key in chuck safety device

[mklotz]

I've seen the equivalent setup used on drill presses. As Olderdan points out, it's the least infuriating solution.

The only problem with it is the fact that it's easily defeated. Simply shove a screwdriver or similar in there and the chuck key is free. Not a problem in a one man shop but in a multiuser setup it is a threat.

There are (overly complex) ways to avoid the screwdriver shortcut. For example, mount several switches to contact the wrench at body and tip. These switches would, in effect, read the shape of the wrench and only complete the circuit if all were operated. Defeating something like this would require turning an accurate facsimile of the real wrench and inserting it - something the average bodger isn't likely to do.

As I said, way too complex to be practical.