Can someone explain how squaring is handled on dual motor linear axis?

I currently am building out my machine and have somewhat of a stupid question that is racking my brain. I have a tiny homebuilt lathe that has XZC kinematics plus a stepgen servo spindle.

My plan is to add a dual motor Y axis (in my case it is a vertical axis) onto the lathe cross slide to give Y axis capabilities. Now my actual question is much more simple but I am struggling how to think it through and want to make sure I am capable of taking on this extra axis project.

Here is my issue:

In my case, i will have a rigid steel coupler between both sides of the Y axis to attach a spindle and gang tooling / etc. How can I ensure that the position of the coupler on each side ALWAYS stays at the exact same height, as there is no room for misalignment. My thoughts are:

1. Ensure the home switches are EXACTLY at the same height, but i cant imagine i could do it perfectly
2. Add some sort of adjustment mechanism to the coupler such as oversized bolt holes, allow it to home on both of the home switches, and then tap the coupler level and bolt it down which would account for any home switch misalignment
3. perhaps linuxcnc has some sort of axis offset you can add to account for something like home switch height difference? I.e you calculate the axis offset by jogging it until the coupler is perfectly parallel to the cross slide and then set a difference in height between the two axis?


Its clearly an easily solved issue given how common things like dual Y axis routers are - but I am a bit confused this and was hoping someone could chime in who has already done a dual motor axis?

Easiest example which i am basing my machine off of is the APSX-nano desktop swiss lathe. It uses a dual motor Y axis with a coupler between them that holds various lathe tools. I uploaded a picture off of one of their youtube videos. My concern is that this coupler that holds the lathe tools is rigidly attached to both of the Y axis motors - how do you ensure they are perfectly height-aligned so there is no twist or torsion on the lathe-tool holding coupler. I understand you can use slave axis in linuxcnc but wouldn't this require you to ahve home switches at exactlythe same relative position on each separate axis? What if one of your home switches is slightly higher than the other? Can you offset that somehow in linuxcnc?

I have a dual-Y configuration on my cnc, and what I have is two limit switches - one for each motor. The config has a separate section for each *motor* so you can specify the homing offsets independently. In my case, the two entries differ by 0.036 to bring the gantry into square. So I'm using your #3 solution I figured out the offset value by homing, measuring how off-square I was, updating the config, and re-homing; repeating until it came out square.

Your alternative is to mechanically tie the two motors together (or use one motor and two screws) and tell linuxcnc you only have one "motor"

Squaring the gantry is done during homing and relies on the HOME_OFFSET for alignment.
It is super easy to do if you read the most important part of the documents, homing configuration
linuxcnc.org/docs/stable/html/config/ini-homing.html
Except you will probably need to read this page 3 to 10 times....

Forgot to mention whatt the docs don't say. To square the machine, making marks in each corner of the bed with the spindle and measuring diagonals is the most accurate way on a large bed. Adjust until equal.
Me, I just measured each side with a dial indicator from a common reference.