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Thickness of back rail cloth and hammer rebound rail

  • 1.  Thickness of back rail cloth and hammer rebound rail

    Posted 11-19-2018 09:52

     I am trying to wrap up a project on a grand piano that has been a real challenge. It is a Huntington grand that had prior work done to it and it sort of worked. I replaced all the hammers, shanks,flanges, knuckles with new parts. Also all new backchecks, front punchings and balance rail punchings. I matched the felt that was on the back rail and the hammer rebound rail but am now questioning if that was all wrong and I need to experiment with different thickness in both places. One major issue is that I have not bee able to get hammer letoff close to the string. I replaced all the felts on the letoff buttons but maybe these were the wrong size to begin with. Finally the middle rail of the action frame has 4 glider studs and there are 5 that come up through the keybed under the front action rail. So where do I start with this beast to tame it ? One problem I have had to deal with recently since the owner is taking lessons is random key jams. Yesterday I pulled out 18 whippens and took them to the shop. I am finding very little resistance on the rep levers and getting only 1-2 grams on spring gram gauge. I am thinking that I should replace the action center bushings because I do not get much more friction going up a half size center pin.

     Susan Graham had a great article on felts and action repairs but I have not been able to find anything that describes the role of the back rail felt, how thin or thick it should be, what changes the felt introduces or removes. Same goes for the hammer rebound rail felt. How thick or thin should it be. By observation I can see how thicker backrail felt/cloth changes the key height and moves the capstan. Perhaps I should just experiment with various thickness and presume what was there was bad to work from

    James Kelly
    Pawleys Island SC

  • 2.  RE: Thickness of back rail cloth and hammer rebound rail

    Posted 11-19-2018 15:16
    Edited by Jon Page 11-19-2018 15:18
    You need to start with measuring action elevations and work from there. On a Bechstein recently, I had to add 4 mm shims under the key frame, front and back rail. then had to install a 4mm shim under the b/r/ felt to sandwich the back rail. That was just to satisfy the elevation parameters and allow the capstan to be in the key stick enough. (The HCH & WCH were 8 mm too low in relation to hammer bore and string height).

    The thickness of hammer rail felt is dependent on the action elevations and hammer bore.


    Jon Page