EtherCAT Closed-Loop Drive Options for Lathe

Hello,

I am new to the CNC world, and would like to convert my small-ish lathe to CNC.
I think motors with around 2Nm for Z and around 0.6Nm for X will be sufficient, based on some preliminary measurements. For X I am constrained to Nema 17 size to be able to integrate them well.
For I/O and the spindle encoder, I would like to use a Raspberrry Pi and Beckhoff EtherCAT terminals, which I have already gotten to work (thanks for all the great ressources on here!). I would also like to use EtherCAT-connected drives for the axis (and maybe later the spindle), though I am unsure, which path to take there.

Initially, I was looking at closed-loop stepper drivers such as the Rtelligent ECT60 or the Lichuan CL3-E57H , which close the loop on the driver. But then I also found the Beckhoff stepper terminals  EL7041 and  EL7047 , which would make integration quite elegant as I am already using other Beckhoff terminals. With these however, I am not quite sure if they support closing the loop on the driver. The EL7041 manual mentions some closed-loop control aspects (differing between the standard and the -1000 model), but I don't fully understand what it actually can and can't do. The EL7047 supports closed loop in conjunction with FOC, but it is officially only supported with Beckhoff motors and requires them to be unloaded on startup for referencing. I could not find out if non-FOC closed-loop operation similar to the ECT60 or CL3-E57H is possible as well.
What approach would you recommend here?

In general (e.g. if the Beckhoff drivers can only act as open loop drivers with encoder interfaces), is it advisable close the loop in LinuxCNC when using such an EtherCAT based setup without any FPGA for low level control?

Another option would be AC servo drives (probably the  Lichuan ones due to their comparable cost), at least for the Z axis as I haven't found a Nema 17 sized option that would fit X. These would probably provide better performance, but seem more complex to set up and tune.
What do you think about this alternative?

I am looking forward to your comments, and hope the questions are specific enough. Please let me know if any details are missing.

Best Regards
Daniel

Personally I would close the feed back loop with linear encoders, this will give actual feed back position, with a mesa FPGA this is a very well worn track with plenty of info available. Same for the spindle and encoder that also employs an index.
Sorry I'm too broke to have experience with Ethercat so really can't make a comment that maybe of use.
What kind of lathe are you working with ?
I'm kind of lucky with my Frankenstein Myford ML7\Super 7 in that I have plenty of room for the stepper motors, the only issue was the X axis, but I was able to use 10mm ballscrew and unlike most other lathes the nut is fixed to the carriage casting rather than running under the cross slide.

And for my techno babble mate, lathes conventionally use a XZ setup, Z being the carriage and X being the cross slide.
Also very few lathes, I can't think any that the average Joe would have access to lathes that use linear rails, mostly dove tails for cross slide and top slide and either plain rectangular ways for the bed,eg Myford, rectangular single prism, think 7x14 mini lathe or dual prism for the more industrial type. These are just the ones I can of off the top of my head.

Sorry to the OP for getting a bit off track.

Yes, its an old XZ lathe, a Maximat Standard. Quite comparable to the Myford ML7 actually.
Similarly to the ML7, the cross slide (trapezoidal) screw moves with the cross slide, with the nut mounted on the carriage. That limits the motor mounting a bit, as I would like to keep it simple. But if I limit this motor to Nema 17, I have a solution that works well.

Linear encoder feedback is actually on the wishlist as well, not only for CNC operation but also as a DRO when running it manually. I'd first like to get it set up with just motors with feedback though. If I get around to it, I'd also like to implement the linear encoder readout via EtherCAT if possible, as it seems like the most elegant solution when already using EtherCAT. The controller would neeed to run in LCNC on the computer in that case, which leads to a similar question as in the original post.

I'm undergoing a similar lathe project using a pi5 and beckhoff modules however I'll be using the drive itself for the fully closed loop. I'd suggest looking at leadshine's EL8 drives. They allow a dual encoder input so you'll have your typical rotary encoder mounted on your servo, as well as a linear scale (in my case magnetic) connected to the second input. I'm also splitting the linear scale input to a beckhoff module. I hope this might help.