Probe Basic — 4-axis XYZB wrapped rotary backplot support

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15 Apr 2026 10:44 #345574 by dredivan
Hi,

Setting up Probe Basic 0.6.6 on a 4-axis gantry machine (MPCNC with a fixed rotary B axis mounted at the end of the Y travel).

Configuration:
- LinuxCNC 2.9.8
- Mesa 7I76E (Ethernet)
- trivkins coordinates=XXYYZB, 6 joints
- B axis is a rotary chuck, fixed position at Y=700mm

What works:
DRO displays all 4 axes correctly using DRO_DISPLAY = XYZAB (A axis is unused but present — there is no XYZB option available).

What does not work:
The backplot renders the toolpath as 3-axis only — B axis rotation is not applied when building the path. For wrapped rotary applications (tube machining) the toolpath preview is not meaningful.

Also, machine bounds are not displayed in the 4-axis config, while they display correctly in the 3-axis config on the same machine.

Are there any plans to support wrapped rotary backplot rendering in Probe Basic / qtpyvcp?

3 axis configuration - mpcnc_probebasic.ini
4 axis configuration - probebasic_4b.ini
Attachments:

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15 Apr 2026 20:07 #345579 by Lcvette
do you have the plot turned on for machine bounds in the ui? sidebar tab "PLOT"

for the dro display, you can use the user custom dro template and setup however you desire, just remove the rows for a and c and leave xyzb

for the wrapped rotary, this will be something coming down the line, we are currently working on multi axis plotting and simulation so if you have a model of your machine and would like to be a tester for the currently existing test branch you can give it a try if you like, the feedback would be good for us to have someone outputting multiaxis gcode for testing.

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