Soundboard Crown measurement and evaluation

[Farrell]

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Well, he doesn't say whether the measurements are being made on the =
bridge side of the soundboard or the rib side. You are correct if the =
measurements are made on the bridge side. His method should kinda-sorta =
work if measurements are made on the rib side of the soundboard. =
However, the string method offers much more flexibility for where to =
make your measurements. A hard, 4-foot-long straight edge won't work =
very well to measure crown in the killer octave area. One crown =
measurement in the middle of the board won't tell you much.

When accurately measuring crown with the string method - usually only =
done when setting up a new belly - I have a series of little wooden =
blocks with thicknesses in one-millimeter increments. When measuring =
crown by myself, I take a piece of masking tape and tape one end of the =
string near the soundboard edge and hold the other end of the string at =
the opposite edge parallel to a rib. Then I simply take my little wooden =
thickness-measuring blocks and use the go/no-go method of measuring the =
gap between the panel and the string. This works infinitely better than =
trying to accurately read some sort of ruler. You can also get a real =
good characterization of the shape of the panel (how even the crown =
profile is) along the full length of each rib with the string method.

Terry Farrell
  ----- Original Message -----=20


     By the way this doesn't work because of soundboard thinning. The =
board is thicker in the middle, thinner at the edges.  This method will =
show positive crown even when there is none. Follow me?
     Dale  Erwin
    Here's the method I read about:  You take a straight edge as long as =
the back=20
    of the piano (I'm assuming they meant an upright), attach to EXACTLY =
7" blocks=20
    at a right angle to each end, then measure from the bottom of the =
straight=20
    edge to the  soundboard at the mid point.  Subtract the middle =
measurement=20
    from 7" and that's the amount of crown.


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