Servo vs 3 phase for mill spindle?

[Karl_T]

My two cents. Don't get into creeping elegance here. Set that reeves drive at one speed, about 3/4 way to fastest, and use the VFD for speed control. I have ran two mills this way for decades.

 

[mattthemuppet2]

Don't forget that the counterweight and head servo are designed for that particular motor weight and balance. Not sure how important any changes to that would be, but it's something to think about especially if there advantages aren't all that large.

On a related note though. i remember seeing one of the youtube machinists make a step pulley direct drive system for their RF45 clone (or similar). It was really slick in that it had two pulleys (1:2 and 2:1 or something like that) and two belts, both always on the pulley. The neat trick was that only one belt was tensioned and transmitting power at any one time. It had a funky air or hydraulic plunger set up that would engage/ tension one belt and disengage the other and vice versa. I thought that was dead neat.

 

[coolidge]

Don't forget that the counterweight and head servo are designed for that particular motor weight and balance. Not sure how important any changes to that would be, but it's something to think about especially if there advantages aren't all that large

I think I'm covered there, the cast iron counterweight is enormous and the Z servo motor is 2hp. I was stunned that I was able to turn the Z screw pulley by hand and move the head up/down. Just one hand, with light effort. It's exceptionally well balanced. I guess the whopper 2hp servo motor is more for forcing the head down into the workpiece than lifting the head.

 

[coolidge]

My two cents. Don't get into creeping elegance here. Set that reeves drive at one speed, about 3/4 way to fastest, and use the VFD for speed control. I have ran two mills this way for decades.

VFD control must happen since I don't have 3 phase power so that's a given. I'm am recoiling a bit on a whole conversion idea, ripping out the Reeves, engineering a direct drive belt etc.

 

[mksj]

With the size of the variable pulleys, you will most likely not want to use them at high speeds, this also holds true of gear trains, not a good idea to run them at 2 or 3 times their designed maximum speed. The motor end is simple replacement, the spindle end it depends on the what you have. Option up front is to keep everything stock if you want to start out, but for CNC at higher speeds I would move on to other options. My mill came with a factory digital head with a vector motor which runs from 20-200 Hz single pulley drive with back gear.

 

[coolidge]

With the size of the variable pulleys, you will most likely not want to use them at high speeds, this also holds true of gear trains, not a good idea to run them at 2 or 3 times their designed maximum speed. The motor end is simple replacement, the spindle end it depends on the what you have. Option up front is to keep everything stock if you want to start out, but for CNC at higher speeds I would move on to other options. My mill came with a factory digital head with a vector motor which runs from 20-200 Hz single pulley drive with back gear.

Understood. This mill did come in a direct drive version, pretty much everything is the same in the head other than they removed the Reeves stuff. Bull gear and the rest is the same.

 

[coolidge]

Final decision - I'm retaining the VS belt drive and adding a VFD with a target max spindle rpm of 5,000.

Studying the direct drive inverter version in the machine manual, with it's shorter spindle and shorter head housing, the conversion would be a hack job. As would ripping out the rest of the VS belt drive controls and bits. My goal isn't to end up with a hack job mill that just won't float my boat.

Besides this is a big heavy hog heavy cuts machine not a speed demon when it comes to X/Y speeds and rapids. Not slinging that kind of weight back and forth. The Y saddle is (yeah the saddle) is 49 nine inches wide and 8-9 inches thick, good lord! The table is a 17x60 inch slab of cast iron. So while in theory a direct drive conversion might hit 6,000 - 7,000 rpm spindle speeds, the rest of the mill isn't a fit for high speed machining.