It would be nice to see all of this in person, because I get lost in
the forces, axis, perpendiculars, parallels, etc. I have 2 Vicmarcs.
The dovetails on the jaws go all the way down. With the big chuck, and
bowl being 16 inches plus, my mortice is about 1/4 to 5/16 inch deep,
and 1/16 or so wider than the jaws. This allows enough hold to safely
core with the McNarghton system, and no tailstock. On smaller pieces, I
go no less than 1/8 inch deep, depending on size. The top of the jaws
must bottom out on a flat spot in the mortice, and the mortice can't be
deeper that the jaws. Wet wood seems to compress more than dry wood, to
the point that sometimes, I have to retighten the chuck once or twice
while turning. You can tighten the jaws too much, which can break the
mortice before you begin to turn, or if and when you catch, the added
stress, can break your grip. When tightening, there are 2 places on my
chuck to insert the wrench for tightening. I snug it up in one hole,
then go to the next and snug it up some more. I may rotate it a couple
of times, snuging it up a little until I am satisfied. Having enough
shoulder on the mortice is important also. With a little shoulder, you
have to be gentle when turning out the inside, with a bigger shoulder,
you can be more aggresive. Because woods are so different, there are no
fixed rules on how much is enough (shoulder size, mortice depth, jaw
tension). Trial and error will help you learn.
robo hippy