hammer travel

[Frank Emerson]

If all shanks are perfectly traveled, and all hammers mounted perfectly perpendicular to the keybed, while the shanks are parallel to the keybed, the bass hammers will APPEAR to travel to the bass.  The lower tenor hammers will appear to travel to the treble.  This is a function of the angle of the hammer bore and the width of the larger hammers toward the bass.  Once you get into the treble where the hammers are bored parallel to the sides of the hammer, they will appear to be as perfectly spaced when one is raised between its neighbors, as it did with all the hammers were at rest. 
 
Next time you replace a set of hammers, try this.  Knurl the shanks for note 1, 2, and 3 just enough so that their respective hammers fit with sufficient friction that the hammers will stay in place without gluing.  Do not taper the hammer tails yet.  Mount the shanks for these three hammers.  Travel the shanks as perfectly as you can.  Mount the first three hammers on these shanks.  Position these hammers along the shank to the achieve the correct strike point.  Rotate the hammers on the shank so that the center lines of the hammers are plumb, and perpendicular to the keybed, while the shank is parallel to the keybed.  Verify that the spacing between the first and second hammers, is the same as between the second and third hammers.  With the first three hammers dry fitted in this fashion, lift the second hammer between the first and third hammers, which remain at rest.  As the middle hammer rises, it will appear to move away from the hammer to its right, and closer to the hammer to its left.  While the hammers are all at rest, the adjacent faces of the sides of the hammers are parallel.  You can measure the distance between the hammers at the crown, at the tip of the molding, or at the widest part of the felt.  These distances will all be equal for both pairs of hammers, if all has been done correctly.  Once you lift the center hammer, these faces are no longer parallel.  With the middle hammer shank held parallel to the keybed the point of closest proximity between the middle hammer and its neighbors has changes.  As the hammer rises in its arc of rotation, any given point on the hammer is moving away from the keyboard, as well as upward.  The point of closest proximity between the first and second hammer is the lowest point of the second hammer’s molding, and a point on the felt of the first hammer beyond its centerline.  This point beyond the centerline of the first hammer is further to the right than the centerline of the hammer, due to the angle of its bore.  Nothing has moved left or right, but the hammer
 tail of the second hammer has moved enough away from the keyboard to place it closer to the felt of the first hammer angling in its direction.
 
Now, rotate all three hammers on their shanks very slightly toward the bass.  Changing only this, you can find an angle where the distance between hammers are equal, while the middle hammer is raised between its two neighbors, at rest.
 
Tapering the hammer tails mitigates this condition, but does not entirely eliminate it.  Over time, with misalignment of hammer spacing, shank warpage, etc., there is a greater risk of bass hammers rubbing the hammer to its left, since it is inherently closer to this hammer when the first is elevated and the neighbor to its left is at rest.  
 
Recognizing this, many manufacturers deliberately tilt the bass hammers slightly to the left, and the tenor hammers slightly to the right.  The degree of this tilt is calculated to precisely correspond to the angle of the hammer bore.  In smaller pianos, with greater hammer bore angles, this condition is exaggerated, and more apparent.  As the tenor hammer bore angle becomes less and less, so does the tilt to the right.  Once you get high enough in the treble that there is no bore angle (parallel to the sides of the hammer), there is, correspondingly, no further tilt to the right.  This creates another problem.  If hammers are tilted in this fashion on a piano that was not designed for it, the hammer shanks will have to be moved out of perfect alignment to the whippens in order to center the hammer under the strings.  However, when the piano has been designed for this left to right tilt, the action scale is altered to correspond to the exact amount of tilt intended for the hammers.  You can determine if this is the case by measuring at the point with the difference is the greatest.  In the bass, where the hammers tilt left, the hammer flange screw are shifted to the right, corresponding the degree of tilt.   In the tenor, where the hammers tilt right, the hammer flange screws are shifted to the left, corresponding the degree of tilt.   This makes the space between the highest bass flange screw and the lowest tenor flange screw less that the corresponding distance at the strike point at the strings.  If you carefully measure the distance between the strike points of these two notes at the strings, and find it to be greater than the distance between the corresponding flange screw, the foregoing explains why.  If you propose to replace the hammers on a piano designed in this way, you must tilt the hammers right to left, as the original hammers were installed in order to maintain perfect alignment between the shanks and whippens, while maintaining perfect spacing of the hammers to the strings, and also optimizing th
e clearance between hammers as they move between the at-rest position and the fully elevated position.  If you, on the other hand, you find the spacing of the strike point at the string to be identical to the spacing of the flange screws, you can still tilt the hammers left to right to optimize the clearance of the hammers in motion, but it will be at the expense of perfect alignment of the shanks to the whippens.
 
I am sure that this is difficult to visualize from my feeble attempt to describe it, but demonstrate it for yourself with the three hammers, as described above.  You will clearly see it for yourself.

Frank Emerson
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