Wood – How to bore deep straight holes through wood

Buy a self centering dowel drilling jig. Lee Valley has them, as will virtually all wood working supply sources, Rockler, for example.

The jig clamps to the end of your board, and then you drill through a hardened drill guide into the board, using a hand drill. These dowel jigs used to be much more common in the days before biscuits, pocket screws, etc.

Update 5/12/2013

While my jig below does work, this product is even better!

Big Gator Tools V-DrillGuide Standard Size Portable Drilling Guide

Original Answer

I am answering my own question here with an awesome, home-grown solution to my problem. I fastened two pieces of wood together at a 90 degree angle. Corner clamps made it easy to get it perfect. I then took a third piece of wood and cut a 45 degree bevel off the corner. This piece is my drill bit adapter that fits a number of larger-sized drill bits, but was made with my 3/8" bit in mind. I also made another for smaller sizes (not shown).

To hold the adapter firmly in place and tight against the bit, I use one of my smaller c-clamps. Using this custom guide, I was able to drill a near-perfect hole into the subject. I also used another similar custom assembly that works with a plug cutter bit for my power drill.

No expensive equipment required!