Hi all I would appreciate some ideas to troubleshoot a weird issue. I have built multiple 3D printers of different types and this is my own design of CoreXY, of which I have built several examples, so I am surprised to be having this issue, and it's either going to be something ridiculously simple I forgot, or something tricky to troubleshoot. I need to try to fix this by Monday...! Environment: 2 Printers in one chassis, each is running: Arduino Mega 2560 Clone RAMPS 1.4, Diode D2 removed. ATX PSU Latest Marlin. Pronterface Marlin has been heavily tweaked for optimal behaviour on a CoreXY. On one of the 2 3D printers, it behaves correctly. It homes first -X to a min X opto endstop, then positive Y to a Y max opto endstop, then negative Z to a Z min inductive sensor. On the other 3D printer, wired identically, with the same components, same firmware installed one after the other, I get a different behaviour: It homes first -X to a min X opto endstop, then negative Z to a Z min inductive sensor. Y homing is skipped altogether. I tested both machines having already homed manually each axis, then powered off, unplugged USBs and closed and re-opened Pronterface. The weird thing that is throwing my troubleshooting, is that on the misbehaving printer, I can home the Y axis perfectly, every time, and the endstop always reports correct status. I have already tried swapping out the Y endstop and wire for a new one that works perfectly on the other printer. What on earth could be causing this different behaviour in homing, on one of the two identically built printers running the same firmware? https://reprap.org/forum/read.php?1,641477,641477#msg-641477 Sun, 16 Aug 2026 00:12:22 -0400 Phorum 5.2.23 https://reprap.org/forum/read.php?1,641477,641895#msg-641895 https://reprap.org/forum/read.php?1,641477,641895#msg-641895 1) Homed x, then y.
2) z +20
3) Motors Off
4) Manually pushed X carriage to about Y -100, X +100
5) Home all - behaved correctly X-Y-Z

Repeated steps 2-5 4 times - all perfectly.]]> alexgibson3d General Sat, 19 Mar 2016 19:02:53 -0400 https://reprap.org/forum/read.php?1,641477,641890#msg-641890 https://reprap.org/forum/read.php?1,641477,641890#msg-641890 1) Homed x, then y.
2) Sent Y -100, X +100
3) Motors Off
4) Home all - behaved correctly X-Y-Z
Repeated steps 2-4 4 times - all perfectly.

Test 2:
1) Homed x, then y.
2) Sent Y -200, X +200
3) Motors Off
4) Home all - behaved correctly X-Y-Z
Repeated steps 2-4 4 times - all perfectly.

Test 3:
1) Homed x, then y.
2) Sent Y -200, X +300
3) Motors Off
4) Home all - behaved correctly X-Y-Z
Repeated steps 2-4 4 times - all perfectly.]]> alexgibson3d General Sat, 19 Mar 2016 18:49:21 -0400 https://reprap.org/forum/read.php?1,641477,641882#msg-641882 https://reprap.org/forum/read.php?1,641477,641882#msg-641882
It seems to be intermittent, and may depend upon where I have pushed the carriage to before homing...

Test Method:

1) Home X-Y-Z via Pronterface
2) Note behaviour A
3) Motors off
4) Push carriage to rough middle of build bed
5) Home X-Y-Z via Pronterface
6) Note behaviour B]]> alexgibson3d General Sat, 19 Mar 2016 18:27:51 -0400 https://reprap.org/forum/read.php?1,641477,641848#msg-641848 https://reprap.org/forum/read.php?1,641477,641848#msg-641848 alexgibson3d General Sat, 19 Mar 2016 16:13:47 -0400 https://reprap.org/forum/read.php?1,641477,641498#msg-641498 https://reprap.org/forum/read.php?1,641477,641498#msg-641498
Off-topic (kinda): do you mind posting picture of the printer? I am intrigued by the "2 printers in 1 chassis". Also, what tweaks did you do to optimize Marlin for a CoreXY?]]> gmh39 General Fri, 18 Mar 2016 16:51:31 -0400 https://reprap.org/forum/read.php?1,641477,641484#msg-641484 https://reprap.org/forum/read.php?1,641477,641484#msg-641484
X backs off 5mm, then returns to home (min endstop), then Y homes to max endstop as it should! Then Z homes correctly.

So the incorrect behaviour is narrowed down to on one of 2 identical machines, if X is not already homed, G28 will home X, skip Y, and home Z.

Ideas anyone please?
Thanks, Alex]]> alexgibson3d General Fri, 18 Mar 2016 16:19:03 -0400 https://reprap.org/forum/read.php?1,641477,641477#msg-641477 https://reprap.org/forum/read.php?1,641477,641477#msg-641477
I would appreciate some ideas to troubleshoot a weird issue. I have built multiple 3D printers of different types and this is my own design of CoreXY, of which I have built several examples, so I am surprised to be having this issue, and it's either going to be something ridiculously simple I forgot, or something tricky to troubleshoot. I need to try to fix this by Monday...!

Environment: 2 Printers in one chassis, each is running:

Arduino Mega 2560 Clone
RAMPS 1.4, Diode D2 removed.
ATX PSU
Latest Marlin.
Pronterface

Marlin has been heavily tweaked for optimal behaviour on a CoreXY.

On one of the 2 3D printers, it behaves correctly. It homes first -X to a min X opto endstop, then positive Y to a Y max opto endstop, then negative Z to a Z min inductive sensor.

On the other 3D printer, wired identically, with the same components, same firmware installed one after the other, I get a different behaviour: It homes first -X to a min X opto endstop, then negative Z to a Z min inductive sensor. Y homing is skipped altogether.

I tested both machines having already homed manually each axis, then powered off, unplugged USBs and closed and re-opened Pronterface.

The weird thing that is throwing my troubleshooting, is that on the misbehaving printer, I can home the Y axis perfectly, every time, and the endstop always reports correct status.
I have already tried swapping out the Y endstop and wire for a new one that works perfectly on the other printer.

What on earth could be causing this different behaviour in homing, on one of the two identically built printers running the same firmware?]]> alexgibson3d General Fri, 18 Mar 2016 16:01:56 -0400