I've been struggling with this for quite a while. My present goal
is to be able to make a 6-prong crown setting for an 8mm round
faceted stone, with repeatable success. I'd be happy with a 50%
success rate, at this point.
After reading complete post, I can say that you are on the right
track. Few refinement should be of some help.
First, you must accept that annealing has to be done more often that
recommended. Natural question is about damage to structure of metal.
We will deal with it later.
Thickness of metal matter here, so start with 1.2 mm. Starting disk
diameter should be double length of side of intended cone. I am not
talking about height of the cone, but actual length from point to the
rim. This is more metal than you need, but we need some extra.
Form half-dome and than proceed like you described by forcing into
smaller and smaller dies of the bezel block. Here are few details
that should help you. Polish inside edges of the block dies. They are
way to sharp in original condition. The whole inside surface has to
be polished. There is a lot of friction between wall of block dies
and the metal. You need to create conditions where metal can slip. It
means polished surfaces and lubrication.
Another important factor is tool that is used to drive cone in and
the force applied. By forcing cone into smaller and smaller dies, the
thickness of walls of cone must increase. Unfortunately, this is the
most unlikely scenario of metal behavior when cone is relatively
unconstrained. Metal will do anything else but that, so care is
required. If you use too much force the upper edge of the cone will
flare, if you use too little, nothing will be accomplished. Examine
cone frequently to see if any progress is been made. Anneal if metal
does not move. If any flaring starts developing, file it away. That
is why we started with more metal than we need.
Remember to file off a bit of thickness after every couple of dies,
or metal grow too thick to be moved. The tool used to force cone into
dies are very important consideration.
I know you have my DVDs, so review Coronet Cluster again. You must
use tool shown there. If tool is too hard, it will cause edge of the
cone to flatten, which will cause the edge to be caught on edge of
bezel die and split eventually. If tool is too soft, the surface of
the tool will simply be eroded by edge of the cone and once again no
progress will be made. There is a relationship between hardness of
the tool and the cone.
If there are tearing of the tip of the cone, it means that inside of
dies are not smooth enough. This can be overcome by polishing of
inside or simply making cone taller and discarding the tip.
When cone of the required size is obtained, place finished cone in
the die and do some hammering using collet punch that came with the
block. This is necessary to repair metal structure, which was
impaired by frequent annealing.
The last point is that in this process friction is your main enemy.
Metal will move in desired direction if it will be more difficult to
move in any other direction. So technique, tools, methodology should
all be geared towards this goal.