cracked plate

[Farrell]

I wonder if, after stringing up to tension, the jack was in there so tight because there was already a crack - letting the pinblock/plate rotate that little bit and press down on the jack. You say you heard the crack - was it pretty loud? I've never heard a plate crack, but I can only imagine that it would be a pretty loud event.

Did you simply unscrew the jack at a normal rate? I'm assuming you didn't whack the jack with a sledge and remove it instantaneously (I'm sure you didn't - just covering that ground). If you let it down slowly, I have a hard time understanding how your actions could be responsible for the plate cracking.

Terry Farrell
  ----- Original Message ----- 

  This was just a normal screw type jack.  And maybe this had nothing to do with the plate cracking, but after stringing the piano, it was in a lot tighter then when I first put it in.  I had put it in just snug enough so that I couldn't move it.  I guessed that the string tension pulled that corner of the plate and maybe the jack gave it that borderline amount of support(?)  Probably didn't have the plate in position as well as I thought.

  Anyway, the crack happened as I released the jack, so I'm thinking there is some connection.  It's about 5 hours since this happened, and the strings are still at pitch.  

  I don't consider myself a rebuilder.  This project was more of a change of pace for me (I'm primarily a field technician) and this particular instrument was a good one to screw up (if I had to screw up a piano!)  since it had little value to begin with.  I AM feeling gun shy, however.

  Gordon Large





  -----Original Message-----
  From: Farrell <mfarrel2 at tampabay.rr.com>
  To: Pianotech List <pianotech at ptg.org>
  Sent: Wed, 2 Apr 2008 3:35 pm
  Subject: Re: cracked plate


  What Dale said.

  Support jack? A pinblock support jack? I'm having trouble visualizing how a pinblock support jack could cause the plate to crack. You reference "releasing" the jack. What type of jack is it? I'm only familiar with screw-type pinblock supports.

  When you put the pinblock support in place, I guess I've never been instructed one way or another, but I just snug it in - I don't jack the pinblock up at all. So if the jack didn't move the block, and hence the plate, and then you remove the support with tension on the strings, okay, so the plate/block will adjust some tiny little bit, but why would it cause a crack? Seems to me the plate would be in that position anyway and would be experiencing whatever stresses it does either way.

  I just don't see how removing a pinblock support would cause the plate to crack. Thoughts?

  Terry Farrell
    ----- Original Message ----- 
     Check the Archives for www.Lock-n-Stitch.com. Been lots on it
     Dale Erwin

    -----Original Message-----

    I have a Chickering 1/4 grand in the shop with a hairline crack on the treble strut between the two capo sections.  This is right where a nose bolt passes through, so the crack extends from the top of the strut to about halfway through.  

    I'm sure it was my error that caused the crack.  (I restrung the piano, chipped it, and had it up to pitch before realizing that I still had my support jack in the high treble.  With all the string tension, it was really wedged in.  It was very difficult getting it to release and when I released the jack, I heard the crack.
    SNIP
    Gordon Large, RPT


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