Steinway M Backcheck Problem

[David Skolnik]

Al -
Steinway's spec for key dip is between .390" and .420" so,at 10mm 
(.394") you're well within range.  The only reason I mentioned dip 
was relating to the jack binding the rep lever window butt felt.  If 
that's not happening, there would be no reason to play with the 
dip.  I think Mike Spaulding's image of the self-locking taper is the 
paradigm to use as you look at your piano again.  I had another 
Steinway this morning on which I had done the action some years 
ago.  The treble checking was OK but I was having some trouble in the 
bass.  I noticed that the convergence angle of the tail and check was 
a tiny bit too severe, so I gently sanded the tail a bit flatter 
(less radius) and slightly more angle, so that the convergence was 
more congruent, and it worked fine, even without re-roughing.  Good 
luck tomorrow.

David Skolnik



At 08:24 AM 3/16/2008, you wrote:
>David,
>
>These are all original parts and I did check jack clearance, which is good.
>
>One thing you mentioned is very interesting. In order to get the 
>proper after touch, I had to set the key dip at 10mm which is a 
>little more than Steinway recommends. If all else fails, I will 
>reset the touch to Steinway specs in the bass to see if that helps 
>any, but I'm sure the problem is elsewhere.
>
>I also agree;
>(snip)
>"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"
>
>Al Guecia
>
>
>----- Original Message -----
>From: "David Skolnik" 
><<mailto:davidskolnik at optonline.net>davidskolnik at optonline.net>
>To: "Pianotech List" <<mailto:pianotech at ptg.org>pianotech at ptg.org>
>Sent: Sunday, March 16, 2008 1:02 AM
>Subject: Re: Steinway M Backcheck Problem
>
> > 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
> >
> >
> >
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