Eliminating bobbling

The usual rules of checking the regulation apply, so look for inadequate aftertouch. However, I notice the photo is of what looks like a Japanese vertical piano. Another lesser known cause of bobbling hammers is a damper return spring that is too strong, which occurs in modern-design uprights such as Yamaha or Kawai, and only on medium or soft blows. A strong spring creates a type of lack of aftertouch in the form of shallow key dip: your finger meets resistance near the bottom of the keystroke and can’t quite overcome the spring to allow the hammer to go into check. I once encountered an old upright that had a severely bobbling hammer—just one, and that note was ridiculously heavy feeling as soon as the wippen spoon contacted the damper lever. Upon investigating, it was obvious that the damper spring had been replaced with a gonzo sized one, way stiffer and larger in diameter than the originals. I can’t remember whether I was able to adequately weaken the spring or had to replace it (I think the latter) but the cause was definitely a rambunctious damper spring. Old American uprights tended to have weaker damper springs and ring longer; newer designed upright pianos have stronger damper springs which aid in clean, immediate damping. To correct a slightly too-strong spring, capture the spring with an appropriate tool (a Hart spring tool for a Steinway rep spring comes to mind) and gently bend it toward you. Try this in small increments, because if you weaken it too much then you have to bend the spring away from you, which is quite a bit more difficult.—Margie Williams