Squiggly lines on Boss LS3655 with Lightburn

Squiggly lines on Boss LS3655 with Lightburn
We got another Boss LS3655 delivered and setup went smoothly, belts are tight, lens is tight, mirrors are spot on, Bed is level, Head is 90^, alignment is perfect. We double checked everything. no issues. But, it’s printing squiggles on smaller font 1" size in light burn. these are Pre-loaded Fonts in lightburn, so no squiggle in the Original. Tried Sending to machine, vs. Start from Computer, no difference. Slowed everything way down no difference, until we hit about 50mm/s then it starts to go away. But, no way should it require that slow. Again 3" Letters, no problem 1" letters, gets Squiggly. Any recommendations on what this could be ?


I can see it when it’s drawing the X axes, but it’s in the Y direction.

This has got to be mechanical… I’d double check the Y axes, something like backlash may be to blame.

On mine, these are the most difficult to get too and adjust…

Good luck


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The first column of small Ss (Esses?) seems to squiggle in the same places. The Second column of Ss does not. If you changed engrave speed, you’ve probably found the cause.

I would repeat the test with the small letters. then with the laser powered off, move the engrave head to where the letters are being produced incorrectly and mark the x-axis drive belt where it wraps around the drive and idler sprockets (or pulleys).

Dust or debris on the hidden tooth-side of the belt can make an error repeat sporadically but always along a vertical or horizontal line. Here, it seems to be along one vertical line in one batch of letters and in a different vertical line further over in another batch of letters.

With the line being vertical, it appears to be introduced by a horizontal position.

I would check the toothed side of the X-Axis belt (where I suggested it should be marked) to see if anything is being run-over by the drive or idler pulley. Running over a bit of debris will tighten the belt and may make the engrave head move slightly. You may even feel binding of the mechanism by debris (or a damaged belt, or just a dry spot on the gantry) if you move the laser head by hand (with the power off of course).

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I’ve had similar in the past, in my case it was a loose lens in the laser head.

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Thank you for all the feedback.
I’ve read on other posts about adjusting the JERK, but that seems to have been removed from lightburn. Just wondering if the accelerations numbers are causing too much stress on the belts?

Doubt it, these are timing belts for engines. heir real only drawback is they are designed to run in one direction. They have virtually no stretch compared to the old belts I was used to… they can still stretch, but I doubt that’s the problem. If anything, I would think it would manifest itself as backlash.

Can’t help you with jerk… I run Ubuntu Linux, so RDWorks is a mystery to me as far as what’s available on it. I have it on the spouses machine. I’ve seen that it runs…

Good luck


So did another test print. It definitely, seems to be a X Axis only issue.
Notice the mm on the bottom right are good, but on the Top Right are not.

That being said, I cannot figure out why, it happens in the red lines, vs. the Blue lines.

If you look at the Lines noted in Blue they are good.

Just above or just below in Noted in Red, they are squiggly. Both are X-Axis Movements.
Makes no sense.
It’s very odd.

Any feedback or opinions ??

FYI All these letters/numbers were cut a the exact same speed.

Just to verify: when you say “Both are X-Axis Movements”, the X axis is left-to-right in that picture.

If that’s the case, then there’s mechanical backlash in the Y axis, because it does not begin moving when it should and continues moving after it should stop. The squiggles are perpendicular to the X axis, which is dutifully hauling the laser head along.

There’s a loose screw somewhere between the Y axis motor shaft and the laser beam. My first guess, as always, is the setscrew securing the pulley to the motor shaft, so that’s a good place to start.

The number of times I’ve been absolutely certain I checked something, only to eventually find the problem was right there and how could I possibly have missed it right before my eyes is too large to mention.

But it only does it when it comes OFF an arc. Regardless of direction.

Loose Screws, or loose belts or something loose… would show up more and be less consistent.

These samples show a very consistent behavior.

Still Just makes no sense.


The Third Rule of Debugging in the poster over my electronics bench reminds me:

Stop Thinking and Look

Otherwise, I’ll spend a remarkable amount of time telling myself why that reason can’t possibly cause that failure.

Another rule, taught by the best engineer I ever worked with:

When you find an unrelated problem, fix it

Mostly because there are no unrelated problems.

You’ve got it failing on command, which is incredibly valuable. Now you must methodically examine everything to find out what’s happening. Anything you ignore because that can’t be the cause will stay there, waiting patiently.

Source: been there, done that. Need a t-shirt? :grin:

If it’s not a violation of copyright, please post an image of your troubleshooting poster in Community laser talk.

I just saw the link - thanks!

There’s a phenomenon in 3D printing called Ringing. In the current project - oscillating behavior is more pronounced so it could be that.

Resonant mechanical structures will fall out of the resonant range when the speed is increased or decreased by 10-20%. The ringing or oscillating isn’t in the direction of travel but it is in the direction of deceleration.

If the engraver is exiting the arc with a little too much centripetal motion it might be ringing the gantry.

Would you be willing to retest with 20% lower maximum acceleration at the same speeds (all other things equal)?

Same thing with a motorcycle… high speed wobbles are generally caused when you slow down. The proper fix is to accelerate out of it… otherwise it’s asphalt rash time, at best.

This goes against most riders intuition, so you head has to override the intuition to slow down…


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A dirt motorcycle rider I knew put it this way:

When you get in trouble, screw on more power!

Which, when taken to extremes, can get you into more trouble:

I think that was a guerilla art project and, OK, it’s a dirt bike, but, anyway …

Great information everyone. Thank you

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