Tech Talk - Repetition Lever Spring Adjustment
When determining the correct spring tension in our next adjustment, the hammer must be played in a mezzo-forte manner to allow the hammer to be captured in its “checked” position. In other words, just play the note. The hammer should come to rest around 5/8” from the string. From this resting position, again in a very controlled manner, lift the key ever so slightly. You should notice the hammer make its way toward the string on its own. This movement may be terribly slow, or quick and abrupt. The speed at which it is set is determined by a variety of other adjustments and considerations. Many speeds may work, but only one will be optimal.
Having the backcheck leather in good condition as well as the hammer tail sufficiently textured will also come into the equation of what the correct tension on the spring may be. In this case, stronger is not necessarily better, and too much can be bad. In the next Tech Talk, we will be looking at the last of the primary four adjustments to the grand piano action regulation, back check.
Now that we have addressed let off, drop, and repetition lever spring adjustment in our previous discussions, rounding out the four primary adjustments is the back-check.
The back check itself is a small wooden block covered with a small piece of felt, over which, a strip of leather is stretched. It is mounted to the back end of the key with a wire that provides easy adjustment.