Pre-crowning ribs

[Erwinspiano@AOL.COM]

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In a message dated 3/16/2002 9:33:29 PM Pacific Standard Time, 
RNossaman@KSCABLE.com writes:


> Subj:Re: Pre-crowning ribs 
> Date:3/16/2002 9:33:29 PM Pacific Standard Time
> From:<A HREF="mailto:RNossaman@KSCABLE.com">RNossaman@KSCABLE.com</A>
> Reply-to:<A HREF="mailto:pianotech@ptg.org">pianotech@ptg.org</A>
> To:<A HREF="mailto:pianotech@ptg.org">pianotech@ptg.org</A>
> Sent from the Internet 
> 
>          Yo Ron

              Yeah what you said. Who made you the king of articulate anyway?
               >......Dale----Good day!

> 
> >My questions are... What system or jig arrangement do the seasoned
> >soundboard folk use for shaping (precrowning) the ribs?
> 
> Everyone seems to do it differently. They can be planed, sprung and sawn,
> or laminated to whatever radius, radii, catenary curve(s), parabola(s),
> cosmic loop(s) you may consider to be optimal this month. I assume you will
> reasonably reserve the right to change your mind later as the resulting
> cumulative evidence indicates. Meanwhile, there are fairly recent
> descriptions of jigs and methods in the archives. 
> 
> 
> >Also for this model piano are there improvements to be made in altering
> >(reducing) the soundboard thickness?
> 
> From what, to what, for what reason, and in the interest of what specific
> improvements? Universally applicable magic numbers only work when they
> happen to fit in with all the other variables of the design.
> 
> 
> >We are going to increase the rib height from the original minimal 19mm to
> >somewhere near 23 to 24mm, but will be happy to incorporate advice and
> >suggestions from those of you familiar with this model piano and who have
> >successfully altered / improved some of the original soundboard / rib 
> specs.
> 
> While I'm not familiar with this specific piano, the same set of criteria
> apply to most everything. First off, what determines your choice of rib
> depth? How about width and number and placement of ribs? Were the originals
> crowned, or was the crown originally forced into flat ribs by the
> rehydration expansion of a severely dried panel? Your choice of dimensions
> and crown for each rib (along with the panel thickness, grain angle, and
> rib angle relative to the panel grain) will determine both it's load
> carrying capacity and vibrational response characteristics. What crown
> radii are you planning to use? A lighter rib with a higher machined crown,
> deflected to the same resulting (under load) crown as a heavier rib with a
> lower machined crown, will support the same load, but be more responsive in
> action. 
> 
> If you typically have killer octave problems in these pianos, just crowning
> the ribs and adding a couple of millimeters to the height will help. Beyond
> that, the variables are cumulative and it gets a whole lot more complex.
> 
> 
> Ron 


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