Pianotech

  • 1.  key end damper lift felt

    Member
    Posted 10-03-2018 11:56
    I am working on a Steinert 1904  6' grand. 
    What is a trick method for determining the thickness of the key end felt. 

    I replaced the back rail cloth and by measuring, the new cloth was maybe .020. thicker. It is stretched over a softer under felt (original was used) and glued on both sides like a Steinway. The height of the new appears to be the same as the old where it butts against the key frame stack joists. 
    The old key end felt appeared to be 6 mm. The damper lever ends were digging into the felts and had worn divots. I figure this was from the dampers compressing from age and was never regulated.

    Obviously,,,, I say that so easily,,,, From the way I look at things,
    The angle of the key end at full stroke vs the key bed needs to be determined. 
    The height of the key end at full stroke should be known.
    Full stroke = .430 or 11 mm dip possible. 
    If I set the end of the damper level so it matches the angle of the key end felt at full stroke,,
    How many mm do I need to lower the lever so I don't have the end felt roll up the damper lever and changing the lift point? 
    Should I use the up stop rail as a guide since it has probably never been moved? I take the action to the piano on Friday.
    What's the angle the lever starts gouging? 
    Or should I measure from the relative angle at point of lift?



  • 2.  RE: key end damper lift felt

    Registered Piano Technician
    Posted 10-03-2018 12:41
    Keith -
    The 'trick' method would be to look back at the last few years of PTJ issues and find the articles that went into this aspect of regulation.  Otherwise, a few things:
    - The 'divot' you mention is likely to be as much a result of excess damper lever angle as it would from simple wear. That would have to be corrected first and somewhat regardless of keyend thickness, since it's unlikely that you are itching to redesign the actual geometry of the back action.   
    Going through your post:
    - you say new cloth is .020" thicker, which translates to re-establishing key height and dip. If the damper levers would now be resting on the new key end felt, that would obviously be another reason why you'd need to regulate damper wires, even apart from correcting angle.
    - you said  glued on both sides like a Steinway, except we see both this AND one-side-only gluing on Steinway.  The latter has the potential advantage of  reduced noise but requires careful fitting to prevent puckering, which could affect key level.  Also, from a noise perspective, you might have benefited from replacing the underfelt as well.
    - have never heard them referred to as 'joists'.  'Cleats' perhaps.
    - trying to work backwards from the final key or damper height is a mistake, unless there's a lot more askew with this action.  If you hadn't changed the backrail cloth at all, you would have still wanted to use a thicker keyend felt and raise the starting height (reduce the angle) of the damper levers.  
    - I don't know the exact (ideal angles), but you know that the existing angle is wrong.  

    Should I use the up stop rail as a guide since it has probably never been moved? I take the action to the piano on Friday.
    Frankly, if the keyend felt is as worn as you say, (and if you have to re-regulate damper height), you should probably be taking out the stop rail, replacing the felt and repairing any damage to the wood around the screw slots (if that's the way it's mounted).  




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    David Skolnik [RPT]
    Hastings-on-Hudson NY
    914-231-7565
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  • 3.  RE: key end damper lift felt

    Posted 10-03-2018 12:58
    The divots on the key end felt is a result of the extreme angle of the underlevers causing sliding friction. The tray pivot is too high.

    You should have measured the height of the end felt before you replaced the back rail felt. Have you replaced the end felt? You should.

    The way to reconfigure back action geometry is to measure the height of the end felt with the key fully depressed. Measure the height of the underlever when it is lifted to being parallel with the keybed.  The key should lift the u/l to that height.  Subtract the end felt lift from the previous u/l measurement, that is the amount that the tray has to be lowered. The key should lift the u/l to being parallel with the keybed. Pay attention to the back of the tray and the dags for clearance.

    There is more info in the archives.

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    Regards,

    Jon Page
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  • 4.  RE: key end damper lift felt

    Member
    Posted 10-04-2018 12:45
    Thanks, I have replaced at least 10 back actions for Erwin in his shop. 
    I think the wear on the key end felt was probably due to the dampers having compressed and the levers dropped creating too much lift angle.
    That and maybe who ever replaced the original end felt got the wrong felt. There could have been compression of the original back rail felt, I believe the back rail felt I choose is what the original was, judging from the height of the felt at the cleats when I was done. The under felt on the back rail looked like it was just out of the box. I'm going to try and attach a picture

    Would the distance at the step down at the end of the key indicate the thickness of end felt?

    Jon,, It seems to me that the damper lever can't be level at the end of the stroke.
    Since the lever contacts the key end about 10+ mm from the key end,, as the end of the key rotates up to or past level, the contact point will move to the very end of the key. That will add extra lift to the damper lever at the very end of the stroke. Wear or compaction of the felt at the point of contact will increase the problem so there should be a slight down angle of the damper lever at the end of the keystroke. 

    Hopefully from the picture you can see the end of the key has a slight tilt to the front at the end of stroke. 



    IMG_0830.JPG





  • 5.  RE: key end damper lift felt

    Posted 10-04-2018 13:27
    It has been my observance that most if not all tray pivots are too high creating excessive sliding friction on the felt. The least sliding friction is created when the underlever is lifted to parallel with the keybed. The end felt is not at an exaggerated angle to have the u/l crushing the end of the felt block.

    Extreme slope digging into key end felt.
    Lifted Parallel to keybed


    Relocate pivot holes, this can be done with dampers installed. It will delay lift timing due to the top flange acting as a pivot witht he u/l suspended by the wire. Sometimes the timing is corrected from compressed felts, a two-fer.



    U/L set to key rise

    New u/l configuration


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    Regards,

    Jon Page
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