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22 Jul 2018 06:15 #114656 by rpseguin

OT-CNC wrote: I'm using the 750w DMM servos and drives on my lathe. So far they work well for the price. I did have some config issues trying them as steppers with encoder feedback. You can use them as steppers or with +-10v input.
Tecos look similar and there's Yaskawas etc...
You can do C axis with VFD and encoder using a closed loop vector drive. I'm lacking a brake at the moment to get that to work beyond temporary positioning. I did tinker with a special config but I'm not up to date with what the current C axis control methods are. In normal lathe mode you can read in the spindle encoder to linuxcnc for rpm and direction control. This allows threading and rigid tapping. Beyond that you are looking at a custom /advanced config.


Thanks for the response and info!

So, are you saying that it would be difficult to drive the spindle like a regular RPM spindle with a step & direction and then also use it as a position controlled C axis?
I would like to be able to do regular turning, facing, boring, threading, ... with the spindle turning at a specified RPM. It seems like it should work as a step & direction pulse stream at a given frequency to get it to a specified RPM.

C axis continuous contouring with live tooling is the other thing I'd like to do with the same AC brushless spindle motor.

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23 Jul 2018 15:59 #114713 by OT-CNC
If you do a search on C axis lathe you'll get an idea on some of the things involved. The switching between regular rpm spindle and position spindle is not part of standard lathe config. The experts will have to chime in on what's the current preferred way to control a lathe spindle with stepper pulse stream. You probably still need an encoder with index to keep track of position.

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26 Jul 2018 12:40 #114874 by andypugh

OT-CNC wrote: If you do a search on C axis lathe you'll get an idea on some of the things involved. The switching between regular rpm spindle and position spindle is not part of standard lathe config. The experts will have to chime in on what's the current preferred way to control a lathe spindle with stepper pulse stream. You probably still need an encoder with index to keep track of position.


A system like this could be used:
wiki.linuxcnc.org/cgi-bin/wiki.pl?SpindleOrient
Except that the mux2.N.out would be sent to a velocity-mode stepgen module.

As for the earlier questions, I would very much suggest LinuxCNC over Mach for a lathe. In honesty they both work fine for a mill, but the Mach lathe implementation is not as good. This might be why Tormach switched to LinuxCNC when they decided to make a lathe.
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26 Jul 2018 13:03 #114876 by tecno
I have been poking around with lathe from the Mach2 era and it is still not up to the task with Mach3. When Mach4 came nobody cares about updating Mach3 or try to get lathe functions working 100% or errors fixed. This is the reason I jumped over to LCNC.
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