Lathe Spindle Drive Options - AC Servo vs BLDC vs Stepper vs DC Brushed

So I am trying to wrap my head around a few things. Watts generally is power (consumed and delivered) - and here is where I believe that I am getting confused (on several fronts).

I have the following motors and controllers available for playing around to use as a motor on which to drive my Frankenstein mini lathe (7x16 with 3" and 5" chucks - .750" bore)

Option 1. The original 350w 110VDC 1.5Nm peak (maybe) brushed motor and driver from the 7x10 HF mini lathe @110VDC rated rpm: 5000
Option 2. Longs 57BLF03 188w 24VDC 2.4Nm BLDC motor with BLDC-8015A BLDC motor driver running @ 48VDC rated rpm: 3000
Option 3. Link Motor 23H2A2442-01B 4.2A 2.7Nm Stepper motor with a MA860H stepper driver @ 72VDC rated rpm: 1000 (maybe)
Option 4. Stepperonline 34HS46-5004D 5A 8.5Nm Stepper motor with a MA860H stepper driver @ 72VDC rated rpm: 200 (maybe)
Option 5. Yaskawa SGM-08A312 750w 3000 4.4A AC servo using a Yaskawa SGDA-08AS servo driver @ 200VAC rated rpm: 3000

Compared to the original 350w 110v brushed DC motor at low RPM, the BLDC seems like a beast (even at 24VDC) and at 48VDC seemed even more rabid (the driver is rated for it, but would the motor survive?). I think the 750w SGM-08 is probably overkill for my lathe, although tempting me to use it. I was considering using the stepper motors, but they probably won't reach the RPM's I want to do higher speed work.

What is the deal, the 350w motor seems weak in comparison to a 188w BLDC, is it my imagination? What is the highest reasonable voltage to run a 24VDC BLDC motor assuming it's not limited by the driver (which can handle 80VDC)?

So I think I have a few things figured out. I found a handy little stepper motor calculator here: Stepper Motor Calculator

In terms of power the StepperOnline NEMA 34 stepper is capable of about 360 watts at ~200 RPM (assuming 5.0 amps, 11mH, and 72 volts)
In terms of power the Link Motor NEMA 23 stepper is capable of about 216 watts at ~1000 RPM (assuming 3.0 amps, 3.8mH, and 72 volts) or
In terms of power the Link Motor NEMA 23 stepper is capable of about 302 watts at ~675 RPM (assuming 4.2 amps, 3.8mH, and 72 volts)

So that essentially rules out the steppers!

For contrast, I have some horrible Long's NEMA 23 steppers with much higher 6.8mH inductance which I now understand is completely bad for speed and adds nothing to the motor's ability to get the job done. It looks like this:

In terms of power the Long's NEMA 23 stepper is capable of about 216 watts at ~530 RPM (assuming 3.0 amps, 6.8mH, and 72 volts), which I had been running at 36 volts previously, and wondering why they sucked so bad when I pushed them a little.
Well at 36vdc I would be lucky to get 275 RPM out of the Long's 23HS9430B! Where the Link Motor 23H2A2442-01B can run away from it at nearly 475 rpm at 36vdc and the same 108 watts of power.

Naturally, you can get higher RPM's out of these motors than what is listed above, but with no real torque/power. Current by necessity would have to fall off to increase speed, leaving you with a relatively powerful slow speed motor, but nothing on the high end.

I guess I should just not F around and put the Yaskawa servo in place to run the spindle, because at 750w it should have plenty of power everywhere for a mini lathe (8Nm from 0-3000 RPM peak).
I really don't see a need on the little lathe for anything over 2500 RPM and I can gear reduce it from 3000 RPM max to about 1200 RPM max with the spindle head.

I think you came to the correct conclusion. The Yaskawa motor is overkill, but you won't run out of power on that lathe. I would never use a stepper for a spindle drive, if for no other reason than the steps at lower speeds, they are not smooth. In addition the torque drops off dramatically as the RPMs increase. The Yaskawa will give you a nearly flat torque curve throughout the rated operating range, and I'm guessing that while rated at 3000 RPM, the max safe operating RPM on that motor is around 5000 at full HP, but the torque drops off at greater than 3000 RPM.

If you found a good deal on the yaskawa then go for it. I think you would do ok with a 400W AC servo, you can find a set cheaper than the 750W.
I am using a delta 750W servo for the spindle drive on my lathe project, the headstock I am using came with a 60hz 370W motor that is long gone.

Advantage of the AC servo, depending on series, you will have between excellent positioning resolution.

Quote:

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Originally Posted by alan_3301

If you found a good deal on the yaskawa then go for it. I think you would do ok with a 400W AC servo, you can find a set cheaper than the 750W.
I am using a delta 750W servo for the spindle drive on my lathe project, the headstock I am using came with a 60hz 370W motor that is long gone.

Advantage of the AC servo, depending on series, you will have between excellent positioning resolution.

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IIRC I managed to get the Yaskawa's for around $200 for the servo and servo driver together shipped... So, ya, I stole them.

I feel like between 350w and 500w of BLDC or AC servo would be more than acceptable given the other limitations of my frankenlathe.

The overall goal is to build (eventually) a 7x16 slant bed lathe (crazy, I know) that would do 95% of everything I would ever need to do.

Hi,

So how did the story end? Do you still use the servo as spindle motor? How do you control it?

Using PWM?
Using 1-10v ?
Using step/dir commands?

I have a NIB set of 1500w servo and want to use it as spindle motor. However, I'd like to control it using step/dir and encoder (closed loop?) because my motion controller (Pokeys 57E cnc4pc M16 board) have an encoder input for spindle.

Quote:

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Originally Posted by Azalin

Hi,

So how did the story end? Do you still use the servo as spindle motor? How do you control it?

Using PWM?
Using 1-10v ?
Using step/dir commands?

I have a NIB set of 1500w servo and want to use it as spindle motor. However, I'd like to control it using step/dir and encoder (closed loop?) because my motion controller (Pokeys 57E cnc4pc M16 board) have an encoder input for spindle.

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Subscribed. Interested to find out as well. Just purchased a small 2nd hand Sieg C4 mini lathe all cnc'ed already and there is absolutely no way to control the spindle motor other than "manually".
Not exactly sure how to machine parts radially on that thing with a static speed rpm :/ Does work great for threading though (linear) with its encoder linked to M3's index, but that's just about the only thing it does correctly.
Looks like I'll need to add a controlled motor too

Quote:

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Originally Posted by Mecanix

Subscribed. Interested to find out as well. Just purchased a small 2nd hand Sieg C4 mini lathe all cnc'ed already and there is absolutely no way to control the spindle motor other than "manually".
Not exactly sure how to machine parts radially on that thing with a static speed rpm :/ Does work great for threading though (linear) with its encoder linked to M3's index, but that's just about the only thing it does correctly.
Looks like I'll need to add a controlled motor too

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Mecanix, I have already been down that road with the spindle motor. Good news, you can control it. See here. https://www.cnczone.com/forums/bench...-sx4-bldc.html