Jerk after plunge move, with spindle on

Hi! I just came across this curious thing with my 3axis CNC router. It started by noticing a jerk of the X axis (or Yaxis for that matter) happening only after a straight plunge move by the Z axis. What is curious is that it only happens with the spindle ON. I have attached a couple of Scope screenshots showing both scenarios, and also included G-code I am running to replicate the issue. Does linuxCNC plot different trajectories based on spindle state? Thank you!

Kind Regards,
Terence

Are these servos? I wonder if it some kind of interference from the spindle/drive.

I don't think so as I got exactly the same result on a simulated machine.

I don't see it running your file on a stepper setup in 2.7.4. What version are you using? Are you using any backlash compensation?

I just upgraded to 2.7.4 today from 2.7. No difference in behaviour. My machine runs 3 servo drives, no backlash compensation.

No I don't have spindle encoder feedback so i shouldn't be in feed-per-rev. No spindle-at-speed either ....the jerk is also noticeable in plunges at later stages of a run, when the spindle has been long enabled.

On the otherhand, replacing G64 P0.25 by G61 produced perfectly linear motion graphs, with a complete stop at the corner...as one would expect This time, spindle state ON/OFF does not affect the motion whatsoever.

Could you post an archive of your config files. I have an idea what might be going on.

Nevermind posting the config.

Ok I've attached a zip with all the files in the config folder. Also note that I get the exact same result on HALscope when running the gcode file I attached earlier in sim.axis_mm

I was having trouble getting a Halscope shot of exactly the right point in the move where the problem exits. I finally got a shot of it. Your talking about a little pause in the X axis move right after the blend of the Z to X move.
It is looking like a little bug in the trajectory planner.
If you put more moves after your first one, the pause disapears.