# Concentric curves.

• posted on November 8, 2007, 11:11 pm
Say you need a curved piece of wood 6" wide with an outside radius of 23 feet and it needs to include a cord length of 13 feet. How would you do it? (No CNC allowed.)
I've got a few ideas, but I'd like to hear what folks have to say.
JP
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• posted on November 9, 2007, 12:06 am

R = 23 C = 6.5 RC = sqrt(R*R-C*C) = 22.0624 D = R - RC = 0.936
w = acos(RC/R) = 16.416 degrees
See http://www.delorie.com/wood/segturn.html
Say, five pieces, 22.5 to 23 feet (270 to 276 inches) at 33 degrees...
Radii: 270" (22' 6") - 276" (23') Segments: 5 Width: 6 19/32" Length: 31 27/32" (2' 7 27/32") Total Length: 159 3/16" (13' 3 3/16") Miter: 3.3 deg
To cut a 3.3 degree angle on a 1x8 (7.25" wide), offset one side's mark by 7.25*tan(3.3) = 0.418 inches.
That gives you a blank the right size and approximate shape.
Now, get a 23 foot long string or wire (wire stretches less)...
You can approximate a circle using a bent batten; get one twice as long as the "segments" and bend it so that it touches the middle of each long edge of three adjacent segments, and trace only the middle. Repeat for each segment.
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• posted on November 9, 2007, 4:48 am
Well, I would lay it out in AutoCAD. Which would take about 1 minute.
Now, assuming you wanted it out of solid wood, I would glue up 6 or 8 pieces with angled end cuts and splines to strengthen the joints. Then I would lay it on the floor and attach it in place (somehow). Then I would create a trammel out of some long 2x4's with a piece of play at each end, one to pivit at a center point and one to mopunt the router. Then, assuming it is 4/4 thick wood, I would cut it out in 3 ror 4 pases on each edge.
For solid wood cutouts I actually usually trammel cut a pattern in MDF, use it to trace on the hardwood, cut it with a jig or band saw close to the line, then use the trammel to trim cut. But this extra step might be too expensive (in time) for this big op so I would just do several shallow cuts as noted.
If you give more info, you can get better answers rather than assumptions of what you might mean.

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• posted on November 13, 2007, 9:43 pm
http://flexibletrim.com /
Jay Pique wrote:

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• posted on November 13, 2007, 10:44 pm
wrote:

Just go pick one up from the Borg?
Tom Veatch Wichita, KS USA
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• posted on November 13, 2007, 11:49 pm
On Nov 13, 5:44 pm, Tom Veatch wrote:

Heh. They've probably got a few!
I need to revisit this topic now that the job is done. Let's just say some MDF, metal strapping, a custom router base and a helical head on the shaper produced excellent results. Plus a couple of holes in the floor. Details to follow.
JP