Improve Drill-Depth Accuracy with Plastic Tubing
For a depth gauge that lasts and lasts, I use a short piece of clear plastic tubing (available at the hardware store). The tubing should have the same or slightly smaller inside diameter as the drill bit's diameter. Chuck the drill bit into a portable drill and slip a section of the tubing over the bit. Make sure the tubing is pushed up firmly against the jaws of the chuck. Then, cut the tubing to match the hole depth.
—Craig Holden, Ames, Iowa