K40 not moving correctly when taking big leaps

Machine: Blue and white K40

Board: cohesion3D laserboard

Firmware: Smootie

Problem/ Question: I just replaced the board (m2 nano to cohesion3D laserboard) and I wanted to test the machine. Settings are still stock settings. When the machine starts up, it goes to the home position.
When pressing the “frame” button however the machine hardly moves along the Y axis (forward, to front of machine), but it moves ok along the X axis.

When doing some test lasering (actually a tryout for a new control panel) it messes up the parts where the Y axis needs to do some big “leaps” towards the front of the machine. It does not move the necessary amount, so it offsets parts of the design on the wrong place.

Included are some pictures that show the problem. The problem is consistent (tried 3 times), but the offset error is not always the same. When engraving (and thus moving slow steps backwards) the problem does not seem to be there.

Anyone have a clue what’s going on here? Didn’t have the problem with the m2 nano, so I hope it’s a config problem

IMG_4778 IMG_4779 IMG_4780

Sounds like your steppers are skipping steps. Check your speeds and acceleration settings and make sure your linear rails are clean and move freely. Make sure your belts aren’t over tight.

Hi Tim,

thanks for the feedback. Based on your reply ( and a post I found after writing down my problem) I tweaked 3 settings

default_seek_rate 24000 -> 9000
acceleration 2500 -> 1000
beta_current 0.6 -> 0.8

Now both axes are moving as they should.

Now to a new problem, and it might be related to my tweaking. In the attached picture you can see that the the topmost design has really much darker (deeper) engravings than the parts in between. This is where the laserhead comes to a stop (and goes to the other side)

The lower image is much clearer, but that is because I added 2 lines to the left and right of the image (not shown) so that I force the lasercutter to move all the way to those lines.

What setting can cause the much deeper engraving at the line ends?

best regards,


I think if you have to decrease your speed and acceleration that much and increase the current you have a mechanical problem on the Y axis. I’d double check how easy the Y axis moves and how tight the belts are.

As to the burns at the edges you might enable Overscan in Lightburn in the cut settings editor. Thats basically what you did by adding lines to the sides.

ETA: Also I’m not exactly sure what the Acceleration setting under Planner Module is, if it’s a global setting for all axis or for something else entirely but if your having problems with the Y axis I’d try only changing control settings under that, for example beta_acceleration, beta_max_rate in your case since it seemed you were missing steps on the Y axis.

Thanks, I’ll try your tips. Especially the overscan is interesting!



Hi Tim,

overscan worked perfectly, thanks! The gantry needs some rework, but if i lower the speeds enough the shapes come out the way I want them. Thanks for all the help, guess the way forward is to build my own laser now :slight_smile:



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