Electric motor on KBC mill

At an internet auction a few days ago I bought a KBC bench mill. The model is Grip-16.
The pictures neglected to show a view of the mill that is clearly
stamped "3 phase". I thought the motor was single phase because the auction listed it as "230v". Until today, apparently in error, I thought that 3 phase motors were 208V.
However, the KBC tools web site for this mill almost leads me to believe that the motor can be wired for single or 3 phase.
Will somebody help me out here? A motor is either single or 3 phase but can't be changed. Yes?
I already understand that a 3 phase machine can be operated from single phase with a phase converter. And I may have to go in that direction unless I can get a single phase replacement motor.
This mill was built in 1989. Since even when new it wasn't a high end precision machine would it be prudent to check the accuracy of the X Y table? As we get deeper into machining I'm sure I will join the quest for split hair precision. But for now, we just wanna play.
On Monday I will call KBC and look into my options. But meanwhile, any advice on how to logically approach the aftermath of a possibly illogical purchase will be appreciated.
Regards and thanks,
Vernon
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Buy a VFD to run the mill. Three phase works very well. Many VFDs can be driven from 220 volt single phase, with a derating.
Joe Gwinn
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Joseph,
I'm still trying to wrap my electrically challenged brain around the differences / advantages / disadvantages between rotary converters and VFDs. As soon as I'm able to articulate an intelligent question I'll ask one!
V
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A VFD is a big magic solid state box that delivers AC of from 10Hz to 100Hz. It USUALLY will be one able to deliver 3 phase power. [But there may well be smaller single phase ones, so cabbage emperor...]
How it does that.... Well think of it as an audio oscillator and a BIG amplifier for the speakers err motor.
Its major plus is the variable frequency means whatever motor it feeds will be variable speed. It's almost a waste to buy one just for a single speed task, but a friend did to drive an air compressor.
A rotary converter is a semi-kludgey way of getting 3 phase from a single speed source, at the line freq. [60 Hz]. Ditto the capacitor-based schemes. They may work well enough for your case. But neither one will deliver the large starting torque a true 3ph supply will offer.
Does this help?
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Hi David,
It does help. But I don't understand this part:
"They may work well enough for your case. But neither one will deliver the large starting torque a true 3ph supply will offer."
Are you saying that a VFD is "a true 3ph supply..."? Or are you saying that "nothing's as good as having 3 phase and not NEEDING a box"?
V
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A 3ph VFD will deliver real, balanced, 3-phase. The other two hacks do not; you may or may not be able to live with their limitations.
Utility 3phase has one major plus -- a LOT of starting capacity courtesy of the grid. Well, two -- the cost! But the minus is -- single speed.
I've not taken one apart, but I assume a VFD is really a switcher supply [thread tie-in!] within. In short, it takes single phase 240VAC, makes DC, has an oscillator and inverter and makes AC with it.
That's basically how the VFD built into a rail transit car such as Metro here works; except it starts with 700 volt DC from the third rail. You can hear some of the cars sing as they start up; I think the upgraded 300 series are the most obvious. Before we had VFD's, we needed DC motors to have speed control; I think all the DC-motor cars here are upgraded by now.
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    There are smaller ones designed to *run* only from single phase, and power a 1/8 HP motor (I have one -- about the volume of a brick and a lot lighter).
    But not for driving normal single phase motors at variable speeds. The tricks which start single phase motors are rather frequency sensitive. Most capacitor start ones will need a different value of capacitor for each frequency range -- rather impractical.
    Shaded-pole induction motors (such as old phonograph motors or little fan motors (pre muffin fan style) use a trick consisting of a heavy shorted winding around only part of each pole, causing a phase shift at that end of the pole to nudge the motor to a start. This is rather frequency sensitive as well. I've played with such a motor and a VFD -- and you get some range of variable speed, but for below say 60% speed, or above perhaps 120% speed, the motor will simply stall. So it is not practical.

