linking U axis to X

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11 Jul 2026 20:27 #347693 by foam man
linking U axis to X was created by foam man
hi I have a 4 axis hot wire foam cutter. i move each axis separate, but I'm wondering if the text below makes sense for, essentially moving U and V with X and Y commands. Thanks

The Fix:
How to make UV emulate XY while keeping their own step calibrations.
To force U and V to mirror X and Y while preserving their independent step calibrations, you must link the signals before the math calculates the motor steps.
In LinuxCNC, you do this by linking the motion controller outputs to both sets of joints, rather than linking the step generators directly.
Open your machine's main .hal file and look for the lines connecting motion.coordinate-system to your joints. Change them to route like this
:hal# Force Joint 2 (U) to listen to the X-axis motion command
net x-output motion.coordinate-system.0.pos-cmd => joint.0.motor-pos-cmd joint.2.motor-pos-cmd

# Force Joint 3 (V) to listen to the Y-axis motion command
net y-output motion.coordinate-system.1.pos-cmd => joint.1.motor-pos-cmd joint.3.motor-pos-cmd
Use code with caution.Why this fixes the calibration issue:
The Signal: LinuxCNC outputs a raw request in millimeters (e.g., "Move X to 50.0mm").The Split: The HAL lines above take that 50.0mm request and send it to both Joint 0 (X) and Joint 2 (U) simultaneously.The Calibration: Joint 0 looks at its own SCALE setting in the .ini file to convert 50.0mm into steps for the X motor. Joint 2 looks at its own independent SCALE setting in the .ini file to convert 50.0mm into steps for the U motor.

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11 Jul 2026 20:51 #347695 by tommylight
Replied by tommylight on topic linking U axis to X
Was this same question asked before on this forum?
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P.S.
Still did not finish my build of a 4 axis foam cutter, so not yet at this point.

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12 Jul 2026 06:07 #347703 by Aciera
Replied by Aciera on topic linking U axis to X
Same post here:
forum.linuxcnc.org/38-general-linuxcnc-q...n-4-axis-mode#347523

No double posting, please continue in the thread linked above.

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14 Jul 2026 13:29 #347763 by foam man
Replied by foam man on topic linking U axis to X
sorry, I posted on that one, but when nobody replied, I figured the post was too old and wasn't active anymore

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14 Jul 2026 13:53 #347765 by tommylight
Replied by tommylight on topic linking U axis to X
We (this forum) do not close or retire topics as some forums do, i have no clue why they do that as the only thing that does is cause chaos and makes the forum unusable with many instances of the same Q&A that mostly never conclude or solve anything.
The following user(s) said Thank You: foam man

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