When I swing the arm around, the ring stays in the same position
relative to the moving arm, just rotating around the inner post, so
all it does is make a ding in one spot.... ... What am I doing
Don’t crank the “micrometer” handle down so much. Start with light
pressure so it’s only rolling the shank a very little bit. You want
it putting just barely enough pressure on the shank so it’s actually
stretching it a little. If the pressure is so much as to actually
dent or ding the shank, it’s too much. If it needs more stretching,
increase the pressure just a little more and roll again. You can’t
take too much of a bite on one pass. Also, while tools in general
like being oiled, the center post on these things is an exception.
Make sure it’s clean and dry. By the way, taking only a slight pass
at a time with these stretchers is a good idea in any case, because
even a slight reduction in thickness of the shank can give you a
surprising amount of increase in ring size. It’s very easy to
overshoot the desired ring size. So just a little bit at a time, with
frequent checking of the ring’s size as you go. Doing it just a hair
at a time also helps you to feather in the rolled reduction so you
don’t get a strong step in the shank at the shoulders. On rings with
a tapered shank, start with pressure settings that don’t even contact
the shank at the bottom, but only just hit it where it reaches the
desired spot at the shoulder. Roll that part slightly on each side.
check size. Then again, slightly more pressure, but not rolling up
the side quite as far, etc. In many cases, you can stretch a ring a
substantial amount by only rolling the sides like this, so you don’t
have to reduce the shank’s thickness at the bottom, where it’s
thinnest, at all.
Again, the basic answer to your problem is “easy does it”. And be
careful. These stretchers are quite capable of doing a whole lot of
damage if you’re not careful. Go at it gung ho, and that size five
ring you wanted to stretch up to a six, will suddenly turn out to be
a size 10.