    Except that it is normally done by PWM (Pulse Width Modulation) so the transistors driving it can simply switch fully on or off (both low power conditions), and avoid the half-on state where the maximum power is dissipated in the transistor -- generating heat and leading to failure.

    Whatever *three* *phase* motor will be. Single phase will not be happy. :-)

    Air compressors can draw a *lot* of power, and running one from a VFD (if you run it a lot) will probably cover the cost of the VFD in power bill savings over two or three years. They are close to 100% efficient because of the switching mode output, while a RPC is rather inefficient.

    Actually -- a *larger* idler motor than the load motor (1.5x or 2x) will probably provide all the torque you need -- especially if you take time to balance the converter by adding capacitors between the generated phase and the other two legs to produce approximately equal current in each leg.
    The capacitor start only certainly throws away motor horsepower, at least for full-time operation. Someone here has measured produced horsepower from the cap start trick and found that the motor will produce that full horsepower -- but the current through the only powered winding is much higher than that when it is driven from true three phase, so long term operation can wind up burning out the motor's windings.
    Enjoy,         DoN.
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In the case of this mill it has an instant reverse switch on the left
side. Today KBC priced a single phase replacement motor at over $500
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In the case of this mill it has an instant reverse switch on the left side. Today KBC priced a single phase replacement motor at over $500 dollars plus almost a hundred for the replacement instant reverse switch. Grizzly has some single phase motors that might work for less than half of KBC's price.
It's beginning to sound like the advantages are tilting to a VFD. That seems to be the most direct path to instant gratification.
By the way, I probably don't understand what an "instant reverse" is or why its needed. But if I understood one of the explanations of the pros and cons of VFDs if I buy a VFD I will need to remove the instant reverse switch and start / stop switch wires from the motor circuit and route them to the input side of the VFD.
Provided I do this correctly and get a VFD of adequate capacity I will have nearly perfect 3 phase, full horse power, and full use of the instant reverse switch.
Did I understand correctly? If so, I may pull out my credit card tomorrow while it still works!
V
To get the near instant reversing, you will probably need to add a correctly sized braking resistor to the drive to bleed off excess energy regenerated into the drive when the motor is being stopped or reversed quickly.
John
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    [ ... ]

    Ouch!
    Yes.
    Well ... picture using the mill to drive a large tap through steel or some other metal.
    Now -- assume that it is thick enough so you need to bury almost the whole length of the tap in the workpiece.
    And -- that you are using a rigid tap holder (most commonly used in a CNC (Computer Numeric Control) controlled mill which can feed downward at precisely the right speed linked to the spindle speed), or a "floating" tap holder (which allows the spindle to feed a little faster or slower than the thread wants to feed), but you do not have a "relasing" tap holder, which will stop driving the tap when it is pulled a certain short distance down from the spindle. Since as long as the spindle rotates, the tap will keep feeding in -- or break when you run out of threaded part of the tap.
    So -- you want to be able to hit a button which will start the tap rotating the other way, so it backs out of the hole -- *before* you break the tap.
    The "instant" will be a little slower than the instant from commercial three phase power (the "plug" reversing which I mentioned in another article in this thread), but it can be tuned to be fast enough so your reflex time will be the true limiting factor. (And it can be tuned a lot faster on a mill spindle than on a lathe spindle with a big heavy chuck and big heavy workpiece adding to the rotational inertia.
    Of course -- you could use something like a Tapmatic tapping head, which will stop turning the tap when the tap gets a certain distance ahead of the feed, and when you reverse the feed, the tap starts turning backwards faster than it went in -- all while the mill's spindle is rotating the same direction. I use a couple of these of different sizes on my drill press.

    That is right.

    Yes -- except just very slightly slower in the reverse -- but also will minimize the high current spikes which you would otherwise put into your power panel.

