Single Phase Pulse

My bigger import lathe is not bad. I can dial stuff in by hand to about

3 tenths. The problem is under power the indicator needle turns into a blur about 1.5-2 thousandths wide. For 99% of what I do that is fine, but that other 1% is growing. Is the only answer to install a 3 phase motor? I'm not completely against it, but its a bit of a job to move the lathe, swap the motor, and reconfigure the controls. Not something I can do in an afternoon.

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Can you disconnect the motor from the drive train? If you can, and the needle still vibrates, the motor may be unbalanced.

Been busy at the computer on design work, but my next thought was to try a "coast" test first. Spin it up to speed, and then shut it off to see if the vibration persists when costing. If it vibrates when coasting then "something" is out of balance. If it doesn't its probably single phase motor pulse.

I was surprised to find Surplus center sells a 3HP 3 phase 4 pole motor pretty reasonably. Its a Marathon, but it is rated as continuous duty. Now whether or not that would drop onto the current mount I don't know... Some of those imports seem to have odd ball motor frames. I can certainly make anything I need, but I am not sure I want to spend several days int he shop without my big lathe. I hate doing anything but the simplest light work on the smaller lathes anymore.

Put a big torsional ramper - or even just a flywheel on the motor or the primary drive

I rigged up a 4 cycle engine to a motor as a fake generator, with no extra flywheel. The 15Hz flicker was real visible, even with incandescent bulbs. Sort of surprised me, but it makes sense with engine speed of about 1800RPM.

Are sure the problem is the motor and not the gears driving the spindle? Paul

Are sure the problem is the motor and not the gears driving the spindle? Paul

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The motor may be the easiest potential cause to confirm or eliminate.

I'm not 100% sure of anything anymore. I may just not have dialed it in as close as I thought. Just for the heck of it I turned a piece of medium hard pin stock and slapped an indicator on it as cut and only got a couple tenths runout with the motor turning the chuck at 300 RPM. Now I am thinking I must have shifted the chuck at some point when I was adjusting the set tru part. Either that or there was a bad spot on the first dowel I used that was making the indicator jump when running.

Either way I'll have to loosen it up and reset it when I need to do a job that has to be flipped in the middle.

Anyway, a motor swap is probably not needed at this point.

Good to know. Good luck. Paul