[pianotech] Reversing Crown

[David Love]

That's right.  Anytime you have negative bearing, the strings are pulling
the bridge up just as with positive bearing they are pushing the bridge
down.  If you were to detach the strings from the bridge pins where there
was negative bearing they would hover above the bridge.  You would have to
push the string down to reattach it to the bridge thus the force from the
string would be upward.  

 

David Love

www.davidlovepianos.com

 

From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of Noah Frere
Sent: Wednesday, December 30, 2009 9:14 PM
To: pianotech at ptg.org
Subject: Re: [pianotech] Reversing Crown

 

Sounds good. I don't understand this though: "that means that the bridge is
being pulled up by the strings" in the second case. It was my understanding
that negative bearing means the bridge is lower than it should be, causing
the strings to be slightly v-shaped rather than ^-shaped. 

On Thu, Dec 24, 2009 at 11:39 AM, David Love <davidlovepianos at comcast.net>
wrote:

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

 

 

 

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