# Making a circle/arch, is there a smart way to do it?



## hg1027 (Aug 23, 2012)

I'm making a bed for my daughter with play space under the bed platform (5 feet up).

The entrance to the play area has a curved top, and the whole facade is a 2×4 frame sandwiched between 1/2" ply. Overkill is my favorite kind of kill.

When I made the 2by support for over the arch (black lines and circle), I put in a vertical (red) to the point it started to curve, then started cutting scraps (blue) at angles that overlapped the half circle I'd drawn on the ply, leaving enough meat outside the circle without leaving voids in the corners.










What I'd like to find is a more math based answer for the next time I do this. I guess I could also ask for my little program to ask if you're keeping the inside or the outside, to minimize waste. Is there a template, a calculator, a quick and easy:

Input
Radius of circle = 24 inches
Width of boards = 3.5 inches
Desired number of sides = 10

Result
Long side = 8 inches (whatever)
Short = 6.22345
Angle = 32 degrees

I realize I could sketch it out, go buy a protractor and a compass and a sextant and a sphygmomanometer, waste 8 pieces of paper, and end up winging it anyway, but it would be nice to know if such math has already been done.


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## HokieKen (Apr 14, 2015)

Like this ?


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## hg1027 (Aug 23, 2012)

That should get me most of the way there, thanks. I can at least figure out what would get me close.

If anyone has one that's based on ID, that would be great.

Edit: with the word Segment added in to my googling, I found this page:

http://www.delorie.com/wood/segturn.html

Which appears to do what I wanted. Thanks!


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## BinghamtonEd (Nov 30, 2011)

If you're skinning it in plywood, do you need to do the segments? Could you cut out the plywood skins and screw cross-members between the skins? 3/4" ply with some cross-members would be plenty strong. You could enclose the top/bottom of the arc by tacking on some 1/4" hardboard, which bends pretty easily.


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