Seems reasonable. I suspect you're right that no escapement occurs, and my initial thought was that the hammer was somehow bouncing off the wip assembly, but then as I watched, it sure looked like the rest rail was the culprit. Now I'm starting to think it's as you've said, the two combined. I thought of replacing the rest rail felt with something less dense and thicker - the current felt strip is thin and dense, relatively speaking. Not sure how altering blow distance would change things for the better. I would think increasing it may simply increase the velocity of the return back to the string as the assembly loads even further. Of course the distance to travel would then be greater. Then again, maybe decreasing it simply makes it all happen quicker. What I really need is a deadblow hammer shank. ;-] William R. Monroe On Fri, Jul 30, 2010 at 10:47 AM, Ron Nossaman <rnossaman at cox.net> wrote: > William Monroe wrote: > >> Yep, >> height is good - slight gap at let-off (mm or 2) and angle is good, >> (increasing resistance when pushed further into check, etc.) And, checking >> is just good all the way around. When this hammer rebounds, it's rebounding >> with unchecked force from the rest rail (so it appears). Rep spring >> strength can't create this kind of velocity. Basically, if you closed your >> eyes you would suspect let-off/drop/aftertouch based upon the double >> striking sound you hear, but it's a full distance rebound. >> > > My take is that the key stroke isn't bottomed out on the staccato blow, so > there is no let off. The hammer rebounds off the string with the jack still > under the knuckle. Since the back check hasn't "checked" all that rebound > velocity, the hammer levers the wippen and key on down until the key end > hits the back rail cloth. The hammer continues down past that point, > compressing the knuckle, capstan cushion, back rail cloth, springing the key > itself slightly, until it hits the shank cushion. That cushion is intended > to catch the shank as the hammer drops out of check, and even then will > bounce some as the knuckle, back rail cloth, etc, decompress. Add the > considerably higher velocity of an unchecked hammer rebound, and you get a > big bounce from the shank cushion as well as all the other pre-loads. If the > shank cushion is firm enough, it can bounce the hammer back to string > contact. > > Did you ever see the hammer rest rail on the high end Disklavier verticals? > Each shank has it's own little lightly spring loaded pneumatic piston to > minimize bounce. In this case, it was to keep the sensor from recording an > unintentional hammer stroke, but it's the same principal. On most, or at > least many verticals, you can get that double strike staccato without trying > too hard. > > So the problem is the bounce. A free hammer center will aggravate the > problem, but it's not the key balance rail hole, or the rep lever pinning, > spring strength, or anything to do with the back check because they aren't > involved. After I was satisfied the hammer centering was decent, I'd play > with the blow distance next. Shank height relative to cushion at rest will > determine how much "pre-load" is available for bounce, and ought to have > some affect. The firmness of the back rail cloth will also have some affect. > Then the cushion itself. Is it a tall loose felt, or compacted with a strip > over the top? > > I don't have a simple canned answer here, but I'd try to spend the time > looking at logical possible causes instead of grasping at straws. I get to > the straws often enough as it is without starting there. > > A view from the cheap seats. > > Ron N > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://ptg.org/pipermail/pianotech.php/attachments/20100730/ef824c93/attachment-0001.htm>
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