Would this make a decent spindle motor?

[Halfnutz]

I just dug this out of my pile and was wondering if this would be a good drive for a lathe?

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[Halfnutz]

can't upload for some reason, its a yaskawa R88M-M700012-b motor and the matching R88D-MT20 drive

[Jim Dawson]

Depends on the motor spec's and the size of the lathe, along with your expectations of the cutting performance. But a servo motor makes a great spindle motor for a lathe. A few weeks ago I replaced my lathe 7.5kW spindle motor with a 7.5kW servo motor and it works great, actually better performance than the original. The max RPM is now reduced to 3500 vs. the original 5000, but I never have ran it over 2500 anyway.

[Halfnutz]

Jim, the motor is huge, its about 16" long and a Nema 42, but it is only 700 watts and 1200 rpm. I have it running with mach 3 on Step + Dir. Do you understand why it is so large and only 700 watts?

[Jim Dawson]

It does seem large for 750W. I didn't look up the spec's but that sounds like a high torque (for it's size) motor. 1200 RPM is the rated RPM, most servos have a absolute max RPM that is 2X the rated RPM, not sure if that is the case here.

Most servo motors have a flat torque curve from 0 up to the rated RPM, so are really well suited for a lathe spindle. A high torque 750W would be suitable for smaller benchtop lathes, maybe up to 12 inch swing or so, either with 1:1 or a 1.5:1 timing belt reduction. This would really depend on what your normal cutting parameters are.

Look up the spec's on the motor, and compare the torque curve to the torque of a standard 750W (1 HP) induction motor to really see where you are at. I would expect that the performance would be better than a standard induction motor.

[Goemon]

I've been looking at these servo motors for myself:

https://www.ebay.com/itm/18466227706...Cclp%3A2047675

10nm of torque for a 1hp motor is probably enough to get away without gears on a small lathe or mill. They seem fairly cheap considering they come with the drive.

They also offer a 2hp version but they still advertise 10nm of torque so I guess it's only better at higher speeds. Both look fairly light and compact for what they are.

What makes a motor good for a spindle besides being rated for continuous duty and having enough torque and speed for the application?

Most of the load is taken by the spindle cartridge. I guess some motors have a better "heavy duty" cast iron case and a larger shaft.

But, if you have one sitting on the shelf unused, maybe just try it and live with it if it breaks...

[Halfnutz]

Those motors look nice, Goemon, but the description says theres no way to control them externally, yet. Yeah, I will probably just give this thing a try. I have one of the ebay 8.75 x 29.5 inch mini lathes, or I just ordered one. Who knows, if it runs good, maybe i'll leave it stock and just put an optic index on it.

[Goemon]

Those motors look nice, Goemon, but the description says theres no way to control them externally, yet. Yeah, I will probably just give this thing a try. I have one of the ebay 8.75 x 29.5 inch mini lathes, or I just ordered one. Who knows, if it runs good, maybe i'll leave it stock and just put an optic index on it.

What do you mean? They come with a stand-alone controller. The seller also offers a kit for a mini lathe.

The first issue to correct on a mini lathe IMO is plastic gears. No point in upgrading a motor if you just strip the gears when you try and use the extra power.

[Halfnutz]

Goeman, Theres no way to control it from a computer or controller it says, but honestly you could always hijack the potentiometer with an analog signal, its probably +- 10V. No big deal.

[Goemon]

Goeman, Theres no way to control it from a computer or controller it says, but honestly you could always hijack the potentiometer with an analog signal, its probably +- 10V. No big deal.

Where does it say that?

The listing says it comes with a controller with internal speed control allowing it to be set anywhere from 300-4500 rpm (for the 1hp model) and 300-3500rpm for the 2hp one (in 100 rpm increments).

Nobody would buy a servo motor that can't be controlled in any way...

If you are talking about adjusting speed via the cnc software (for ATC) that's different and would require a mod.

But, turning it on and setting the speed is done with it's stand-alone controller.