Controlling a lathe with a stepper spindle

[TheMechanix08]

Hello,

first of all thank you for developing such a nice motion control software!
I'm building a small CNC lathe at the moment and am unsure, whether grblHAL supports my needs.

I am using a (closed loop) stepper as a spindle motor since I want to do light turning, threading and C-Axis indexing.
I've seen that there a stepper spindle is supported which is nice unique feature.

Does the stepper spindle allow the user to seamlessly use the stepper as a normal C-Axis? I was also planning to use the stepper to do threading without an extra encoder.
Would this setup work in conjunction with iosender and are there special requirements regarding the board to effectively use the stepper spindle?

Best regards!

[terjeio]

Does the stepper spindle allow the user to seamlessly use the stepper as a normal C-Axis?

Should be possible since the stepper spindle binds to an axis motor. Seamlessly might be an issue, it may require some code changes to sync the current position on a switchover. The stepper spindle uses a 64 bit position counter to avoid overflow since it may run continuously for a long time. The axis positions are 32 bit so a conversion must to be done on a switchover? Or C has to be homed before it can be used?
Another, for now, is that the stepper spindle binds to the highest numbered axis so you will ned a board or a board map with support for six axes. A and B can be "faked" in a board map by "wiring" their signals to the Y motor. Or I have to add specific support for XZC in the core - a bit like the LATHE_UVW_OPTION.

I was also planning to use the stepper to do threading without an extra encoder.

It should be possible to use standard gcode for threading since the stepper spindle provides the encoder signals - derived from the position.

Would this setup work in conjunction with iosender and are there special requirements regarding the board to effectively use the stepper spindle?

It should work but until I add the option to specify axisletters to use for axes > Z it will display positions for A, B, and C. And the 3D viewer is currently limited to displaying X, Y and Z. For board requirements see above.

Anyway, the functionality you require is within the scope of what should be supported and it would be nice if you would try it out/refine it together with me. I cannot do it on my own since I do not have a lathe with a stepper driven spindle to verify on nor do I know the finer details of how it should work.

[TheMechanix08]

Seamlessly might be an issue, it may require some code changes to sync the current position on a switchover.

As long as I don't need to rewire anything or reflash I firmware, I would consider this seamless enough for now!

Another, for now, is that the stepper spindle binds to the highest numbered axis so you will ned a board or a board map with support for six axes. A and B can be "faked" in a board map by "wiring" their signals to the Y motor. Or I have to add specific support for XZC in the core - a bit like the LATHE_UVW_OPTION.

Ah, that's sad. I was planning to use an Espduino or a Nucleo board with a cnc shield to allow me to use 36 V and maintain a smaller formfactor compared to a BTT octopus or similar.
Do I understand correctly that this plan won't work in any way currently?

It should be possible to use standard gcode for threading since the stepper spindle provides the encoder signals - derived from the position.

Do you mean that I would be able to use G76 or that I could create a custom gcode that links the rotational and linear movement through basic motion commands?

Anyway, the functionality you require is within the scope of what should be supported and it would be nice if you would try it out/refine it together with me. I cannot do it on my own since I do not have a lathe with a stepper driven spindle to verify on nor do I know the finer details of how it should work.

I would love to help with that! My machine is almost finished mechanically and is just waiting for its controller in the next few weeks.

[TheMechanix08]

Sorry for the second message!
Just as a quick sanity check:

Is there any reason against me using a Nucleo F411RE or a F446RE in a 4 axis configuration? I could just ignore the Y and use the A axis as the stepper spindle/rotary axis. As long as my gcode calls for movement of the A instead of C axis the naming should be arbitrary, right?

I do not plan on using an endstop on the rotary axis. Thus, pins should be enough or am I wrong?

[terjeio]

As long as I don't need to rewire anything or reflash I firmware, I would consider this seamless enough for now!

I believe I have to make some changes to the code, the main one could be how to handle switching from spindle to C control. Is there any manual workflow for that? Somehow align the workpiece after turning and before starting C controlled motion? Or just reset the C position to 0? If you have gcode with combined turning and C controlled motion that may help answering this. Or does the CAM output separate files forcing a manual step?

Do you mean that I would be able to use G76 or that I could create a custom gcode that links the rotational and linear movement through basic motion commands?

You should be able to use G76. I have not tested it yet though.

Is there any reason against me using a Nucleo F411RE or a F446RE in a 4 axis configuration?

No.

I could just ignore the Y and use the A axis as the stepper spindle/rotary axis. As long as my gcode calls for movement of the A instead of C axis the naming should be arbitrary, right?

That will work - but I would rather map the A pins to Y in a custom map file and use C since I understand that this is how it is normally done. BTW which CAM are you going to use?

I do not plan on using an endstop on the rotary axis. Thus, pins should be enough or am I wrong?

There are plenty of pins for this application on a Nucleo-64. And I would prefer that you chose a Nucleo board over an Espduino since I use aF446RE as my main development platform.

[TheMechanix08]

BTW which CAM are you going to use?

The main parts that I intend to machine should be basic enough for conversational/manual programming or gcode generation through a quick script.
I think I still have a valid student license for MasterCam somewhere. So in case I can help with CAM compatibility, we can figure something out.

