rim laminations

[Delwin D Fandrich]

----- Original Message -----
From: "Ron Nossaman" <RNossaman@KSCABLE.com>
To: <pianotech@ptg.org>
Sent: October 03, 2001 1:25 PM
Subject: Re: rim laminations


>
> What kind
> of time is taken up edge gluing the vertical grained laminations, and how
> do you handle something that long and fragile? Or are they just assembled
> in the stack as you go? 'Splain please.

Time. Depends on how automated you are. For Yamaha? Milliseconds. For us?
Minutes. Probably many of them. We're just gluing and clamping since the
veneers are thick enough for this process. If they were thinnner we'd have
to stitch or something and that would take a bit longer.

Handling. Very carefully. But we're using 2.5 mm veneers so it's really not
all that much of a problem. And, yes, they're assembled in a stack.


>
> I don't know that it does all that much harm either. Like the "cheek lift"
> discussion earlier, I'm not sure what the effects are. At least I haven't
> identified anything specifically detrimental.

In the case of the more-or-less conventional 'modern' grand, I'm not sure
'cheek-lift' is the appropriate term. As I understand the problem of
cheek-lift, it is the result of an inadequately supported frame (relative to
the string layout and tension) and the rim is twisting under the stress of
the string load. In the case of the more-or-less conventional 'modern'
grand, unless the plate is woefully underdesigned--surely not the case with
the S&S Model C--we have to look elsewhere. Since the whole piano appeared
to be built around the twisted rims--and the twist is not consistent from
piano to piano--I suspect most of the twist occurred between the time it was
initially machined and the time it was bellied. That's a guess, but, I
think, a reasonable one. It could have occurred later but--considering the
amount of twist--I'd expect some visible damage somewhere. There was none.

As may be, I suspect at least some judicious cross-banding would have helped
to stabilize things some.


>
> Yep, and that's an outer rim. I was originally talking about the inner.

Well, why not both? I don't think I'd want to crossband one without the
other. The whole idea would be to come up with a more stable overall
structure which, when laminating, generally means a well-balanced structure.

Now, before someone cries out, "But, an all longitudinal laminated structure
is balanced," let's recall that the upper part of the rim assembly (where
just the outer rim is present) is generally only 25 mm or so thick and the
lower part is generally 60 mm plus (sometimes plus quite a bit) thick. In
terms of drying and stabilizing under varying climactic conditions, that's
not balanced.


>
> Perhaps not. I was just considering bending resistance, which may be a non
> point. We do know that cross plied beach is acoustically solid enough to
> make pretty fair bridge caps, so as long as long as the hardwood is hard
> wood, it may very well work in rims too.

I expect so.

Del