33) Let-off (continued)
Previously discussed were the regulation steps that affect the point of let-off, namely the jack alignment to the knuckle and the raising or lowering of the whippen either through altering the key height or by turning the capstan. The amount that these changes would affect the point of let-off is marginal. It is far more important to realize that regulating the let-off affects other steps more than the other steps affect it.
The two steps which are affected by regulating the let-off are dip and drop. Remember that in this discussion dip includes aftertouch. Looking first at how let-off affects drop, let us define drop as the amount of downward movement that the hammer has after the point of let-off. Keep in mind that the regulator has to move the key downward very slowly in order to see this drop of the hammer. During normal playing, this drop as such would not be visible, as the hammer would just rebound from the string into check.
If a graph were drawn to show the movements of the hammer versus the slow, downward movement of the key by the technician, the amount of drop and how it is affected by the let-off becomes clear. In all of the graphs shown, the key dip is set to a specific measurement which will not be changed. In figure 1 the hammer travels upwards from the point of rest and lets-off (marked “A”) at 1/8” from the string. The hammer then drops away from the string let’s say another 1/8” (marked “B”), and then rises back up yet another 1/8” (marked “C”). This last upward movement of the hammer coincides with a small downward movement of the key which we will define as aftertouch.
Figure 2 illustrates what happens when the hammer lets-off closer to the string, all of the other regulation steps staying unaltered. The point of let-off has changed to 1/16” from the string, the drop increases to about 3/16”, and the aftertouch decreases to about 1/2” of what it was in figure 1. The aftertouch decreases because it took more key dip to raise the hammer to a higher point of let-off, and it took a fraction more dip for the hammer to drop the farther distance compared to figure 1. The pianist will complain that the piano now “plays hard” since there is insufficient aftertouch. The action also feels a bit sloppy because of the excessive drop. He might even notice that when playing very lightly the hammers have a tendency to “bubble”.
Figure 3 tells what changes happen when the let-off is too far from the string. Here the point of let-off is 3/16” from the string. The drop now decreases to about 1/16” and the aftertouch increases to about 1-1/2 times as much as in Figure 1. The aftertouch increases here for the same reasons why it decreased in Figure 2. It took less dip to raise the hammer to the point of let-off, and less dip for the hammer to drop the smaller distance. In this case the pianist will complain that the keys feel spongy, as there is too much aftertouch. I doubt that he would complain of too little drop, as he would not normally be able to feel it. The complaint may be heard of slower repetition.
As can be seen from these graphs, a change in the point of let-off can really affect another regulation step. I will explain now why it is important to know that almost nothing affects let-off while let-off definitely affects drop and especially the aftertouch portion of the key dip. Remember the circle of five steps? By adding let-off and drop to this circle all seven main steps of section IV The Touch portion of our 50 point checklist are shown in their relationships to each other.
If it were your job to regulate an old action that had just had new hammers / shanks / flanges installed, where would you start regulating on this circle? Let us assume that some years previous this action had been regulated to compensate for the wear which had then taken place. It is reasonable to expect that the capstans, let-off buttons, and drop screws had all been tuned up. Now with new hammers and knuckles these screws would be too high. The hammer line is too high as well as uneven. Because the escapement is set too high most of the hammers block upon the strings, or with the action out of the piano, the hammers “bubble” on top of the jacks.
The repetition springs are also weak from hours of playing. You could start regulating by setting the hammer line back down to about the correct blow distance, but you cannot even begin to set it perfect since the repetition springs are weak. The springs cannot be strengthened yet since the backchecks are out of regulation. The backchecks cannot be set because the escapement is so high the hammers will not go into check, but rather “bubble” on top of the jacks. The dip could be set with a dip block, but correct aftertouch could not be proved out. So, what do you do?
I would suggest that in such circumstances, once the key height has been established, the place to begin is with the escapement. Yes, that is right! Let-off and drop can, indeed sometimes must, be set first. It has already been stated that changes in the capstan and jack alignment minutely affect the point of let-off. The only step which affects drop is let-off. So by regulating the let-off and drop first and then continuing through this circle of seven steps a very accurate regulation can be made almost the first time through. I realize that if you are used to regulating the backchecks last that this method may seem a little strange. However, it is the only way out of the maze.
When turning the let-off screw, check to make sure that the drop screw is down far enough in order to see the hammer let-off. Otherwise the hammer will continue to rise right past the point of let-off if the drop screw is up too high. Since regulating the let-off must always be done in the piano, double check your work previously completed. As the hammer is seen to rise against the string, recheck the hammer to string alignment. When looking under the pinblock. Inside the action as you turn the let-off screw, recheck the jack tender to let-off button alignment. After a while rechecking your work in this manner becomes second nature.
If you are wondering what special tool is used to set the let-off with the action inside the piano, take a Mason & Hamlin screw stringer tuning lever (still available through all supply houses) and grind the tip so that it fits well between the let-off screw and the let-off rail (see figure 4). This is of course the tool used on regulating screws as found for example on Steinways. On pianos with let-off dowels, use a special tool made to fit the hole in the dowel. Yamaha for example sells a tool made to fit the holes in their dowels. A regular capstan tool will not work unless the tip is ground down to make it smaller in diameter. I once purchased a ratchet-type Mason & Hamlin let-off tool which was supposed to make it easier to set the let-off screw where you wanted it without having to keep taking the normal tool off the regulating screw. I tried this new invention, but quickly went back to the original tool, as it is faster for me to use.
To be continued.
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