Is there any manual workflow for that? Somehow align the workpiece after turning and before starting C controlled motion? Or just reset the C position to 0? If you have gcode with combined turning and C controlled motion that may help answering this. Or does the CAM output separate files forcing a manual step?

For my personal usecase I would be fine with just resetting the C position as I won't be doing multiple milling operations with intermittent turning. The C position would thus remain consistent through all milling operations.
The personal F360 license does not allow millturn operations for example (afaik not even machining using a rotary axis) so for most hobbyists, millturn operations would need to be created using a different piece of software or by just pasting different gcodes into one file.

Again, in case I can help out by doing some research, generating gcode or testing features, I would be I would be happy to do so.

You should be able to use G76. I have not tested it yet though.

That's amazing!

I use a F446RE as my main development platform.

Then I will order this board.

[TheMechanix08]

My 446RE just arrived! Do you have any tips on tests I could do/firmware to install while I'm finalizing my controller build?

[TheMechanix08]

I configured the firmware for the board today and installed it to try out whether the interaction with iOSender works as planned.

Everything mostly worked out, except for one thing:
G33 and G76 moves lead to an ALARM 14. Is there anything less obvious I need to change in order for the stepper spindle to work for threading?

[TheMechanix08]

Hi @terjeio ! :-)
I just hooked up one of my axis steppers as the C axis/ spindle for testing.

Unfortunately it shows somewhat weird behaviour:

• C Axis indexing works perfectly
• The motor does not move when the I turn on the spindle. When I try to move the C axis while the spindle is active the motor turns in a weird jiggery way.
• When I try to perform a G76, the motor spins up to the requested 100 rpm but stops after some time and throws an alarm 14.

I've tried to catch this in a quick youtube short:
https://youtube.com/shorts/gXMAofVLJzY?feature=share

Do you have an idea what I might have configured wrong?

[terjeio]

I have A axis bound to the spindle stepper and I can control it via spindle commands but not A-axis commands. I'll have to look into that.
There are several settings that has to be set for spindle synced motion:

$38 - pulses per revolution (PPR). This has to be the same as step/rev for the axis ($103 for A).
$340 - spindle at speed tolerance. Set to a low percentage, I set it to 3 for my test.
$90 - spindle sync P-gain. I set it to 3 for my test.

Microstepping should be set as low as possible to keep processor load low.
With PID logging enabled I got this result from a G33 command in the ioSender PID Tuner tab:

Not bad for a single pass.

I had to change the stepper spindle code a bit for this, the step count/angular position had the wrong sign due to how the direction was configured. If you are compiling yourself then here is the changed code:

stepper.zip

I have to look into why spindle/axis control changeover is not working as it should, but not today - it is nearing bedtime...

[terjeio]

Which board map do you use?

To enable axis control of the A-motor I have to permanently enable the A-axis with setting $37 - Steppers to keep enabled.
I think I should add a new setting for the stepper spindle for options such as "allow axis control" and "sync position".

[TheMechanix08]

$38 - pulses per revolution (PPR). This has to be the same as step/rev for the axis ($103 for A).
$340 - spindle at speed tolerance. Set to a low percentage, I set it to 3 for my test.
$90 - spindle sync P-gain. I set it to 3 for my test.

That makes sense. Your logging graph looks great!

If you are compiling yourself then here is the changed code:
[stepper.zip]
I have to look into why spindle/axis control changeover is not working as it should, but not today - it is nearing bedtime...

Thank you for the late night shift! :-) I've copied it into the IDE

Which board map do you use?
To enable axis control of the A-motor I have to permanently enable the A-axis with setting $37 - Steppers to keep enabled.
I think I should add a new setting for the stepper spindle for options such as "allow axis control" and "sync position"

I am using the Protoneer v3 board map but I modified it by assigning the A and B step/dir pins to the Y axis. The C axis got assigned to the spindle PWM and DIR pins instead as suggested by the Protoneers board.
I then commented out the original mapping of these pins. Are there any issues to this or is this exactly what you meant earlier in the thread?
//#define AUXOUTPUT0_PORT GPIOA // D13 - spindle PWM or spindle direction //#define AUXOUTPUT0_PIN 5 //#define AUXOUTPUT1_PORT GPIOA // D12 - spindle enable //#define AUXOUTPUT1_PIN 6

[terjeio]

The C axis got assigned to the spindle PWM and DIR pins instead as suggested by the Protoneers board.

How is your spindle defined in my_machine.h? Like this?

#define SPINDLE0_ENABLE         SPINDLE_STEPPER
//#define SPINDLE0_ENABLE         SPINDLE_PWM0_NODIR
//#define SPINDLE2_ENABLE         SPINDLE_NONE
//#define SPINDLE3_ENABLE         SPINDLE_NONE

Since the Protoneer board only connects to a limited number of the Nucleo-64 board pins you may assign Y, A and B to pins outside of the Arduino connector and C to the Y motor socket.

I have added a new setting and supporting code to the stepper spindle, and fixed some inconsistencies. I'll commit an update soon.

[terjeio]

Update committed, new setting $677 for enabling axis control of spindle and syncing position between spindle and axis. The latter needs to be verified in a machine.