Replies

1. 
   SantaFeTom | Jan 04, 2009 12:29am | #1

   If I understand the question right, the chord of the circle is 26.5" long and the distance from the middle of the chord to the circle is 12". That would be a circle of radius 13 5/16". I got the answer by drawing what you described in my CAD program, drawing the circle through the three points defined by what you said and then looking at what the radius was for that circle.

   The math solution is:

   If "y" is the distance from the middle of the chord to the circle and "x" is the length of the chord, then the radius "r" is:

   r=(y/2)+x**2/(8*y)

   Note: x**2 means x squared.

   
   

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   Edited 1/3/2009 4:52 pm ET by AustinTom

1. 
   flairwoodworks | Jan 04, 2009 02:13am | #3

   Tom & Philip,Thanks a bunch. Here is the formula with the values, step by step.r=(y/2)+xˆ2/(8y)
   r=(12/2)+26.5ˆ2/8x12
   r=6+702.25/96
   r=6+7.31510417
   r=13.31510417Which rounds to 13.3125 or 13-5/16".Chris @ http://www.flairwoodwork.spaces.live.com(soon to be http://www.flairwoodworks.com)

    - Success is not the key to happines.  Happiness is the key to success.  If you love what you are doing, you will be successful. - Albert Schweitzer

2. 
   philip | Jan 04, 2009 12:54am | #2

   Chris,
   There is a formula: Radius= (Length squared/8 x Rise)+ (Rise/2) which looks the same as Tom Austin has posted.
   You could also draw it full size and get it by trial and error...

   
   

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   Edited 1/3/2009 4:57 pm by philip

   
3. 
   trialnut | Jan 04, 2009 02:55am | #4

   Easy one for me to remember and real easy to figure is; 1/2 chord squared plus rise squared divided by 2 times the rise = radius.

   This would be, chord is 26.5 so 1/2 the chord is 13.25.

   13.25 times 13.25 = 175.5625

   rise is 12 so 12 times 12 = 144

   175.5625 plus 144 = 319.5625

   319.5625 divided by 24 (2 x rise) =13.3151 or 13 5/16

   All simple multiplication and division that can easily be done with a pencil on a scrap of wood. Batteries not included. ;o)

   Rich

   The Professional Termite

1. 
   RalphBarker | Jan 04, 2009 09:29am | #5

   "All simple multiplication and division that can easily be done with a pencil on a scrap of wood. Batteries not included. ;o)"But, all of my pencils have batteries! They're needed for the laser guide, so I know exactly where I'll be writing. ;-)