[3axisrookie]

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.

[LeeWay]

I would say that would be good practice for anything without soft start.
If the machine is small enough, it could be turned by hand too.
Sometimes when chucking up tiny drill bits, they get off center and i can't really tell till is spins. Every now and then I chuck up some brass rod in a 3 jaw chuck and it catches some instead of centering. I am thankful for soft start then.
When I swap blades on my tablesaw, this is how I turn it on the first time. Just bump it on them back off.
I've had my share of brand new blades that were warped. Even name brand blades. They do a number on a nice zero clearance throat plate.

I would say the old timer was basically right in this case.
Your switch contacts may have arced and your switch might be toast though.

[Geof]

.....Your switch contacts may have arced and your switch might be toast though.

No it is not good practice and the quote above explains why.

When you turn on a big motor it draws a current many, many times the maximum current draw under full load. As an example I had a Herbert #8 Turret Lathe that had a full load current of 40 amps and a starting surge in excess of 280 amps.

Most times the switch that turns the machine on and off will be rated to interrupt the circuit at full load amps; when you turn the motor on and off before it gets up to speed you may be severely overloading the switch by turning off the starting current surge. The large current can cause arcing and literally burn the contacts off the switch. Or worse, weld everything together and make it impossible to open the circuit or arc between adjacent contacts and blow a fuse.

What the old time machinist should have told you to do is spin the chuck by hand; the reason for the advice is to check that the gears are all correctly engaged. If they are not when you start the machine they can fail to drop into engagement and the dogs or teeth get rounded off, or they drop into engagement when the motor is at speed and the shock can b reak something.

Turning by hand lets things drop into engagement gently.

[3axisrookie]

Thanks for the replys. Was just a fuse luckily.

[LeeWay]

That is good. I just reread my response. I did kinda hit both sides of the fence on that, didn't I. :idea:

I guess it's not real good practice to do it all the time, but if you are swapping stuff out and can't turn things by hand, then I would take the chance and bump it anyway. You may loose a switch or fuse, but Might be safer if things aren't just right.

I just remembered doing bandsaw blades on my metal cutter. I bump that switch after every blade change. Kinda hard to turn by hand because of the gearbox.