bobbling hammers, again

[Jeff Tanner]

Hi Wim,
There is one other inconsistency I have seen with my S&S grands that I
haven't seen mentioned.  That is the firmness of the backcheck felt.  I've
found on some of my pianos that a hammer which won't check and appears to
be geometrically identical to it's neighbors will either have a firmer or
softer backcheck.

I encountered this problem on our performance D the other day on a mid
treble hammer.  The backcheck was particularly spongy compared to its
neighbors and the hammer just bounced right off.

Jeff

>Several months I asked about bobbling hammers in a grand. I discovered
>that the shank lenght was too long.
>
> I now have a similar problem with a D. But this time, I've rebuilt the
>action with new Steinway parts, (new h,s,f and wipps). There are three
>notes that are driving me nuts. Unless I really smack the note, the hammer
>doesn't want to check. They boble so bad that they hit the string on the
>rebound.
>
> The regulation is just like the other notes, (dip, l.o.,drop, etc.). Not
>only is key dip just like its neighbors, but when I increased key dip, it
>didn't solve the problem. There is enough damper lever clearance. I've
>adjusted the back checks to where the hammer checks almost back down on
>the cushion. When I try to make it check earlier, it catches. I've bent
>the checks so that the rake is enough to clear the hammer on the way up,
>but still catches it on the way down. I've reduced spring tension to the
>point of almost no rise, and I've sanded the backs of the tails. I even
>changed wippens on one key, but the problem is still there.
>
> What are some other things I should look at?
>
> Wim