Mortise Centering Jig
With this jig I can rout mortises
exactly centered on the workpiece—
no measurement or layout necessary.
First I drilled and tapped two holes
in my router base plate to take 10-32
machine screws. Both holes were located
directly opposite each other along a line
that runs through the center of the
router base. Then I mounted roller bearings
with lock nuts and washers, as
shown in the illustration. Finally I cut
slots in two 1-1/2 by 1-1/2-in. guide
beams to match the diameter of the
bearings. Make the beams about 1 ft.
longer than your longest mortise.
To use the jig, lay the beams on the
bench with the work face down between
the beams. Clamp the assembly, turn it
right side up and put it in a vise. You
can either mark the limits of the mortise
in pencil or clamp stop blocks.