So Dale... When you alter the strike line, do you also add in a compensating rake to bring the hammer back to 90 degrees? I never have, but it strikes me that there is quite possibly a tonal difference attributable to the over-centered hammers that are part of the deviation set. I also remember Chris's class on the power stroke and the energy train. Do you remember (does anyone) his class on bridge design as a series of catenary curves? I love the guy's brain. Paul In a message dated 2/8/2010 6:48:46 P.M. Central Standard Time, erwinspiano at aol.com writes: Thanks David The underlined sentence below is part of my thought. Imagine it this way, all the hammers and shanks are magically being held horizontal to the keybed. In my protocol with the shanks in that position there is 1 mm between the hammer crown & the string. The reason I choose to do it this ways is so that escapement/let-off occurs after the shanks have passed the horizontal position. The goal is max power. If memory serves, in class long ago with Chris Robinson, he made the case that because of the action geometry, maximum power occurs in the action train between the hammer/shank at its rest point and the horizontal shank postion. If let-off happens before horizontal this would rob some power. Let-off for me a tight is 1.5mm tenor 1 mm top trebles. 2mm bass. I'm not saying, I'm right, I don't care. It makes sense to me. Some folks subscribe to boring hammers so that they are bored longer than the center pin to string height distance. The shanks by necessity will sit closer to the shank rest as a downward capstan change will be made to accomadate the longer bore distance. This method can change the efficiency of the geometric relationships. Usually makes them worse. ie heavy action,more initial friction, & capstan set lower than the magic line etc. Over centering is actually the lesser of two evils to my mind. Also our dead ancestor can't speak to this, but they set up many a piano action to overstrike, and some by huge amounts. I dont' see any set up to under center. Perhaps they knew something? Maybe Frank Emerson could run some configurations on his computer model and get back to us. He probably already has! Dale -----Original Message----- From: David Love <davidlovepianos at comcast.net> To: pianotech at ptg.org Sent: Mon, Feb 8, 2010 12:08 pm Subject: Re: [pianotech] boring, (was Hammer strike line) True it depends on the degree but the point of the comment was that subtracting the 1 mm from the string height - flange center pin difference will not place the hammer at right angles to the string only when the string plane is parallel to the keybed. It will accommodate some rise in the string plane toward the bridge. The amount of rise it will accommodate will depend on those factors you mention. David Love _www.davidlovepianos.com_ (http://www.davidlovepianos.com/) From: _pianotech-bounces at ptg.org_ (mailto:pianotech-bounces at ptg.org) [_mailto:pianotech-bounces at ptg.org_ (mailto:pianotech-bounces at ptg.org?) ] On Behalf Of Ed Foote Sent: Monday, February 08, 2010 11:17 AM To: _pianotech at ptg.org_ (mailto:pianotech at ptg.org) Subject: Re: [pianotech] boring, (was Hammer strike line) Dale writes: Original hammers and shanks over centered a good bit. Our shop does not do it this way. My formula is :String height minus center pin height minus 1 mm in each section. I said, This will place the hammer at right angles to the string upon contact ONLY when the string plane is parallel to the keybed. What do you do when there is a considerable rise of the strings from the capo to the bridge? David asks: >>Why is that? Wouldn’t subtracting the 1 mm compensate for some rise in the string toward the bridge? I don't know, that would depend on the actual angle of the rise, and if it does, then it sets all the other sections out of square, no? and if the strings are parallel, the missing 1 mm will cause over-centering at the beginning of the hammers' life. I have seen quite a few pianos with a very sharp rise to the bridge. In those cases, new hammers bored short enough to create the 90 degree match to string would have been too short to regulate properly,(shanks way off the rests). It is sometimes necessary to hang the top section with an acute angle to the hammer, plus boring a short as possible. Regards, Ed Foote -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://ptg.org/pipermail/pianotech.php/attachments/20100208/5b0d57fc/attachment-0001.htm>
This PTG archive page provided courtesy of Moy Piano Service, LLC