[ Warren Officer wrote in 160428 MMDigest:

> The complaint was the pump is making the piano shimmy.

There have been many thoughtful causes suggested for Warren Officer's
reproducing piano vibration.  In vibration problems, it is very helpful
to know the vibration's dominant frequency.  An easy and quick way to
determine this is to lay a smart phone on the vibrating piano and
measure the vibration with an app such as VibSensor.  The app should
give you the "resonance" or "primary" frequency measured.  It will be
in cycles per second (cps=hertz=Hz).

Could the motor be causing the piano vibration?  The motors
nameplate RPM can be divided by 60 to tell you it's frequency in cps.
If this matches your bothersome vibration, the motor is stimulating the
vibration.  (A 1200 rpm motor spins at 20 cps.  That's pretty fast to
see visibly in piano motion.)

Could the vacuum pump be causing it?  Measure the diameters of the
sheaves on the motor and on the vacuum pump.  The ratio of diameters
times the motor cps tells you the cps of the pump.  Does this match?

Is a bump in the drive belt causing it?  Paint a white mark on the
belt and count how many times it goes around in a minute.  Divide
this amount by 60 to gets its cps.

Once we understand the bothersome vibration's frequency and the
frequency of the possible suspected causes, the solution should be
easier to find.

Wayne Finger