I've been following this thread with much interest would like to chime in, if I may.
To David Hughes, Glueing the block to the stretcher and doweling it to the inner rim shelf when this is the original configuration is certainly an advisable approach and I wholeheartedly endorse overdesign with regards to structural integrity. There is an alternative approach to accomplish this and maintain a removable stretcher. Our plate has both a front and rear plate flange (photo 001) so the block is surrounded by cast iron. There are two massive lag bolts on each end of the plate which go into the inner rim, coupling the plate with the front flapping wings of the rim.
It's been my experience that the weaker link in the unattached version is the glue joint between inner and outer rims because many who use this system press the rims separately, belly the inner rim, and then bring the two rims together after the fact. We've begun doweling the inner and outer rims together at the front of this joint (photos 011 and 025). The reason for this is because many people like to move the big concert pianos by grasping the top of the outer rim at the front of the piano and pulling it around. This really stresses the inner/outer rim glue joint and there's nothing like hearing a lovely cracking sound as the piano is being spotted on stage prior to a performance.
To Nick, yes we use TP bushings and I too would be concerned about the roll factor in a non bushinged plate if the block were not glued to the stretcher. But I have to wonder how much of the proposed 3000lb force the flimsy stretchers on most pianos could withstand without the pinblock screws. The stretcher is typically attached to the inside of the outer rim with a simple butt joint (typically meaning that I understand some are morticed and some "are the pinblock"). So how much is this piece of wood really capable of supporting being attached at only two points? If roll is a concern, perhaps an upgrade to grade 8 machine screws would be more benificial. I have removed bent pinblock screws from blocks that have, shall we say, "drifted".
To all, I also agree with Del and have rebuilt a couple of the Stark pianos like the ones he posted where the pinblock is screwed to the plate from the bottom and has no contact with the rim or stretcher. No tuning stability or sound issues with these pianos. "Most" manufactures who employ the unattached version will ensure that the plate design is sufficient to support this. Also notice worthy with Del's photos is that Stark used machine screws.
Isn't it interesting that Yamaha changed their approach from not fitting the block to the flange or attaching it to the stretcher, years ago. However, I was informed that this was more of a marketing enhancement than a structural one. The techs in the US were convinced that an unattached, unfitted block is inferior and were continually complaining to the US office about this being a cause for tuning instability, which ultimately had the potential of impairing sales.
To Ron: absolutely agree that the place to focus additional support is between the plate and belly rail. This tend to not be an issue if perhaps one were using falconwood belly rails and godzilla designed plates . However, the belly rail of most pianos is the weakest link in the perimeter support of the board assembly. If one is not up for replacing it, I would encourage that the belly rail be doweled into the inner rim at each end. With the addition of bass cut-offs, the primary focus would be the treble end. On most pianos, one can install at least 2 meaty dowels that will add support to the weak glue joing of belly rail to inner rim and also help prevent rolling of the rail. It's not unusual to experience glue oozing out of the belly rail/ inner rim joint when hammering the dowels in, which tells me this a highly stressed, often overlooked, underdesigned joint.
To David Love, I think the attribute to the removable stretcher, unattached block scenario is the ability to extract the plate, block, and strings in order to repair the cracks in the CC boards of many of the pianos that come to the dry west climate from factories where the instruments are constructed in an environment that has no RH control (you can read between the lines on that one!).
To Fenton (yes, I'll be nice too), I'm not convinced there is much sound enhancement potential with gluing everything together in order to attain the circle of sound ideal; some of the greatest instruments I've heard have floating blocks. When rebuilding, I did make the pinblocks of the floating design nearly impossible to remove for the next technician by bolting, gluing, welding, doweling, etc. them in because "more is better". I cannot quantify this because there were other enhancements made to improve the sound, but I don't believe the glue-all approach offered any significant improvement to the sound. It did make me feel better though, that is, until I begin receiving letter bombs from those of you having to replace the blocks in those pianos.
Michael Spreeman http://www.spreemanpianoinnovations.com
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