A good place to start when chasing down the optimal capstan location is with the Magic Line. There are three ways to support the key at half blow. Set a tri-square to the h/b measurement and prop it vertically with a spring clamp, place a weight on the front of the key and block the hammer on the square. I usually do this. Place a shim (~9/16 drill bit) under the front of the key and place weight. But a way I just thought of which may be easiest of all is to insert a wedge (mute?) under the back of the key to raise the hammer to h/b. I'll definitely try this next time. Set h/b, run a thread for the ML and place a mark at the wippen cushion at the intersection. Draw a line on the side of the wippen perpendicular to the heel profile at that mark. Straight heels are easy because you only need to hold a ruler parallel to the repetition support post. With the assembly blocked at h/b, extend that line onto the side of the key. That is the bore angle and first check for capstan location. For argument's sake, one could have the capstan perpendicular to the heel at let-off, I haven't tried it but it sounds logical. I do this check on C1 and B7 because I can remove the adjacent keys and wippens for easy access, a few in the center if you want too. SInce you've already determined your bore length and selected the knuckle radius and key dip, place your temp capstan at this location and depress the key, is the jack clearance optimal? If the jack is buried into the stop felt the capstan has to move forwards. If not enough clearance, move the capstan back (not every balance rail is in the optimal position either). Locate the capstan for optimal regulation: sufficient jack clearance effecting minimal after touch. Think of it as the wippen being moved through a required distance and how where along the levers the lift is provided regulates that distance. Bore the holes at the derived angle. Many actions I've improved regulation by addressing the capstan angle and not move it forwards or backwards, the angle corrected the distance the wippen was propelled. Think of it in terms of the arc of the travel, as the capstan moves further from the balance rail, it's arc increases. It also moves closer to the wippen fulcrum which has a greater result at the front of the wippen. Because as the lift provided to the wippen moves closer to its fulcrum the end moves a greater distance. Of course, conversely, moving the capstan forwards reduces the travel at the front of the wippen. But you need to bear in mind present touchweight. Increasing touchweight by moving the capstan away from the balance rail for regulation may be counter productive. I get the feeling I'm about to get into a circular predicament. -- Regards, Jon Page
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