Foolproof tenon tuning
that perfect fit has proved a challenge for me. Ideally, a mortise
should slide into its tenon with only hand pressure (no mallet
required) and you should be able to pull it back apart with your hands
- no mechanical assistance should be necessary. If it is any tighter,
it will be difficult to assemble when the glue applied to both mortise
and tenon causes the parts to expand. Any looser and it could result in
a weak joint.
Despite the fact that I have a thickness planer and usually mill my
stock to a uniform thickness at the beginning of a project, it seems
that some parts still end up being slightly thicker or thinner than
others. Additionally, the process of cutting the tenon faces slightly
increases to the existing variation. The result is some joints that are
too loose and other that are too tight.
To deal with this problem, I usually cut the tenons slightly thicker
than I need - this results in a few that fit perfectly, but most are
too thick. I then fine-tune the fit by hand. However, I have had
significant difficulty in acheiving consistent results in the
fine-tuning process. I have tried several methods...with varying
- block and shoulder planes
- rabbet plane
My hand-tool skills are nowhere near good enough to get consistent
results with chisels -- and I'm not sure they will ever be. I can get
slightly better results with the block or shoulder planes, but it is
very easy to round over the sides of the tenons - and very difficult to
ensure the tenon faces remain parallel with the stock sides. A rabbet
plane with a depth stop can help considerably, but it is still too easy
to end up with tenons that are not uniform thickness.
I have found a method that is virtually foolproof for me and allows me
to fine-tune the tenon fit in tiny increments. Suprisingly, my tool of
choice for this task is a router plane. In my case, it is a Stanley 71
1/2. This plane (and the 71, IIRC) has a threaded adjuster that allows
the cutter to be raised/lowered by tiny increments - this allows the
thickness of the tenon to be adjusted in tiny increments. The other key
is that the cutter is referenced from the face of the stock from which
the tenon protrudes. This ensures that the tenon faces remain parallel
with the stock...which also means that the tenons maintain a uniform
But enough talk...let's see some pictures:
First, here is the stock to be tuned. This particular example is a 1/2" stub tenon from a frame & panel construction.
Next, we need a stable working environment. The force applied to the
plane will take the plane cutter across the face of the tenon (across
the grain), so the workpiece should be secured accordingly. Here is one
To prevent tearout of the shoulders, I score the edge of the face along
the shoulder. Some tearout on the far edge of the tenon is almost
inevitable. On most M&T joints, it will not be visible, so it does
not matter. If the tenon end or edges will be visible, the tearout can
usually be avoided by taking very light passes.
Next, place the plane base on the part and lower the cutter so that it
barely touches the surface of the tenon face. The micro adjusting
feature of the plane can now be used to lower the cutter slightly.
Now, the tenon face can be trimmed slightly. Depending on the
application, it may be necessary to trim both sides equally. Since the
cutter of the router place can easily be micro-adjusted, I usually take
several passes to reach the final result. Of course, this depends on
how far off the tenon was from the desired thickness.
And the final result, a perfect-fitting tenon:
A key to the technique is to put downward pressure only on the plane
handle that is over the stock. Apply forward pressure only to the
opposite handle. It may result in a slightly arcing motion, but that is
ok. Take as many passes are necessary to cover the entire tenon face.
I have used this technique on tenons up to 1 1/2" long. However, with
an additional piece of stock to support the other side of the plane, it
may be possible to extend up to 2 1/2" or maybe 3".