On Sun, Feb 26, 2012 at 1:39 PM, jhargrovewright2@...
<jhargrovewright2@...> wrote:
> Dave,My, "feel" is 6" + with the wrapping rather close (2-3") together.

That agrees with Skip's feel. According to calculators here:
http://www.mathopenref.com/arcradius.html that's about a 200" radius.
If you could get it to 9", that'd be 132". Probably enough (either
one) for esthetics--could make a nice cross beam with reflex ("S")
curve, or a wicked curved boom or gaff.

> The 1/8" is a potential problem.  I have never tried less than 3/16".  Also
the
> glue would need to be epoxy because others tend to form a bond as soon
> as it is tight and that might cause a problem.

You're right; epoxy's best. OTOH, I've had pretty good luck delaying
the grab of simple wood glues by wetting the wood--in this case maybe
soaking it for a bit. ;-)

> The bending will require all of the sides stave to slide against the others.
> The bending is going to tend to flatten out the material....just like any
> tubing...at some point

If I were going for a max bend, think I'd include a few short plugs
inside the spar--just to avoid this. Kinda like packing metal tubing
full of sand before bending to avoid flattening. I bet with a 4'
section you could get away with just 3 plugs--one perhaps 12" long to
leave 6" sticking out for the join, another one 6" in from the
opposite end, and the third in the middle.

Still be miles simpler with a 4-sided spar; no bending, no jigs. To
get that same radius (200") in a 4' piece only means a bend 1 3/8"
high--so could cut it out on a bandsaw. (I know, intuition says halve
the length and halve the height--4"--but the calculator says it ain't
so!) Then again, with that bandsaw (or saber saw--or heck, I've cut
curves like this with a skill saw), you can go hog wild--specify any
radius you like for esthetic's sake. It's only money (requires wider
and wider pieces of wood for the staves--and leaves more scrap)

There's another issue with sectioned spars--hoop strength near their
ends. This is an old kite spar problem--deserving an old kite spar
solution. Wrap the ends of the spar sections with a couple of layers
of uni-directional glass or kevlar, set in either epoxy or
polyester--even "whipping" the ends with kevlar (or glass) twine, then
epoxying will work (with kite sticks we just used a couple of layers
of 3M strapping tape--or whipped the end with ordinary polyester
sewing thread, followed with clear fingernail polish)

Dave Culp