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CSS/G96 for other than X-axis?

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03 Apr 2026 08:10 #345100 by Aciera
Replied by Aciera on topic CSS/G96 for other than X-axis?

So the NML description in the LCNC manual isn't accurate? Or perhaps not exactly clear what happens?


Not sure but looking at motion/control.c gives me the impression that 'GET_JOINT_ACTIVE_FLAG(joint)' is used in motion mode FREE only:

github.com/LinuxCNC/linuxcnc/blob/c760c1...ontrol.c#L1217-L1219

but apparently not in modes TELEOP and COORD. So maybe it was only ever needed in FREE mode but who knows.

However I'm not sure this is the right place to implement what we want as we would still seems to cut things after the trajectory planner. Even if we are not updating the pos-cmd pin for that joint the internal position in the planner might still be updated and cause problems when reactivating the joint.

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03 Apr 2026 14:47 - 04 Apr 2026 08:03 #345106 by Aciera
Replied by Aciera on topic CSS/G96 for other than X-axis?
This may be of interest:
github.com/LinuxCNC/linuxcnc/compare/mas..._axes_in_interpreter

Adds a magic comment (disable,xyzabcuvw) to the interpreter. This allows the operator to disable any axis words (ie any of 'xyzabcuvw') in the interpreter. If the interpreter finds a disabled axis word in a line of gcode an error is raised.
Works for MDI and Gcode programs.

Interpreter: Add magic comment to disable certain axis words
(disable,<if none of 'xyzabcuvw'> )    ->  no restrictions apply [default]
(disable, z)   ->  if the interpreter finds a 'z' word an error is raised
(disable,zAb)  ->  if the interpreter finds a 'z', 'a', or 'b' word an error is raised

Notes:
 Only the first nine (9) characters (including spaces) after the comma (,) are considered.
 Upper- and/or lowercase letters can be used
Last edit: 04 Apr 2026 08:03 by Aciera.
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03 Apr 2026 15:10 #345107 by spumco
Replied by spumco on topic CSS/G96 for other than X-axis?
I think I just found what may be a stupidly-easy solution:  set MAX_VELOCITY to zero.

I set AXIS_X & JOINT_0 max velocity to 0 in a test INI file and LCNC started up with no complaints.

Z-axis homed first, then X just sat there doing nothing - as expected.

Next test will be to edit the switchkins M-code and try it after everything is homed.

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03 Apr 2026 15:44 #345109 by spumco
Replied by spumco on topic CSS/G96 for other than X-axis?
That worked like magic.

I removed all the jog-disconnect stuff from the M-codes and substituted
hal setp ini.v.max_velocity    0
hal setp ini.0.max_velocity    0

in the switched-mode M-code file, and the opposite in the normal-mode M-code.

Switchkins still works: parting slide is still connected to the X-axis controls, but the V-axis/Joint_0 simply doesn't move.
  • Axis GUI jog controls do nothing (!)
  • G-code V-axis moves do nothing
  • MDI does nothing
  • V-axis jogging does nothing (via MPG or continuous buttons)
  • No following errors or other issues noted
Best part is if I command a G0 Vnnn via MDI and then switch the axes back to normal, nothing 'jumps' like there's a blocked command waiting to be unblocked or re-enabled.

I'm probably missing some odd situation where this could bite me, but the fact is I'm only planning to use this switched mode briefly while the parting tool is in action (during a program) and then immediately restore the kinematics.

See any 'gotchas' with this?
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03 Apr 2026 17:39 - 03 Apr 2026 17:44 #345114 by Aciera
Replied by Aciera on topic CSS/G96 for other than X-axis?
Interesting. Just checked on a sim on 2.10pre and setting ini velocities to 0 does not quite work for me. The tool moves to the start of the spiral and then moves back. A bit strange really:

 

Same on 2.9.8
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Last edit: 03 Apr 2026 17:44 by Aciera.
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03 Apr 2026 18:30 #345124 by spumco
Replied by spumco on topic CSS/G96 for other than X-axis?
Hmm.  I didn't check on a sim, just my real hardware.

My backplot jumps when I do the switchkins switch, but no amount of fiddling could get the hardware X-axis to move when I had velocity set to zero.

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04 Apr 2026 17:08 #345166 by spumco
Replied by spumco on topic CSS/G96 for other than X-axis?
So here's an interesting problem for anyone following along...

