[pianotech] Reversing Crown

[David Love]

If you have positive bearing and positive crown then you have downward
pressure on the board with residual crown so if you take off the strings the
board must rise, i.e. the crown remains positive.  Good sign.

 

If you have positive crown with negative bearing that means that the bridge
is being pulled up by the strings and to what degree that is responsible for
the crown formation you can't tell until you take off the strings.   Bad
sign.

 

If you have positive bearing with negative crown you can't tell whether when
you remove the strings the board will rise to show positive crown or not
since you don't know how the bearing was originally set or exactly how far
down the bearing is pushing the crown.   Bad sign.

 

If you have negative bearing and negative crown that means the board is
being pulled up but even with that is not achieving positive crown.
Definite burnt toast.

 

Keep in mind that each section of the piano may show different relationships
to crown and bearing and, as Ron mentioned, several measurements are
necessary across the panel.  

 

David Love

www.davidlovepianos.com

 

From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of Noah Frere
Sent: Thursday, December 24, 2009 7:52 AM
To: pianotech at ptg.org
Subject: Re: [pianotech] Reversing Crown

 

Hmm..I didn't measure bearing. Are you saying that finding positive bearing
and crown decreases or eliminates the chance of the board reversing after
string removal? Or are you just saing that the more carefully we analyze the
instrument before rebuilding, the more accurate our estimate will be? I
believe the latter. -Noah


"Yes. This is why you measure both crown and bearing, with a "what's wrong
here" approach, rather than a "this must surely be just fine" attitude.

The cynic always wins, being either right, or pleasantly surprised. Being
pleasantly surprised is, though preferable, the less likely."

Ron N

 

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