(Modified 7/2016
(Page AA-9))
End Pin Adjustment for best tone and performance...
...This acoustical agreement is important for the tone of the instrument to be clear. When the end pin tap tones is 'off', the tone may sound 'garbled', like radio static when a station is not coming in clearly. or the tone may 'break' when playing loudly. We want the tap tone to be 198 HZ, same as back plate, bridge.
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...The adjustment is simple. If the end pin tap tone is too low (below 198 HZ) then the end pin can be removed and the inside end is sanded or filed to shorten it, which will raise its tone. Constantly check the frequency as you adjust.
...You may either tap the end pin sideways against a hard wood table top or similar surface or quickly reinstall and tap in position; both methods should give the same indication. I use a 6" length of sound post stock and tap down on the side of the head of the end pin with one hand and immediately following, tap with the other hand (holding an identical tapping tool) on the wood reference tool at 198 HZ so I can hear the two sounds closely one after the other;.. thus leting the ear/brain have a good indication to judge from.
... If the end pin is too high (compared to the nut) then you need not remove the end pin from the instrument, simply cover the varnished surfaces on the back of the violin with lightly applied blue masking tape, to protect the varnish, and then file or sand the out side perimetere of the end pin head, probably with a small sanding stick, (on its outside surface) to bring the tone down to a perfect match with the nut. You can polish the sanded surface with a piece of leather or canvas (or what ever works best for you) to bring the ebony wood surface back to an acceptable luster finish.
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...Another way to raise the tap tone of the end pin is to drill a hole in the center from the outside {or inside} (but not going all the way through to the far end). Mark the center and drill straight along center line. Begin small (say 1/16") and work up to larger sizes in small steps constantly checking tap tone until the 198 HZ goal is reached.
...You will probably find the end pin as supplied new will be close to the ideal 198 HZ. Because of this, you should probably not use the peg shaver to try up the roundness of the tapered shaft as that will lower the tap tone too much.
...I imagine that you will be surprised how much difference this adjustment can make!
...Listen to the comparison to the downward tap of the end pin (pretend that one is done with the left hand and the other with the right... it is hard to show correctly when the camera is in one hand).
...If the end pin tap is too low then sand the inner end until the frequency comes up to the nut tap frequency. Constantly turn the end pin while you sand to keep it a uniform shape..not 'lop' sided on its inside shape.
..Do not shorten the end pin beyound the inside edge of the end block. If still too low; support vertically on a shaped wood block support and mark the center point and use a center drill to mark center. Then drill a small drill hole about 2/3 through length and check for side tap tone at head end. If too low, then increase drill size in small stips constantly checking side tap tone until it reaches 198HZ (same as back plate).
..There is a further thought you might want to adopt in your instrument making as it relates to the end pin:
..The end pin is most responsive when tapped in the direction of the wood grain. Just tap the head for different directions noting the most brilliant tap response. Turn the end pin so this direction is vertical. Now file a small mark on the top center so you can reference it for future removals. It is easier to see if you put a tiny bit of white paint in this filed notch to remind up of orientation in future.
...Now for the finishing touches. You will notice that there are two tailpiece tail guts in effect, and the two sides need to be tuned so that each one is at 176 HZ. Tap downward right next to the contact point of each with the wood of the end pin and listen for differences.
...A tap in the center of the end pin on the large diameter will be an average of the two sides tap at the tail gut to end pin connection.
...Now is one side slightly higher than 176 HZ, lower by filing from the large diameter shape immediately near that gut string.
...If one is slightly too low, and if there is now a center hole drilled in the end of the end pin, then file the hole slightly larger in the direction of the too low tail gut until the tone matches 176 HZ.
...Another method to make small adjustments to the tap tone frequency of the end pin is to simply file the outside head area of the end pin. (be sure to cover varnish and ends of plates with blue masking tape first).
..If the vertical tap of the head of the end pin is too low; raise it by filing down the two sides evenly until 198 HZ is reached.
..If tap tone is too high, then file a small amount from top and bottom edges evenly until 198 HZ is reached. (same tap as back plate tap tone).