I hand-sawed and -chopped a double tenon with haunches
on a 17" wide glue-up for a bed footboard. It goes in
most of the way into the mortised leg and then stops.
Is there a trick for how to tell what the problem is?
How can you tell exactly where along the 17" of joint
the problem is when nothing's visible?
I'm assuming that the problem must be in the mortise, as any problem with the
tenon should be instantly obvious. I'm guessing there's a spot, somewhere,
that you didn't get chopped out deep enough.
Is there some reason you can't look into the mortise with a flashlight? That
ought to show you where the shallow spots (if any) are.
If the problem is that the tenon is being pinched (i.e. tenon too thick, or
mortise too narrow) somewhere along the way.. make a test fit, then take them
apart, and examine the tenon on both sides for signs of wear or compressed
wood fibers. That will tell you where the fit is tight.
Doug Miller (alphageek at milmac dot com)
I haven't tried this, so someone else please correct me if it won't
work, but why not color the sides and end of your tenon with chalk or a
soft-lead pencil, try it in the mortise, and see where the chalk rubbed
off most inside the mortise? Seems to me like it should work. In the
past I've always been able to figure out which sides need more chopping
or paring by just wiggling the tenon piece and noting where it feels
like it is stuck. Does that make sense?
IMO it almost certainly would work to identify the problem area. I've never
tried it, though, because I worry that the chalk or graphite may interfere
with the glue bond. Maybe I'll try an experiment some day...
That's what works for me most of the time...
Doug Miller (alphageek at milmac dot com)
Use a set of calipers to mic the width and thickness of the tenon to see if
it is consistent. If it gets thicker toward the shoulder you can reduce the
thickness or width. If it the same all the way across the tenon the mortise
is to small at the bottom or the tenon is too long.
If you look real close you should see that the high side will generally be
shiny on both parts from the friction of the trial fit. Those are obviously
the areas to spend your time on.
Since it's a double, you also may have a situation where the mortises were
not cut parallel, which may require some shimming once you get past the
mating of the two components.
I have an engineer's (metal machinist's) depth gauge. It's a chunk of
thick steel with a thin wire that slides vertically through it, with a
small clamp. Excellent gadget for probing how deep mortices are clean
Another useful gadget is an internal caliper with a screw thread
adjuster. Hard to use as you need to hold it square, but it will often
pick up a narrow spot that needs paring.
If you suspect tha the mortise is the problem, take a narrower (2")
piece of wood, and cut a tenon in it. Drag this through the mortise to
see where it catches. If necessary, thin the tenon slightly so you
won't be wearing the inner surfaces of the mortise.
If the tenon might be the problem, then, cut a mortise-sized dado in
maybe a 3" length of stock and drag that along the length of the tenon
to see where there's interference. If you must hand-chop, then chop a
3" mortise into a longer piece, then cut the ends off to turn it into a
...just some ideas,
I'm not having the problem. Mike suggested cutting a dummy mortise to
find why the real M&T wasn't fitting.
I'm just saying instead of cutting a dado, which will fit 2 sides, and
may not be deep enough, to glue up a mock motise with p`4 pieces of
plywood. A tablesaw can cut pieces squarely. You might be able to
use a rubber band just to hold the pieces together.
Personally - I would first try the "look for the shiny bits" method.
Or inside and outside calipers (if you have them).
And only use the mock-up if you can't find the problem.
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On 19 Oct 2005 19:22:05 -0700, with neither quill nor qualm,
Ah, but it IS visible if you know what to look for. As you assemble a
joint, the wood will burnish at any heavy contact point. Look for
shiny spots on the tenon and in the mortise. Pare or sand those down
and try again. Repeat until you have a snug joint which fully comes
You would also be better served by several tenons rather than a single
long one. The footboard will probably crack on you as the wood in the
panel dries. If I were doing this and had already cut a long tenon,
I'd probably glue it only in the center of the mortise, about 2", then
rely on the rails to provide the majority of the strength.
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