I use snap-on, sanding discs with my flex shaft and frequently
break the sand paper part off leaving the center brass disc behind.
Is there a "trick" to get those brass discs off the mandrel? (I
currently use a pliers)
I find the jaws of an old side cutter get under the brass a bit
easier than pliers. But the pliers are quicker if you first have to
rotate the stuck brass part to align with the square part of the
mandrel before you get it off. Other than that, one other trick is to
switch to the plastic backed disks, or adalox, if you're using
wet/dry. The adalox is thicker and lasts longer than the wet/dry, and
the plastic versions (made with the 3M high tech sanding films),
simply don't break off. They'll get dull, but won't break away from
the center. Only downside to em, aside from higher price, is that
they're tough, so harder to trim to a true concentric outer edge if
you're in the habit of doing that...