Only uses the top 10 mm of y axis

K40 with M2

Cohesion3d Laserboard

Firmware: _Smoothie

Summary: Everything seems to try to burn in the top 10mm zone of the y axis. If the image is larger than 10mm, Lightburn tries to move the laserhead above that section to continue burning but, of course, just keeps banging on the gantry.

In the video, I use Lightburn to burn a 5mm square so that its top left hand corner is at x1,y205. The burn works perfectly and in the right location. However, if I move the same 5mm square to x1,y100 in Lightburn, it burns the square at something like x1,y200. The second square burns the right size and shape - but it is in the wrong place. If you try to burn an image larger than 10mm, the laser head bangs on the gantry at the top, apparently because Lightburn thinks the laser head is where it should be (i.e., around x1,y100).

I’ve set the bed size to x300, y210. You can access pics, video and configuration files at


Hi Rab,

Welcome to the forum!

Please check your dropbox link, as it is directing me to a URL to sign in using your email address.

We recommend starting with this article, specifically with the origin video at the bottom. Some of the features in LightBurn have been updated since it was created, but the fundamentals are the same: Laser Head Crashing Into Gantry

If you still continue to experience issues, please provide clear pictures of your machine, control panel, board, other electrical components, and wiring. We need to see how and where everything is connected.

Thanks for the quick response. I will begin the troubleshooting tasks you suggested. Sorry for the link failure Please try this link for pics, videos, etc.:

Results of M119 test follow. Am I right in thinking that these are correct?
Head in middle of bed (no contact with endstops):
X_min:0 Y_max:0 Z_min:1 pins- (X)P1.24:0 (X)P1.25:1 (Y)P1.26:1 (Y)P1.27:0 (Z)P1.28:1 (Z)P1.29:1

Head at X Endstop (left side middle):
X_min:1 Y_max:0 Z_min:1 pins- (X)P1.24:1 (X)P1.25:1 (Y)P1.26:1 (Y)P1.27:0 (Z)P1.28:1 (Z)P1.29:1

Head at Y Endstop (top middle):
X_min:0 Y_max:1 Z_min:1 pins- (X)P1.24:0 (X)P1.25:1 (Y)P1.26:1 (Y)P1.27:1 (Z)P1.28:1 (Z)P1.29:1

Head at Home (top left of bed):
X_min:1 Y_max:1 Z_min:1 pins- (X)P1.24:1 (X)P1.25:1 (Y)P1.26:1 (Y)P1.27:1 (Z)P1.28:1 (Z)P1.29:1

I’m still working my way through the troubleshooting list you provided. Number 2 was to check the endstop cables. They are connected and do not seem to be at all loose.

Troubleshooting step 3 says to consider changing stepper motor currents on the LaserBoard if you are experiencing stepper motors which are buzzing, whining, skipping, or not turning as expected, In my case, this has not been an issue. The stepper motors work fine when making manual moves via the Lightburn software “Move” module. (I’m not sure this is relevant but I hooked up the M2 board and the stepper motors work fine using it.) Just let me know if you think I should pursue that step.

I have followed the instructions for troubleshooting step #4 for “Setting Up the Correct Bed Size”. Lightburn is set up for a 300,210 bed and the config.txt file is set up to match it. When I use the Home button and then check the Get Position button, it reads “X: 0.00 Y: 210.00”

In troubleshooting step #5, I found that the alpha_fast_homing_rate_mm_s and beta_fast_homing_rate_mm_s were already set to 50. I assume these should not be decreased further. Please let me know if you think I should try that.

Troubleshooting step #6 says to ensure that optical endstops are clear of debris. That doesn’t appear to be a problem here.

Troubleshooting step #7 says that “If your endstops are not stopping the job when triggered” I should uncomment and enable the alpha_limit_enable and beta_limit_enable values. I tried this but it seems to cause problems. I could no longer use LIghtburn’s “Move” module to jog the laser head. Each time I tried to move it, the console responded with:
error:Alarm lock
On or near line 0:
I have reset the original settings. Please let me know if this tells you something about what might be wrong.