I cut the parting slide stepgen scale by half (JOINT_3) so the V-axis can be programmed in diameter mode.  When set like this jogging/MDI/g-code is just like X in diameter mode - very intuitive.

Getting ready to test G96 CSS and double-checking everything - set G54 offsets, etc.  I enable switchkins and everything's fine...

But now the virtual X parting slide is only moving half the distance it should.  DRO is following the movement - it's moving at half the distance it should as well.

Ok, got it - I've got the scale cut in half, and LCNC is cutting that in half again when I switch the kinematics and am commanding an X move.

Easy solution: change the JOINT_3 scale back to full-distance value when switchkins is active.  But...

LCNC instantly throws a JOINT_3 following error when the scale switches.  Bugger.

I can double the V-axis/JOINT_3 scale and fiddle with the jog values, but that will still leave the V-axis G54 offset wonky.  I write the V-axis offset to the X-axis when switchkins is enabled (along with max/min limits) so the parting slide tool-tip at centerline can be set to "X0" for CSS.

How can I have my cake and eat it, too?
  • V-axis/JOINT_3 to be in diameter mode when switchkins is not enabled, and
  • X-axis/JOINT_3 to be in diameter mode when switchkins is enabled
  • No following error when enabling switchkins
  • All programming in G7 mode - switching back and forth between G7/G8 is going to cause my brain to hurt and a crash.

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04 Apr 2026 17:38 - 04 Apr 2026 17:41 #345168 by Aciera
Replied by Aciera on topic CSS/G96 for other than X-axis?
You could also try to create V-axis/joint3 diameter mode in the kinematics component.
Using the initial example with V-axis/joint2:

Forward:
case 0:
pos->tran.x = j[0];
pos->tran.z = j[1];
pos->v = 2*j[2];
break;
case 1:
pos->tran.x = j[2];
pos->tran.z = j[1];
pos->v = 2*j[0];
break;

Inverse:
switch (switchkins_type) {
case 0:
j[0] = pos->tran.x;
j[1] = pos->tran.z;
j[2] = 0.5* pos->v;
break;
case 1:
j[2] = pos->tran.x;
j[1] = pos->tran.z;
j[0] = 0.5*pos->v;
break;
}
Last edit: 04 Apr 2026 17:41 by Aciera.
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04 Apr 2026 18:08 #345169 by spumco
Replied by spumco on topic CSS/G96 for other than X-axis?
Well that's a clever idea.

Just so Im clear, the pos->v = 2*j[2];function results in the V-axis moving twice the distance of JOINT_2?

And the reverse forj[2] =0.5* pos->v;in the Inverse section?

Which means in case 1 I'd want to adjust the X-axis:pos->tran.x = 2*j[2];So the X-axis moves the correct distance when connected to the parting slide joint?


Which means I can adjust the INI stepgen position scale so it's not cut in half, and then adjust both case 0 and case 1 so the V-axis moves half the distance (diameter mode).

case 0:
            pos->tran.x = j[0];
            pos->tran.z = j[1];
            pos->v        = 0.5*j[2];
            break;
        case 1:
            pos->tran.x = j[2];
            pos->tran.z = j[1];
            pos->v        = 0.5*j[0];
            break;
  • Don't adjust the case 1 X-axis/joint_2 relationship, because X-axis will move at half-distance when in diameter mode.
  • DO adjust the case 1 V-axis/joint_0 relationship, because LCNC doesn't have a diameter mode for any axis other than X.

Make sense, or have I got something wrong?

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04 Apr 2026 18:35 #345170 by Aciera
Replied by Aciera on topic CSS/G96 for other than X-axis?


Just so Im clear, the pos->v = 2*j[2];function results in the V-axis moving twice the distance of JOINT_2?

And the reverse forj[2] =0.5* pos->v;in the Inverse section?

yes, the dro readout for V will show the double of the joint_2 position or, in other words, joint_2 will move half the commanded V axis position.


Don't adjust the case 1 X-axis/joint_2 relationship, because X-axis will move at half-distance when in diameter mode.
DO adjust the case 1 V-axis/joint_0 relationship, because LCNC doesn't have a diameter mode for any axis other than X.

Sounds correct. Famous last words :)
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  1. Configuring LinuxCNC
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