After turning literally several thousand calls on my lathe, I recently found a new (to me) method of reducing splintering/chipping when drilling my sound holes. First off, I drill 1/8" pilot holes for my sound holes prior to turning my calls. Since I turn using a faceplate, 4 of the 6 holes I use receive screws through my faceplate. This sometimes lifts/chips the surface at the hole. After turning, I remove the pot from the faceplate and sand with 220 grit on belt sander.
(http://www.hunt101.com/data/500/medium/1679.jpg)
Next (newly discovered tip), dab a bit of shellac around the holes to be drilled. On this pic I used a paper towel. I have also used a cotton swab with good results. You basically want to cover an area a bit larger than your sound holes.
(http://www.hunt101.com/data/500/medium/2381.jpg)
Allow this to dry for a few minutes before drilling your sound holes. I have found that using a good quality forstner bit creates the cleanest hole for me. The shellac has greatly reduced the chipping/splintering at the edge of the sound holes for me.
(http://www.hunt101.com/data/500/medium/3285.jpg)
After drilling my holes, I go back to the belt sander and run them on 320 grit belt to remove the shellac and finish sand the call back.
(http://www.hunt101.com/data/500/medium/4214.jpg)
This method may be old news to some. I tried it a few weeks back after trying to figure some way to reduce chip/splintering. I wish I had known about it several thousand calls ago...
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