Servo VFD direct drive conversion.

[akjeff]

With the mechanical side of the install complete, it's time to play sparky and hook up the power/controls. The model I chose, requires a 3P/240V supply. You can also order it in a 3hp 1P/240V if you don't have 3P power in your shop. Since I have a 3P load center fed with a 10hp Phase Perfect, I went with the 5hp/3P option in the hopes of preserving more low RPM power in the Hi/direct drive range.

So, I piped in a 3P/240V/30A circuit to a twist lock outlet behind the mill, and used 10 AWG SO cord to go from the outlet to the input of the Servo main box; the heart of which is a good old tried and true Hitachi WJ200 VFD. That's about all there is to it on the electrical side, as the unit comes with the control wiring already done, and run in flexible non metallic tubing between the main box and the control box, and another to feed the 3P power to the peckerhead.

I mounted the main box on the left side of the mill column, as it was the most convenient/accessible location for me. I don't use flood coolant, so there's no risk of liquid getting in it, and while it's not a sealed box, it's tight enough that chips/swarf won't be an issue. If you commonly tilt/knod the head of your mill, you'll want to carefully choose where you mount the box, and you may find that you'll need to extend the control and power leads. Same if you run your mill wet.

 

[akjeff]

The Servo provided/prewired hoses have fittings on the ends, and the motor power simply threads into the tapped hole in the peckerhead, and wired per the motor data plate.

Next is a feature that I really like. It's a magnetic contact that's attached to the Hi/Lo selection handle. It then signals the VFD when you go to Lo/Back Gear and it automatically reverses the motor rotation. With this, Forward and Reverse are always Forward and Reverse whether you're in Hi or Lo. Very handy. I decided to use the old factory switch housing to act as a junction box for the quick connect pigtail for the magnetic switch. There was a tapped hole for the old electrical fitting. I modified a nipple to accept the Servo fitting. I parted off the collar of a seal-tite fitting and then tapped the inside 5/8"-18, which was the closest tap I had to whatever the servo fitting was. The plastic threads on the fitting deformed and tightened right up in the tapped hole. Then an existing screw hole out the side of the housing was enlarged to take a grommet for the pigtail.


The magnetic pickup with the pigtail gets attached to the fixed block that the handle pivots on, and the magnet gets attached to the handle block so that when in Lo/Back Gear it activates the switch. You'll have to fiddle around with positioning these so that they allow the lever to operate, but they are still close enough to each other to function. Do it with the system powered up, and you'll be able to hear the contact closure, and you'll see the decimal place move on the display. This makes positioning the contacts a simple matter. Servo supplies a two part glue to attach the mag switch, but I chose to just use 3M trim mounting tape instead. It worked just fine.

 

[akjeff]

Last thing was to mount the control box. I stacked it on top of the mount for the power drawbar. Had to make a slightly taller mounting plate for the drawbar control, and then space the VFD control mount with a pair of ferrules to make enough clearance. Then a couple of blank plates to cover the former switch box, and the old variable speed display.

On the initial run, there was a great deal of carrier frequency howl coming from the motor.( factory setting is 2kHz. ) So, I just started increasing the B083 parameter a kilohertz at a time, until it went away; which was at 10kHz.( you can increase it to a max of 15kHz. ) That was the only parameter I had to change. Otherwise it was a flawless plug and play install. Nice product Servo! The mill is now extremely quiet running, and really smooth! Very pleased with the new addition.