No downbearing ?

[Delwin D Fandrich]

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  ----- Original Message -----=20
  From: Erwinspiano@aol.com=20
  To: pianotech@ptg.org=20
  Sent: January 02, 2004 10:37 AM
  Subject: Re: No downbearing ?


  In a message dated 1/2/2004 8:41:36 AM Pacific Standard Time, =
pianobuilders@olynet.com writes:
      ----- Original Message -----=20
      From: Erwinspiano@aol.com=20
      To: pianotech@ptg.org=20
      Sent: December 31, 2003 5:56 PM
      Subject: Re: No downbearing ?


    At least until the transition from hot animal hide glue to "modern" =
synthetic adhesives (for this industry this took place between roughly =
the mid-20s to the mid-30s) all pianos, grand or vertical, had at least =
some amount of compression-crowning. This is regardless of what curve =
may or may not have been machined into the ribs. Of manufacturing =
necessity the soundboard panels were heated to approximately 120=BA F =
for several hours before ribbing. It was long enough to thoroughly heat =
the panels and dry them to some very low moisture content -- and, hence, =
shrink them -- prior to ribbing. By definition this is =
compression-crowning.
    >> I have no doubts that there was some sort drying prior to ribbing =
but with the uprights a mere few hours of heating isn't really going to =
take a soundboard panel to an adequately low emc level for compression =
crowning. None of us would expect that result in our own shops.=20
     I suspect any amount of crown achieved was mostly dependent on =
circumstance I.E. it was a cold dry time of year & the pre ribbed boards =
were already at low emcs.=20
Few of us run soundboard conditioning rooms at anything like the =
temperatures used by these early pianomakers. We certainly don't. You =
put a batch of already reasonably dry and properly stickered soundboard =
panels in a room running well upwards 120=BA+ and they are going to =
shrink quite nicely overnight. All you need to do is get them down to =
4%. Standard practice, I'm afraid.

Del
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