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Hey fellas

Another question: I have done a fair bit of reading and researching (and head scratching) trying to find a reliable method for tracing an arc for, say, a circle of 60ft radius, other than physically making a 60ft long piece of wood on a pivot with a pencil at the end.

Do you use a mathematical formula to be able to find the amount of vertical deflection to use for a given length of a flexible piece of plastic or metal with a nail at each end and one in the middle, as outlined in Cumpiano's book? For instance, if my piece is 12 inches long and I want a 60ft radius arc, how much to I need to raise the middle nail so that I get the proper arc?

Comments and suggestions greatly appreciated!

This may help

http://www.liutaiomottola.com/formulae/sag.htm

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Ken Cierp

http://www.kennethmichaelguitars.com/

YES!
Thank you!!

a very accurate way is to use a shipwright compass. You can use it in combination with the formula for a sagitta. Here is a post for the down under forum describing its use. http://www.anzlf.com/viewtopic.php?p=70212#p70212

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And remember if you actually hit 58 foot or 62 foot it really is not going to make a big difference.

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I use a CAD program. I draw a 60' radius circle, then trim the part I want to use, then print it out.