This just started happening a few days ago. At first I thought it might be the new project. So I re-did a project from over a week ago and the same thing is happening. Nothing has changed (that I know of) in the software or hardware. Any ideas on what could be causing this oddness?
What speed are you running and what are your GRBL settings? Looks like you are scanning bi-directional and are losing steps after direction changes. Are you hearing any unusual noise when the laser changes direction or see it “jump” a little?
This burn is 1200 mm/min as I have on many tiles. The feed and speed was set long ago that seemed to work well. I thought it might be something to do with my missing overlap setting but that turned out to not be the case. I have not made any setting changes to the controller in many weeks. No new noises like something is skipping or jumping. I am burning bi-directional.
Belt tension I guess if you haven’t increased the speed of the x axis and you don’t hear any noise either.
Belt tension and freedom of movement were the first things to be checked. I made some settings changes to see if that would help. I need to do a little more burning to see. I made sure to have an overlap set so the laser would travel past the edge of the burn. I also changed the movement speed to be the same as the cutting speed. We will see if that helps. I haven’t needed to do this in the past. It just started on Monday this week (6/29/2020).
Here are two burns I did using the same project. The difference is the one on the left was burning at 1,200 mm/min at 85% power and the one on the right was 1,000 mm/min at 100% power.
The one on the right has much better lines than the one on the left where there is so much wavy burning where it should be straight.
Your example shows that it is a mechanical problem you are battling with. I guess if you slow down to 800mm / min everything will be ok. Are you sure your settings are the same ?, I’m thinking about your acceleration setting, for example …
And, if you rotate your subject 90 degrees, is the problem also rotating 90 degrees?
The only setting change between the two tiles in the last image was the speed and power setting. I agree there seems to be a mechanical issue that seems to be somewhat random. I did find a couple loose set screws and tightened them up. I will do some burns to see if that was it. But those would have been loose for months as they were very loose.
I was wondering if it was a acceleration/deceleration issue as well. The machine will run at 10,000 mm/min so I am running around 10% of full speed. I did make a setting change to it would not speed up when it was just moving and not burning. That didn’t seem to help at all.
I will try your suggestion of rotating 90° and see what happens. I do not think it is software.
I rotated the image and burned it. It is still wavy. The wavyness is different now as you would expect with a physical issue with the machine. I did notice there is a slight wobble in the gantry. It was like that when I got it and I had put a fix in place. I re-did that fix as it isn’t really a permanent fix and I am testing now to see if that helps. At first glance, it is looking much better. I hope this is the issue as I would like to crank the speed back up a little when the laser isn’t burning. Just to make the overall burn faster.
I was thinking, have you recently added something to your laser head? My cable channel pulls up the entire laser nozzle slightly when it reaches the outermost positions.
Good thought. I haven’t made any changes to my laser or software. That is why it is so odd. I did have a string attached to the wiring that goes to the lasers head and servo. I took that off to see if it had started causing an issue. I am burning right in a sweet spot for the laser to there is minimal movement of the wiring.
I have done one burn since I tightened up a couple set screws. That burn did turn out better. Still some wavyness going on. Once I get some more burn in and see how they do, that will let me know if I am on the right track to figure this out. 
strange …, then there is only the speed left. If you set your speed, very far down, how is the result? (for testing only;-)
That might be what I end up having to do. I can run some speed tests to see if and when it start/stops being wavy. I have reached out to the manufacturer as well to see if they have any ideas or have seen this before.
I have tried a few things. I have removed the worn out electrocutions tape that I added to help reduce some slop in the X axis gantry. That helped some with a new layer but did not resolve all of the issue. I tried removing the tape all together and that didn’t help. Still better than it had gotten. I spent some time cleaning up the sticky left behind from the tape to see if that would help. No change. I am doing a test burn now with a single layer of a thicker tape but only on one side. That is going OK but still some issues. I may go back to electrician’s tape and try two layers to see if I can remove all of the wiggle of the laser gantry.
Very frustrating when the laser had worked very well for several months and then all of a sudden, wavy burns. And nothing seems to eliminate them. I may do this one last test with the tape and if that doesn’t fix it, also try rolling back the LightBurn software to see if the older version I had been using makes any difference.
You can always test drive your laser with an alternative control software if you suspect a problem from this site. On the other hand, it is also hassle-free to switch between the different versions of Lightburn, it takes me approx. 3 minutes on my Mac and 2 minutes on my old Win7 PC. Good luck!
I really do not think that LightBurn is the issue. I am running out of things to try and rolling back a version or two is easy enough to do as I have several versions back to try. I will do that and let everyone know how that turned out.
no, I did not think so either but to test all possibilities it is ok. I still think it’s due to a mechanical problem.
I rolled back to .11 as that was the last version I had installed before .14 and it is still not burning quite correctly. I am going to try adding a little more support on the bottom of the gantry to see if that does anything. If that doesn’t fix it, I am at a loss on this one. 
Not sure what is going on. I have tightened the belts, squared the frame and the gantry to each other, tightened, adjusted, lubricated, changed speeds, changed resolution, change fast movement, and tested. Some burns look good, some don’t. It seems that faster burns work OK and slower ones get worse. I have tried to slow down or eliminate the fast movement between burns and that seems to help. So with slower burns I just might have to start doing that. With faster burns, it didn’t seem to matter.
Something is different as I can run older projects and not get the same results I had when I first ran them. I am at a point where I just want to be able to burn something and not worry about it working correctly or not.