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
dado.

....just some ideas,

-Mike

nireedmot wrote:
Hi there-

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?

-Tom