I'm assuming you don't have a lathe available since that would be the best for making the couplers.
On a drill press the best procedure would be:
Load your 1/4" bit in the drill press
Clamp your blank in the vice
Center the blank as closely as possible under the bit and secure the vise on the drillpress table
Drill the 1/4" hole through the blank
Change to the next larger sized bit, say 5/16 without moving the alignment of the piece
Set the depth stop on the drill press if you want
Drill a little less than half way through the blank with the 5/16 bit
Step up to the next larger bit and repeat
Work your way up to the 1/2" bit in as small increments as possible. This will help prevent the bit from being pulled off center as it might if you went directly to the 1/2" bit due to the heavy cut. When you get to the 1/2" bit, drill the last little bit to the half way point to clean up the bottom of the hole.
This should get you about as concentric as you're going to get without a custom stepped drill bit or a lot of hassles trying to align things.
Good luck.
Pete  |