Is there an established general guideline with respect to the height of the damper flange center such that with a given damper flange center height the height of the key end felt off the key bed should be x. My own approach, like many, has been to simply to set the action and back action on the bench, pull a string, depress the key, twist my neck into some position that might see where things should go and make a best guess as to what should be changed and how much, do it again. But with a given back action whose damper flange downward angle is too acute it seems that there are two approaches. You can either lower the height of the back action or increase the thickness of the key end felt. Increasing the height of the key end felt is easier and on the surface has fewer related problems (dag interference, hole relocations, etc.). While the distance from the damper flange center to the balance rail changes from action to action and with it the slope of the line drawn between them, it seems it would have to change a lot before the any significant change in the height of that line off the key bed at the flange/key end felt interface would change. Just thinking out loud here. Nevertheless, it shouldn't be that hard to develop a plug in formula that measures the flange center height, the distance from the flange center to the balance pin, the height of the key/balance rail contact point (off the key bed) and the distance from the balance pin to the key end felt and come up with the optimum height of the key end felt (off the key bed). Has anyone done that (before I take it on)? With overly acute angles of the underlevers being a common problem it would be an easier approach (I hate trying to pull all those strings in line and get my eyeballs on some plane that hopefully sees what's really happening). Am I missing some downside to doing it that way? I prefer math to mock up and best guess when I can get it. David Love www.davidlovepianos.com From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf Of Jon Page Sent: Sunday, March 15, 2009 6:54 AM To: pianotech at ptg.org Subject: Re: [pianotech] key position at rest Sorry I don't quite get it ... but 1 1/2 inch from where ? From exactly what point on the whippen to exactly what point elsewhere does this 1 1/2 inch come from ? >From the key bed. Generally a S&S will have the key end lifter felt at rest at ~1 3/8" from the key bed and the underlever at rest is around 1 1/2" from the key bed which is lifted by the key to around 1 3/4" from the key bed. As an aside, knowing the height to which the underlever is lifted allows you to determine if the underlever is situated at an optimum angle. Measure the height of the end felt with the key depressed. Lift the front of the underlever to that measurement and notice the lever's angle relative to the key bed. If it is parallel, that is ideal. If it is still angled down then that indicates that the lever is scrubbing too much on the felt (increased friction) and there is probably a trough worn into the felt. Lifting beyond parallel is counter productive as well. I think it was in the same class (involute gear) with Chris Robinson that he drew a chart with an x and y axis. Friction is minimal along each axis but as you migrate further into each quadrant, the friction increases. So looking at the underlever as being dropped down from the horizontal x axis with the center pin on the y axis, it makes sense to lift it to a point of least friction (x axis) which also happens to be the point of Let Off at the end of the key stroke. This is why I reset the tray pivot such that the underlever is lifted to parallel to the key bed or to the x axis. Lifting beyond parallel crushes the corner of the felt and reintroduces sliding friction (getting into the upper quadrant). >...capstan angle...why is the standard today then perpendicular to the key ? Ease of installation. Mark a point under the cushion, drill them straight in; no need to waste time fiddling around with an angle. -- Regards, Jon Page -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://ptg.org/pipermail/pianotech_ptg.org/attachments/20090315/869c7fb9/attachment.html>
This PTG archive page provided courtesy of Moy Piano Service, LLC