If you want to calculate the optimum height for the underlever center, it isn't all that difficult. Measure the height from key bed to bottom of key (a). Measure from the balance hole at the bottom of the key to a point in the top of the key end felt about midway within the contact of keyend felt with underlever (b). Measure the height of the bottom of an underlever (well-regulated) at half its travel (c). Measure the distance from an underlever center to a point along the bottom of the underlever midway within the contact with the keyend felt (d). (c) minus (a) divided by (b) will give you the slope of the line that ought to extend to the underlever center. (d) times that slope will give you how much higher than (c) the centerpin should be. Say the bottom of the key is at 1". Length (b) is 10". Height (c) is 1 5/8". The slope will be 1 5/8" minus 1" (ie, 5/8") divided by 10", or 1/16" per inch. Say the underlever length as defined is 3". The underlever center should be 3/16" higher than 1 5/8", or 1 13/16". (Much clearer to do these calculations in metric, and I would strongly encourage it). The caveat is that this assumes the existing thickness of keyend felt. It might be much more efficient to change thicknesses than to move a tray up or down. Regards, Fred Sturm University of New Mexico
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