Darcy, A tension setting is a spring. It is an homogenous band of metal
wrapped around into a ring. Any thin area will give in time. Any
welded or soldered area will tend to give. A lump will tend to cause
the area on either side to to give. This band should be heavy enough
to accept a good deal of abuse. It doesn’t have to spring a lot, just
enough to close back down onto the stone when struck. A cast piece, in
my shy, quiet and humble opinion, will not form a spring of quality
enough to do this job.
The last time that I made a tension setting, I rolled a strip about
8mm wide and 2.5mm thick. I then wrapped the band around into a ring.
I then ground a flat directly onto the opening. I added about 6mm of
thickness to the flat on the opening. From there, I shaped and split
the top again to accept the stone. After cutting what I estimated to
be a good seat for the stone, I slid the ring up a mandrel to open it,
dropped the stone in and slid it back down the mandrel. I may have
needed to use a pair of bow benders to tighten it up. It’s been gone
for over a year now.
Better luck next time.