When I used to use a vent hole I placed my thumb in the ball and marked it where the center of the back of my thumb was and placed the hole on that marking 1/4" away from the edge of the slug then just eye balled the angle to have the hole come thru near the bottom of the thumb hole using a 1/8" bit in a hand drill.
However I no longer do this since I started using Ron Clifton's Magic Carpet available at
http://www.bowl4fun.com/magiccarpet/magiccarpet.htm this wonderful product is a loop style carpet that allows you to have a snug fit without sticking due to the fact that it allows the thumb hole to breath and compresses slightly. I find that I use tape much less now and am getting a much cleaner release than I got without the carpet even when I had a vent hole.
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STORMIN1
Edited on 10/20/2004 1:00 PM