Grand Regulation – part XV

33) Let-off (continued)
For those technicians who find it difficult to set the let-off in the piano by watching the space between the top of the hammer compared to the thickness of the corresponding string, there is another method. Find someone in your area who sells magnetic signs such as those found on the sides of cars or trucks. The magnetic backing for these signs comes in 1/8” and 1/16” thicknesses, which are perfect for use as let-off gauges.
Purchase at least two strips of this material, one of each thickness, about one inch wide by around twelve inches long. The one inch width is sufficient to place the strips against the under sides of the strings without having to worry a lot about whether the strips will cover the hammer strike line. The twelve inch length is variable with the piano. The lengths should be no longer than the sections between the plate struts or else the strips will be too long to adhere. The larger the piano, the more sections are created by the struts, and the smaller the widths are of these sections. You may want to carry an assortment of lengths of this magnetic material.
To use, remove the action and set it aside. Take something such as a felt wedge and block up the sustaining pedal to left the dampers away from the strings. Otherwise, if there are bichord or trichord damper wedges in the area where the magnetic strips are to go, they will prevent the strips from adhering. Position the strips against the undersides of the strings, being careful to place them directly at the hammer strike line. Reinstall the action and check to see if the strips are positioned correctly. If not, carefully reposition the strip with a small tool.
Now comes the easy part. Seat yourself at a comfortable height so that you can see and work on the let-off rail. There is no need to see what is happening at the string level. Depress the keys one at a time and adjust the corresponding let-off button until a very slight resistance is felt as the hammer lets-off against the magnetic strip. When regulating in this manner it is important to remember to continuously depress the key and feel how the hammer lets-off.
Try to get each key regulated so that exactly the same amount of resistance is felt at the point of let-off. Use the 1/8” thickness for the tenor and low treble sections, the 1/16” thickness for the top treble. After all are adjusted, remove the magnetic strips and check the point of let-off visually. This step must not be overlooked! Invariably there are slight corrections which must be made. Despite the fact that the resistance which was felt was uniform, the actual point of let-off will vary a little.
There are both pros and cons to regulating in this manner. The pros are that it is by far easier and faster to set the let-off with a magnetic strip, especially if the regulation was way off from where it should be. However, the cons are important. Obviously, these magnetic strips will not adhere to the bass strings, so approximately 1/4 to 1/3 of the let-off must still be set by eye! As was mentioned above, those which can be set with the strips must be double checked by eye for accuracy. Most importantly, the best let-off is one that is tapered uniformly from note 1 all the way up to note 88. The magnetic strips do not give a tapered let-off. Instead, they give a noticable break where the change was made between the 1/8” thickness strip to the 1/16”.
Despite these drawbacks, I still like to use these magnetic strips. When the let-off is way out of the ballpark as it often is, I find it far easier and faster to use the strips to get the let-off close and then refine it by eye than for me to completely adjust the let-off by eye. I believe it impossible to perfectly regulate the let-off in a uniformly tapered line the first time through no matter what method is used. Therefore, being somewhat reluctant to work harder than I have to, using these magnetic strips gives me a known setting for the let-off according to the thickness of strip used, and from this I can easily achieve what I want. There are two exceptions to the rule. One is where the let-off is nearly correct as on a fairly new piano. For such instances I simply regulate by eye. The other exception is when I have help available. Using another person relieves the strain of constantly looking above at the point of let-off and then bending down to turn the let-off screws. While I depress the keys and watch the hammer let-off, my assistant (usually my wife) turns the let-off button up or down at my instruction.
One piece of helpful advice when watching the point of let-off in the top treble sections is to use an old mirror. Normally the plate obstructs the view to directly see the hammer let-off. By using a mirror set at about a 45 degree angle to the strings, the hammer can be seen to rise against the string from the side and clearly show how far the hammer is letting-off.
Before ending our discussion on step#33 of the 50-point checklist, I would like to caution technicians on a few things. Be sure that the let-off rail screws are securely tightened. It takes only a slight movement of that rail to cause the hammers to block upon the strings. Secondly, if the let-off button felt has been worn, replace it! It is very frustrating to try to regulate the let-off when this felt is worn. You all know what I mean. You turn the let-off screw 3/4 of a turn without getting the hammer to let-off close enough. Then with a slight additional turn of the screw the hammer now blocks! You back the screw off a little and it goes back to being too far. Gradually you ease the screw to the right until the let-off is correct. You know darn well that the jack tender is riding half-in, half-out of the old groove in the button felt.
How stable is this kind of regulation? How long before the felt wears again and causes the hammer to block? How much time does it take to replace this felt? I doubt that it takes me a whole hour to remove the old felt and glue on new ones, and the time spent is almost made up in the ease of regulating with new button felt!
Finally, pursuing this worn felt problem a little further, do not assume that even a new piano is in perfect regulation. I have frequently found new pianos where the hammers were blocking, or almost blocking. There seems to be two main reasons for this problem. One is pure negligence on the manufacturer’s part. The action was regulated on a bench at the factory and the strings of the piano did not match the height of the let-off rack. If the strings were a little lower than the let-off rack, the hammers will block because the let-off is too high. The other, somewhat more subtle reason, is that the let-off button felt was not of sufficient quality for the job. It compacted too easily and after a little playing the let-off became too high. If the let-off were quite close before this felt compacted, it will cause a blocking hammer.
I realized a long time ago that no matter how old or new a piano is, or how prestigious the manufacturer, the piano invariably needs some refinement of the regulation. After a while a pattern even starts developing. Name me a manufacturer and show me a new piano from that factory and I’ll tell you what points to look at that probably need refining. One piano always need work on the action centres and voicing. Another always has tight centre holes on the keys and too little aftertouch. A third usually has problems with the bichord bass dampers. And so on. A good craftsman who knows his art can pretty well know in advance what a certain piano will need before he sees it for the first time.  
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