I gotta problem. Well, actually lots, but one immediate piano related problem. After reading Bob Hohf's recent articles on action geometry and reviewing my Renner action geometry info and Nick Gravagne's info and Journal reprint info, I have delved into my 7 year old Boston GP178's action. It appears that the action is less than optimally efficient. My analysis shows that my action stack is set too low. My hammers appear to be over-centering, the capstan/heel cushion contact lies below the "magic line" at key rest, and just barely touches it at full key depression (so it is arguably on the low side), the knuckle/rep lever contact lies about 3 mm below the line between wip center and hammer center and full key depression, and the perpendicular from the knuckle wood to the jack center lies about 4 mm aft of the jack center (on the B+ side) - which is good that it is on the B+ side, but I wonder if this is too far. Also, sighting down the action rails, one can clearly see that the middle portion of the stack sags lower than the far bass and hi treble ends. I placed hardwood shims under the stack feet to bring the hammer rail up to a elevation where the shanks would be parallel (or nearly so) to the strings. I put about 2mm at bass end, 3mm at bass break, 2mm at tenor/treble break, 1mm at treble/hi-treble break, and no shim at high treble end. Sight down rails now and all is very straight. Capstan/wippen heel contact point appears unchanged :-( , perpendicular from the knuckle wood to the jack center is improved and now lies about 1 or 2 mm aft of the jack center (on the B+ side). BUT, Downweight in the most-raised section went up 2 grams (from 45 to 47) and Upweight went down in same section 2 grams (from 26 to 24). Bass and treble had smaller changes, and Up and Down weight were the unchanged in hi-treble (where no elevation change occurred). Now what does all this say? I would think my geometry improved, although maybe I didn't change action geometry much, but rather only the angle at which the hammer strikes the string. Do I have to pay for better string-striking angle with action efficiency? My thoughts are now turning toward considering moving the capstan in toward the center pin to improve its relationship to the "magic line". The bottom horizontal piece of wood of the wippen (what is it called?) to which the heel is attached is nice and horizontal on my Boston. The keys are nearly horizontal. The capstan is 90 degrees to the key. But my wippen heel cushion is not horizontal, but rather it slopes upward toward the pianist. As such, the heel cushion contacts only the back portion of the capstan and this relationship is exasterbated through the downstroke of the key. Is this a bad thing? I know that if I decide to move the capstan line I may need to do something with the wippens. If my heel are all funky because of their wierd angle, maybe that will help me decide whether to move the capstans if other info suggests that would be good to do. How important is it for the capstan/wip heel to cross the magic line at half-keystroke? Eyegh, yie, yie. What a nightmare - but I sure am learning - I think. ;-) I started this crap at 4 am this morning. Maybe I need to get a life. Terry Farrell Piano Tuning & Service Tampa, Florida mfarrel2@tampabay.rr.com
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