Steinway M Backcheck Problem

[David Skolnik]

Mike -
I think the self-locking taper image is an apt analogy.  I had 
occasion this afternoon to be working on a recent vintage Steinway D 
which has what I think is the same condition that Al has described, 
and I would just add a few details to my previous summary:
- the buckskin & felt on the newer checks offer almost no resilience
- the profile at the top of the backcheck face forces the tail to 
bounce off, as you describe in your post.
- one other regulating parameter can have a significant impact on 
checking: if either the dip is excessive, or if the particular 
combination of parts employed in rebuilding force the jack to firmly 
contact the butt felt in the rep lever window, the resulting friction 
can absorb enough energy from the hammer rebound to compromise checking.

As for the particular version of the problem in the low bass, the 
requisite stiff, heavier spring might have something to do with it.  Or not.

David Skolnik


At 10:45 AM 3/15/2008, you wrote:
>David,
>
>Good comprehensive summary of the issues, and I agree with you on 
>all points, particularly the folly of roughing the tails or check leather.
>If roughing improves checking, there is an unresolved problem somewhere.
>
>I like to think of the backchecks and tails as a self-locking taper.
>This is the same mechanism that keeps the chuck in your drill 
>press.  As long as there is some amount of friction, no matter how 
>small, there is a taper angle below which the taper will lock, and 
>above which it will fall apart.  In the context of backchecks, if 
>the check is laid way back then adjusted to contact near the tip of 
>the tail, the hammer will bounce off the check.  Go to the other 
>extreme, with the check near vertical and contacting up near the 
>shank, and the hammer will check, but not at a consistent height: 
>the harder you play, the lower it will check.  Somewhere in between 
>is the optimum, where the hammer will reliably check,  and will be 
>difficult to push further down.
>Admittedly, there are pianos where this sweet spot is not easy to 
>find, especially in the low bass.
>
>Mike