What exactly does that dimension refer to? If #12 is used for
1.2mm thickness edge, that's pretty darned big. Yeah, my cheap side
is showing I don't want to buy the whole bunch of them.
Personally, I’d say it’s safer to just consider the numbers as
arbitrary size labels, not relating to a given and useful
measurement. Among other things, sizing of the tools from one to
another, or one shipment to another, isn’t all that consistent. And
the thickness of the edge you’d use a millegrain tool on depends some
on how you want it to look. On some pieces, the long line that goes
down each side of a line of grains when the tool is narrower than
the edge, or the edge not a sharp enough ridge, can be a detail some
people like, since it defines the line of the millegrain more. On
other pieces, that line is mostly a scar, a toolmark to be avoided.
The sizes you’ll need depend on the work you do. In the pieces I
make for my employer, most everything is done with #8 millegrains. A
few with a 6, and some with a larger 12. The 12 is hard to use on
harder metals when hand driven. Even driven with a power handpiece it
can take several passes to get a decently full impression instead of
just the train track crosshatch markings…
By the way, if you do get in the habit of driving millegrain tools
around with a power handpiece (Lindsay or GRS), you’ll find the
little axle pins on which the tool wheels spin are pretty soft steel
that doesn’t last long. They bend, shear, and otherwise quickly fail
when driven by an impact handpiece. If you have a laser welder
though, you can easily fix them. I do this with new tools, just so I
don’t have to do it later. lightly sand the sides of the tip, taking
down the rivited over ends of the pins until you can drive the pins
out. Replace it with a suitable length of the shank of a high speed
drill bit. I think it’s the #76 bit that’s the right size, but I
could be wrong, so check that measurement. Since the drill bit is way
too hard to rivet over, you use the laser to weld the ends of the
drill bit back to the side holes of the millgrain tool. With that
hardened axle pin, the tools will wear out as they’re supposed to,
ie the impression wheel will get worn and dinged, rather than the
axle pins shearing off. You probably don’t need to do this for
millegrain tools used the normal way, ie by hand, and for smaller
sized tools, that works better anyway. But the power handpieces do
make it very easy to steer the tools around tight curves consistantly
if needed, and they help getting a fully formed impression if you’re
working with both a larger size tool and a hard metal, like some of
the white golds.
Peter