rib glueing

[Ron Nossaman]

>Anyone,
> Having taken the plunge to replace soundboards, I need a rib press. The
>traditional go-bar press won't do because of space limitations. Having
>searched the archives and back issues of the Journal I'm thinking of
>building a variation of the pneumatic presses as described by Claire Davies
>in the 10/87 Journal and David Hughes in 9/93. In the archives I saw
>references to "individual rib clamps" being used by several people on this
>list and would be interested in knowing more specifics. 

Hi Garold,
I use pneumatic clamps, much like those Claire described, only made of
maple and the caul shaped to final radius rather than depending on bowing
from pneumatic pressure to form the crown. I thought 100 psi was pretty
extreme too, and run mine somewhere between 40 and 50psi. 35 is probably
quite adequate too.


> Another question concerns bottom caul configuration. If one is using
>straight ribs and compression crowning (I am), does pressing into a curved
>surface have any material effect on the crown or is Jack Krefting correct
>when he stated in one of his series of articles that it does not.

If you're asking what I think you're asking here, no. There isn't any real
difference between a crown being achieved by pressing panel and straight
rib into a curved caul, and one resulting from rehydration of a severely
dried panel glued to a flat rib on a flat caul. Neither method is, in my
opinion, a very good way to crown a soundboard since the rib is resisting
the crown in both instances, and the panel is doing all the work. I would
highly recommend machining your crown into the ribs, and gluing ribs to
panel in a curved caul. The panel needn't be dried down quite as much this
way, and in use the ribs are actively supporting their share of string
bearing load, which takes some of the abuse off of the panel.   


> Also, I plan on using the individually inflatable system with "Schrader
>valves" as in the Hughes article but must confess these are unfamiliar to me
>and I need to know where to obtain them and also what sort of supplier I can
>try to locally get 1 1/4" mill hose.

I got some cheap new brass T valves with 1/4"NPT male/female ends from a
local surplus and salvage yard. I tapped one end of my pneumatic tubes'
plugs and screwed in a valve. A quick disconnect screwed to that lets me
connect an air hose, and open the T valve slowly to control the clamping
rate so I know I have everything under control as pressure in the hose goes
up. When I'm ready to move the clamp to the next rib, I close the valve,
disconnect the air hose, and bleed the pressure off slowly with the valve.
I have five clamps of different radii that I move around as needed, and a
"pig", consisting of a capped length of pipe with one hose in, and five out
to accommodate the clamps. The hose, I got from a firehouse supply place.
It was 50', with brass end fittings, for $60. With all the air fittings,
the whole mess cost around $120. 

The thing I like about the pneumatic system is that I can crown, shape, and
feather the ribs before gluing them to the panel, without having to figure
out how to clamp the ends down.


Ron N