Andrew - I am only a tiny step up the learning curve from where you
are, but I’ll be happy to tell you what I can. Feel free to mail me.
Whether you plan to or not, your first few cuts in the silver are
bound to be a bit experimental. You should probably plan to do the
initial surfacing more than once, for example. It might even be worth
designating a lump of your ingot for test cuts. Twenty minutes of
fooling about with it will tell you more than any amount of
discussion. That also mitigates the stress of trying to get the first
cut perfect!
If I was you, I would polish by hand with the Dremel. It doesn’t
take long, but you need to be looking at it to see the process
working. A more automated CNC-based setup might be worth building
later, but there are a lot of variables you want to understand first.
Yes, rougher polishes can substitute for sandpaper, within its
limits. Face your silver, bung a suitable felt in the Dremel, run it
on the yellow polish, and set to with it. You’ll see when it removes
the machining marks, or you’ll get fed up with it obviously not
removing them, and then you can reach for a bit of wet & dry paper.
Which, by the way, I would apply with my thumb, not a CNC machine,
for all the same reasons.
Incidentally, I have never applied polishes wet. I don’t know if
that’s standard practice, but I wouldn’t bother. You also need to
make sure that each of your three polishes goes on its own wheel, and
that you clean your work between polishes, so you don’t get any of
the coarse stuff in the fine passes.
Here are a couple more pictures for you - this is CNC-machined
sterling silver which has been surface-enriched then enamelled:
http://www.jarkman.co.uk/catalog/jewel/rachelwengravedenamel.htm
And this is fine silver enamelled by my wife, Donna:
http://jarkwoman.co.uk/JewelleryPics/Enamelling/LargeCNCPendant.htm
And this is an experimental bit of acrylic-in-acrylic inlay, which
turned out to be extremely easy. Not a great aesthetic success, mind
you, but the actual inlaying worked perfectly. The most awkward bit
is at the design stage, making sure that the shapes of the hollow and
the inlay part respect the cutter radius and width constraints
correctly:
Richard