To make a bridal joint with the recess for the glass
window and its frame the sequence of cuts needs to be planned out. Because it’s easier to fit the tenon to the
mortise than the other way around that’s where I will start. Short outline is:
- Cut the end mortises in the top and bottom rails ¼” wide and 2 ¼” deep.
- Cut the recess where the glass piece will go.
- Match tenon thickness in the rails to the mortise in the stiles which should line up with the recess for the glass. Here is where any variance in the material thickness will require some adjustment.
The mortise is cut with two ¼” stack dado blades like
this. I like to use the stacked dados
because I can make the cut in one pass knowing that it will be a ¼” wide and
have a flat bottom.
After switching out the rip blade that was on the saw and
installing the dado blades next is to set the depth. Here I got an ugly surprise, my dado blades
are 8” in diameter and could not cut a deep enough mortise. I was a bit over 1/16” short whereupon I directed
some nasty words at the blades then moved on to “Plan B”. 
Plan B is to use my rip blade and make multiple passes to
get the appropriate width. To start the
blade is set so it is roughly in the center of the rail. This is the jig I use and what the first cut
looks like. After the first pass the
board is rotated 180 degrees and a second pass makes a centered mortise in the
board.
This is after the second pass and the gap to the left of
the blade shows the offset from center.
Next the jig is moved a bit closer to the blade by loosening a couple of
locking levers, making the adjustment, tightening them down then two more
passes are made. This continues until I
get the desired mortise width. You can
just see the locking lever immediately to the right of the saw blade.
Once the initial passes were made and the mechanics of
the process verified, I cut all the pieces to length using the chop saw and a
stop block. I had rough-cut two of the
blanks long enough so that if I blew the first cut I had enough material for a second chance.
The completed cutting results in a mortise with the sides
within one thousandth of an inch. All of
the measurements ended up being a little over ¼” as the finished thickness of
the door pieces are a shade over ¾”.
One of the advantages of using a good dado blade set is
when making a cut you end up with sharp corners and a nice flat bottom. Using my rip blade did not give me that
result. Take a look at the photo on the
top left and you can see the irregular bottom of the mortise which is not going
to make a nice tight joint. A little
hand work with a file as shown in the bottom photo gives a flat bottom as in
the top right photo.
Next is to cut the glass recess using the stack dado, two
¼” blades with a 3/32" chipper in between.
A sacrificial fence is attached to the rip fence, the saw
turned on and the blade slowly raised to cut a small inset into it as shown in
the top photo below. With the saw off
the depth of cut is set using a height gauge shown in the bottom photo and the
width set just a couple thousandths of an inch less than the mortise
cheeks. That’s to allow for the slight
variance in board thickness to give me some cushion when the tenons are fitted
to the mortise. Test cuts are made to
assure that the settings are correct adjusting as necessary.
Once set the rails and stile are cut. The top photo shows the setup and cut top
rail. On this piece one end has a small
chip left while on the other end it is completely gone. That’s the result of the very, very minor
variations in board thickness. The
bottom photo is a closeup of the barely hanging on chip.
Cutting the tenon is next. In theory because the just cut dado is right
at the thickness of the mortise cheek to cut the tenon all I need to do is use
the same blade height and cross cut the long rails. However, when I made the test cuts on my
sample piece the tenon was too thick by about .03”. That led to some head scratching trying to
understand why there was a difference.
Doing some measuring and looking at the saw setup it seemed like the
culprit is the table saw insert. When I
press down on the board being cut to make the tenon the insert flexes ever so
slightly resulting in about 15 thousandths deeper cut than the test cut when I
was not pressing down as hard. Since the
cast iron saw top does not flex in making the crosscuts the cut is not quite as
deep and the tenon is too thick. Raising
the blade that 15 thousandths worked allowing me to get a good fit. The photo on the top shows the overall table
saw setup using a stand to support the end of the stile. The photo on the bottom shows the business
end of the setup.
As you can see in the photos below things don’t yet quite
fit together right. That’s because the
tenon needs to be a 5/16” longer on the side with the rabbit for the
glass. This cut has to be made just
right. To short and the inside of the
stile will not butt up against the top and bottom rail. Too long and there will be a gap on the
outside face of the door. After some
trial and error with my test piece the table saw is set up and ready to
go.
Next up – Door Joints Part 2 & a Patch
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