key in chuck safety device

[Frank S]

I see nothing wrong with your idea of disconnecting the power when the key is removed from its holder. I would have an issue with the idea that the spindle appears top be on lock down when the key is removed. I find it best to rotate the chuck when tightening stock in a 3 jaw to check concentricy with a dial indicator. this is a must when using a 4 jaw
The first thing I would have to do if any lathe of mine had an electro magnetic brake on it would be to install a foot switch which releases the brake but does not allow for motor start up That way the the spindle could be rotated with the key out of the holder but the motor could not be started