Beginner. do not understand when do we have to use CW rotation and
CCW rotation? for grinding silver shank ring for exemple. is it
just a question of dust direction?
Mostly, yes. You can control whether the dust and dirt flies towards
your face or towards your bench. But you also have some control when
using things like polishing brushes, where the direction of rotation
can give you better access to some shapes, and give you better
ability to reduce things like drag lines.
However, I wouldn’t recommend spending lots more money on a machine
that offers both directions. Cutters, rotary files, burs, drills,
etc, all need to turn in the one “standard direction”, which is
counter clockwise as you look at the end of the rotating bur. The
other direction is useless for these very commonly used tools. And
with the abrasive tools that can go in either direction, the
advantage of being able to reverse direction is probably over
emphasized by tool dealers. I have never needed it on my flex shaft
machines (which don’t have that option), and never really use it or
find it essential or useful on my micromotor handpiece (which does
offer that option). As I said, there are some things reversing the
direction can be useful for, but it’s a very minor advantage at best.