Plate stress couplers

[Dave Smith]

Del, thanks for the reply.  My Knabe plate stress coupler is back in it's plate stress coupler position, awaiting stringing.  Appreciate your insight.

Dave Smith
SW FL

  ----- Original Message ----- 
  From: Delwin D Fandrich 
  To: 'Pianotech List' 
  Sent: Monday, October 15, 2007 2:23 PM
  Subject: Plate stress couplers






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    From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf Of Dave Smith
    Sent: October 13, 2007 7:31 PM
    To: Pianotech List
    Subject: Re: Mystery part



    I almost hate to ask the question, but is this brace a good idea in the first place?  At least for someone who is just trying to restore at least as good as the original.  Not yet to the point of improving on piano design perfection!?!

    Dave Smith 
    SW FL 

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  Well, although plates can obviously be designed to function quite well without them, they are not a bad idea. Often when these mechanisms are used the plates are also a bit lighter so it's a Really Good Idea to properly fit them and replace them during the final plate setting. This is not so much a worry about the middle of the tuning pin panel deflecting down as it is one of possibly overstressing the bass/tenor plate strut once string tension is applied. These mechanisms keep some of the bending stress off of the bass/tenor plate strut (generally a weak point in the casting). 

  While better than nothing, the design found in your small Knabe is not the best I've seen. The horn and wedge system found in Steinway construction, for example, is a much better system. As is the system found in certain larger Knabe grands: 



  This type has the advantage of being easily adjustable both during original construction as well as later during rebuilding.

    
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  [Quote] 
  Del, A manufacturer's rep once told us the plate stress coupler (a bolt in this case) served to enhance the tone by transferring vibrations from plate to belly rail.  Any truth to that? 
  Bob Maret, RPT
  Piano Technician

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  I'm not sure what advantage there would be to transferring vibrations from the plate to the bellyrail. Bellyrails are not generally designed to function well as energy transducers; i.e., soundboards. Their advantage is to structurally stabilize the plate and, if anything, prevent energy losses by helping to prevent spurious plate vibrations and resonances. 

  As well, while the older Knabe plates I've encountered have generally still been quite massive, Steinway took the opportunity to significantly reduce the mass of their plates without any compromise in overall stability.

  Del
  Delwin D Fandrich
  Piano Design & Manufacturing Consultant
  620 South Tower Avenue
  Centralia, Washington 98531  USA
  Phone  360.736-7563
  <mailto:fandrich at pianobuilders.com> 
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