Probe Basic — 4-axis XYZB wrapped rotary backplot support

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

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.

Regarding DRO — I already did exactly that, edited dros_user.ui removing the A and C rows. DRO now shows only XYZB. However the A+/A- jog buttons remain — they are controlled separately from the DRO file. Is there a way to remove the unused jog buttons without touching system files?

Regarding wrapped rotary — very interesting! I am ready to test. What do I need to get started with the test branch and what machine model is required?

   
Update: DRO is now showing only XYZB.

Edited dros_user.ui and offset_dros_user.ui removing the A and C rows and fixed the ZERO ALL command.

Added to INI:
DRO_DISPLAY = USER
USER_DROS_PATH = user_dro_display/
OFFSET_COLUMNS = XYZB

Screenshot attached.

The A+/A- jog buttons are still present — is there a way to remove them without touching system files?

Regarding the wrapped rotary test branch — ready to test. My setup is a standard XYZ milling machine with a B axis mounted parallel to Y. Where can I get the test branch and how do I get started?

Hi Lcvette,
Following up on your offer in this thread to test the multi-axis plotting / simulation branch — I'd like to put my machine forward as a test case. It's a different geometry from dredivan's MPCNC, so flagging that up front in case it's useful (or not) for what you're prototyping.
Machine: — 4-axis cylindrical/polar additive system tower-crane style. Not a wrapped-rotary gantry; the entire arm rotates around a stationary work area.

Configuration:

LinuxCNC 2.9.8 on Raspberry Pi 5 (Bookworm + PREEMPT_RT)
Mesa 7i96S
KINEMATICS = trivkins coordinates=XBZA kinstype=1 (joints 0–3 = X, B, Z, A)

Axes:

A — base rotation, 0–360° continuous, carries the entire Z tower + X arm + B head
Z — vertical linear, 0–2470 mm, rides up the rotating tower
X — radial linear, 952–2760 mm (radial distance from tower center to B housing — not Cartesian X)
B — end-of-arm rotation, ±90°, rotates about a vertical axis at the end of the X arm; B=0 means the 652 mm tool arm is aligned with the X arm (radially outward)

G-code is pre-computed in polar/cylindrical space by the CAM post-processor and emitted as dense waypoints in G93 inverse-time.

Sample line:
G93 G1 X2054.287 Z6 A118.183 B11.055 F423.731

→ B housing at radius 2054.287 mm, height 6 mm, base 118.183° CW, tool arm tilted +11.055° from radial; move duration ≈ 1/423.731 min ≈ 0.14 s.
Stock backplots render this as joint space and produce nonsense, which is why a wrapped/transformed preview would be a big deal for us. If the test branch can accept a custom transform (or already exposes a forward-kinematics hook for the canon), I can supply realistic .ngc files and run them on the actual machine.

let me know how I can be useful. Hope we can find a way for me to be a tester for your multi axis plotter!
— David

@ dredivan

I just pushed an update on the develop branch for bookworm version that specifies the jog buttons to display based on the display>geometry= setting in the ini file, if you update and specify your desired axis buttons there for jogging it will be correct now.