This is the bottom of
the fixture. Two screws hold the drilled 2◊4, they
are placed so they will not interfere with the
clamping slot on the top side. Itís easy to align
the fixture on the drill press table, insert the
threaded arm from underneath through the hole in the
table about half way into the fixture. Lower a 3/4
forstner bit into the top of the hole, lock the
table, and set the clamps.
I sawed the stripped
arm off about an eighth inch from the foot. That
left an inch or so of threadless wood on the shaft
to practice on. In fact, I used a piece of 3/4 dowel
up in the fixture to make the first practice tenons.
The first operation is
to drill down on the sawn face with the 3/4 Forstner
bit. That leaves a center dimple and faces the end
The mortise will be
drilled with a Forstner bit so I made a half inch
hole in a piece of hardwood scrap to test the size
of the tenon. I believe this is called a Mullet.
I considered a few
alternatives to make a tenon. Maybe a hole saw (too
sloppy). I looked at a half inch plug cutter (would
have to regrind the tip to get a shoulder). I
decided to use a cheap circle cutter, which can be
tuned and has an angled bit that would make a nice
The inside of the bit
is ground flat so it was easy to sharpen with
diamond paddles, and the pilot drill is smaller than
the #7 size needed to tap the hole. I also ground a
relief angle on the inside of the cutter.
It was not
designed to make a clean cut on the inside, making
an angle of 15-20 degrees away from the cutting edge
helps a lot. You only need to grind the cutter up
about a half inch from the bevel, leave it flat
where the set screw clamps.
It was very difficult
to set the diameter accurately. I hit on using
feeler gauges to measure the gap between cutter and
pilot drill. I would hold the cutter against the
feelers and tighten the set screw, which allowed me
to add or subtract a few thousandths from the tenon
diameter in a controlled manner.