In a message dated 2/8/2010 9:24:09 P.M. Central Standard Time, erwinspiano at aol.com writes: Hi Paul I used to add 1 degree of rake but I was forever hanging the hammers and then re hanging them closer to the player. SO pointing the strike point in the wrong direction didn't help. After a while I came to my senses. So, my thought is that unless I am duplicating the standard bore hammer of the S&S (whatever that means) which in my opinion more often over centered from the git go than not,... why bother?If some one has a better thought, I'm all ears. Pun intended. I guess I still have a sneaking suspicion that there is a tonal effect from the over-centering resulting from the strike-line deviation. But I have no data, just lines of reasoning. Perhaps the idea Ed was getting at was that whatever degree the string slope is that there should be a corresponding amount of over centering and rake so the string and hammer are at right angles to each other ant the keybed. However this means calculating the slope on each piano or just checking it and averaging the bore. I think I just devised an A B Expereiment. I'll work on it Actually it means calculating the bore and rake on each of the hammers as they deviate from the straight line of the original hanging scale. The rest might be a section by section calculation. Is it worth it? Is there an effect (tonal or otherwise) that is significant enough to warrant this? Dale 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_ (mailto: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 accommodate 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_ (mailto:davidlovepianos at comcast.net) > To: _pianotech at ptg.org_ (mailto: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/20100208/45ed8778/attachment-0001.htm>
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