New spindle motor - Servo or Induction?

[spumco]

All,

I'm planning to upgrade/change my mill's spindle motor and am seeking input from the CNCZone braintrust having reached my wits end searching for just the right motor...

I currently have a Marathon Blackmax Y551 2HP induction motor on my mill with a Hitachi WJ200 VFD. Motor has an encoder for speed mode feedback to the VFD. Running a 1.5:1 pulley and limiting the top spindle speed to 7500RPM to save my bearings and motor a bit of wear.

Two issues are driving the planned motor change.

First, the motor is extremely heavy and the cast-iron case means it has a very large OD for the rated HP. The large OD means I cannot use a standard 3-4 stage air cylinder for a PDB (R8 spindle w/TTS system) - the air cylinder simply won't fit centered over the spindle without raising it up about 15 inches on some kludgy riser. I currently have a home-made hydraulic intensifier installed on the spindle and an off-set air cylinder with a rocker-arm mechanism pushing down on the drawbar (with Belleville stack). This mechanism is not reliable - the fluid weeps out and after about 30-50 tool changes there isn't enough stroke left to reliably release the tools.

Clearly, I don't have the tools or skills to make a high-quality hydraulic intensifier that doesn't leak a little.

Second, the slow-speed performance is not very good - below about 500RPM the motor is very erratic. The VFD + encoder combo should give excellent performance down low. It's possible that my PWM source (PMDX-107 daughter board) is sending erratic 0-10V signals, but this is a minor gripe.

The Marathon motor is otherwise performing very well. No bogging, overheating, or other performance issues. However, as I'm getting more paying work recently, the need to stop and fiddle with the hydraulic PDB for an hour in the middle of a job is just not going to cut it. Plus there's no way I could build/buy an ATC without a reliable PDB.

I have 230v single phase, 30 amps available. I do not plan to invest in a significantly larger electrical supply or a 3ph converter. Besides, my mill isn't rigid enough to take advantage of more than 2-3HP. Also need a motor w/encoder (or provisions for same) so I can continue rigid tapping.

So...

I'm looking for a suitable spindle motor in the 2-3HP range that can achieve 5000-6000RPM. I can try a smaller-cased induction motor with a decent CT ratio such as this:

https://www.ebay.com/itm/Gator-Stain...kAAOSwp1RZgKUB

This appears to be a 145-frame 3HP motor with a 10:1 CT ratio and a smaller OD than the Blackmax. I could pull the fan to fit an encoder and put an external electric fan on it. Price is decent, and my current VFD should run it fine. Downside is that it weighs almost as much as my current motor and doesn't gain my a whole lot of space. Some, but not a ton.


The alternate is to find an actual AC spindle-servo motor and drive. My somewhat limited experience shows that a PM motor should be physically smaller than a comparable induction motor of the same HP rating - meaning I could finally fit a reliable PDB mechanism on my mill.

This would be preferable as I could (hopefully) run a 1:1 belt drive and still have 7k+ RPM top end. I know, these are expensive, and hard to find single-phase drives in the 2kw range.

All of the Fanuc/Mitsubishi/Yaskawa/AB/Baldor/etc. servo spindle motors I've seen have built-in fans for continuous use. They do not appear to be re-purposed 'standard' axis servos, given the RPM range on the nameplates.

Installing a DMM Tech 1.8kw servo was my first thought, but the 3kRPM top end means I'd have to give up a ton of low-speed grunt with the pulley ratios needed to get to 7500RPM. And I really don't want to drop my top spindle speed any lower than it already is.

I'm not willing to spend $3k (and up) for a new motor/drive, but I am willing to spend well over the $500 for an induction motor if the soulution is easy. I found a Alibaba vendor selling just the thing (2.2kw, 1-Ph 6kRPM spindle servo), but I'm unwilling to spend $1200 if the vendor won't even send me a datasheet/drive manual in English.

Nor do I have the expertise to troll eBay and find just the right servo and determine what an appropriate drive would be from the squillions of surplus items.

Does anyone have a suggestion on an appropriate spindle motor and/or drive? Weighs less than 65lbs, wide RPM range & torque curve, smaller than the Y551 Blackmax, and doesn't require 3-phase?

Thanks,
Ralph

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[RBeaubien]

Following. I too am looking for a similar spindle solution. This one caught my eye: https://www.ebay.com/itm/153070187109 , although I'm not sure what I can use to drive it. I have a cheap chinese 2200w spindle and VFD (24000rpm).

