Hi Bob. Cant really answer your question as to why such thin gaps seemingly did not change under tightening. But it does seem obvious there are several things going on at the same time relative to the basic question at hand. Pulling strings off a whole section of the treble could feasibly cause changes in both the soundboard and release stresses on the plate in more the one direction. The movement in remaining treble string pitches reported are probably the result of a combination of these rather then of one or the other. Your plate may be rather stiff around the screws in the direction you <<want>> it to flex... or maybe there is some other explanation. Bechstein used to have an interesting plate installation procedure, and it had everything to do with this whole plate flexing thing. I've never been to their factory, but the way I have heard it was that you fastened the plate to the pinblock first (which was solidly mounted into the sides of the piano so it couldnt float), then starting at the high treble you moved round the plate towards the bass tightening the screws. By the time you got half way around you'd notice the whole bass area floating quite a bit in the air. The whole thing was to be pre-flexed as it were along the direction of the unwound strings, apparently in an attempt to counter any stability problems related to plate flexing. Cheers RicB Bob Hull wrote: >Questions about this theory: If the plate is able to >flex like this then why am I having the following >experience: > >I have just done soundboard repairs on an older 5' 6" >Weber grand including coating the board with epoxy. >Instead of resting on dowels the plate sits on a >continuous ledge about 1/2 inch (12.7 mm) high around >the perimeter of the soundboard. In order to increase >the downbearing I have lowered this ledge to approx. >.42 (10.6 mm). The db will still be minimal but I >don't want to overstress this old board. Since it was >difficult to know just how this lowered ledge surface >would mate to the bottom of the plate,- where the two >would meet-, I used slips of paper between the bottom >of the plate and the top of the ledge (like when >bedding a keyframe) to feel where the two were >meeting. I found there was a small gap between the >two - enough to freely slide the paper strips along >almost the entire area(if the paper was .003 then the >gap was maybe .006 but I hadn't tightened the >perimeter screws yet. It did have contact with three >small areas. Surely when I tightened the screws the >little gap would disappear - right?, the plate is >somewhat flexible as you have been discussing - but, >tightening the screws did not eliminate the gap or >change it as far as I could detect. > I lowered the places where there was contact >which still didn't improve the mating of the plate and >ledge. So, I created highpoints or resting spots >(using WEST epoxy)on each side of each screw as if it >was sitting on really short "dowels". Protecting the >board and plate with wax paper I lowered the plate >back down and tightened the screws to make the epoxy >fit the gaps - - like pinblock final fitting. >Of course, if I remember correctly the plate is >thicker around the edge and maybe it's elasticity is >too limited there to flex. The plate as a whole is >more capable of flexing/bowing because it is a lengthy >span which is anchored around the perimeter and at >tiny nose bolt locations. The original design, if the >plate and continuous ledge were well mated, seems like >it would have a different effect on plate behavior >characteristics than a plate that rests only on dowels >or lag screws. > >A long explanation to ask "Why didn't the plate flex >down when the screws were tightened?" >Also, what other/better ways would you have approached >this plate height situation? > >--- Ron Nossaman <rnossaman@cox.net> wrote: > > > >>>It seems to me that the following may prove this >>> >>> >>theory. >> >> >>>The next time you experience a broken string, >>> >>> >>measure the pitch change on >> >> >>>adjacent strings/notes. Then press down on the >>> >>> >>bridge about 7 lb. worth. >> >> >>>If there is no effect on the pitch on these >>> >>> >>adjacent strings, you will >> >> >>>know it is not the downbearing change on the bridge >>> >>> >>causing the pitch >> >> >>>change. After the new string is installed, check >>> >>> >>the adjacent strings again. >> >>If someone who uses an ETD tries this, please post >>the results to the list. >> >> >> >> >>>Do you think this will prove the point? I've not >>> >>> >>done this, but I will do >> >> >>>this the next time the situation occurs. This has >>> >>> >>been enlightening, >> >> >>>because I've always heard that pitch change takes >>> >>> >>place due to the change >> >> >>>in downbearing on the bridge and soundboard. >>> >>>Sincerely, >>>Gary Mushlin, RPT >>> >>> >>All of us have always heard that, but I don't see >>much indication that it's >>true. >> >>Ron N >> >>_______________________________________________ >>caut list info: >>https://www.moypiano.com/resources/#archives >> >> >> > > > > > > >__________________________________ >Do you Yahoo!? >Dress up your holiday email, Hollywood style. Learn more. >http://celebrity.mail.yahoo.com >_______________________________________________ >caut list info: https://www.moypiano.com/resources/#archives > > >
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