rim laminations

[Delwin D Fandrich]

----- Original Message -----
From: "Ron Nossaman" <RNossaman@KSCABLE.com>
To: <pianotech@ptg.org>
Sent: October 02, 2001 8:22 PM
Subject: Re: rim laminations


> >It never occurred to me before, but today I have made up a trial inner
rim
> >using laminations of three-ply birch, a wood visually and structurally
> >quite similar to maple.  If I were shown this without knowing its
> >composition and without looking extremely closely, I would almost
certainly
> >say the laminations were of birch-or-maple and mahogany or some similar
> >wood, so much does the end grain of the birch resemble mahogany in
> >color.  I wonder if this is really the answer to the question after all.
> >
> >JD
>
> John,
> You don't suppose???? So why would Yamaha compromise the stiffness of rim
> laminations by (+-90°) cross plying layers? To what benefit, and at what
> performance cost? I would have thought (and still do) that the structural
> requirements of a bent rim would require nominally parallel grain amongst
> the laminations to maximize stiffness. Otherwise, why..........? This
> doesn't compute, and will distress me considerably if it proves to be the
> case. Since the remains of my visual acuity dictate that close examination
> is what I can do best, I'll check it out and get back with either a
> raspberry, or some flavor of despair.
>
> Ron N
-------------------------------------------------------

Well, let's think about this just a bit...stiffness in which plane?

I'm not sure there's any immutable law stating that all of the laminates
making up a rim have to go around the long way. In fact, I'm planning on
several crossbands in the new rim.

I'll give you some reasons why I think it might be a good idea and you can
explain to me the error of my ways. Or not....

Stability. Initially there is more twisting and turning going on in a rim
without at least some crossbanding. This is most evident as the rims
initially loses its moisture from the gluing process. But it goes on.
Without at least some crossbanding there is always going to be some inherent
instability within the rim through the seasons. I can't see where this does
the piano as a whole all that much good. Most, if not all, bent laminations
used in the furniture industry are crossbanded for both strength and
stability reasons. Even--especially?--when a compound bend is involved.
Examine the next ubiquitous bent-laminate chair you find in your dentists
waiting room. If she's like mine you should have plenty of time for a really
thorough exam.

Strength. Structural strength is another. I've seen--and repaired--more than
a couple of (outer) rims that were split along the grain line just above the
inner rim on the straight side. Including a couple of S&S B's and one M&H BB
(and you don't get a whole lot sturdier than that!). Typically charged to
'moving damage' I did suspect environmental (humidity stress) damage in a
couple of cases. I rather think at least some judicious crossbanding would
have prevented most of these.

Acoustical stiffness. I've not done any testing at all, but I don't see the
traditional rim, i.e., all longitudinal laminates with no crossbanding,
providing any better acoustical stiffness to the soundboard than one with
crossbanding. In fact, assuming the wood used is the same in both, I could
provide a reasonable sounding argument in favor of the crossbanded rim. At
least I've talked myself into it.

I suppose the argument could be made that the gluing surface of the
traditional rim might be just a bit better, but I really can't see this
being much of an issue with spruce to maple and with any reasonable modern
adhesive.

So, why not?

Regards,

Del