[rowbare]

The slow speed performance is not unexpected. AC motors are essentially constant torque devices up to the rated speed and constant power devices beyond. This means as you slow down, you have less power available. For instance if your spindle is turning 2500 rpm and putting out 2HP at the motors rated speed, at 500 rpm you are only getting about .4 hp. And since metal removal rates are a function of HP, your metal removal rate at 500 rpm is only 1/5 of what it is at 2500 rpm. That is why a lot of machines have two speed ranges because a mechanical speed reduction conserves power.

bob

[spumco]

Bob,

Thanks for the reply. Perhaps I was unclear in my earlier explanation - the slow speed performance issue is RPM hunting under no-load conditions. It can't hold steady RPM - either because of my PWM signal generator, or some VFD setting.

Slow speed torque is awesome - with the encoder/feedback to the VFD it can break tools, slip the TTS collet, and rip stock apart. The VFD/motor combo when set to feedback vector mode can generate something like 200% namplate torque near 0 RPM. Think of a crane or elevator motor.

It just can't hold steady RPM way down low. Not that this is a serious problem as I have no problem rigid tapping 1/2" in mild steel at 500RPM (322RPM motor speed). The speed thing is just a minor complant.


The big issue is the size. I want a simple, reliable power drawbar that can eventually be computer controlled for ATC use. And as nice as this Marthon motor is, it's simply too big in diameter.


I know I can find a higher-speed 1.5-2.2kw servo on ebay, but I just don't know enough about drives to select an appropriate one. Or if a 'standard' servo will survive duty as a spindle motor.

-R

[mick41zxr]

Ralph,
Looking to do a similar setup to your current one. What is max size end mill you can currently run in Al?
From what you have stated your running max motor 5000rpm at approx 180Hz
Regards,
Michael

[spumco]

Michael,

I can run any endmill up to the limits of the TTS collet system, workholding, and my mill's rigidity. No bogging using 1/2" end mills. I dont own any 3/4" endmills, but I'm pretty sure I could switch out the belleville stack with a solid drawbar and figure out where the motor starts to bog down. I have a 2" 5FL face mill, but I haven't been doing this long enough to come across a project where i needed to push it to the point where the facemill bogged the motor.

I have zero complaints about the motor's performance (other than that really low-speed fluctuation). No overheating, no angry noises, and the VFD can actually do simple spindle positioning (homing) if I needed it.

And yes, your calcs are on the money. Motor has a namplate max speed of 5400RPM, and I've set a somewhat arbitrary motor RPM limit of 5k - I don't want to continually bounce it off the rev limiter. Most of my machining is done at max spindle speed with 1/2, 3/8, and 1/4" cutters.

I've not bogged the motor down with a 1/2" drill in steel, or tapping 1/2-13 in same, if that helps. The limit for big drills would be my Z-axis motor losing steps, not the spindle motor.

-Ralph

[Azalin]

Following. I too am looking for a similar spindle solution. This one caught my eye: https://www.ebay.com/itm/153070187109 , although I'm not sure what I can use to drive it. I have a cheap chinese 2200w spindle and VFD (24000rpm).

According to their web page, this is a servo spindle with water coolant port.

PushCorp - Leader in Force Compliance, Spindles and Automation Equipment

[Azalin]

I am also looking for a motor for my BT30 spindle. My target head speed is 6k RPM.

The cheap Chinese 1.5kw servos (110mm) are 3000 RPM. To get 6000 RPM on the spindle I'll need to use a pulley set with 1:2 gear ratio. However this means a pulley on the servo side with diameter of about 100mm which is too big.

1.8kw servos are 2500 RPM.

I also found a (German) Schneider 1.3kw 6000 RPM servo. Sounds perfect for the job but it has a negative. It works with 3PH 400v AC. I have at home 220v AC single phase. I don't know if 1 PH 220v AC can be converted to 3 PH 400v AC.

[spumco]

Looks nice, but that's more of a router spindle. I'm looking for a more traditional motor-belt-spindle arrangement. Of course I'd like to upgrade to a BT30 spindle, but that can wait until I get the motor sorted out.

[Arjay]

Delta (Welcome to Delta Group) offers ac servo motors in the 1 to 2kw range that go to 5k rpm. They also offer a 3kw unit that goes to 4.5k rpm. I recently purchased the 1kw model w/brake (not that you need a brake), drive and cables for about $800 U.S. Motor part # was ECMA-C1010PS. Included a 20-bit encoder. Probably other ac servo mfgs offer equivalent products.

