cutting Arches - Page 2 - Woodworking Talk - Woodworkers Forum
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post #21 of 25 Old 11-03-2011, 01:25 AM
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formula for finding the radius of an arch

The formula for finding the radius of an arch is
R=h2 + ww8h where h=height from chord line to the highest point of the arch and w= the width of the distance where the chord intersects the arch.
For example, if you wanted to trim an arch window that is 48" wide with an arch that is 6"high the following would figure the radius:
62=3 so 3+ 48squared 6(8)
So 3+48=51
51" is the radius which can be traced using the simple expedient of a 51" piece of string, a central pivot point and a pencil attached to the string. Measure exactly 51" from the point where your pencil touches and pivot off of that point. Easy.
This formula always works, you can even create a calculator for figuring radius of arches so that all you need to do is plug in numbers. They are readily available on the web too, so long as you know the formula is for figuring the radius of an arch. As long as you can cut along the line you have drawn, it will fit perfectly. Hope this helps, I have always liked math, it has made me more efficient than anything else I have learned or been taught.
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post #22 of 25 Old 04-21-2014, 06:38 PM
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Originally Posted by beltboy1 View Post
This is FAR & AWAY the easiest and possibly the best way to draw the perfect arch. This takes seriously, like 2 min to complete. 1 million times easier than a string!!!
Anyone have the link to this video?
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post #23 of 25 Old 04-21-2014, 08:34 PM
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Magazine tip I read somewhere... if you do the string trick to get the curve, consider using that beaded pull chain for lights instead, since it will hang better than string

If it jams, force it. If it breaks, it needed replacing anyway!
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post #24 of 25 Old 05-05-2014, 06:51 PM
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You guys are funny. ....arches are so easy that I don't even want to waste time posting the easy way......If someone still wants to know the proper way. ....PM me. ...

Proper elipsess might be a different story. ....
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post #25 of 25 Old 09-04-2015, 10:28 PM
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Smile Arc Cutting

Originally Posted by beltboy1 View Post
what is the best way to accurately make and cut arches for a face frame on an ET center? Approx. 39" wide 3" high. I have tried the thin strip of veneer but it never comes out even.
I have an Arc Radius App on my phone and it says your radius is 64.875 inches. So if you can layout and draw a radius of 64.875 inches... it will be perfect. I deal in Radius cuts every other day and the App is a life saver. I have a long bench for such layouts. Good luck!
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