At 10:08 AM 06/08/2000 -0400, you wrote: > >In a message dated 6/08/2000 9:33:30 AM, Joe wrote: > ><<Hi, > >Is the function of counter bearing bar you speak of, to give greater > >pressure in the string. So that it will have ? And beter termination? > >Joe Goss>> > >Joe; > Ron or Del could give you a better technical definition of these things but >their function is kinda simple so I'll try :-) > "counter bearing bar" might not be the proper terminology but that is what I >have always called them. ON S&S these bars are cast in the plate with three >sections each in treble and middle tenor...in the tenor section this function >is performed by that wide, curved, piece of felt/oilpaper that lies between >the tuning pins and the agraffes. Some instruments use "half-round" steel or >brass bars which are not cast into the plate. > For all of these things the purpose is to provide a smooth rendering surface >for the strings while providing (slightly adjustable in some cases) "up" >pressure directly 'behind' the capo or agraffe. > This, in theory I suppose, provides for a more positive speaking length >termination at the capo or agraffe. >Jim Bryant (FL) Joe, Jim, and all the ships at sea, The counter bearing bar, mound, felted lump, rock, or whatever, or lack thereof, establishes the string bearing angle at the V or agraffe. This angle, as well as the radius of the V, or hole in the agraffe, defines the front speaking length string termination. Too shallow an angle, and there is a lot of leakage past the V, and the front duplex is noisy. The agraffe section usually has understring cloth there so it's not as much a problem. Too steep an angle, and you get string rendering and breakage problems regardless of the V contour. I shoot for 15°+ to 20° deflection at the V, and as short a front duplex as I can get. Del has written that the shape of the counter bearing bar is nearly as critical as that of the V. I assume he was talking about lower deflection angles in tuned front duplexes, because I haven't noticed any problems at the higher deflection angles. Perhaps I've just been lucky. Maybe he'll kick in and elaborate. In the case of the your Knabes, and the old Mason & Hamlins, that 45° counter bearing angle is hard to get around. Assuming you have the owner's permission to modefile their instrument in an attempt to make improvements, there may be a few things you can do. In the Knabe, I'd grind down that cast in counter bearing until it was flush, or a string angle of under 20° was established, whichever comes first. If you get all the way down to flush, clean up the transition between where you had been grinding flat, and the slope down to the agraffes, and use that edge as your counter bearing bar. Then make another counter bearing bar and place it between where you ground off the old one, and the tuning pins. This will re-establish the string height relative to the top of the plate webbing in the tuning pin field. Now, instead of one counter bearing angle at 45°, you will have two at, say 30° and 15°, or however it works out. I don't have any evidence to support it, but I think I'd like to come as close to a 50/50 split as I can, though I have some other ideas for specific circumstances that I haven't had the chance to try out yet. In any case, you will have reduced that extreme counter bearing angle at the V or agraffe. The rendering will be better, in spite of the added bearing point, and breakage at the V will be greatly reduced. You probably won't need any felt at all, and I don't like to put cloth on a bearing point anyway. It's usually some easier to add counter bearing and decrease front duplex length than to reduce counter bearing, but in both cases, you often have to settle for "better", when the reality of the plate design won't let you put things exactly where you want them. Gee, that sounds kind of like about every other thing you try to do with a piano, doesn't it? Anyway, that's my opinion this week, subject to modification by gooder information and/or contrary experience. Ron N
This PTG archive page provided courtesy of Moy Piano Service, LLC