Soundboard 60-ft. Arc

[Ron Nossaman]

>
> Ron, 
>     Would you care to describe your method of rib crowning a board for me?
> Also could you suggest some reading I could do on the subject? (I don't have
> the Journal index on CD) I'm curious to know what I'll be needing. Since I'm
> heading to a woodworker show this weekend it might be a good idea to have an
> idea of what faces me in the weeks ahead. THANKS!!! 
>   
>
> Greg 



Greg,

Back when the earth was young, I made a jig. A caul shaped to the chosen radius
was mounted on it's side on a plywood base. The cut to width rib stock is laid
in on it's side, sprung back into the curve of the caul and held there by four
built in clamps while the jig is run through the table saw to produce the
finished rib height and, when the clamps are loosened and the rib straightens
back out, the machined crown. Ugly, but quick, simple, and effective. I then
feather the ribs and clean them up with a little sanding.

For assembly, the pneumatic presses have an appropriate radius cut into the
caul to accommodate the rib curvature. I will have fitted the panel in the case
and located and marked the ribs positioning on it. The panel is dried to about
6%MC. I start with one of the long ribs, temporarily dry clamping  the one next
to it to the panel to establish and hold the curve so I have one less thing to
fight getting that first rib on. I know I could spend 15 minutes and make a
crude dedicated clamp or two for this, but I never seem to get around to it.
Then position your pneumatic clamp,  glue on the rib, carefully ease the air
in, watching to insure that your rib doesn't skate away from it's intended
position. When you're up to pressure, take off your temporary panel bending
clamp, move two rib positions over and install the next rib until all of the
clamps are on. Then go back and move clamps to get the ribs in between those
already installed. You don't need a lot of press clamps. I use 5. Leap frog
them as you proceed. There is no sacred order of assembly or other magic spells
necessary. I don't have the clamps mounted to a frame of any sort, and they
just go where the panel takes them. It's just simple woodwork.   

I use a little straight through T handle valve (1/4" NPT), with a male quick
disconnect nipple on each clamp. I made a "pig" out of 1 1/2" pipe with five
1/4" hoses with female quick disconnects on the ends. There is no plumbing
between clamps other than the supply line from the pig.    

Decide for yourself when is the best time for cleaning off the glue squeeze
out. It depends a lot on the glue you decide to use.

 That's the gist of it. Details vary with individual preference and/or fetish.

Ron N