[ Ref. 160428 MMDigest, Rotary Pump Makes the Grand Piano Shimmy

My 1923 5'4" Chickering grand shook from day one after I rebuilt it.
It stopped briefly over the winter, but then started shaking again.
I believe the problem is an inherently unbalanced pump (spider crank)
coupled with legs that are not rock solid.

My piano sways side to side at the front as seen in the shake video
[link below].  I put a small wooden 2" x 3" shim with leather on both
sides under the lyre so there is a bit of friction between the lyre
and the floor.  That's all it took to stop the shake.  My piano no
longer shakes and the shim is hidden.  It just took a bit of friction
to spoil the resonance which caused the shake.  My piano legs are
tight.  The shake frequency of the imbalanced pump and the resonant
frequency of the piano mass must have been just right to cause the
shake.

I've uploaded video to YouTube showing the before and after.  I also
included one showing the piano playing "Harmonies du soir" and a brief
tour of my music room, which is in disarray right now.  The audio is
horrible because of the auto gain control of my cell phone.  I need
to find a way to disable it.

  before: https://www.youtube.com/watch?v=IQ-SRmvCS2g 
  after:  https://www.youtube.com/watch?v=15ekBQxrV1c 
  tour:   https://www.youtube.com/watch?v=hxWVieAfbtE 

Mike Clemens

 [ The leather friction pad (shim) acts like an automobile shock
 [ absorber (vibration damper) by dissipating the energy that's trying
 [ to build up in the mass-spring resonator formed by the mass of the
 [ piano and the compliant piano legs.  Good work, Mike!  -- Robbie