    Take the time to pick one which is more affordable. Others here can suggest a couple of sources which give good prices and good service. IIRC, one is called "Dealer's Electric", and they have a web page.
    Enjoy,         DoN.
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Vernon sez: "Provided I do this correctly and get a VFD of adequate capacity I will have nearly perfect 3 phase, full horse power, and full use of the instant reverse switch."
Yeah! And if you get a RPC it will do all these things as well as allow you to run more than a single 3-phase machine at a time.
Bob (RPC) Swinney
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Don, I was specifically trying to keep it simple and on-topic. The OP's concern is getting a VFD {or other solution} for his case. I just didn't want him buying some weird eBay VFD that WAS single phase...because he assumed "VFD == 3 phase"

Again....TMI
This runs a big hammer -- I suspect it's occasional use only. He had 3 phase very nearby, but the utility wanted lot$ to bring it in.

....
And how many ram types would do that?
I will admit I'd not considered the instant reverse aspect. That might be reason for the rotary converter approach.
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    Have you *ever* seen a VFD -- on eBay or elsewhere -- which was single phase output? I haven't, and I think that it because there is not much benefit from variable frequency with single phase motors.

    Perhaps -- but I find people here like to know the "why" of an answer, not just the "you can (or can't) do it" type of response.
    [ ... ]

    O.K. So to him, the benefit is not having a noisy rotary converter generating heat between operations. He can leave the VFD on full time if he wants, and get very little waste power.

    You mean rcm? Quite a few have -- and I first learned about it from the studies that Fitch (used to be a regular here) posted in a series of articles as he studied the construction of a rotary converter for his shop.
    The balancing gives you lots quicker starting (more torque), and the final capacitors across the input line to the rotary converter corrects the power factor, so a 10A load won't draw 30A through the breaker, causing lots of nuisance trips. It also keeps the wiring cooler. Note that it does *not* save much money (just a little for the extra heat generated in the wiring), because *residential* power meters measure true Watts, not Volt-Amps which can be very different with an uncorrected rotary converter.

    It is one reason. The ability to connect multiple machines to a single converter, and not have to play tricks with the forward/stop/reverse switching to pass the commands to the VFD (instead of risking zapping the output transistors by putting a switch between the VFD's output and the motor, as most machine tools are wired, since they expect the three phase to be coming from the power company.
    And *I* can't get commercial three phase (even though it runs past about a quarter block from here (you've seen my place -- just up at the top of the hill there is medium HV three phase passing by)) -- in part because of town regulations -- which prohibit any hobby machine tool with a 3HP or larger motor. Even if I could, the charge from the power company is well beyond what I can afford -- and they charge industrial rates for three phase -- which means that they base the charge on the peak current draw during the month, and you pay as though you have drawn that much full time through the month.
    Enjoy,         DoN.
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    [ ... discussion over whether this was too much information         snipped ... ]

    Good approach.

http://www.driveswarehouse.com/Drives/AC+Drives/Sensorless+Vector+VFD/SJ200-022NFU2.html
    That one looks nice. One thing which you should consider, however, is where the metal chips will fly from your tools. Set it up so they won't get into those louvers in the sides, because it can get exciting if they reach the circuitry. :-)
    Simplest thing would be a wood frame around it with window screening all around it, and some easy way to get inside if you need to use the front panel controls. This should keep the chips out, and let air flow through to cool it.
    If you're going to add a braking resistor (if you decide that you *need* instant reverse), you want it to mount to metal, not wood, to avoid fire. In use those can get fairly hot.

    O.K.
    I understand.

    O.K. A bit marginal, and you may have to take the time to tune it to make it start the saw reliably. And you want the saw located as far from the mill (and other machine tools) as possible. Sawdust from some woods is acidic and can cause rust where you don't want it.

    Yes. If you turn out to need a little more capability to start the saw, hang another three phase motor on the RPC, start it after the RPC is started, and it will help to start the saw.

    That may or may not be sufficient for starting the saw. Try it, and if you have problems, add tuning and then an extra idler motor.

    O.K. You can probably test the idler motor (perhaps with the fan removed) by driving it from the VFD.

