Rib grain orientation (not grain oriented)

[Isaac OLEG]

Hello,

I've been told that Bösendorfer glue their boards at 5% MC, on crowned
ribs in shaped cauls.
So then the board is by evidence going to get some tension by the
rehydrating, and certainly some crown is build then too.

The 2.75 M model is given with a high crown (radius un known) and up
to 8 mm DB(distance bearing del !) that is more than 1.5 ° if memory
serves on these pianos (generous back scales)

Then I can suppose that the down bearing use the responsiveness of the
soundboard, and the remaining crown is only due to the ribbing (that
would be why these pianos are so stable too)

Don't we need to build some internal tension on the panel too ?

I had a few explanations by a friend, about the "neutral fibers of the
panel " being placed differently (more central) on CC and curved rib
solution, and as a result the CC crowned being more stiff (but more
prone to suffer).
Don't figure it yet, any clearing ?

Best Regards.

Isaac OLEG



> -----Message d'origine-----
> De : pianotech-bounces@ptg.org
> [mailto:pianotech-bounces@ptg.org]De la
> part de Ron Nossaman
> Envoyé : samedi 7 décembre 2002 17:57
> À : Pianotech
> Objet : Re: Rib grain orientation
>
>
>
> >Now I can understand the logic behind this with the CC
> guys, since they
> >are likely to achieve a higher crown when the panel
> re-hydrates. However,
> >in the case of rib crowned construction, wouldn't it be
> advantageous to
> >set the grain in the rib such that the growth rings are
> horizontal and the
> >medullary rays perpendicular to the sound board panel?
>
> Could be. I did a deflection test on a piece of spruce, 1.4
> meters long,
> and 0.935" square (that's just how it came out of the
> planer. With a 10
> pound box of tuning pins as a load, it deflected 0.008"
> more with the
> growth rings vertical. I tried all four sides up. I'd
> already decided that
> it doesn't seem to make any difference with laminated
> stuff, but with solid
> ribs, I've always tried to keep the rings over 45°. There
> may very well be
> no good reason to do so. I haven't found any data on
> differences in creep
> rates under load in beams with quarter cut vs flat cut
> wood. Compression
> yes, creep under bending load, no. Have you? Anyone else?
> Hammer shank
> manufacturers sure don't seem to consider it anything to
> worry about,
> though it's kind of hard to tell.
>
>
> >I am contemplating setting the rib grain this way for piano no. 004
>
> If you do, I'd like to hear what you think.
>
>
> >(both 004 and 005 are now sold before completion, which is
> quite a relief).
>
> Good. I'm very glad to hear that.
>
>
> >We increased the cut-off rail section size to 50 mm wide
> by 35 mm deep,
> >using 17 laminates of 2.9 mm thickness.
>
> I typically use 60mm wide, but I come from a long line of
> compulsive
> over-builders. I have no idea what's best, but I figured it
> can't be too stiff.
>
>
>
> >I will try bending it with 4 mm laminates for piano 006.
> When cutting and
> >drum sanding the laminates at 3 mm it is quite wasteful of
> wood. I'll get
> >some photos of the buck and cut-off scanned and onto the
> website soon.
> >
> >Ron O.
>
> Or even 6mm. It's not a very tight curve, and you're
> anchoring it to the
> beams, so it can have a lower glue to wood ratio. <G>
>
> Ron N
>
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