Wavy lines only when raster engrave large area

Hi all, first time post here. I’m hoping someone with more experience can help me out. I have only been using my K40 for 2 weeks. There’s an issue that I can’t seem to get to the bottom of.

When I perform a raster engrave over a large area (approx 150mm), the verticle lines are wavy. However, if I perfrom the same raster engrave over a smaller area (approx 50mm), the verticle lines are straight.

From reading other posts, I have tried the following with no luck.

  • tightening the X-axis belts
  • loosening the X-axis belts
  • ensured the lens holder is tight
  • mirror alignment is good (parallel, and quite accurate)
  • don’t feel any “kinks” when manually moving the x-axis
  • tried different speeds

Here are some test and photos I have performed:
grid test - vector engrave - lines are straight
cirlce test - vector engrave - circles are good, all joins up
grid test - raster engrace - speed 100mm/s vs 300mm/s - verticle lines wavy
scanline test - looks ok to me

K40 Whisperer
Windows 10
tried on two laptops
svg file - 10mm x 10 mm squares, lines 0.5mm thick

Any ideas? help is much appreciated. Thanks.

Hi @Martin_Lim! Welcome to Maker Forums!

When you try to turn the wheels on the carriage and gantry, do any of them spin freely, or do you feel a little bit of resistance to turning on all of them?

Also, you should now be able to post more than one picture. :slight_smile:

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thanks for the quick response. Yes more than one picture helps.

Looks ok to me. I see all 4 wheels spinning.
But I can’t really tell if its good or bad. Here’s quick video.

Forgot to mention I did took the whole carriage apart and tighten the eccentric nuts a few days ago. I tried a tight carriage, and a loose carriage as well.


here is another video from the side.
I do notice the wheel slightly moves up and down.
Not sure if this is severe enough to translate to any issues.

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But at each wheel, if you try to move it with your fingers while lightly putting different loads on the carriage (up, down, front, back, twisting on each axis) do any of the wheels turn at a light touch in any of those cases? If they turn at a light touch, then they are too loose and need to be very slightly tighter. You should feel resistance to turning in each case.

I would expect that if you can notice it going up and down, you would notice the result of backlash from it going up and down while running.

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Loose wheels on the carriage for the laser head would have been my first guess as well. But he doesn’t have issues with vector engraving which is where the issue is typically prominent.

Bit of a head scratcher as I don’t think I’ve seen this before. It’s possible that a bad carriage wheel that wobbles could be the issue.

Can you provide a video of raster engraving a box?

Hmm… One wheel is looser compared to the others. But I wouldn’t describe it as very loose.

I’m scratching my head even more now.

Test 1:
engrave a 20x20mm square. looks ok.

Test 2:
engrave a 100x10mm rectangle. looks ok.

Test 3:
a series of square outlines. wiggly again.

(videos coming up, taking a while to convert them)

Maybe its my svg file?
Test File

If you notice it being loose at all, something is wrong. Is it loose in the sense of moving axially or radially? That is, can you imagine making it tighter with the eccentric or by tightening the screw through the center? In the later case you might add a small washer as a shim.

engrave solid square

engrave solid rectangle

engrave hollow squares - wavy lines

video of wheel radial slip.

do you think this needs some tightening?

Not obviously to me…

I notice in the one streamable video I could see that something seems to be bouncing a little bit when it reverses at the left, enough that the camera loses focus. Is there any chance that the cardboard is shifting slightly?

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After reviewing the videos, I did notice that as well. However, I think it is just the lid of the K40 vibrating when the x-axis changes direction. I just place my phone camera on top of the lid.

Test: Tape vs No Tape
To further rule this out. I ran a test with taping the work piece to the surface, vs no taping.
The results looks quite similar.

Test: Large Engrave area vs Small Engrave area.

again… still consistently getting better results when engraving smaller area.

next steps…
Not sure if I can think of anything else. I might just take apart the whole x-carriage and see if theres anything interesting.

I guess it was a long shot.

Still seems that something must be physically loose though. This really looks like some sort of backlash. Have you checked all the mirrors and the lens?

Did you solve this? I have 2 k40 lasers that have had this problem. I am currently trying to figure it out.

I was having the same issue recently whenever I would have an engraving area over 115mm wide. I ended up fixing my issue from checking my carrier wheels AFTER cleaning my gantry and rails thoroughly. Things had gotten pretty dirty in there, so when I originally checked my wheels, they felt fine. But after cleaning my machine, I noticed that two of the wheels were a bit loose. After adjusting and tightening them, it was better but still would get wavy lines, just not as intense. I checked the tension in my x-axis belt and loosened it just a tad because I could hear a slight whirring noise whenever it would raster engrave and change direction. This seems to have fixed my issues for the moment! I am by no means an expert here, but this is what has worked for me!

Hope this helps at least a little