Rotary axis backplot — centre of rotation not following WCS offset

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6 months 3 weeks ago #345259 by dredivan
 

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Hi,

I have a 4-axis MPCNC with a rotary B axis mounted at the far end of the Y travel (machine Y=700mm). The rotary axis is fixed — it does not move along Y.

G-code is generated by CAM with program zero at the chuck face, all moves go in Y-.

The problem: the backplotter does not display the toolpath correctly. Instead of showing the wrapped toolpath around the tube near the chuck, it draws a large circle. I believe this happens because the backplotter uses machine zero as the centre of rotation rather than the actual chuck position.

Setup:
- LinuxCNC 2.9.8 stable
- trivkins coordinates=XXYYZB, 6 joints
- qtdragon_hd interface
- GEOMETRY = !-BXYZ

Is there any way to tell the backplotter where the centre of rotation is?
Code:
[DISPLAY] DISPLAY = qtvcp qtdragon_hd # qtdragon saves most preference to this file PREFERENCE_FILE_PATH = WORKINGFOLDER/qtdragon.pref POSITION_OFFSET = RELATIVE POSITION_FEEDBACK = ACTUAL MAX_FEED_OVERRIDE = 2.000000 MAX_SPINDLE_0_OVERRIDE = 1.5 MIN_SPINDLE_0_OVERRIDE = .5 DEFAULT_SPINDLE_0_SPEED   = 12000 # spindle up/down increment in RPM SPINDLE_INCREMENT = 200 # min max apindle speed manually allowed  MIN_SPINDLE_0_SPEED = 1000 MAX_SPINDLE_0_SPEED = 20000 # max spindle power in Watts MAX_SPINDLE_POWER = 2000 #MAX_SPINDLE_OVERRIDE = 1.000000 #MIN_SPINDLE_OVERRIDE = 0.500000 INTRO_GRAPHIC = linuxcnc.gif INTRO_TIME = 5 #PROGRAM_PREFIX = /home/user/linuxcnc/nc_files PROGRAM_PREFIX = /home/user/cnc-programs INCREMENTS = 5mm 1mm .5mm .1mm .01mm  ANGULAR_INCREMENTS = 1, 5, 10, 30, 45, 90, 180, 360 POSITION_FEEDBACK = ACTUAL DEFAULT_LINEAR_VELOCITY = 40.000000 MAX_LINEAR_VELOCITY = 100.000000 MIN_LINEAR_VELOCITY = 0.500000 DEFAULT_ANGULAR_VELOCITY = 12.000000 MAX_ANGULAR_VELOCITY = 180.000000 MIN_ANGULAR_VELOCITY = 1.666667 EDITOR = gedit GEOMETRY = !-BXYZ CYCLE_TIME = 100

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6 months 3 weeks ago #345260 by Aciera
Note that the _preview_ does not take offsets into account:
linuxcnc.org/docs/stable/html/config/ini...sub:ini:sec:rs274ngc

 

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6 months 3 weeks ago #345269 by dredivan
I am aware of the ! prefix in GEOMETRY — it is already set in my config (GEOMETRY = !-BXYZ).

However, as the documentation states, this provision applies for liveplots only. I am using qtdragon_hd, not AXIS. Does the ! prefix in GEOMETRY have any effect on the qtdragon_hd backplotter, or is it AXIS-specific only?

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6 months 3 weeks ago #345277 by tommylight

I am aware of the ! prefix in GEOMETRY — it is already set in my config (GEOMETRY = !-BXYZ).
Remove the - after the !
I have never seen a - used there.

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6 months 3 weeks ago #345320 by tommylight
Yes, for hal scaling and output and encoder count direction, but i do not know if that works for geometry.

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6 months 3 weeks ago #345321 by dredivan
But the main question is still open: is there any way to tell the backplotter where the centre of rotation is, when the rotary chuck is not at machine Y=0?

In my case the chuck is fixed at Y=700mm. The backplotter always rotates around Y=0 (machine origin), so the wrapped toolpath displays as a large circle far from the actual machine envelope instead of showing correctly near the chuck.

I have already seen the 2013 thread where andypugh said there is no solution.
Is this still the case in 2.9.8, or has anything changed since then?

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