In troubleshooting step #8, my original settings were:
alpha_max_travel 500
beta_max_travel 500
As the step suggested, I reset these values to equal the bed size and they now read:
alpha_max_travel 300
beta_max_travel 210

However, this did not solve the problem. There was no apparent change in operation. I assume I can leave these settings at 300,210. Please let me know if I should return them to their original values.

Troubleshooting step 9 refers to a situation where “your machine homes to a different location than rear left or moves opposite of what you expect” which is not a problem for me. The machine homes to the correct position so I did not make the changes recommended there.

One of the suggestions at the bottom of the troubleshooting list was to “Try working from Absolute Coordinates in LightBurn”. In fact, that is the setting that I’ve been using all along. When I use the “Current Position” setting, I can jog to any reasonable spot on the bed and the 5mm square will burn just fine. It seems to be only when I use the “Absolute Coords” option that I am limited to the top 10mm zone. Does that tell you anything about what the problem might be?

Hi Rab,

Thanks for your patience while I am getting caught up on posts. I looked at your videos and config file. I really appreciate you walking through each of the steps and providing specific results for each one. It helps us rule out so many factors.

I’ll walk through your posts below:

Yes, your endstop test results look good.


Your currents are set to the default in the config file and should probably be increased. The behavior could be caused if your current is not set high enough on the drivers, potentially causing the motors to not produce the needed torque to operate properly. Double check the current rating for the stepper motor specs that you have installed. I’ll reword this part in the doc about “not turning as expected” to outline this a bit more detail. Thanks for pointing that out.

Step 4 - Perfect, this is expected.

Step 5 - This is fine as-is.

Step 6 - Great!

Step 7 - Keep this disabled with the # at the beginning of the line.

Let me know if the current update changes the results.

Thanks for the reply, Starla. Regarding the alpha_current and beta_current settings, I am having difficulty knowing what setting is appropriate for my stepper motors. The problem is that this is a K40 machine for which, of course, there is little documentation. And, doing a search using the number on the stepper motor hasn’t provided any help. The original setting was:
alpha_current 0.4
beta_current 0.6

I have changed these to:
alpha_current 0.8
beta_current 1.0

Without specs, is there any way to ensure I am not increasing this value too much? I have felt the motors to see if they are getting hot and they are cool. Is that an adequate way to ensure the value is okay? Or is it still possible that this may damage the motors?

I have been trying to narrow the problem down a bit. The problem seems to be rapid movements on the y axis. I have tried to prove this by using the G0 command from the console. The command works fine for any distance on the x axis or for short distances (up to 40mm or so) on the y axis. However, if I try to rapid move on the y axis 50 mm or so, it fails. (Using the G1 command for these distances does not cause any problems, at all.)

Previously, I indicated that there were no “buzzing, whining, skipping, or not turning as expected” problems. I now realize that this is not the case when doing rapid movement. It does, in fact, “whine”!

So, based on previous comments, I assume you would recommend continued increases to alpha_current and beta_current. If that is the case, can you provide some recommendations for how high I should push this?

Also, I wonder if you might recommend I try changing the y_axis_max_speed. It is currently set to 24,000.


Hi Rab,

You mean the so-called “User Manual” was not very helpful? :wink:

Can you get a picture of the stepper motors? They may be difficult to reach, but a clear, bright picture or the model number you have been researching would help.

Yes, you are on the right track here. There are a few settings that are set optimistically. We cover the most common ones that you can update to help dial in your machine: Configuration Adjustment Guide

The problem seems to be resolved with the changes to config.txt, specifically changing default_seek_rate to 12000. If you have any suggestions regarding the ideal current for the stepper motor (see picture above), they would be welcome. Thanks for all your help!

Hi Rab,

I’m glad that resolved the issue. Those are Nema 17 hybrid stepper motors and very common.

The default settings should be a good starting point for the stepper motors, but you can increase your alpha and beta currents, incrementally bumping it up 0.2 amps at a time to fine tune. Just make sure they are not getting hot to the touch. More information: Changing Stepper Motor Currents

You can also try lowering the acceleration settings (ex: 1500) also and test with incremental increases or decreases, until fine tuned, to dial it in further.

However, if you’re getting good results now, I would caution making too many changes to the config at this point.

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