    Hey -- I find that having a project in mind while learning a tool (or a computer program) makes it easier to learn more and faster, because you have something to hang what you read on. Later, re-read wit another project in mind, and you will pick up other things.

    Great!
    Hmm ... bolt some steel or thick aluminum plate to the table, and then bolt the mill to that so it is supported at all sides.

    How far does the table crank from side to side? Is this the green mill-drill which showed up in another thread? I sometimes can't keep the threads tied together.
    Anyway -- since long workpieces are likely to be overhanging one or the other end of the X-axis of the table, you want something to keep it from toppling sideways. I would suggest getting steel tube (rectangular or square) which extends say 18" to either side of the legs on the table, and bolting it to both the front and rear legs so it will prevent tipping. If you have to bolt it a bit above the floor to clear the existing table's feet, add adjustable feet on the ends which you can crank down to contact the floor. You probably won't have a load out to the front of the mill which is enough to be a problem, so you don't need extensions to the front and back which you could easily trip over. Probably a good idea to paint them a bright yellow/orange so you see them. :-)

    You will learn -- and this approach, while it might not give you everything you need, will get you started.

    Good Luck,         DoN.
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" If you're going to add a braking resistor (if you decide that
you *need* instant reverse), you want it to mount to metal, not wood,
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    [ ... ]

    [ ... ]

    The consideration being that with the fan in place, it will probably draw too much for the VFD to run it. But bare, with no load, it can probably be spun up by a 3 HP VFD with no problems -- especially if the VFD is set to a long acceleration time.
    [ ... ]

    [ ... ]

    Right. And the spindle of a mill is not nearly as massive a thing to accelerate as the spindle of a lathe with a large chuck in place, so the built-in resistor in the Hitachi should be sufficient, unless you hang a big boring head on the spindle, and set it for the highest speed -- probably a bad idea anyway, from the likely imbalance of a boring head.

    Well ... color schemes are easy to change -- just a different requested color from the real manufacturers in Taiwan or China. :-) And yours may have been from before Grizzly started selling metalworking tools in addition to woodworking tools.

    Hmm ... how strong a slab are you mounting it on? Is it thick enough to accept drilling for anchors? If not, go for the outrigger legs instead -- which will also make it easier to move things if you decide to re-arrange the shop's layout.

    IIRC -- the cabinet in your case is an open frame table. But if you mount a metal plate on the back for the power lines to go through, and enclose the sides and front in window screening, it should keep the chips clear, and allow airflow to keep the VFD cool. Obviously, plug or tape over the holes in the top which have not been used to mount the mill.

    A good choice. I wish that I had one of that size.

    Hmm ... perhaps -- assuming that you don't use the welder near full power rating -- you might be able to get away with a capacitor start circuit like the Phase-O-Matic -- or like the auto starting circuitry on a rotary converter.
    If it is that old, the horsepower will probably be smaller than you would expect for the size.
    Can you find current and voltage specs on labels on the outside of the device?
    Good Luck,         DoN.
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I'm debating in my head if adding a flywheel to a RPC will improve its ability to start big motors. I can generate arguments both way in my head, but Machines 450 was 20+ years ago, and while I loved the class, they say the mind is the first thing to go...
In one manner of thinking a VFD is just a special UPS. Years ago, I worked at a company that made big 3 phase UPS's, as from the 10KW to 10MW size.
These were ferroresonant UPS's. In mechanical terms, a FR system is a transmission with a slip clutch and a big flywheel. You can lock the output shaft, run it all day and nothing gets bothered. [You may know the brand "Sola transformer"...]
In EE terms, they are short-circuit proof, and the FR 'tank' stablizes the output across several cycles of line glitches.
A standard lab test for new designs involved a large 3 phase motor. I recall it was ~4 ft diameter and 6+ long. No doubt it was surplus from the steel mill.
You started the inverter module [Bigger units were usually collections of 10KW modules...] up, and closed the breaker to the motor. Not much happened; the humming got louder but that was it. If you looked at the metering, you'd see the module was at 100% output power but so what, the motor was still stopped.
Then, if you looked oh so closely, you could see it twitch and s l o w l y turn a little and then more and ever so slowly it could be seen to be gaining speed....
Over 10-30 minutes, the motor would evenually come up to ~850 RPM, and the current would drop to something normal. The module had passed..
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    It has been considered here in the past -- but tests seem to say that it does not help. It might prevent the RPC's idler reversing when you try to "plug" reverse (that is switch the machine to reverse without letting it slow to a stop first). Sometimes, when the idler in the RPC is approximately the same HP rating as the load motor, and the load motor is driving a lot of inertia, when you suddenly switch to reverse, the idler motor reverses instead of the load motor -- allowing the machine to keep on going into the crash which you were trying to avoid. :-)

