PM935TV Motor Reversing Question

[bretthl]

Not sure if what I am experiencing is a problem or just inherent to this machine. The motor will not change direction until the spindle has come to a near complete stop. Probably not a good idea to change motor direction instantly at high speeds but this is a problem power tapping in back gear. I literally have to let the machine coast to a near dead stop before reversing out the tap. If I don't the spindle continues turning clockwise and I buy a new tap. Is there an adjustment I need to make to the machine?

 

[MikeWi]

No adjustment, you just need to let it come to a stop first. Or get a tapping head.

 

[mksj]

It is an inherent problem with single phase motors, not the mill. Also makes it dangerous with single phase motors on lathes. It is not an issue with 3 phase motors.

 

[pontiac428]

The tapping head is cool because it does not require a direction change. There's also the clutched Bilz tap adapters that use belleville washers where you can set an adjustable clutch point. The Bilz can be fiddly to set up the tension on, but they are a lot cheaper than a reversing tap head. These you power in until the clutch trips, then you stop the mill and reverse them out. No more broken taps (in theory anyway).

 

[bretthl]

It is an inherent problem with single phase motors, not the mill. Also makes it dangerous with single phase motors on lathes. It is not an issue with 3 phase motors.

Mark,

The motor on the mill is two phase (220 VAC). When my 1340GT lathe was 220 VAC two phase, it would reverse on dime. In other words it would not continue running forward after switching to reverse.

 

[ddickey]

Split phase which is one phase split. Are you using a VFD? Or is your motor single or 220 split phase? A single phase will keep running in the direction it was going when it was switched. I suppose if you were just creeping it probably would switch rotation.

 

[epanzella]

This is how I solved the power tapping problem on the cheap. I got a tap wrench that had a socket on top for 3/8 drive. I milled a piece of 1/2 shaft at one end for 3/8 drive. When power tapping and I get to the end of the thread I just pull back the spindle and the drive instantly disengages as the 3/8
drive connection is severed. Let the motor stop, re-engage the 3/8 drive and hit reverse

.

 

[bretthl]

Split phase which is one phase split. Are you using a VFD? Or is your motor single or 220 split phase? A single phase will keep running in the direction it was going when it was switched. I suppose if you were just creeping it probably would switch rotation.

220V split. No VFD. The machine has a forward and reverse function on the switch. The motor runs at constant speed. In low gear motor will not reverse until the spindle comes to near dead stop. In high gear the motor will reverse with the spindle turning at near full speed. Obviously reversing quickly in high gear is not much use, but tapping in low where the spindle takes longer to come to stop it would be helpful to get going the other way ASAP.

 

[mksj]

As mentioned split phase is single phase, just that neutral is at the midpoint of the 220V wave. . There is a lot more rotating momentum in low gear that keeps the motor spinning in the same direction and for longer. I often hear that the same problem can happen with lathes and cause some serious damage. Single phase motors reverse by reverse the polarity of the starting coil, so I am assuming that if the motor is traveling at too high an RPM the centrifugal switch prevents the starter coil engaging and the motor would continue in the same direction.

Reversing single phase induction motors

woodgears.ca

 

[bretthl]

As mentioned split phase is single phase, just that neutral is at the midpoint of the 220V wave. . There is a lot more rotating momentum in low gear that keeps the motor spinning in the same direction and for longer. I often hear that the same problem can happen with lathes and cause some serious damage. Single phase motors reverse by reverse the polarity of the starting coil, so I am assuming that if the motor is traveling at too high an RPM the centrifugal switch prevents the starter coil engaging and the motor would continue in the same direction.

Reversing single phase induction motors

woodgears.ca

That makes sense. I was hoping for a fix but alas ...