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Change pierce delay to something much smaller, like 0.2 for up to 5mm thick, 0 for up to 2mm and 0.5 for 5-10mm, etc.
Also show us other settings and the main screen while cutting.

It*s the usual things with isolcpus, coalesce waiting and so on. 

I don't think you can get rid of the jitter sound completely.
The underlying reason is that the position data sometimes misses to update the drives every DC cycle.
Let's not dive into why because we can't fix that here and now, instead see what you can do about it.
Reduce jitter is the start.
Can anything be done with the drive parameters? The drive will see a steadily changing position, every dc cycle a new delta - that's normal. Then suddenly there is a dc cycle without updated position - the drive see this as a full stop and starts doing the electric things to stop the servo. A few dc cycles later the position delta is restored but that means double delta in a dc cycle. The servo drive put the pedal to the floor to increase the speed. So that's what happens. Are there any settings in the drive to handle this essentially very high acceleration? Maybe max acceleration? Match that with the setting in linuxcnc (25% higher is a guideline there). That will reduce the speed change and the jitter noise.

There is a test you can do to see if this mechanism is the problem. Add a ddt component, connect position feedback from one of the servo drives to ddt.in and plot ddt.out in halscope. At a constant travel speed this should be a straight line more or less. When jitter happens you will see the ddt.out making a jump to zero or double value. It's a way to verify but unfortunately not to solve.

Hallo zusammen,

erinnert durch dieses Thread hier, dass ich meine Glasmaßstäbe noch nicht zu 100% am Laufen habe,
hänge ich mich mal hier dran.

Ich habe die Ditron DC11 an meiner Drehmaschine verbaut, diese funktionieren soweit auch,
allerdings bekomme ich kein Indexsignal, also muss ich mit Referenzschaltern arbeiten, was
wieder zu Ungenauigkeiten führt. Das würde ich gerne noch ändern und hoffe, dass ihr mir dabei helfen könnt.

Hier ist die Pinbelegung welche ich an der 7i85 (ohne S) benutzt habe:
 
 

und hier die HAL und INI:
 
 
 

thanks for the hint with the wiki! -). I just added this under "Misc stuff".

i tried changing the governor to performance just now it improved the latency a little bit but the noise still occurs

yes the sound is similar to what you describe and is more of random burst

I use mode 0.
I connected the divided arc voltage to the thcad and now the machine moves when it cuts, but it also goes on and of very often. You can see it here:



Could it also be a grounding-problem as the part is very small and I attached the ground clamp to the aluminium box where a steel grid is inside.

And why does it dive down in the middle of the part ? It seems to stop when the float switch is activated. 

I have found the problem to the error
It should be like this:
N44 G90
M99
not like this:
N44 G90 M99
It does not like to be on the same line

Can you describe the jitter, I suppose you hear clicks or gravel noise from the servos?
Is it always like a steady stream of those noises or are the bursts every few minutes?
Please elaborate.

If i leave G91 and g90
It gives me an error:
Bug: Reached convert_stop() from M99 as subprogram return

Btw I'm on Debian 10 with linuxcnc 2.8.4

After some back and forward i have an analog output. the scale gain is suited for 18k rpm. The rpm limiting needed to be added otherwise an incorrect value, say M3S30000 could be input with 0v output on the pin. Unfortunately this doesn't limit the gui rpm.

# Load required components
loadrt limit2 count=1
loadrt scale count=1
loadrt conv_float_u32 count=1

# Add functions to servo-thread
addf limit2.0 servo-thread
addf scale.0 servo-thread
addf conv-float-u32.0 servo-thread

# Configure RPM limit range
setp limit2.0.min 0
setp limit2.0.max 18000

# Connect motion RPM output to limit2 input
net gui-rpm spindle.0.speed-out => limit2.0.in

# Output from limiter feeds scale
net clamped-rpm limit2.0.out => scale.0.in

# Scale: gain = 1 / 18000 = 0.22
setp scale.0.gain 0.22
setp scale.0.offset 0

# Connect to float→U32 converter
net scaled-float scale.0.out => conv-float-u32.0.in
net final-u32 conv-float-u32.0.out => lcec.0.0.Analog-Output-0

Its a bit tricky to setup a PID speed control with a unipolar analog control
and FWD/REV signals.

I would first try eliminating the feedback by running the spindle open loop
you can do this by setting all PID terms to 0 except FF0 which should be  set to 1.0

If you need feedback (this is rare unless the spindle speed control is very poor)
The structure needs to be like this:

PID command = signed commanded spindle speed in RPM
PID feedback = encoder RPM
PID output --> ABS --> analog out
ABS sign (of PID output) determines the FWD/REV pins

Sorry, I guess the images didn't upload. "hm2_5i24.0.7i83.0.2.analogout0 <= spindle-speed-DAC" reads in forward and reverse. In reverse it shows a reading of 8.25 and stays there, doesn't move when trying to adjust the speed.. In forward it stays around 2.69 with some variation in the next 5 digits. It moves up and down with speed adjustment.

www.welectron.com in Germany has only 7i96S in stock right now
www.eusurplus.com in Portugal has all mentioned above in stock
eusurplus.com/index.php?route=product/product&product_id=64
or
eusurplus.com/index.php?route=product/product&product_id=159
eusurplus.com/index.php?route=product/pr...t_id=105&search=7i85