CUSTOM HAMMER BORE SERVICES
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.
THE PROCESS
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Determine the proper hammer bore distance
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Measure string height, keybed to underside of string, at each end of each section
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Measure hammer shank flange center pin height from keybed to pin center when stack is mounted on keyframe.
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Correct bore distance is the distance between these two measurements.
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Mark the correct bore distance for each hammer
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Mark 1” below bore distance for each hammer
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Using a straight edge, draw line to each tail bore mark.
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Determine bass, tenor, treble, and high treble hammer angles with protractor.
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Set up boring device for proper bass and tenor angles.
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Bore the hammers with a #3 screw machine bit, or drill of your choice.
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Using a slave board or bandsaw, cut off excess tail below the previously marked line (step 4)
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Prepare to cove out hammers with appropriate fixture. Use a 1 ½” forstner bit.
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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
