Sounds to me like perhaps you're putting your flange on before
forming? That could be causing the distortion because the force of
rounding works primarily on the main body of the ring, the part in
contact with the mandrel, which is usually the innermost part of the
shank. You might try rounding in smaller bites. Flip the ring over
frequently.
But if you've got a distorted ring and want to save it try
this...use a large tapered bezel punch of correct size and tap the
punch into the finger hole. The ring should rest over a suitably
sized hole to allow for the point of the punch. The punch has a much
faster taper than a mandrel so it will contact just the edge of the
ring. I've got one here if you'd like to borrow it before investing
in one. They make the punches in two tapers, 17 and 28 degrees(I
think). Come to think of it a large dapping punch might work too.
To unstick a jammed ring there are two ways that work for me. Brace
the mandrel solidly on the bench or stump, preferably with the edge
of the ring resting on the edge of the bench, and pull the mandrel
slightly toward you then whack down hard with a rawhide mallet
straight on the ring. This will cause a slight expansion of the
ring. You can also tap sideways on the ring, like drawing the mallet
along the mandrel toward the small end, hitting the ring in midswing.
Some may frown on this though...I have a very large milling file
(10") with a safety edge that I use in that manner, for really stuck
rings. I suppose a brass mallet would work the same way, but I'm too
cheap to buy one.
