Bending action bracket bolts

[Frank Emerson]

Hi Byron,

It sounds like the problem you describe has more to do with hammer shank lengths and/or vertical alignment of the action, not left-to-right alignment of the action.  Keep in mind that you should control the vertical and left-to-right alignment of the action with the lower action support bolts, and the top bolts serve to control the in-and-out position of the action, and prevent any looseness that would allow the action to move up and down.  

While you cannot rule out the possibility of breaking off an action bracket support bolt, it is not likely to be a problem.  Bending these bolts is routinely done in the building of the piano.  In the field, you can usually bend them adequately by tapping with a hammer, avoiding damage to the threaded portion of the bolt.  You want to make adjustment to the vertical action alignment from the bottom bolt, and bend the top bolt to be centered in the bracket slot, and a tight enough fit that you have to press the action brackets onto the top bolt with moderate force.  To attempt to correct left-to-right alignment of the action by bending the top action support bolts would introduce a force to distort the action from a rectangular configuration to a parallelogram twisting the action at the top, out of alignment with the bottom.

Lowering the action a little from the bottom support bolts would probably improve the apparent left-to-right alignment error that you observed, but there is more to take into account than that simple alignment.  Lowering the action will move the contact point, with the incline of the bass strings, to the right.  Changes to the elevation of the action will obviously alter the strike point.  The solution will probably be a combination of any or all of the following: corrections in action height (controlled from the bottom bolts), realignment from the hammer flanges, and/or shank bending. 

Frank Emerson
pianoguru at earthlink.net
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