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The distance from the tip of the hammer to the center of the hole for the hammer shank, called the hammer bore distance, is a critical dimension to ensure superior performance in touch and feel especially during very soft pianissimo playing. Although there are different methods on how to determine the hammer bore dimension, I use a software created by Nick Gravagne, RPT. Below is a screenshot containing graphics and details on how the software determine the hammer bore dimension.

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  1. Determine the proper hammer bore distance

    • Measure string height, keybed to underside of string, at each end of each section

    • Measure hammer shank flange center pin height from keybed to pin center when stack is mounted on keyframe.

    • Correct bore distance is the distance between these two measurements.

  2. Mark the correct bore distance for each hammer

  3. Mark 1” below bore distance for each hammer

  4. Using a straight edge, draw line to each tail bore mark.

  5. Determine bass, tenor, treble, and high treble hammer angles with protractor.

  6. Set up boring device for proper bass and tenor angles.

  7. Bore the hammers with a #3 screw machine bit, or drill of your choice.

  8. Using a slave board or bandsaw, cut off excess tail below the previously marked line (step 4)

  9. Prepare to cove out hammers with appropriate fixture. Use a 1 ½” forstner bit.

  10. Taper hammer tails. You can use a jack plane or any other professional jig + cutting machine.


Step 1: Boring


Step 2: Tailing


Step 3: Cove


Step 4: Taper


Step 5: Arc

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