanks,Keith

1. 
   Timuhler | Jul 19, 2008 06:15pm | #10

   Please post pictures of the process or just some here and there.  I'd love to watch the progress

5. 
   Captndestructo | Jul 19, 2008 03:10pm | #8

   I use a construction calculator for everything i possibly can but I was not aware I could use it to find the radius of a circle.  I am slightly confused by the calculations submitted.  (I am easily confused)  I will read the manual further to understand the calculations.   I always find the radius with two tape measures.  Pull one tape from the high point and one tape from the low point (properly spaced ).  Intersect the tapes, when the number is the same you have your radius.

1. 
   Framer | Jul 19, 2008 05:02pm | #9

   Sounds like he's coming down from the ceiling on the ends 1-1/2' and in the center 3-1/2" from the ceiling. That would give him 7" from the bottom of the 10/12" up to the center.

   I'm using the Construction Master Pro DT (Desktop) for this.

   Ket's say he has 6' for the width(chord) and 7" for the height.

   6' [Run]

   7" [Rise]

   [Conv] [Diag] = 96 1/6" = Radius

   Or:

   (1/2 Chord x² / H) + H (/ 2) = Radius

   36x² = 1296÷ 7= 185.1429 + 7 = 192.1429 ÷ 2 = 96.07143" or 96 1/16"

   Joe Carola

   Edited 7/19/2008 10:20 am ET by Framer

1. 
   Captndestructo | Jul 19, 2008 07:47pm | #12

   Thanks.  I honestly have to find the proper radius for something atleast 3 out of 5 days a week.  This will make it go a lot faster

1. 
   joewood | Jul 19, 2008 07:59pm | #13

   I don't know if you have SketchUp, but it's one quick way of finding radius's :-)http://woodsshop.com/