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, nut, saddle, and tailpiece proper.
...The adjustment is simple.
... If the end pin tap tone is too low (compared to 198 HZ; tap downward from above to hear the frequency) 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 masking tape, to protect the varnish, and then file or sand the back side if the head, probably with a small sanding stick, (on its outside back surface) to bring the tone up to a perfect match with 198 HZ. You can polish the end of the end pin with a piece of leather or canvas or what ever works best for you to bring the wood back to a shine.
...I imagine that you will be surprised how much difference these adjustment can make!
...If however, the side tap of the end pin is too high:
...Again cover the surrounding surfaces with blue tap and using a file (or for removal of larger amounts I sometimes use a trammel tool with a small sanding disc to go around the perimeter).
... Just a small amount of material removal makes a significant change in tap tone frequency so take small step and check freqently.
...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 side tap is too low then sand the outer end until the frequency comes up 198 HZ frequency. Constantly turn the end pin while you sand to keep it a uniform shape.
...This is the downward tap against the side of the end pin when the end pin is in the instrument. Here it is useful to have two (identical) tapping pencils so the two tones can be heard one right after the other.
..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 bottom center so you can reference it for future removals.
...Tap downward to hear end pin tap tone. Remove material evenly around this rim to lower frequency and from the outside end of the end pin to raise.