Grand Regulation – The Hammer Blow continued – part XIII

32) The Blow (continued) 

To wind up the discussion on blow, I want to describe some different methods that I know of to measure the distance accurately between the tops of the hammers at rest t­o the bottom of the strings. One easy way is to use a small pocket ruler with a sliding clip. The clip is moved to the appropriate mark on the scale, say 17/8“. The ruler is then inserted through the strings until the tip of the ruler touches the top of the hammer to be measured. The clip marking the desired blow distance is then compared to the bottom of the string. The capstan is adjusted until the clip matches this mark.
The good aspects of this method are that the tool used is already in your tool kit and can be used for many other purposes. It is also easily adjustable to provide a blow gauge for whatever blow distance is desired. This can be helpful if the blow distance wanted is measured in millimetres and does not correspond to a normal inch measurement. The drawbacks to this method are that the clip often moves while trying to measure, giving a false reading; and the ruler usually slips out from between your fingers and drops into the action. Both of these problems have forced me to look for a better idea.
A number of years ago while visiting a piano factory I was given a very nice aluminium gauge Figure 1 which can be used to set a blow distance of 17/8“. This tool really caught my eye since it is very easy to use and has a good handle to grab hold of. The technician just inserts the gauge between the hammer and the strings. If the blow distance is too little, the hammer will be pushed downward by the tool. If the blow is too great, the hammer can be seen to rise when the appropriate key is pushed down. Although better than the ruler, the­­ blow gauge also has its faults. Since the measuring portion is fixed it can only be used to set a blow distance of 1 7/8”. It also happens to be too big to fit in the allotted space in my tool kit!
The best solution, as is often the case, is to make a well designed homemade tool. Take a piece of wire and bend it to look like Figure 2. The functional part marked (A) used to measure the blow distance can be made to whatever distance is desired. I made three gauges to carry in my tool kit. One is 44mm (1 3/4“), one is 46mm, the last is 48mm (1 7/8“). They are colour-coded so that I can quickly select the one wanted. Since they are homemade you can vary the length of the tool to fit your tool case or design the handle so it won’t fall from your hand.
An added plus is that by selecting different thicknesses of wire for these gauges the tool can double as a let-off gauge. The part marked (B) in the illustration is held under the string directly at the striking point. As the key is depressed and the hammer  rises to the point of let-off, the technician watches to see it the hammer blocks upon gauge, just touches it, or falls short. After setting a few sample keys for let-off the technician can set the remaining by watching the thicknesses of the strings, as will be explained below.
33) The Let-off
Let us declare some solid ground in talking about let-off. First, let-off is not synonymous with escapement. Second, the definition that we will use here will mark let-off not as being the point of contact which occurs when the jack is tender is engaged by the let-off button, but rather the point at which the jack fully trips out from under the knuckle and the hammer starts to fall, or else the hammer continues to travel towards the string under momentum. Thirdly, adjusting the let-off does affect to a great degree the evenness of touch, speed of repetition, and the power that the hammer has to excite the string. Fourth, the ideal point of let-off is as close as is possible to the string and yet: 1) not be so close as to cause the hammer to block upon the string, 2) allow for seasonal changes in temperature and humidity so that blocking will not occur, 3) the hammer can not interfere with the vibrations of the string, especially in the bass.
The statement has been made to me that for each 1/16th of an inch that the hammer lets-off too far from the string, it results in about a ten percent loss of power. How accurate this is, I do not know. But I can guarantee that for the greatest power to be available to the pianist, the technician must set the let-off as close as is possible. This may mean readjusting the let-off a little for concert level work as the seasons change, or as the let-off button felt begins to wear.
Take note that adjusting the let-off as close as is possible is not the same as setting the let-off on every key at 1/8“. I strongly feel that 1/8” is too close for some bass strings, and yet way too far away for the top treble. The ideal is to set the let-off in a straight line from bass to treble to insure evenness of touch, but for this line to be tapered as the piano dictates. For concert level regulation, it is certainly permissible to have 1/32” let-off for the top treble! For normal in-the-home regulation, a simple rule-of-thumb is to set the let-off for the plain strings at double the thickness of the string, or just a hair greater to allow for seasonal changes. For the bass let-off, approximately the same thickness as the single strings, increasing to around double the thickness of the thinner bass strings. This would mean that for note no 88 with no 13 size wire (which is 0.031” thick) doubling this thickness would give 0.062” let-off. 1/16” is equal to 0.0625”, so the let-off for this note would then be 1/16”. In concert level regulation, the same thickness as the string would give exactly 1/32” let-off for this note.
Be aware that with a tapered let-off the after touch will also become tapered, all else remaining the same. To compensate so that the aftertouch is uniform the hammer line should be similarly tapered. It is interesting that in regulating the let-off, the closer the hammer lets-off from the string not only improves the power that the key gives the hammer, it also improves the speed of repetition! This is in contrast to the way that adjusting the blow distance works. In blow, more power is obtained with a greater blow distance. But this unfortunately results in a loss of repetition due to the fact that the hammer has more distance to travel.
In let-off the power is increased by making the hammer let-off closer to the string, since the jack is under the knuckle for a longer period of time as the hammer rises towards the string. As a result of the jack staying under the knuckle longer, it does not get so far away from the knuckle upon escapement, and hence can return under the knuckle faster giving quicker repetition!
Concluding the jack to let-off relationship, the jack alignment to the knuckle core is the only thing that really affects the point of let-off, outside of the drop being too high or else turning the let-off button.
This should be easy to see since adjusting the jack to knuckle alignment changes the jack’s angle. This causes the jack’s tender to be either closer to or farther away from the let-off button, hence causing the let-off to change. In former articles, I have stated that raising or lowering the capstan also affects the point of let off. By using the blow gauges described above as let-off gauges, I have found that regulating the let-off just perfect to this gauge and then changing the capstan does indeed affect this perfect let-off to gauge regulation. Altering the capstan say 1/8” changes the let-off enough that I can feel it by how the hammer contacts the gauge, but the affect is so minute that if I were not using this gauge the change would not be noticeable. I have stated in the past that altering the capstan does affect the let-off since I have found it to be so. For the concert level regulating that we have to do, this knowledge may become important. Nitpicking in this manner must be done in order to achieve the closest to ideal regulation.  
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