I teach chain making and have worked with a number of power jump
ring cutters. I have been very satisfied with the "Koil Kutter"
manufactured and sold by “Gemsetc” in Tucson, Az. The device is not
very expensive, can be powered by a Foredom or Dremel or Proxon.
I’ve have two and have used them for at least six years for my chain
making classes and workshops with excellent success.
I like to place my coil holder in a vice so that I can use both
hands to draw the cutting head down the slot in the coil holder. You
should have your power tool running at its highest rpm when you
start cutting the coil. You should not move the cutting head into
the coil faster than th blade can cut. If you move the cutting head
too fast, you can jam the blade. A dull blade can also cause an
excessive load on the power tool and cause it to jam.
I hope this is of some help to you.