Converting Grizzly G0709 lathe to 3-phase

[marrtw]

I have a grizzly G0709 gunsmith lathe. Unfortunately, it has one of those cheapo "growling" motors. Here's what it sounds like from a video posted on YouTube (not mine): https://www.youtube.com/watch?x-yt-...yt-cl=85114404&feature=player_detailpage#t=35.

I'm considering replacing this motor with a three-phase motor and VFD. I added a VFD to my Bridgeport clone a couple years ago and it worked great. With the lathe however, I see lots of contactors and other wiring that complicates the install.

At a minimum, I'd like to use the apron lever for forward, stop and reverse, and the foot pedal for emergency stops. I assume the proper approach is to tear out all the contactors and start over with the wiring? Perhaps reusing the spindle switch (from the apron lever) and emergency stop switch from the foot pedal?

 

[JimDawson]

You have it correct. I would use one of the contactors as a control power contactor. That way if you hit the E-stop, or have a power fail the lathe won't restart until you push the power button. You will also want to require returning the apron handle to OFF before going to FOR or REV. Normally this can be programmed into the VFD.

 

[mksj]

If the lathe works well otherwise, you could just replace the motor with a Baldor or other quality single phase motor with little effort.

Going the VFD route, you could strip the high voltage leads (L1-L3 and T1-T3) from the motor contactors KM1/KM2 and use them (L1/T1) for the for/rev commands to the VFD. Depending on the command structure of the VFD for the JOG, you may need another contact block (NO) on the JOG switch to activate the VFD JOG (i.e. some need the JOG command and a direction command, so the forward contactor would close and the second JOG switch block would send the JOG command). You could also have the brake switch (or add a second NO switch block) to send commands directly to the VFD (free run for mechanical brake; or if the mechanical break is disconnected, then a fast deceleration). Lots of options, but in some cases it is easier to strip out most of the wiring/contactors and start with a fresh sheet. The second thread below outlines something similar to this.

Some other threads that might be worth reviewing for alternatives:
http://www.hobby-machinist.com/showthread.php/27108-PM-1236-motor-issue/page2
http://www.chaski.org/homemachinist/viewtopic.php?f=42&t=96363

 

[marrtw]

Thanks guys. I'm still studying the wiring diagram. I wasn't really familiar with contactors but they appear to be a very simple device, similar to a relay, that allow relativity low voltage control circuits for the motor.

BTW, I considered replacing the motor but the 100L frame is one of the few sizes that doesn't have a close NEMA substitute. All the 100L frame motors I find are 3 phase anyway.

 

[Dave Paine]

The 100L is a Chines frame specification. You need to replace with the same frame or else the motor pulley will not fit the shaft on the replacement motor. Shaft diameter is metric, same for the key.

As you mention, you can use the apron switch. Just disconnect the wires in the terminal cabinet and then connect to the relevant terminals in the VFD. Bigger gauge than needed, but will work since. Easier than running smaller gauge wires to the apron switch.

 

[JimDawson]

Thanks guys. I'm still studying the wiring diagram. I wasn't really familiar with contactors but they appear to be a very simple device, similar to a relay, that allow relativity low voltage control circuits for the motor.

BTW, I considered replacing the motor but the 100L frame is one of the few sizes that doesn't have a close NEMA substitute. All the 100L frame motors I find are 3 phase anyway.

You are absolutely correct. A contactor is a relay. A relay is normally called a contactor when it is switching a higher current load like a motor or heavy lighting power. If it is only switching the control power circuits or pilot devices (solenoid coil for instance), it is still a relay. The same device could be a contactor or a relay depending on the end use. Confusing terms like this is why electricians have to serve a 4 year apprenticeship.)

 

[RWL]

I don't know the history of these motors on that particular machine, so if what I say has already been tried by others, please disregard my suggestions. I'd take the motor off of the lathe and run it alone with its pulley on and see if it vibrates. If it does, take the pulley off and see if it vibrates as much. With the motor not running, push and pull on the shaft and see if there's any significant lateral play. If so, maybe simple bearing replacement might fix the problem. If the motor is much quieter without the pulley, it's possible that the pulley is bored off center and reboring that would quiet the motor down.