And I trial and accidental success.

Lose is better than tight in dry season, tight better than loose in the
rainy season.

I use a double taper, myself. The bottom tapers gently into the top, which
still has witness marks from the parting tool to give me a starting point,
and the top is tapered gently in at the bottom, to fit inside a deeper area
outside the "tenon."

I do the lid, including sanding, before I begin the bottom. When the top of
the tenon fits inside the bottom of the lid, I do my tapers. Good thing
about it is if you get a little too loose, no sweat, because you're going to
taper it to fit it in a tighter place at the last, anyway.

"Barry N. Turner" wrote in message
...
Well, I use trial and error.......................