rim laminations

[Ron Nossaman]

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

Yea, there's the rub. I was just considering bending resistance.


>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. 

Good point. Having never bent a rim, this didn't occur to me. I can see how
keeping everything as straight and square as possible would make life in
later assembly a lot easier. Should bend easier too, I'd think. 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.


>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. 

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.


>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.

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


>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.

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. 


Ron N