Concentric curves.
 

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

Concentric curves.
 

Jay Pique writes:
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.)

See http://www.delorie.com/wood/chord-radius.html

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.

Concentric curves.
 

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.


On Nov 8, 3:11 pm, Jay Pique wrote:
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

Concentric curves.
 

http://flexibletrim.com/


Jay Pique wrote:
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

Concentric curves.
 

On Thu, 08 Nov 2007 15:11:24 -0800, Jay Pique
wrote:

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

Just go pick one up from the Borg?

Tom Veatch
Wichita, KS
USA

Concentric curves.
 

On Nov 13, 5:44 pm, Tom Veatch wrote:
On Thu, 08 Nov 2007 15:11:24 -0800, Jay Pique
wrote:

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

Just go pick one up from the Borg?

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