Regarding John Tuttle's experience with a customer's Aeolian upright
with a cracked plate, I agree with Larry Fine, author of "The Piano
Book", that --

  "There are only two ways I know of that a tuner can break a piano
  plate that is not defective while servicing a piano in the home.
  One way is to excessively tighten the nose bolt that supports the
  plate in the center area of the piano.  This is an adjustment not
  normally made outside of a piano rebuilding shop.  The other way
  is to take a sledge hammer to it.  In other words, it is virtually
  impossible for a piano tuner to break a plate during the normal
  tuning and pitch raising of a piano unless the plate is already
  defective and ready to break, in which case any tuner, regardless
  of skill or method of tuning, will be the unwitting agent of such
  breakage by fate alone.  Even in a worst-case scenario, in which
  a tuner sought to sabotage a piano by stretching all the strings
  far above standard pitch, chances are that the strings would break
  long before the plate would.  Tuners are sometimes blamed for plate
  breakage by understandably distraught piano owners, but in every
  such case the blame is misguided and completely unjustified."

An excellent resource on the topic of plate manufacture and design is
a PTG journal issue available on the web at

  http://www.ptg.org/userfiles/file/ptj/plate_issue.pdf 

While I love the Aeolian Duo-Art and other player systems, I would
never recommend an Aeolian piano to a customer, especially one built
after 1930, in part for exactly this reason.  They were designed with
marginal string plates, with thin connecting braces and fewer plate
sections spanning wider gaps, so that with the normal aging and
embrittlement of cast iron they are prone to cracking at the slightest
provocation.

This "lighter" design made them cheaper and easier to move, but plate
failure is remarkably common with them, especially in the mid-treble
as shown in the video.  And while their soundboards were also prone to
cracking, I can't imagine any way that cracks in the soundboard could
add stress to crack a properly designed string plate, although the
release of string tension may make cracks and rib separation show up
more visibly.

While I generally try to "evenly" detune a piano when unstringing and
"gently" bring it back up to pitch after restringing, I think it does
a disservice to the profession to suggest to a customer or in a public
forum like a YouTube video that a plate breakage was caused in any way
by "improper" or "uneven" tuner's technique, no matter their level of
training or certification, unless they were improperly tightening nose
bolts to try to improve downbearing.

Ralph Nielsen
http://www.historicpianos.com/