As a retired machinist, I can tell you some of the reasons for broken drill bits. 1 - Bit has to be sharp. 2- Alignment of bit to hole has to be absolutely maintained. Bits have to be hard to cut, and that makes them brittle. If the operator leans the drill a little to the side,result is almost certainly a broken bit because it cannot bend. Try bending a piece of peanut brittle. 3- Excessive RPM. This generates heat, causing trouble with the chips having enough time to ride the drill flutes up and out of the hole, resulting in a bind and broken drill. It also causes the drill to lose temper and go dull. 4- Use a lubricant. Minimizing friction minimizes heat and helps with chip flow and helps eliminate bind. 5- Feed rate, ( drilling pressure). The harder you push, the larger the chip size. Larger chips are more likely to have interference problems exiting a hole. Too little pressure causes the bit to rub rather than cut properly, resulting in a dull, then broken bit. In my career of building industrial tooling, I had to drill many small diameter holes in tool steel. This can be done successfully by following the tips shown above, plus drill with a pecking action. I have drilled many of these holes with such a small diameter, that I would let the drill turn a few revolutions, then pull it completely out of the hole, blow bit clean, blow out hole, re apply oil to bit, repeat. If it takes a half hour to drill a hole, that’s much less time than will be required to get a small broken bit out of the hole DO NOT GET IN A HURRY WHEN DRIlLING.