On Thursday, May 22, 2014 5:52:55 AM UTC-7, thunk wrote:
Is there a simple set of relationships or formula for one eccentric

inside another?

An eccentric is just a short linkage arm, the arm length being
the deviation of the external cylinder's center to the internal
shaft's center. So, when you have two arms with equal length, you
can make a straight-line deviation from the center by anything
from +2L to -2L, in any direction

If the lengths aren't equal, your situation gets odder, of course;
and you'll never be able to hit the center though some long straight-line
segments that miss the center are possible.