The way I do it is, I drill a 1/4" hole, spaced double the diameter of the bit from the spine. (1/4" dia hole = 1/2" below the spine) Then scribe 2 straight lines from the hole to the spine and use a saw or cut off tool to cut it out. Play with angles and see which one looks best to you. Clean up and bevel with a 1/4" round file for the hole and a flat file for the straights.