On Wednesday, April 13, 2011 9:51:01 AM UTC-7, Bob La Londe wrote:
What kind of holding force do mag chucks have? As much as something
like the magnets in the magna bend?

Magnetic attraction of iron is usefully related to the energy
required to break away a clamped item, but not to the
force, because the relation of that force and energy is
very critically dependent on geometry (the force on a
distant lump is inverse-distance to the fourth power).

The spacing of the poles (closer is better, especially for
thin stock) just matters too darned much, as does the
surface finish of the mating faces.

The energy, which you CAN quantify, is the same as the
stiffness times the swing of the clamping lever; the more
work you do to unclamp, the better the original hold was.
And, of course, the hold depends not only on the pull-down
force, but on the lateral friction that that generates...