strobe lighting

Well when strobing something to freeze its motion for inspection, you can alter the strobe frequency up and down very slightly and get the object appearing to be going from a/clockwise, through b/stationary, to c/anticlockwise as the beat frequency between the rotation and the flashes changes and also the phase. If the speed in fact stayed the same having changed the chuck you should still get the same steady state of either a/ or b/ or c/ . I suspect that you saw the last bit of acceleration to full speed. Another possibility is that the fluorescent lamp is using an internal oscillator to generate the striking voltage, rather than mains, and that oscillator frequency was changing as it warmed up and hence the flash frequency was changing.

AWEM

I have seen posts saying it`s not a problem,but I well remember back in the sixties when I served my time it was common for the chucks to appear as though they were not turning due to the effects of the lights. I saw it on a machine recently and the lighting in our works is all metal hallide low bays at about twenty feet up.So yes it can happen. Mark.

it backwards, it was then less

Tim was one chuck heaver then the other some the motor was marginally faster/slower giving this effect when you changed over?

Generally all ac motors have some degree of slip to work.

Cheers

Adrian

Both were 6" chucks, very little difference in weight. Andrew may have something with his suggestion that the AC was 'locally generated' rather than mains. The sequence of events was that I'd been doing bits of the same job over several evenings without noticing a problem - actually with a Pratt 'Concentric' chuck with soft jaws. Then this morning I was making a special gear puller for a one-off job, had to put a centring 'pip' on an M16 set bolt. The soft jaw chuck wouldn't grip the bolt, so I swapped to a normal 6" 3-jaw, that was when I noticed the effect and was genuinely concerned whether the chuck was running the right way. A bit of uncertainty crept in because I used to have a TOS lathe with a similar apron control lever, which worked in the opposite direction. It might have been something to do with the lighting unit starting from cold, *if* it isn't running from mains frequency. I'll try to have a play with it at the weekend, to satisfy my curiosity. I'll report back if there's anything worth reporting!

Tim

Fortunately never had that happen to me, although every time I use the rotary table the room keeps spinning after the table as stopped.

Peter

Yes, but you're not supposed to stand on the bloody thing! --

Chris Edwards (in deepest Dorset) "....there *must* be an easier way!"

I get that effect after a few beers !

AWEM

Better stop using the 70% coolant Peter.:-)