I am using a GRBL MKS DLC32 controller. When I do the “Focus test” The results are not as expected. My first attempt. The bed moved up and down during the test, and to me it looked like it was firing every time at the start position and not at the required new Z position. I then disabled Z optimization. Which fixed the problem with the bed moving up and down. But now the bed moved in the incorrect direction. Instead of moving down after every burn. It’s moving up. But swapping the Z direction will not fix this as the bed moves in the correct direction when using the controls on the move panel. Is there some other setting that I should be looking at to make this work?
I’m using Lightburn 2.0.03
Does that Reverse Z Direction in the Device Settings window affect the Jog direction if you turn it on?
Hi Mikey,
If I turn on reverse Z direction. When I press the up arrow on the move tab. It moves down. So it then moves in the incorrect direction.
It was worth a try. 
Did you try it with LB v1.7.08? Trying to isolate if it is a new “feature” or not.
Homemade machine, what dialect of GRBL are you using?
Curious, you said the table moves. So which direction does it go if you enter G01 X10 Y10 Z-5 S0 F250 in the Console Window?
The X10 Y10 work as expected. But both Z-5 S0 F250 and Z5 S0 F250 move the bed up.Version of GRBL is:
[PRODUCER:MKS DLC32]
[V2.30(8M.H35.20231206)]
[VER:1.1h.2023120602:]
[OPT:VMPH,63,512]
Target buffer size found
[MSG:Using machine:MKS DLC32]
[MSG:No Wifi]
Did some more testing and G1 Z-5 F250 and G1 Z5 F250 work correctly
Which one made the bed move up?
A Zaxis on the trolley (laser or spindle) will move down with a negative command. The tool and workpiece move closer together.
This means a bed should move UP with a negative command, so the tool and workpiece (on the bed) move closer.
Do you see why I am asking which way the bed moves with a negative command?
In other words, an UpArrow Jog should move the table down.
G1 Z5 F250 goes up and G1 Z-5 F250 goes down. But in the generated GCode there is no negative value for Z. So it’s instructing the bed to move in the incorrect direction.
I would expect it to go up so it moved the work closer to the laser. On a CNC, Z always Homes the farthest distance from the Work. I also expect your Table Homes away from the laser, to the lower position. You have not told us where it Homes, so I hope you built it this way.
The question is “How does it know which way to go if there are no negative?” Without knowing how your coordinate system is set up, this will be difficult to answer. As an example, using G90 mode we send it to +5. Then we send it to +3, which would be a negative direction. The controller does the math and says go back 2 units. Remember that although we see Work coordinates, the controller is always working in Machine coordinates.
Summary: If your Table Homes at the bottom position, then there is an easy fix to clear it all up. Using the Lightburn Device window (Laser window button),
- Reverse the Jog direction ($3) for Z only.
- Imagine the UpArrow button as “Increase Separation” instead of “Move UP”.
This should sort everything out. If I am wrong, you can always change it back.
Okay got it to work.
- Create focus test and then save GCode
- Edit GCode and replace G0 Z1 with G0 Z-1. Except last one which moves Z axis back up.
- Then import GCode
- Don’t press run
- Press “Run GCode”
Then it works. I installed Linux Mint on another PC and got it to work on V1.7 as per method above. But I’m sure it will work in the same way on my Windows PC.
But I understand what you are saying about the direction of movement on the Z axis. So I could probably invert the direction on the controller and then also within Lightburn. This may also fix the issue. Will have to do some more testing.
Thanks for the help.
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