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Dave Martindale

writes:

Because the metal chuck at the end is not insulated from the motor.

That's a guy who never had a Dremel apart. They have a plastic sleeve
between the chuck and motor that is the load limiting device. They do
strip out or twist in two if you overload the Dremel. Since the chuck
bearings are set in the plastic case it is isolated.

This seems to depend on the age of the Dremel. I have one that's
probably 20 years old (sold as Sears Craftsman, but identical to the
Dremel-labelled ones of the time) which is as you describe. The motor
armature is carried by two bearings, while the output shaft has its own
two bearings, and the shafts are coupled by a plastic splined piece.

The trouble with this construction is that the output shaft has lousy
stiffness against any side loads because it's carried by two bearings
only a half inch apart, and both bearings are clamped (somewhat loosely)
in a plastic housing. It means this particular Dremel chatters like mad
if you try to use it as a router or with a side-cutting milling cutter.
It's only usable for drilling, buffing, etc.

I have more recent Dremels where the output shaft goes all the way
through the motor, there are only two bearings supporting it, and they
are 3 or 4 inches apart. This design is much stiffer against side
loads. I don't know exactly how Dremel continues to make it
double-insulated without the double shaft design; perhaps there's an
insulating sleeve between the shaft and the armature iron. But Dremel
has changed the mechanical design to eliminate the stub output shaft.

Dave