Has anyone had a similar experience and is there a trick for sawing
[niobium] safely that I just haven't figured out?
The problem with niobium (and titanium too) is that it forms a very
hard surface oxide layer. That’s the effect you want when you
anodize, and anodizing makes that layer even thicker and tougher. The
metal underneath is not actually that hard, though it tends to be a
bit gummy to file or saw. But to cut it, part of the trick is not to
be too gentle. Use as large a size blade as your application will
allow, since the coarser teeth will get a better bite through the
oxide layer, and though you need not pull the blade down quickly, you
should try to exert a little pressure into the metal. Traditionally,
with a saw, one is taught to let the blade do all the work, and to
have a gentle touch on the saw frame, etc. With niobium and titanium,
you need to back track a little on this advice. No, you don’t need a
death grip on the saw frame. But you do need to push the issue a
little bit in order to get the teeth to bite through that oxide
layer and into the metal. Too gentle, and the teeth will just slide
off. And don’t expect the blade to last all that long. It won’t.
As to the problem of where the blade is jumping off to, ie your
fingers, find a different way to hold the coil so your fingers are
out of the way. How 'bout taking an extra ring clamp and cutting a
bit of a groove in each face of the jaws with the flat end, just down
from the outer end. A coil could now rest in that channel. Clamp very
lightly, or don’t even use the wedge, just hand pressure. But this
gets your fingers out of the equation.
Also, your description makes me wonder if you’re trying to cut with
the blade parallel to the whole coil, cutting the whole coil at once.
If so, then in general when cutting coils, angle the blade so you’re
not cutting the entire coil at once. Start at one end and work
towards the other. The beginning of the cut is just in one wire, not
multiples, and once you’ve started the cut in the first ring, that
cut guides the blade into successive rings. No blade jumping. As you
cut into the coil, you can lessen that angle a bit so your cut is
into three or four wires simultaneously, but it works better not to
ever lessen it entirely. As you cut through the rings at the
beginning end, they fall off, or hang on the saw blade, keeping them
out of the way.
If this gives you trouble, make a sawing jig for that size jump
ring. That amounts to a mandrel similar to what you wound the rings
on, but with a slot cut into one end. The mandrel can have one end
fixed in a vise if you like, or held with pliers (though you start to
need more fingers than you were born with sometimes (grin). The saw
blade can start in the precut slot in the mandrel, angling into the
first rings in the coil. As you cut, you’ll slide the coil down the
mandrel so you’re always working near the end of the mandrel, which
also allows the cut rings to drop off as you cut them free from the
coil.
Personally, though, when cutting jump ring coils (and I do this with
other metals too, including platinum and gold), my preference is to
avoid sawing at all. I get the very thin seperating disks. These
puppies, at.006 inches in thickness, or the slightly larger.010
inches, leave a cut as thin, or thinner, than many saw blades (the.006
leaves a cut not much larger than an 8/0 blade would do). Run them at
medium high speed, use a bit of bur life or other lube if you like,
and they’ll slice down a coil of jump rings a lot faster than a
sawblade will do. Often, I’m making very tiny rings, which I wind up
on the shank of a small drill bit. Try sawing a coil of.4 millimeter
wire wound on a #70 drill bit… But wind it up, leave it on the drill
shank, hold that shank, and one loose end of the wire coil, in
pliers, and thus steadied, the other hand is free to zip down the
coil with the seperating disk. Done deal. The only down side to this
is that the disks do wear out fairly quickly. But then it’s not like
sawblades last forever either, especially on difficult to cut metals.
Buy the disks in a box of a hundred, and you’ll be happily cutting
jump rings for quite a while. Note that the very thin.006 ones are
quite fragile. Use those for the smallest wire and jump rings. For
most, the.010 size is more suited. I should note that usually, the
quantity of rings I making at any one time is not more than a couple
dozen or three. If you’re making hundreds at a time, then the little
seperating disks likely won’t be long enough lasting to keep you
happy. But for that quantity, if you do it often, you’ll likely be
wanting one of the dedicated tools like a jump ringer and it’s
cutting jig anyway.
Hope that helps
Peter