<HTML>In a message dated 4/29/2002 7:52:54 PM Pacific Standard Time, mfarrel2@tampabay.rr.com writes: <BLOCKQUOTE TYPE=CITE style="BORDER-LEFT: #0000ff 2px solid; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px; PADDING-LEFT: 5px">Subj:Curve on Bridge Bottom Date:4/29/2002 7:52:54 PM Pacific Standard Time From:<A HREF="mailto:mfarrel2@tampabay.rr.com">mfarrel2@tampabay.rr.com</A> Reply-to:<A HREF="mailto:pianotech@ptg.org">pianotech@ptg.org</A> To:<A HREF="mailto:pianotech@ptg.org">pianotech@ptg.org</A> Sent from the Internet           Terry</BLOCKQUOTE>       If you're rebuilding a Stwy or Mason these pianos both cut crowns in the bridge bottoms already. SO no extra cutting needed. To check this lay the bridge on the floor, press down on the ends of the bridge and the middle will come up a bit or with the board dry fit in the case lay the bridge on it and see if it conforms to the boards curve. Usually it will.     These makers intended there to be some crown along the grain and it's quite easy to induce if you wish. Steinway refers to this as double crowning and there contention is that it supports crown along the grain. I'm not sure it helps that much after the bearing load goes on but it is measurable before that especially if you're using a jig such as a torsion box with a 60 to 80 ft. radius. With the board layed down on the box the bridge is then glued on. There are 2 by 4 blocks placed on the box to fit between the ribs to give support when the pressure is applied. I use my old go bar deck.  The curve in the box being greater than the hollow in the bridge bottom allows the bridge  to be bent a  little bit more than its cut crown. At least this is how I do this. The resultant crown along the grain is significant and measurable with a straight edge. I personally have done it both ways and frankly  In my humble opinion I like the sounds of the treble better this way all be it subjective. Others I know who do it this way have stated similar opinions. Also with the crown along the board/rib it does require less force to glue the board in at the top.   I can still measure the crown along the grain after the board is installed by the way.     It may well be possible that in some designs it's an advantage and in other it's not.        Clear as mud? Hey you asked>>>>>>>>.Dale Erwin>>>.. <BLOCKQUOTE TYPE=CITE style="BORDER-LEFT: #0000ff 2px solid; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px; PADDING-LEFT: 5px"> I know some rebuilders cut a radius curve on the bottom of new bridges. I know some folks here have indicated that they do not. I will not dispute that it may well not make any significant difference which way one goes. Is there any good technical argument either way? It sure seems to me that the biggest, stiffest, longest rib on the board should be an integral part of shaping the board. Has a straight-bridger measured crown on an installed board without the bridge, and then measured it after the long bridge was installed? Does it not flatten the board a bit? Is some of the ribbing theory (tighter radii) designed to compensate for the small (??) flattening effect of a straight bridge? It can't hurt to cut a nice little curve into the bottom of a new bridge - can it? Terry Farrell   </BLOCKQUOTE> </HTML>