# For you math wizards

I need to draw an arc for a piece of trim. The end points of the arc are 5 feet apart and the depth of the arc at the center point is 2 inches. What is the radius of the circle?
There ought to be an equation for this that would be far superior to trial and error, oui?
Larry
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On 4/15/2013 9:14 AM, Gramp's shop wrote:

feet apart and the depth of the arc at the center point is 2 inches. What is the radius of the circle?

http://www.mathopenref.com/arcradius.html
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On 4/15/2013 9:14 AM, Gramp's shop wrote:

feet apart and the depth of the arc at the center point is 2 inches. What is the radius of the circle?

http://www.handymath.com/cgi-bin/rad2.cgi?submit=Entry
http://www.ehow.com/how_7846775_radius-arc.html
http://mathcentral.uregina.ca/QQ/database/QQ.09.98/riddleberger1.html
http://www.woodweb.com/knowledge_base/Radius_of_an_arc.html
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On 4/15/2013 10:14 AM, Gramp's shop wrote:

feet apart and the depth of the arc at the center point is 2 inches. What is the radius of the circle?

R"6" according to Sketchup.
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On 4/15/2013 11:38 AM, Leon wrote:

Trigonometry concurs. :)
http://www.flickr.com/photos/gdguarino/8651887015/in/photostream/lightbox/
Thanks to the O.P. for a pleasant lunchtime puzzle.
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On 4/15/2013 1:41 PM, Greg Guarino wrote:

It was more fun to try to work it out for myself, but I just looked it up and there is (of course) a more direct way to find it.
Radius = H/2 + W^2/8H
Where H = the height of the arc (2") and W= the width of the base (60")
In our example that's:
2/2 + 60^2/8(2)= 1 + 3600/16 = 1 + 225 = 226
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Greg Guarino wrote:

Greg, We both drew the same picture. How much math background do you have (if you don't mind me asking)?
Bill
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On 4/15/2013 3:26 PM, Bill wrote:

Nothing too advanced. Algebra, geometry and trig in high school, a little calculus in college. That would all have been in the '70s.
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"Leon" wrote in message
On 4/15/2013 10:14 AM, Gramp's shop wrote:

R"6" according to Sketchup. ==========================================================================My calculator says that your program is right.
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On 4/16/2013 7:57 PM, CW wrote:

I'm glad you were able to verify the accuracy of your calculator. ;~)
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On 4/15/13 10:14 AM, Gramp's shop wrote:

According to those cool calculators, 18'10".
--

-MIKE-

"Playing is not something I do at night, it's my function in life"
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Hah! Now all I need to do is figure out how to draw an arc with an 18 foot radius :-) I have a couple of ideas and will post pix of the process.
On Monday, April 15, 2013 10:14:29 AM UTC-5, Gramp's shop wrote:

feet apart and the depth of the arc at the center point is 2 inches. What is the radius of the circle?

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On Mon, 15 Apr 2013 09:10:54 -0700, Gramp's shop wrote:

Bend a piece of thin cutoff around the points?
--
When fascism comes to America, it will be wrapped in the flag and
carrying a cross.
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On 4/15/2013 12:43 PM, Larry Blanchard wrote:

My sense of the physics involved tells me that that method will not produce an arc of a circle. Will it matter? Might the resultant curve be subtly nicer than a circular arc? That's up to the designer.
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My plan exactly, Larry. I'm going to start with drilling screws into the waste side of the end points and the top of the arc, attach a thin strip of one-by with spring clamps and then add a couple of screws/clamps along the arc.
The other Larry
On Monday, April 15, 2013 11:43:27 AM UTC-5, Larry Blanchard wrote:

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"Larry Blanchard" wrote in message

+1
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On 4/15/2013 11:10 AM, Gramp's shop wrote:

feet apart and the depth of the arc at the center point is 2 inches. What is the radius of the circle?

!8' string with a pencil died around one end. Nail in the ground on the other end.
Or use sketchup to print out a template.
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On 4/15/2013 12:20 PM, Leon wrote:

An 18 foot radius template?
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On 4/15/2013 12:47 AM, Richard wrote:

Did he say wanted the full circle or the 5' arc?
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Leon wrote:

He said he wanted the 5' Chord!
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