About Steve Kretchmer and his patents. He has only one patent
that I can find. It relates to his SK platinum sold by Hoover &
&O S=IN/k retchmer&RS=IN/kretchmer
Kretchmer has patents on multiple processes. The following covers
heat treatments for four different gold alloys:
There are others out there. Note that he calls them "compression
spring settings" which is suitably generic to cover items that are
compression set without a ring involved, and/or avoids using the term
"tension ring" which may or may not be patented by someone else :-).
What I believe is important to know is that the shank acts as a
spring. Any thick spots or thin spots in this spring will cause
failure. It is virtually impossible to maintain structural
integrity if one cuts or solders the shank. The tension in the shank
needs to be spead evenly. As the ring is worn, natural burnishing
occurs on the outer surface. This tends to spread the metals only on
the outside further tightening the stone.
It's not true that a thin or thick spot will cause failure. If the
ring is thin in one spot, that part of the ring will be the weakest.
Furthermore, the stresses on different parts of the ring are NOT
equal. The tangental force being applied on the stone is reacted to
with an equal and opposite force from the stone. These vectors of
force are tangental to the circular ring.
This puts the most force on the opposite part of the ring because the
two halves of the ring (when cut vertically) act as levers. Think of
prying open a paperclip or a jump ring... the first bending occurs at
the opposite end to the opening, where the forces are most magnified.
The actual force there is a "pulling apart" force being exerted by
the stone, on the inside surface of the ring. The outside surface of
the ring is being "pushed together", and the midpoint of the two is a
fulcrum for the levers.
As long as your ring is thick enough to resist the forces applied to
it in the various locations around the ring, you will be OK. In places
of less stress, it is OK to have the ring thinner, and thicker in
places of higher stress. Of course, when designing this kind of thing,
the easiest thing to do is to make the whole system uniform, and
suitable to handle the stresses at the point of greatest force.
I have a proof for this. Given any particular working tension ring, I
can add metal to any part of the ring, thereby making some parts
"thicker" and others "thinner." This does not add any extra stress to
the ring, and since I'm adding material, and thereby strenghtening
the ring, it will still meet the minimal requirements for structural
As for the hardening over time... this is not from surface
burnishing, but a property of the alloys involved. Kretchmer refers to
it in his patent above.
(Note too that a cast ring is not going to be of uniform strength
even though it may be of uniform strength, due to impurities in the
metal, or inconsistencies in the crystalline structure...)