Broads

[Carl Meyer]

Richard,  Several years ago I made a crown checker by taking a 2 foot length
of 1 x 2 lumber, drilling a hole thru the two ends and middle across the
piece (perpendicular to the 2 foot length and parallel to the 2 inch
dimension.  Use three 6-8 inch pieces of brass or steel threaded rod (8-32
or so).  With two nuts put the rods at the ends sticking down  and the
center one with two wing nuts.  Now set it on your table saw or other flat
surface and adjust the center for a straight line from end to end.  Now you
have a rocker gauge like the small one used to check down bearing only
larger.  Use this to check crown at any convenient spots.  Don't have to lay
on your back, either.
Now you have some idea of crown with the strings still on.

Regards

Carl Meyer  Assoc. PTG
Santa Clara, California
cmpiano@attbi.com

----- Original Message -----
From: "Richard Brekne" <Richard.Brekne@grieg.uib.no>
To: "PTG" <pianotech@ptg.org>
Sent: Wednesday, January 09, 2002 7:53 AM
Subject: Broads


> Hi folks.
>
> Well, I finally got around to opening up my 1836 (methinks) Broadwood
> that I will be attempting to put back together and I have a few
> questions  I'd like to have some answers to. Number 1 and first and
> formost... Was there any real crown built into the sound boards of these
> things. I will describe what I have in front of me as best I can.
>
> Sitting at this square piano and looking over the more or less
> triangular shaped sound board from that angle, you see the grain moving
> off at about 45 degrees.  There are ribs going at about 20 degrees, not
> exactly all that much across the grain, and these lengths are broken by
> three ribs that run straight out at 90 degrees which are found right
> under the bridge area.  Am I mistaken here or would this do little or
> nothing to balancing cross grain and with grain stiffness ? Certainly
> doesn't seem like a recipe for a compression crown in any case.
>
> The Bridge has that typical reverse in direction relative to sound board
> grain for these... and in this the greater part of the bridge is more or
> less at right angles to the grain, except in the treble area after where
> it swings around and follows the grain. What was that discussion about
> mass in the treble rim and stiffness in the bass rim ? There is also a
> coupling from the board to the pin block in this area, presumably to
> address both mass and stiffness.
>
> So... back to the original question. Are these boards meant to be
> basically flat ?. Strings come off tomorrow and I can give you some more
> info about what observable crown there is (real difficult to ascertain
> from underneath here) and what down bearing looks like.
>
> Thanks for any advice / observations.
>
> RicB
>
> --
> Richard Brekne
> RPT, N.P.T.F.
> Bergen, Norway
> mailto:rbrekne@broadpark.no
>
>