I am currently considering this kit: https://www.ebay.co.uk/itm/393192724008

It's a 4 Nm closed loop closed loop stepper, and my intentions are to replace the 1.8 Nm stepper which is used in my "poor man's lathe" project: http://www.mycncuk.com/threads/14589...or-man-s-lathe which I started just for fun and to see if a rotary axis can be used as a simple "lathe" type of machine. It turned out that at least drilling works well, so I continued with this activity and will test even turning probably during the weekend. Currently I manage to run the stepper at 2280rpm reliably but because of the 1:6 gearing, that results in 380rpm on the chuck, which I am well aware of is a bit low, especially for soft material. So I have two changes which I planned.

1. To replace the gearing with a 1:3 ratio. This will result in double speed, but also half the current torque. Maybe that's still better on soft material than low speed and higher torque, but to compensate the loss of torque, I also plan...

2. to replace the stepper with a closed loop stepper. In theory, it should mean I get much better torque all the way because the driver compensates for the step loss and applies more current when higher torque is necessary. In theory, I should also be able to run the motor at faster speeds than a stepper motor could run. So the combination of those two is beneficial (higher motor speed and torque), the motor I am aiming at is a 4 Nm motor which is more than twice of the stepper I now use. Of course, I still plan to change the gear ratio also, so with all that, I aim at having around 1000 chuck rpm which would be phenomenal considering this fairly cheap solution.

I have no experience with closed loop steppers, so I have a few questions.

Are all closed loop steppers and drivers equal? I don't mean specification wise, but more like quality wise. Does it make a difference who is selling them? What about the drivers? Does it matter which one is used for the same motor? Any pitfalls? I know you prefer AC servos, but currently I am concentrating on DC. I also know there are larger motors which are better suitable for this sort of task, but those are too large for my current ambitions, so I'd like to keep the NEMA 23/24 form factor and also don't want to build or buy a new PSU, so I plan to use my latest 48V 340W DIY PSU, even though the above kit comes with a PSU. Can I trust the torque table? I know it says 1600 microstep, which is wrong since they must mean 8 microstep (1600 steps/rev) but if that is true then at least at 1500rpm I will get much more torque since I intend to run it at 2 microstep (400 steps / rev).

A last question, which is maybe the most important to find an answer to. The listing says maximum rpm is 2000. I asked the seller if that is true and he replied within an hour (very good response time) that the maximum rpm is indeed 2000 rpm. He did not explain why, even though I asked. The encoder is good for 5000 rpm, so why is there a limit? Or is it possible that the seller does not know everything? I mean, normally, a stepper can be run at almost any speed in theory, as long as the pulses are supplied within the specifications. In theory. In reality, that's different, which is why my stepper stalls at 2400 rpm, but at 2280 rpm it is running happily forever. So why is there a 2000 rpm limit on the closed loop stepper? Is that a built in sort of hard limit? Or is due to something else, or maybe it is like the stepper, after a certain rpm it becomes unreliable, so the seller says 2000 rpm is the maximum, because he knows that it works up to that value?

OK, many questions and long text, but I hope I can get at least some answers, hopefully at least the last part will get answered, because I would like to increase the speed, and my hope is to be able to run the stepper at 3000 rpm. Maybe that's too ambitious...