Jeffrey, I do all of my work, exclusively in titanium, on a Sherline
converted 4-axis CNC. I have never, and probably never will use
anything nearly as big as an 1/8" endmill, so I have no idea what
your depth of cut per pass is going to have to be. I built the CNC
conversion myself, including the power supply and motor driver board
(this was a kit I assembled). There is no material that the Sherline
machines are incapable of cutting, it is simply a matter of staying
within the bounds of the machines strength. As the material gets
harder to cut, you just take lighter cuts, assuming you have the
correct cutting tools.
My endmills used are always 1.0 mm or less (as small as 250 microns)
in diameter, and these will break long before the machine rigidity
comes into play. Assuming you have the machine setup properly and
you understand how to program it, the precision and accuracy can be
anything that you desire. Remember, this is jewelry, and not
aerospace engineering. You need to be realistic on what tolerance
you need or want.
I assembled my own 4-axis CNC for less than $1500, including
EVERYTHING even the dedicated computer for motion control. Since I
built it, I can also repair ANYTHING that breaks.
Daniel J. Statman, Statman Designs