The design went through several iterations including a cordless version that turned out to be a bit too bulky.
A voltage regulator transforming 9v into 6v gives the servo just below maximum voltage, speeding it up.
A lot of work was put into stabilizing the bit. This included the most recent version which uses two instead of one 608zz ball bearings to straighten things out.
All the files are available on Thingiverse.
