On Sep 13, 8:45*am, Spehro Pefhany
wrote:
On Tue, 13 Sep 2011 10:38:39 -0400, "Ed Huntress"

wrote:

Right. It's not that they can't be EDMed (Sumitomo even makes, or made, a
conductive ceramic that can be EDMed), but the speed, settings, overburn and
wire reaction (and deflection) get tricky with refractory metals.
Superalloys and other refractory materials have been wire-EDMed for decades,
but I suspect that pure niobium is a very rare one, if anyone does it at
all.

It's not unheard of. I know at least four places that have done it
successfully to a relatively high standard. As you say, it is going to
take time to optimize the setup.

It's nasty to machine conventionally. I'm told, gummy like copper.

Long time ago I designed a sub arc second pointing system. I found
out with really tight dimensions all sorts of usually not thought
about issues pop up.

Things like thermal expansion, internal stress, modal vibration and
loading stress.

If edm doesn’t work out you might try oversize edm then ion milling or
chem etch to bring the part into tolerance.

Sounds like a fun project.