Some old school machinist taught me this about 6 months ago, and have been doing this since then, without an issue. Until today. Not positive though it was my fault.

Was setting up a job on an old warner swasey lathe. Whenever I change the chuck, collet, gears, etc I always turn it on and off immediately. I was changing gears on a bridgeport one day in class and when I turned it on, the gears started to grind. I froze up for a second and stalled turning it off. The old machinist (which was a friend of the instructor that came to hang out) came up to me and told me it's a good idea to turn it on then off immediately after messing around with gears because if you did make a mistake, the machine will already be off before your brain realized something is wrong.

Sounded like a great idea because of all the stuff it can prevent, so that's what I have been doing. Have been working on this lathe all week and everything was fine. But when I did it today, went on, then off. Turned it on right away since everything was fine and didn't seem to have the speed it usually does, so I shut it off. Couldn't get it back on.

The maintenance guy had no idea what was wrong. There were only about 30 minutes left before it was time to go home, so have to wait until monday.

So what does anyone think? Bad thing to do? Don't know much about electronics, but when I think of what is actually going on, probably not such a good idea to turn something on, then off, then right back on. But then again, a fuse should protect it I would think.

Thanks.