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How to setup simultaneous tandem Y and tandem Z

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27 Mar 2024 22:28 - 27 Mar 2024 22:30 #296945 by Antonio Gross
Hi,

Relatively new LinuxCNC user here. I'm currently putting together the control cabinet for my new gantry CNC mill and I have a question. Is it possible to run dual motor tandem Y and tandem Z without splitting pulses between two stepper drivers? I know that I have the options in stepconf for tandem Y but how do I put together tandem Z and allow it to all run together? And, if this is possible, can I use limit switches to auto-align both sides of Y and Z during the homing procedure to square up each axis? And on top of all of this, can it all be done from a single parallel port? My breakout board has 5 axis drivers (XYZAB) so I know I have the outputs physically available.

The mill has one X axis motor, and on each side of the frame there is a Y motor and a Z motor left and right. I initially wanted each side to be coupled with timing belts, but this didn't end up being possible with the scope of the project. For the future I am eyeing a Mesa 7i96s, but I this is my senior design project for school and Im pretty hard up against a deadline and I'm already over budget, so I'm sticking to the parallel port for now. If this cannot be done in hardware for tandem Z, I will simply run tandem Y and tie the step pins together for Z for now.

Thanks in advance!
Last edit: 27 Mar 2024 22:30 by Antonio Gross.

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27 Mar 2024 23:50 #296954 by tommylight
Most probably yes, it can be done.
What do you mean by "splitting signals"?
That would require 10 outputs for 5 stepper drives and 5 inputs for limit switches, leaving you 2 outputs free for spindle on/pwm.
No idea if StepConf can make such a config, but PncConf might, although that would require a lot of editing.
Just checked, no Z tandem, so make X and Y with tandem Y and then another Y with tandem Y on the other pins, then edit the hal and ini files to reflect Z axis for the last two stepgens/outputs.

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28 Mar 2024 11:54 - 28 Mar 2024 11:55 #296990 by rodw
We don't need to split signals. Each joint (motor) will have its own driver. Versions 2.8 and above support joint axes so in you ini file, you need an XYYZZ machine (joints 0,1,2,3,4). Each of the Y & Z joints must have its own home switch. Squaring is done by adjusting HOME_OFFSET in your Ini so its squared when the machine is homed.
Joints are made into joint axes by using negative HOME_SEQUENCE
Read the chapter in the docs on homing configuration about 10 times, its all in here!
linuxcnc.org/docs/stable/html/config/ini-homing.html

You will end up with something like so the Z axis is homed first for safety.:
[JOINT_0]HOME_SEQUENCE = 3
[JOINT_1]HOME_SEQUENCE = -2
[JOINT_2]HOME_SEQUENCE = -2
[JOINT_3]HOME_SEQUENCE = -1
[JOINT_4]HOME_SEQUENCE = -1
Last edit: 28 Mar 2024 11:55 by rodw.

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28 Mar 2024 20:21 #297033 by Antonio Gross
Thank you! I am in the process reading through all the documentation, but putting it all together is challenging. Slowly its all starting to make sense. Once the machine is a little further along and wired I'll give this a try and go from there!
The following user(s) said Thank You: rodw

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