Q: I borrowed a drill to bore holes into wooden beams. The bit broke on a hidden piece of metal embedded in the wood. Am I liable for the bit?

A: A person who borrows an item is liable for it even if it was damaged through uncontrollable circumstances.

Nonetheless, if it was damaged through routine use, the borrower is exempt. This is called “meisah machmas melachah” — died on account of use. The rationale is that the item was not borrowed to sit idle; it was borrowed to be used (B.M. 96b; C.M. 340:1).

Some extend this exemption to include any uncontrollable damage that occurred during the course of routine use (C.M. 340:3; Sm”a 340:8). Others, however, limit it to cases where the item malfunctioned, in which case the lender is considered partly at fault for lending an item unfit for the task (Shach 340:5-6).

Thus, you are legally exempt for the bit, based on the first opinion. [If you gave a deposit, though, you would not be entitled to a refund, based on the second opinion.]

Of course, this exemption applies only if you used the drill as planned, but not if you misused it to drill into metal or concrete.