My first step in cutting the tenons is to precisely lay
them out on the top and bottom rails carefully marking which parts get cut off
and which needed to remain. That sounds
simple but it is not all that hard to set up a jig to cut on the wrong side of
the line which is not a good thing.
The order and criticality of the cuts is next. In this case the back of the rail needs to be
flush with the back of the leg. That
means the critical measurement is the distance the mortise is from the back of
the leg and it needs to match the distance the cheek of the tenon is from the
back face of the rail. In a perfect
world that would be the ½” shown on the drawing. However, when measured it’s 1/32” larger or
17/32”. The mortise is 3/8” so the
tenon needs to match that. Last, is the
distance from the outside face of the tenon to the outside face of the rail and
that’s whatever is left over. The
drawing below shows how everything is supposed to fit together at the bottom
rail/leg joint. The top rail is similar
except the top of the rail and the top of the leg have to align.
Since the back cut on the rails is the most important
one, I start there. Using the tenoning
jig test cuts are made until the cut is the right size. Blade height is 1 7/16” which is 1/16” shy of
the final tenon length. That will be cut
to exact size later. Here is what the
setup looks like after my first test cut.
As you can see, I need to take a bit more off to get to the line. When set it’s a matter of cutting both ends
on all eight pieces.
Next is cutting the tenon to width. Here the top rails are being cut. Their easy as both the top and bottom are the
same dimension. In this case rather than
cut the tenon to the exact width of the mortise I am making it 1/16”
smaller. That way I have a little wiggle
room to align the top of the leg and the top of the rail.
The bottom rail uses the same method except the top and
bottom are different measurements requiring two setups. Here is what I mean.
At this point three sides of the tenon are done leaving
just one to go. Here is what the rails
look like at this point.
On the last side I am not concerned what the distance the
cut is from the face of the rail. What
is critical is when done the tenon needs to fit snugly in the 3/8” mortise. Ideally it would be 3/8” but I am going for a
hundredth of an inch oversize. I can
remove material but if the joint is sloppy it won’t give me a strong glue joint
and fixing that can be done but it’s a lot more time consuming. Being a few thousands of an inch too wide is
much less of a problem as I can shave the tenon to fit with a hand plane or
work on the mortise with a rasp. The
actual cut on the table saw is the same as above.
Once the tenon is sized I cut the waste off on the
bandsaw. Mind you this is
not the final length of the tenon, it’s about 1/16” short. The final cut will be made later. Now I want to do is free the tenons up and
fit them to the mortises.
For as much care as I take in doing setups and making
test cuts to assure the pieces are identical when the top rails were lined up
ready for the bandsaw, I noticed that one of them was shorter than the other
three. Not the most pleasant revelation. A chip must have gotten between the stop on
the chopsaw and the board when it was being cut to length causing it to be cut
short. Fortunately, finding it now makes
the fix pretty easy. The important
measurement is not the overall length of the rail but the distance between the
shoulders of the tenon. That’s what
establishes the distance between the legs so all I have to do to correct the
problem is to make one tenon shorter by the same amount the rail is short.
Making a snug fitting tenon and mortise joint is
next. After looking at the two parts I
decided that since the inside of the mortise was the roughest, I would adjust
its width in lieu of adjusting the thickness of the tenon. The thin light-colored piece of wood is a
pine blank exactly 3/8” thick that will be used to gauge the mortise
width. When it is slightly loose the fit
between the mortise and the actual tenon will be just about perfect. A couple of rasps of differing coarseness are
used for the fitting. The rasp with the
blue tape is the coarse one and what I start with. The tape is set ¼” longer than the tenon for
a couple of reasons. First, no need to
size the mortise where there will not be a tenon. Second, and more important is I do not want
to damage the other side of the mortise.
There will be a faux through tenon set in it later and I want a tight
joint between it and the mortise. Any
minor cleanup of the opening will be done from that side and the sizing will be
done on the faux tenon piece. More on
that later. Once I got into the rhythm
of fitting things went pretty quick only two or three minutes for each of the 16 joints.
Next up – Finishing the Leg/Rail Tenons
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