[pianotech] Soundboard Analysis

[David Love]

I'll have to look at the tool.  It sounds interesting and useful.  I haven't
found the string method to be particularly difficult or inaccurate, at least
for my purposes.  I can get a reading easily to the .25 mm with a simple
graduated wedge gauge and combined with bearing readings above a change in
the crown can be calculated and then verified as the tension either
increases or decreases.  

 

The exact amount of crown that exists on new boards once I've made them is
not really something I worry too much about.  I'll check it, but if it's a
little different than I anticipated that's not really a big concern.
There's always some variation from what was anticipated and what is actually
delivered.  When stringing the piano I rely pretty much solely on
downbearing measurements to track what's happening to the board as I'm more
concerned with how it's loaded than how the exact amount of crown I have.
I do track the loading pretty carefully topside with a  Lowell Gauge.  

 

The purpose of my posting those numbers was for those who don't necessarily
take these kinds of measurements or try and calculate how an old board might
react in order to determine whether the board is useable or not.  Not
everyone does, I find.  You clearly do and your method with this tool is
certainly fine.  I've found the string method works quite well and haven't
found it burdensome.  As Ron mentioned, it can tell you things that the
gauge can't as easily or quickly, like the overall shape.  On old boards I
use the amount of crown combined with downbearing measurements during
teardown to determine if I will be able to load the board adequately and
where it is that I might be concerned with overloading the board and pushing
it through positive crown.  On old boards I don't have a problem with
squashing them flat or close to it but I don't want to go beyond.  With
crown and downbearing readings during teardown you can determine if you
enough crown to adequately load the board.  If you need 700 lbs under normal
circumstances but can only load the board with 250 lbs before pushing things
past flat then you have a problem.  If the cushion I have there has to be
measured in thousandths of an inch then I'm probably changing the board.
This is a fairly simple method to make that determination and doesn't
require any fancy gauges.  Still, I might contact Jude and buy one if he's
offering them.  I'm always interested in new devices.  

 

BTW make sure are aware of humidity levels before you take measurements.  We
didn't mention that but you'll certainly get different results at 70% as
compared with 30%.  

 

David Love

www.davidlovepianos.com

 

From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of Encore Pianos
Sent: Thursday, June 23, 2011 2:52 AM
To: pianotech at ptg.org
Subject: Re: [pianotech] Soundboard Analysis

 

Hi David:  

 

If you reread my post you will see that all the readings are taken with the
board glued in and at the various stages of the process working up to and
including stringing, tuning, and loading the board.  I can throw the  gauge
on the panel when it is ribbed and out to be worked on, but I don't think
that is of as much value as the in piano readings.

 

I do use it to analyze boards prior to teardown.  Certainly when I am doing
an estimate I take it with me and can take readings on every rib I can get
to, along with bearing readings on the topside.  And once the piano is in
the shop, do all this as part of the teardown process, particularly if I am
going to be using the old board again.  

 

You are correct that in some places the access will be more difficult or
impossible, particularly in the high treble where things get much more
crowded.  The beams can be in the way in other places.  Sometimes I shift
the location to one side or the other to avoid the beam, but generally try
to center it under the treble bridge.  You may have better access with your
string in the problem areas.  Otherwise, it is no more difficult than laying
on the floor, reaching up with gauge in hand and setting it next to the rib,
and taking a reading with sufficient light.  That takes only a few seconds
to do.  In those places it is easier and faster.

 

As I said earlier, it will not measure negative crown, but neither does the
string.  A straight edge won't give you a measure, but will tell you that it
is negative.

 

Will

 

 

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