Del wrote: It's the plate. Unless there is some kind of horn or other coupling mechanism. Could you elaborate on why a horn would couple load but you don't feel the nose bolts do? I don't see the functional difference. Maybe we are talking about different things. Are you talking about the horn inside the action cavity under the pin block at the bass break? Or the contraption bolted to the rim on the picture in a previous post? Also on the screws and compression set, that is a good point you make. It is why it is important to check plate screws for tightness. But I would think the amount of compression would diminish exponentially to a maximum. Perhaps the compression nearing its maximum is one of the factors affecting when a piano reaches tuning stability. Del wrote: Not exactly. I have, however, watched factory workers remove the screws holding the plate/pinblock to the inner rim and install or remove shims to raise or lower the front of the plate assembly without dropping tension. I wonder what it was that was supporting all that string load while the plate assembly was being adjusted for height? Certainly not the rim assembly. This is an interesting observation. I've often wondered what that plate was capable of. But you've got to admit that the front of the plate with all of those wide flanges is considerably more rigid than the back part that goes around the rim. I'd be curious to know what that did to the tuning of the piano. I am not arguing that the plate is incapable of carrying all of the load by itself- especially the massive front end. Only that the wooden frame adds rigidity and thus, stability. I really appreciate your insights, Del. Blessings, Dean Dean May cell 812.239.3359 PianoRebuilders.com 812.235.5272 Terre Haute IN 47802 -----Original Message----- From: pianotech-bounces@ptg.org [mailto:pianotech-bounces@ptg.org]On Behalf Of Delwin D Fandrich Sent: Monday, April 05, 2004 11:18 PM To: DeanMay@pianorebuilders.com; Pianotech Subject: RE: AB Chase Concert Grand > -----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. Del _______________________________________________ pianotech list info: https://www.moypiano.com/resources/#archives
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