[skrubol]

Looks like that PushCorp spindle is for grinding. Don't think it would hold up well for milling.
I see tons of Fanuc spindle motors on Ebay, sometimes for cheap. They're usually huge, but occasionally there are low single digit HP units.
A thread about getting one to work right here:
https://www.cnczone.com/forums/spind...tachi-vfd.html
Looks like there are synchronous/PM motors out there as well as async/induction (sync/PM won't work with a normal VFD.)

[skrubol]

Delta (Welcome to Delta Group) offers ac servo motors in the 1 to 2kw range that go to 5k rpm. They also offer a 3kw unit that goes to 4.5k rpm. I recently purchased the 1kw model w/brake (not that you need a brake), drive and cables for about $800 U.S. Motor part # was ECMA-C1010PS. Included a 20-bit encoder. Probably other ac servo mfgs offer equivalent products.

AFAIK Delta servos are 3-phase only past 1.5kw, and the only 1.5kw models they have are 2000/3000 RPM (rated/max.)

[Arjay]

AFAIK Delta servos are 3-phase only past 1.5kw, and the only 1.5kw models they have are 2000/3000 RPM (rated/max.)

You are correct. The chart on page 9 shows 1phase/3 phase for the motors I mentioned, but the drive specs near the end of the catalog show 3p input for the 2kw and 3kw motors. The 1kw motor is 1p or 3p 220v input.

[Azalin]

What about deep well pump motors?

https://www.ebay.com/itm/Franklin-23...itleDesc=0%7C0

Some pumps are 3ph. 1.5 - 2.2kw pumps are about 90-100mm in diameter so the stator inside the pump should be even narrower in diameter. The motor in these pumps are basically induction motors so it should work with a VFD (in theory). I'm thinking of getting one. Plan is to remove the rotor and the stator from the pump, make a new enclosure in my lathe and put the stator and rotor in it. In the end I'll have a compact size induction motor. If it overheats then I can make a water cooling jacket for it.

I don't know how it will end but I think I'll give it a try.

[spumco]

What about deep well pump motors?

That's an outrageously clever idea! I deal with multi-hundred HP motors similar to this at work but it never occurred to me they come in smaller sizes - I don't have a well, so big blind spot.

Need to do some research on dimensions, shafts, etc. Shouldn't be too hard to make an aluminum heatsink tube on my 4th axis instead of a water jacket.

Damn - another internet rabbit hole to run down...

-Ralph


A quick review of the datasheet indicates these are not really suitable for spindle service. Regardless of the mechanical conversion, electrically there are a few no-go's:

• The motor must reach or pass the 30 Hz operating speed within 1 second of themotor being energized. If this does not occur, the motor bearings will bedamaged and the motor life reduced.
• The best stopping method is to turn power off followed by a natural coast to stop.
• A controlled stop from 30 Hz to 0 Hz is allowed if the time does not exceed 1 second.
• In all cases a minimum of 7 minutes must be allowed between a poweroff and the next restart attempt or consecutive restart attempts.

I'm thinking not so much.

-R

[Al_The_Man]

What about deep well pump motors?

Some pumps are 3ph. 1.5 - 2.2kw pumps are about 90-100mm in diameter so the stator inside the pump should be even narrower in diameter. The motor in these pumps are basically induction motors so it should work with a VFD (in theory). I'm thinking of getting one. Plan is to remove the rotor and the stator from the pump, make a new enclosure in my lathe and put the stator and rotor in it. In the end I'll have a compact size induction motor. If it overheats then I can make a water cooling jacket for it.

.

Considering the dia of the 3ph motor and appears to have some kind of controller, I am guessing that it is high rpm in order to get that HP from small dia induction motor.
This is similar to the ones sold with Huanyang VFD's, there is insufficient inductance in the motor to run on anything but high rpm.
If so then an efficient cooling system is needed.
Al.

[Jim Dawson]

A quick review of the datasheet indicates these are not really suitable for spindle service. Regardless of the mechanical conversion, electrically there are a few no-go's:

• The motor must reach or pass the 30 Hz operating speed within 1 second of themotor being energized. If this does not occur, the motor bearings will bedamaged and the motor life reduced.
• The best stopping method is to turn power off followed by a natural coast to stop.
• A controlled stop from 30 Hz to 0 Hz is allowed if the time does not exceed 1 second.
• In all cases a minimum of 7 minutes must be allowed between a poweroff and the next restart attempt or consecutive restart attempts.

