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CNC under $30K?

Hello All,

I am looking for a CNC mill or a ARP desk top machine. I am using
Rhino 4.0as my CAD program and Rhino CAM Pro as my manufacturing
program. I make small sculptures (50mm or less) as well as
traditional jewelry items. I need a machine that will produce my
designs with minimum distortion and an accuracy to approximately
0.05mm. I would like to hold the cost under $30,000. I don’t know if
this is realistic. I would very much appreciate your suggestions and
recommendations. Thanks.


Well, I have a Solidscape MMII additive prototype machine that’s
going for $7,500. It takes .stl files.



In general, mills will give you a better surface finish than pieces
produced by an RP machine which will give you a wood grain effect,
some more noticable than others. As far as an accuracy of .05mm,
you’ll get responses from equipment reps/manufacturers touting thier
accuracy down to (pick a measurement). Those measurements tend to be
a little misleading for the real world as they might be the
theoretical mechanical resolution of the machine, the smallest
movement it can make, which doesn’t take into account the smallest
movement the software will tell the machine to move, which tends to
be bigger, or that the minimum thickness of the layer does not
provide you with usable detail of that same thickness. I find that
a.05mm detail included in a CAD model would no longer exist after a
piece is cast and finished, even if you could see it in the original

The advantages with mills are the superior surface finish, speed and
the ability to work in many materials and they tend to be
significantly less expensive. The disadvantages are that you have to
learn how to run the thing and in effect, learn how to be a
machinist to some extent, a considerable outlay in time. You can
create just about any shaped object with a 4 axis mill, but you
might have to be creative depending on the overall shape of your
scultpure and/or mill a piece in sections and assemble later.

An RP machine requires less investment in time and training and can
produce pretty much any shape your heart desires. It’s slower, which
isn’t a huge issue as you can just run it overnight and will give
you a slightly rougher model. I’m not wild about some of the
materials used in some RP machines, wax based materials are pretty
fragile, it’s tough to touch up at all, but they burn out well,
whereas the resins, which you can file and sand to smotth the
surface, are a little touchy to burn out.

That said, both mills and RP machines are used widely and with
success by many, it just depends on your needs and pocketbook. I’d
suggest sending out some models to service bureaus using a varitey
of systems, so you can compare.

I use a Minitech Minimill Pro 3, which is a great mill, capable of
producing very accurate models with great surface finishes. The
Minimill 2 is a very capable machine as well, suitable for jewelry
models and @ $10K

If you like to get feedback from users of a different mills and RP
systems, check out a free forum for jewelers
working in CAD. The best place for such info IMHO, I have no
affiliation, just a member.

Harry Hamill


It’s certainly possible to get a CNC mill for that amount of money
or less that will hold those tolerances. But an Additive Rapid
Prototyping system that’s that accurate would be difficult to get
for that price unless you got a used machine or a special deal on a
new one. Either alternative would probably get you there; the CNC
option would work with RhinoCAM, while you’d need other software like
Magics for instance, with the RP system, to clean up the geometry and
generate the supports that make it possible to build the parts in
space. A CNC system would let you make parts in any material the
machine could carve, but it’s limited to surfaces that can be
reached by your cutting tools. The RP systems allow more design
freedom, since there are no restrictions like that - you can make
parts with all sorts of undercuts, balls within balls, even whole
gear trains where everything turns if you rotate one part. But of
course if you need to cast and/or finish these parts, you’ll still
need to reach them somehow…

Andrew Werby


A late answer, I can’t comment on $30K mills. My really fancy taig
cost about $3k, home built frankenstein monster about $300. Both
hold the type of tolerance you are looking for, the $300 one just a
little better. I feel that it is more a matter of understanding
exactly how your tools really work. Operating and programming errors
will not be fixed by expensive hardware, but it is really amazing
what can be accomplished with just a pointed stick and an
understanding of the needed process

Demand Designs
Analog/Digital Modelling & Goldsmithing