Ortur LM3 Y-Axis issues

ggosling · August 29, 2023, 11:34pm

An ongoing issue with my LM3 since I got it a few weeks ago is that the Y-Axis is off. Didn’t notice it at first as I was happily showing off to myself at how much quicker it was than the LM2 Pro it was replacing.

Then I went to cut out a quick circle and noticed it was slightly flattened in an odd way. Some quick tests to do rectangles of say 20mm x 100mm and it was clear that the on the Y axis they were always shorter.

All the usual YouTube searches and nothing resolved it. My extension kit then arrived and I went through the set up and it was identical. Spoke with Ortur support and they suggested the Y-Axis alignment (hadn’t seen that on the set-up for some reason). Did that and it made it far worse - any movement on the Y-Axis was extremely noisy and Lightburn reported back that there was a vibration error. Also it would home about 30cm from the actual home.

Took it apart again and loosened the alignment slightly (possibly 2 or 3mm) and the Y Axis is no longer noisy and the home is correct, but the circles are still crazy.

Back on to Ortur and have sent photos along with Lightburn files that I was using to make sure I’m not going mad.

I saw that someone else had a similar issue although they were concerned that their machine was a refurbished unit. Unfortunately there was no ultimate resolution posted.

Has anyone else had this issue?

ggosling · August 31, 2023, 9:06pm

A quick update from Ortur was simply to check that the tension on the Y-Axis was set up correctly.

I’ve gone back and rebuilt the machine again and loosened the tension which was suggested by Ortur tech support but it has had no impact whatsoever.

I think that most likely cause is a faulty stepper motor on the Y-Axis. Unless there’s some magical setting in Lightburn that’s causing this.

All very annoying as I can’t produce anything with confidence at the moment.

JohnJohn · September 1, 2023, 6:04am

This sounds like mechanical backlash. This can be caused by loose components or by running a machine too fast when it has a little bit of ‘give’ in it.

What speed in mm/minute did you select for testing?

Some folks attempt to work in mm/second and the lighter machines and smaller motors aren’t really designed for it. We’ve also seen odd shapes caused by ‘Compliant work surfaces’. A tea-cart or a TV tray can flex and generate unanticipated geometry. I’ve seen it a couple of times so I felt I should mention it.

This is strange and it sounds like a questionable Y-Axis motor drive (4 wire) cable or mechanical binding.

Do you have a link to the Y-Axis alignment procedure that you applied?

I really would like to understand what is meant here.

If you read this message in the Console window in LightBurn, this would be the controller in the LM3 reporting it. This distinction is important and it will help greatly with troubleshooting.

This could be mechanical binding as well.

Previous engravers would have tried for a while and thrown an error message related to ‘Failure to home’. More recent engravers have a load sensor watching the stepper motor. With this enhancement, homing will complete when the motor finds a sufficient obstacle - like the maximum travel toward home, or something binding up and pushing the motor toward overload.

The good news here is that if the Y axis cable was bad, it wouldn’t have been able to find ‘load’ and complete homing.

I don’t have this engraver here so I need to ask a few questions.

Are there two stepper motors moving the gantry along the Y-Axis?
Is there a ‘jack-shaft’ connecting the belt drives (and/or motors) on each side together?

Not if it’s binding.

The controller firmware has a Machine Setting in steps per mm and thankfully, Ortur publishes the settings.

$100 = 100 steps per mm (X-Axis)
$101 = 100 steps per mm (Y-Axis)
$102 = 100 steps per mm (Z-Axis - usually)

https://ortur.tech/latest-firmware

Here’s a breakdown of what the settings mean:

github.com

gnea/grbl/blob/master/doc/markdown/settings.md

## Getting Started

First, connect to Grbl using the serial terminal of your choice.

Set the baud rate  to **115200** as 8-N-1 (8-bits, no parity, and 1-stop bit.)

Once connected
 you should get the Grbl-prompt, which looks like this:

```
Grbl 1.1d ['$' for help]
```

Type $ and press enter to have Grbl print a help message. You should not see any local echo of the $ and enter. Grbl should respond with:

```
[HLP:$$ $# $G $I $N $x=val $Nx=line $J=line $SLP $C $X $H ~ ! ? ctrl-x]
```

The ‘$’-commands are Grbl system commands used to tweak the settings, view or change Grbl's states and running modes, and start a homing cycle. The last four **non**-'$' commands are realtime control commands that can be sent at anytime, no matter what Grbl is doing. These either immediately change Grbl's running behavior or immediately print a report of the important realtime data like current position (aka DRO).

This file has been truncated. show original

The first step is to request the Machine Settings from the controller and see if the factory values are present and identical.

In the Console window in LightBurn type the following:
$$
then press Enter.

Scroll back in the window and look at $100, $101, and $102. and make sure they’re the same. You can get unusual shapes and terrible results by applying axis calibration to a machine that’s binding. So, I’m half-hoping these numbers are way out.

With the extended Y-Axis kit installed, you should have a larger value for $131, Please confirm that you’re seeing 700 or 750ish instead of 400.

You can change the steps per mm back to the factory values the same way you hopefully changed the Y-Axis Length for your extension kit.

In the Console window in LightBurn type the following:
$101=100
then press Enter. If the setting was already 100 it won’t change anything.

Since the published numbers for the three axes are the same, the pulleys that contact the belts should all be the same and have the same tooth count.

A bad pulley could cause binding but I haven’t seen a single case of it.