    Without the extra power storage (normally lead-acid batteries) which allows the UPS to keep providing power after the line power vanishes. :-) But the output part is similar.
    But the VFDs normally use PWM to simulate the output sine wave, not a true sine wave (which you get out of the better UPS, since some computer power supplies are allergic to the voltage spikes from a PWM emulation of a sine wave.)

    Hmm ... Best Power Systems, by any chance? I really *like* their USPs, and have three of them running at the moment -- all Ferrups models.

    Yep -- "Sola constant voltage transformer". I've also got a DC power supply in which the only regulation is that it was built around a Sola style transformer. Probably a bit more efficient than normal linear regulators, but less so than a switching regulator.

    Wow! *That* is impressive.
    VFDs commonly start (from a full stop) by starting to output something like 0.5 Hz (and an appropriately low voltage) and then sweeping the frequency up to the full 60 Hz (here, or 50 Hz in the UK and some other places). This allows control of the starting surge which otherwise is present when a motor is simply just switched on. Most VFDs have a parameter to control how long the ramp-up time is to keep from drawing too much current and tripping the current limit error shutdown. It can range from something like 0.1 second to several seconds.
    Enjoy,         DoN.
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The ferro-resonant tank circuit was what gave you sine wave. Most give a rotten waveform but they knew a thing or two about building them.
Such came with a big price tag, however. Those custom-wound magnetics were big heavy, noisy & expensive 30 years ago; today you could buy a wall-street bank with 2 of them.

Long since gone, I suspect -- Lorain Products, later p/o Reliance Electric, LorTec and then who knows. [I see "LTI Power Systems"] They made "Perpetuac" units as well as lesser ones.

VERY inefficient at anything but 100% load. A FR draws 30% of FL at 0% out; they are great heaters. But they eat all kinds of line crap and never blink. They will coast past a few missed cycles with no problem.

Damn right.
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wrote:

There are a few tricks you can still try - Are you in a single family house with two or more stories and a handicapped occupant or frequent visitor? Or one that wants to be a frequent visitor? Or a small farm or rural property with a private water well? (And you're willing to sink some serious money on an upgrade...)
For safety reasons you really need 3-Phase power to make sure that larger well pump or elevator pump/traction motor always starts in the right direction, you should have better luck getting real utility 3-phase for a Well Service or an Elevator Service - compared to "I want to run big machine tools at my house" which you've already found ranges from 'frowned upon' to 'Verboten!'
You just have to refrain from volunteering any information when they ask why you need a 200A 3-Ph service for a 40A well pump or a 60A elevator machine. You just say you got a great deal on a New Old Stock (or used) 200A service that was far cheaper than a new 100A service.
Memorize: "That's my story, and I'm sticking to it." Then wink.
(But allow the power company Service Planner to see what's hiding under the tarps in the garage, they do have to make sure the service transformer they place is big enough.)
And even then, it might take multiple tries to make it happen, as you figure out ways to go around the roadblocks and find a sympathetic ear at the County Building & Safety and Local Power Utility levels.
Never give up, Never give up that ship! ;-P Or the corollary: "Always look on the bright side of life..."
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