general VFD thread

[jetflatline]

Digging around, I find various places where VFD are mentioned but no clearinghouse/catchall thread, so I thought I'd start one.

[jetflatline]

I have my mill apart for a CNC retrofit and I figure, why not put on VFD while I'm at it?

It looks deceptively simple, so I might be missing the obvious. :-)

Here's one page I'm using as a guideline:
VFD Control Box

And I'm looking at using the GS2:

<http://www.automationdirect.com/adc/Overview/Catalog/Drives/GS2_%28115_-z-_230_-z-_460_-z-_575_VAC_V-z-Hz_Control%29>

My current questions:

- does the GS2 really replace a phase converter?

- should I go direct drive between the motor and the spindle or should I keep my gears and just lock it into the lowest ratio?

[saabman]

Many VFD are phase converters, but not all. You should select your motor besides deciding your spindle issues. A VFD may have a frequency range that extends from 5-120 hz. From a practical standpoint, your motor will lose torque at higher frequencies, so you should not expect to run at 120 hz, perhaps 90 hz is a better target. So if your motor turns at 3200 at 60 hz, it will turn at 4800 at 90 hz. You will want HI 2 or 3 rather than low (at least for working in Aluminum). Of course in lower gears at low RPM a 3 HP 3 phase motor is a beast.

[UUU]

Keep the gears. On my mill I've got a fixed ratio that gives me a top speed, at 90Hz, of 4900. That's probably the limit of the bearings in the spindle. So at 9Hz I'm at 490, but that's not slow enough to run a face mill in some materials, I'll not get much torque, and the motor cooling is fairly non-existant. So if I had a geared head, I'd be better off.

[jetflatline]

Ah, good point. I was thinking about how to do engraving without major modifications, if I keep the gears (and get better bearings) I could probably manage 10-20K RPM just by changing gears.

[UUU]

I was thinking of engraving, too - but plan to have a supplementary spindle to attach to the side of the head, either with its own motor, or belt driven from an adapted toolholder in the main drive.

VFD is definitely the way to go.

[jetflatline]

The secondary/supplemental spindle was what I had originally been thinking. There are several things, from engravers to grinders to polishers, that I've thought would be useful to have attached to the mill. My plan had been to make R8 adapters, leave the motor at zero, and manually turn the accessories on and off.

[saabman]

This company

2L Inc

Claims the combination of spindle speed and table speed makes it practical to engrave using the mills spindle and their spring loaded holders.

[UUU]

Back to the VFD, rather than the spindle: How are you planning to control the VFD from your computer?

[jetflatline]

Probably PWM. It seems to be pretty standard on the software side and I'm used to using/debugging it on microcontrolers. The CNC kit from IH includes a Mach3 license, it supports PWM control as does EMC2. I've been dealing with *nix and Windows on PCs long enough that I'm probably just going to use EMC2 unless Mach3 is ponies and Rainbows enough for me to put up with Windows.

Edit: Or were you asking about the actual VFD controller? I'm looking at something like the Automation Direct GS2. I've seen various mentions of TECO/Westinghouse controllers, but I haven't looked into them yet.

[skullworks]

Ah, good point. I was thinking about how to do engraving without major modifications, if I keep the gears (and get better bearings) I could probably manage 10-20K RPM just by changing gears.

This IS an IH mill your talking about - Only balanced from the Chi factory for 1600 rpm....

Anything over about 6000rpm is an exercise in Darwin survival. You want to run a high speed spindle, fine, build yourself a nice strap on piggyback unit that has a diegrinder motor with 1/4 and 1/8 collets and your all set.

[jetflatline]

This IS an IH mill your talking about - Only balanced from the Chi factory for 1600 rpm....

Interesting, I hadn't considered balance issues. I've built a few engines and dealt with crankshaft/flywheel balance -- would it be worth my time to balance the shaft/gears in the head for 2k-6k performance on metal and plastic?