Generally, the reasons drill bits, reamers, burrs & other rotary
tools break when using them, is movement between the tool & the work
piece. Most tools can stand all the twisting (torque) motion applied
by the power source. It’s the lateral bending motion they can’t
The same lateral motion can cause the work piece to break if it’s
weaker than the tool.
The secret to preventing (or at least reducing to a minimum) the
lateral motion is, not hand holding either the work or the tool. The
tool providing the power, Dremel, flexshaft or some other device
should be held as solidly as possible (in a device similar to a drill
press). The work piece should be held in a vise or clamp that prevents
it from moving laterally, relative to the cutting tool. Depending on
the size of the work piece, hole size & depth & the strength of your
fingers, hand holding may be adequate.
There are accessory drill press type tools that a Dremel or flexshaft
handpiece can be attached to. These usually have a table that allows
the positioning & clamping of a work piece. If you’ve got lots of
pieces to drill, it might be less expensive in the long run to get a
small drill press. The accessory tools for the Dremel & flexshaft
handpieces may not provide the necessary degree of rigidity required.