VFD install on Mori MR2000 Lathe

We just went through replacing the gearbox input shaft spline and hub due to the hammering that the input shaft takes every time we start / stop this lathe. It really bugs me to hear all the gears slam when you flip the lever into Forward or Reverse . . . no clutch = slam-bam on the entire geartrain every time. Stomping on the brake essentially does the same thing.

Next step is to put a VFD on the lathe. The lathe really only has 3 switches on it related to the spindle.

Forward - obviously closes with the lever in forward
Reverse - closes with the lever in reverse
Brake - drops out spindle motor starter coil power when the brake pedal is pressed.

I decided that I want the drive to Dynamically Brake the spindle to a stop whenever the FWD/REV lever is put into Neutral or when the operator wants to do a direct reversal. But that if someone steps on the brake pedal, just disable the drive and let the brake do its thing.

I came up with the following simple control schematic to make this happen. I could have done this with fewer relays, but this allows quick / easy trouble shooting in the event a switch goes bad.

I have a 24VDC power supply already in the control cabinet - so I'll run IDEC Ice Cube Relays with LED indication. (Similar to these)



I'll use 2 pole relays and FWD, REV, ENA dry contacts will go directly to the drive. I'll eventually put a speed pot on it as well and likely a rate counter on the spindle shaft to read RPM directly and put the display up near the DRO. Updates as I get it installed and working.

This is a perfect case-history for someone who's looking to further their understanding of the advantages a VFD offers on a machine that already has rapid stop/reverse features...

Well - the VFD is installed and set up. A few photos of the installation.





We used an old decommissioned Control Techniques UniDrive and a few odds and ends from our surplus shelves. No purchased parts so far.

The FWD / REV lever allows starting / stopping the lathe as well as direct reversal - all using the Dynamic Braking capability of the drive for nice snappy response. The DB Resistors shown are too small, we are going to go ahead and buy the correct resistor as it takes too long to slow down now.

Pressing the brake pedal causes the drive to go to inhibit and the operator can use the disk brake as normal.



As noted in the first post - we used 5 relays so make troubleshooting easy - all relays have LEDs so you can tell when they have power or not. They switch the FWD and REV inputs on the drive as well as the ENABLE line.



The 24VDC power supply on the left powers up the DRO and the large contactor is for the coolant pump. The control power transformer in the upper left makes 120V from the 480 feed and this is used for all the relay coils and DC power supply.




Lastly - we put the drive heat sink outside the enclosure to reject heat into the open air. Keeps the box cooler even if the fan noise is a little annoying.

Should have the proper resistor in next week and I'll shoot a video of the lathe spinning up and direct reversing.

Top-notch build! Very pretty, well done.

Followed to here from another post- where’s the video??!


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