[pianotech] Rib/Panel Clamping Methods - was: Fire hose failure!

[Ron Nossaman]

Greg Newell wrote:
> Well, the ribs could be glued either one or a few at a time making the
> process somewhat easier. I was thinking of attaching one end with a  spring
> clamp or even a screw that could later be removed and plugged to hold one
> end. The other end would conform within the melamine pattern.

Doesn't that pretty much shoot the ease and simplicity concept 
of vacuum bagging in the foot?


> Assuming everything else works out happily, your clamping 
> pressure (unless you make a wide footprint caul for each rib) 
> is limited to some fraction of atmospheric pressure. It looks 
> like 12 PSI is about the best you'll do. Most everything but 
> epoxy ought to reasonably have at least three or four times 
> that. Some say a WHOLE LOT more than that. So what's the glue 
> used that waits that long for setup, and doesn't need over 12 
> PSI clamp pressure?
> 
> 
> This is not what I read about vacuum clamping. As I understood it the force
> is quite high indeed. I suppose that it remains to be seen. 

Yea, I've seen the fantasy numbers too. They typically quote 
the total pressure on a big square inch area, which sounds 
really impressive. When you reduce these big acreage numbers 
to PSI, it comes to about 12. A vacuum clamping system isn't 
going to produce a higher PSI than the atmospheric pressure 
allows at the assembly altitude unless you have a clamping 
caul of a greater square inch area than the footprint of the 
glued surface.


>One of the
> benefits to this type of clamping is the claim that the glue permeates the
> pores of the wood better and makes a more lasting joint than otherwise
> attainable.

Cute, I hadn't seen that one. There are lots of claims. Does 
this one mean anything real? What's the established life of a 
glue joint, for any given glue/wood/prep/clamp 
method/atmospheric pressure compared to any other? The folks 
making the claims don't seem to have any real information either.


  > I'm not sure if there will be a benefit or not. Time and 
trial will tell. I
> am at least willing to give it a try and find out. I hope the education
> isn't too costly. Thanks for your input.

This is the realistic stuff. Pending actually trying it and 
generating real data, it's not all that clearly superior, or 
even adequate, a process.
Ron N