reboots used a Micromot 50 rotary tool and a modified rack from a hamfest to build a very precise drill press for his homemade PCBs.
Mounting the motor was tricky. The nose of the Micromot is a machined steel collar, but the body is ABS plastic with perceptible dimensional variance. If the motor was not exactly inline with the Z-axis, the drill would snap from side-loading as it descended through the workpiece. I added aluminum blocks to the carriage to approach the diameter of the collar, and used stainless steel shims for final spacing and to keep the collar from bedding in to the blocks. Once the collar was tightly clamped, a hose clamp kept the plastic upper body secure. Although I have no way of measuring the axis of the drill relative to the carriage, it seems to be extremely on-axis.