Chuck rules are the day #1 instruction item for a reason. I&#x27;ve seen that one replay many times over only a couple of years but always with inexperienced machinists. The older ones all have their ritual before engaging the &#x27;on&#x27; switch of the spindle drive, which usually includes a nice 360 on the main spindle by hand to make sure it all runs free.<p>While it is definitely true that making dangerous mistakes is not limited to CNC machines GP has a point, with CNC machines the potential for accidents is quite a bit larger because of the much longer time the machine will spend with the workpiece during which even a trivial change in setup will cause serious damage to workpiece, machine, operator and the environment. And because a proper trial run will take as much time as making the workpiece and people get overconfident accidents are all too common, especially when you put a bunch of inexperienced machinists and very high power tools in the same space.<p>It&#x27;s a pretty harsh way to learn that servo motors don&#x27;t actually care about you at all.