AB Chase Concert Grand

[Delwin D Fandrich]

> -----Original Message-----
> From: pianotech-bounces@ptg.org [mailto:pianotech-bounces@ptg.org]On
> Behalf Of Dean May
> Sent: April 05, 2004 8:02 PM
> To: Pianotech
> Subject: RE: AB Chase Concert Grand
>
>
>
> Del wrote: ... a couple of large wood screws on
> each end don't count. Dowels and glue joints do as long as they are still
> structurally sound. But many pianos do not have glued-in
> pinblocks. So then we have to consider how stress from the strings is
supposed to
> coupled down through the two ends of the pinblock, across a floppy
bellyrail
> and into the bellybraces which are supposed to be carrying all this string
load.


>
> Stress will be transmitted through the two screws, across the
> "floppy" belly rail and to the beams. I have never done a pull test to see
how much load
> those large screws will hold before they pull out, but I suspect it is
> significant, at least 1000 lbs. And I've seen many pianos with screws
> through the plate into the rim and belly rail, bypassing the pinblock.

What happens in a short-term test does not matter. It's over the long term
that matters. Screws, even big ones, that are side loaded tend to deflect
over time by virtue of compression set in the wood.


>
> And the floppy belly rail supported by the keybed makes for a pretty
> substantial member, it seems to me. I guess it would be easy
> enough to load test and measure deflections. (something tells me you've
already
> done this).

Again, not over any prolonged period of time.


>
> I am not arguing that the beams are carrying a significant portion of the
> string load, only some, and in that measure they are adding to
> the rigidity of the plate.

Consider also all of the old grands that had one or more bellybraces simply
removed to accommodate pneumatic player or reproducer mechanism. If the
bellybrace is no longer there it can't very well be supporting any string
load.

It's the plate. Unless there is some kind of horn or other coupling
mechanism.

Del