Nice Piece of Trapwork

I found a design flaw in a Boston grand.  Boston is the brand designed by Steinway and built by the Kawai factory in Japan.  They're really beautiful pianos.

The notes were making a clanking sound, and I guessed the problem right away.  I could feel it - the dampers were jumping up too high at the end of the keystroke, and instead of being stopped by the stop rail, they were hitting the metal sostenuto rail.

So the damper stop rail was positioned too high.  That's easy enough to fix, but I had to find out first why the rail was out of position.  The usual culprit is that the damper pedal isn't being properly stopped.  As a result, every time the pedal is depressed, the damper tray pushes all the dampers hard into the stop rail.  Over time this succeeds in pushing the damper stop rail up out of the way.  Hence, clanking.




The usual way to stop the damper pedal is by stopping the damper trap lever, which the pedal moves by pushing up on the pedal rod.  I got under the piano and took a look.  The stop consisted of a capstan screwed into the case underside.  Whenever the pedal was depressed, a piece of felt glued to the top of the lever contacted the capstan, stopping the lever.  The capstan made it adjustable, the felt reduced noise.  The felt, though, was soft - it was the kind of woven felt used for the hammer rail in an upright.  The capstan was quite small, and it had driven a divot into the soft felt, rendering the stop useless.

I thought of simply adjusting the capstan, but I would have had to adjust it quite a bit, which is not a lot of fun to do lying on one's back.  The possibilities also existed that the capstan might not have been long enough to fill the gap, and that the felt was now too thin at the contact point to provide any padding.  I also thought of simply adding more felt, but the misshapen felt really needed replacing, so I removed the trap lever from the piano.

If there's anyplace where a manufacturer is going to try to save money, it's the trapwork.  But this was the most beautifully made trap lever I had ever seen.  The coil spring sat in a lovely felt-lined cup, and had a piece of felt carefully woven through it to avoid creaking.  The pitman sat on a buckskin/felt cushion inlay, and there was a generous piece of hard leather where the pedal rod made contact.  There even was a piece of buckskin wrapped across the bottom and up the side of the lever to protect it from contact with the guide hook.  The only flaw was the soft stop felt.  What was needed was a chunk of hard felt, like the kind used for hammer heads, and that's what I installed.

The design error was that the felt was too soft for the capstan.  If the capstan had been much larger in diameter, and therefore exerting less pressure (pressure = force/surface area), it might have worked.  I was actually tempted to remove the capstan and install the traditional stop: a piece of wood glued to the underside of the case, with the hard felt attached to it, and no felt on the lever itself.  This works well, and eliminates the possibility of a divot, but it's not as easy to adjust.  So I'll have to keep an eye on my new stop felt; this piano gets a lot of use.