I'm thinking not so much.

-R

I think that is referring to the rubber bearings in the pump section. The motor ball bearings are isolated from the rest of the world. I also think that the restart specs refers to full load restarts under normal operating conditions, and may apply more to the single phase motors rather than the 3 phase where you have a controled startup.

Just a few things to concider.

[Azalin]

Considering the dia of the 3ph motor and appears to have some kind of controller, I am guessing that it is high rpm in order to get that HP from small dia induction motor.
This is similar to the ones sold with Huanyang VFD's, there is insufficient inductance in the motor to run on anything but high rpm.
If so then an efficient colling system is needed.
Al.

I asked the seller the RPM of this motor. He just received his reply. RPM of the motor is 2850 and outer diameter of the motor is 12cm.

3450 RPM but 1ph
https://www.ebay.com/itm/Deep-Well-S...itleDesc=0%7C0


3450 RPM 3ph
https://www.ebay.com/itm/Grundfor-MS...itleDesc=0%7C0


There are too many on e bay.

[Eldon_Joh]

I don't know that you could run one of those well pumps at twice the intended rpm because the entire motor is water lubricated. i would try it though. if you call up well companies, you can probably get them for free. they throw them away even though the motor is good, its the plastic pump impellers that wear out after the bushing at the end of the pump fails.

if you remove the rotor and replace the bushings with ball bearings, you can also remove the stainless steel sleeve that is laser welded to the inside of the motor. removing it should reduce the no load losses. the stainless steel is very thin and has a high resistance, but it is effectively a shorted turn in the motor.



anyhow, I have a 2 hp marathon face mount motor 56 frame, weighs 32 pounds (3600 rpm), number is 5k49sn2185. you can have it for shipping plus 40$, because I will need to re-lace the wires and clean up the conversion from 9 to 12 wires.
You can wire it for 138 volts delta, and run it from your 3 hp 240v vfd and get 3 hp from this motor at 6200 rpm before the torque starts to drop due to reduction in volts/hz.
its nameplate amps are 5.4 at 230vac, so the amps would be 9.3 at 138 volts, less than the maximum of 11 that your vfd can deliver.


this one is 33 pounds
https://www.surpluscenter.com/Electr...or-10-2899.axd

this one is 45 pounds
https://www.surpluscenter.com/Electr...or-10-3122.axd

you'll need to add extra forced air cooling if you want to run them at heavy loads at less than nameplate rpm. but that is relatively easy.

of course, you'll have to take the encoder off your existing motor and install it on the new one.

edit: can you put the encoder on the spindle and tell the vfd the belt ratio? (or lie to the vfd telling it the encoder is 300 lines instead of 500 or whatever it is)

[spumco]

edit: can you put the encoder on the spindle and tell the vfd the belt ratio? (or lie to the vfd telling it the encoder is 300 lines instead of 500 or whatever it is)

Never to lie to the VFD

Kidding aside, I'm not sure that's a great idea. I could put the encoder on the spindle and run the VFD in sensorless vector mode. UCCNC control software has a belt/gear ratio feature that permits me to assign the spindle encoder to the motor OR on the spindle. That might help as I've got a separate index trigger on the spindle for rigid tapping. On the other hand, I'm not sure where I'd fit an encoder on my spindle at this point - I don't have much room, even for a belt-driven offset encoder.

The 56 frame motors are the same as my 145, but I need a face-mount with a removeable (or no) foot. And the cast-iron motor from surplus center is, more or less, what I have right now.

because I will need to re-lace the wires and clean up the conversion from 9 to 12 wires.
You can wire it for 138 volts delta, and run it from your 3 hp 240v vfd and get 3 hp from this motor at 6200 rpm before the torque starts to drop due to reduction in volts/hz.
its nameplate amps are 5.4 at 230vac, so the amps would be 9.3 at 138 volts, less than the maximum of 11 that your vfd can deliver.

Um... you just blew past my motor knowledge bank. At high speed.

I think I'm going to keep trying to find a servo drive with 230-1p inputs and then try to find a suitable AC servo. There are quite a few servos in the 90mm frame range on ebay at any given moment which appear to have, more or less, the speed & torque I'm looking for.

Thing is, I know that a 90/100mm frame servo will give me plenty of room for a 'standard' drawbar actuator. I don't know that even a sheet-metal 56C or 145TC motor will be much better than what I've got now. And as long as this doesn't blow way past $1k money isn't really the issue.

-R