laminated ribs

[Farrell]

----- Original Message ----- 
> How do you get the bathroom scale at the exact height of the top of the
> bridge?  Do you just place it on the board near the bridge and try and 
> shim
> it to approximate that height?

Essentially, yes. All you need to do is measure the distance from the block 
you place on top of the bridge to prevent damage to the ceiling (bottom of 
the go bar deck of sorts) and then reproduce that distance so that the go 
bar has the same bend to it.

> Have you experimented to find how much
> difference in force there is with variations in height?

Yes, and I also have go-bars of different dimensions to help refine the 
amount of pressure they exert. I install enough go-bars to approximate the 
downbearing pressure each section of the string scale will have. I do this 
in part to evaluate crown reduction after loading and also to set bridge 
height. I find it time consuming, but I don't get surprised after stringing. 
I don't know that others building RC&S soundboards go through this process, 
but I find it tremendously educational - it's like doing something for years 
that has always been a mystery and then suddenly finding an authoritative 
textbook that details everything you wanted to know about it - maybe after 
I've installed 50 or 100 bellies this way it will be second nature and I 
won't bother with stress-testing the soundboard, but for now I find the time 
invested provides great rewards in better understanding and making the 
process (nearly) goof-proof.

> Do you know if
> there may be any significant flex in either the upper go bar deck as you 
> add
> more bars, reducing the force on the previous bars, or if the deflection 
> of
> the soundboard as you add bars is enough to reduce force appreciably on
> previously installed bars?

I don't think so, but I measure with the scale when most/all the other 
go-bars are installed so I get a fairly accurate idea of the pressure the 
bars are providing.

> Not nitpicking here, just very interested in the subject, particularly how
> much error is tolerable in these things.

Oh, my guess is a fair bit of error is tolerable. Every time you stick the 
bar in place, it will be ten pounds different - so none of that is exact. 
And 20 or 50 lbs. of downbearing this way or that doesn't move the 
soundboard any real measurable amount. But it all gets you pretty darn 
close. And then there is the beauty of the vertical hitch! I don't rely on 
them to set downbearing, but you do have a few millimeters up or down to 
play with to really refine that downbearing after the belly is strung.

Terry Farrell

> Regards,
> William R. Monroe