[borne2fly]

The mill is expecting 220V 3-phase power, but all I have is residential 220V. I was told that as long as I was willing to accept a little less power from the spindle motor, that I could connect the center phase of the mill to one of the adjacent phases and run the whole thing directly from the dryer outlet. This would avoid having to buy a rather expensive phase converter. Anyone else ever heard of "fooling" a 3-phase motor like this?

[Al_The_Man]

Won't work unless the Spindle drive takes 1 phase in.
If this is a 3 phase motor that connects across the line then it will not work.
You either need a phase converter or a VFD.
The rest of the controller and system is most likely 1 phase anyway, so normally it is only the spindle motor that you need to worry about.
Al.

[borne2fly]

Al,
That sounds right. If it was as easy as just plugging in to the dryer outlet then no one would be selling phase converters
I thought about a VFD but discovered VFD's like steady, smooth loads like spindle motors. They don't like things like servos that stop, start, reverse all the time. Steady load = good. Heavy transient load = bad.
I ended up ordering a 7.5hp RPC today. With a 3hp spindle motor and servos on three axes, hopefully 7.5hp RPC will do the trick. My understanding of 2.5d machines like this is that the z-axis servo is not normally moving if the xy servos are, so little chance of having all three servos and the spindle all drawing full power simultaneously.

[Al_The_Man]

This is why I mentioned checking for the usual set up that the controller and servo's both may be on 1 phase fed inside the enclosure, if the only 3 phase item is the spindle motor, then that is all you need the VFD for, the rest can be fed from 240v (or120v) 1 phase.
Al.

[borne2fly]

Yes, that's how it's set up ...... 3phase directly to the spindle only, then 3phase through a transformer to generate simple 110. Indeed I could use a VFD on the spindle (I do this on a manual Bridgeport and it works great) if I were willing to hack into the electronics and feed the 110V stuff with a seperate line (and if I did that, I would have to decide whether to use the 220V ground or the 110V ground, ..... not sure I'd want to connect them together). For now I'm reluctant to hack it so I'm biting the bullet and getting the RPC. Once I see it working as it should I might poke around inside with a voltmeter and see what's what, then consider seperating the supplies in the future to free up the RPC for other equipment. As I understand, the VFD is more efficient than a RPC, is that right?

[Al_The_Man]

I would have to decide whether to use the 220V ground or the 110V ground, ..... not sure I'd want to connect them together). For now I'm reluctant to hack it so I'm biting the bullet and getting the RPC. Once I see it working as it should I might poke around inside with a voltmeter and see what's what, then consider seperating the supplies in the future to free up the RPC for other equipment. As I understand, the VFD is more efficient than a RPC, is that right?

If you are talking about your residential service then the 120v neutral and ground are the same for the 240v?
If your enclosure has 120v via a local transformer then it is most likely bonded to your res. gnd or at least it can be without any problem.
If requiring 3 phase for just the spindle motor then I would pick a VFD anytime.
Al.

[borne2fly]

"If you are talking about your residential service then the 120v neutral and ground are the same for the 240v?"

I would expect so. However, it's always a good idea to use one single point as ground to avoid any potential ground loops. You'd be amazed how even a short ground-loop circuit can ruin your whole day

[Al_The_Man]

However, it's always a good idea to use one single point as ground to avoid any potential ground loops.

Agreed.
Any machine enclosure should have a central ground point where the service ground is taken to, and also all machine bonding conductors as well as any local control neutral's that may be set up from 120v isolation transformers etc.
Al.

[Ed_R]

I'm going to have a Phase-o-matic CNC PAK R-15 wired in next week, to hook up a Leadwell V-25. Glad I'm letting an electrician do it- I'm confused!

[borne2fly]

Ed, that's not a bad idea. The first time I fiddled with phase converters it was a rotary converter I got from someone on Craigslist. He demo'd it for me, and it ran without making any funny noises, so I bought it.
Got it home and plugged it into the lathe and everything ran like it should. But something in the back of my head said "never touch a newly wired machine until you verify that the frame voltage is truly at ground". So I measured the AC voltage between the lathe and the base of a mill that I knew was wired correctly, and got 220V! Apparently the phase converter output plug had been replaced and wired incorrectly. Caveat emptor, as they say!

[Ed_R]

I'll let the guy who does it for a living do it for me. Heck I'll even pay him. That's what he does for a living after all, and I support the guy who works for a living, because they support me.

[MBG]

Get yourself a phase perfect pt-330 will run you about $2800 but it will get you a three near perfect sinusoidal waves.