I'm assuming you're talking about America for RP service bureaus.
But if you want to know who to ask in the UK, I'd be happy to give
you that too. Let me know.
Right now are two approaches to CAM for jewelry: One way is to grow
the model with a main material and supporting material. This is how
the various kinds of Rapid Prototyping work, sometimes called Wax
Printing when the machine uses wax. The other way is to carve the
model out of a block of metal, wood, or wax. (CNC Milling).
As you've noticed, the RP industry becomes more competitive with
every passing year. Every company is jockeying for position in the
marketplace, and changing their machines quickly to stay
InVision has just recently reformulated their modeling material so
their models can be directly burned out in casting, making them now
a direct competitor to Solidscape's machines (which were, up until
recently, the only machines that produced directly castable parts.)
As for developments in CNC milling, Roland is now selling a 4-axis
mill with a swiveling milling arm (I think it's the MDX-40R). It can
perform undercutting on rings and small hollow shapes. Also, another
company has recently introduced a model lubricant for wax which
makes for a cleaner finished piece.
The list of the most common machines on the market in the USA right
a.. Solidscape T-66: a rapid prototyping machine, that "grows" parts
in a delicate castable wax. Models are brittle, but you can literally
make anything with these machines.
b.. InVision: similar to the Solidscape, but bigger and faster. It
makes parts out of a proprietary plastic, which only just this year
c.. Viper: "grows" models out of resin. Tougher models with slightly
better detail than wax RP machines, but the models aren't castable.
d.. Modelmaster CNC: a line of multi-axis mills for jewelry. Small,
cheap, fast, but limited in production volume and flexibility.
e.. Roland JWX and MDX: Roland's jewelry mills. Riddled with
technical problems (especially with software), but when it does work,
it produces some of the best quality pieces of all the mills.
f.. Revo: Gemvision's proprietary machine. Works about as well as the
Modelmaster, but is hotwired to interface well with Gemvision Matrix.
Other countries use additional brands, but these are the dominant
brands right now in the US.
In addition to these, you can get away with using some of the big
boys from heavy manufacturing on some jewelry work (the ZCorp makes
models out of plaster and can work small enough for jewelry.)
As for getting the best, as of the last time I checked (last week),
CNC milling usually gives the best initial surface finish. Viper's
resin is second, with the Solidscape's proprietary wax and
InVision's resin material falling third. This trades off pretty
evenly with convenience, as I would reverse that order for the speed
of manufacture and the flexibility of the machine.
As far as companies to use, I've always had good luck with
CADSmithing (www.cadsmithing.com) based in Gilbert, AZ. They offer
several different RP and milling machines to choose from. Also,
CADBlu in New York (www.cadblu.com) have great customer service,
although their specialty is the InVision.
Cost can vary, being a bit cheaper for CNC Milling, more expensive
for InVision and Solidscape. A range of $60-$100US is fairly typical
for a single ring, depending on machine, complexity, size, and
volume of models.
Hope that helps. Happy modeling.