OMTech says it’s normal to have wavy/wobbly lines when engraving a circle?

Hi all - hoping someone can help me fix an issue or at least tell me I’m not crazy.

I recently purchased an OMTech 80w 24x35 CO2 laser with autofocus and Ruida controller. Questioning that decision quite a bit. The laser has some signs of previous use or possibly poor manufacturing (or both) but Omtech assures me that it was not previously used.

Anyway, the laser will not cut clean lines when cutting or engraving on a curve or in a circle. The lines have some significant wobble that is clearly visible to the naked eye. The wobbles are there regardless of the speed and power, though they’re less noticeable if it’s below 15 mm/s. I’ve already tried checking all of the set screws and the belts are tight, but not too tight.

I called OMTech and had to pay $49 to talk to a technician for 45 minutes. We walked through a whole bunch of trouble shooting steps that I’d already tried (set screws, belts) and they said it must be a software or settings issue. First they said it must be lightburn and I need to try another software, but I only have a MacBook and I don’t think it’s a software issue anyway.

Then they said it must be a settings issue so they sent me new settings and asked me to load them and try again. I did that and the wobbles didn’t go away. Then after they failed to fix the issue their solution was to tell me that wobbles are normal. They said they did some test cuts on the machine in their office to make sure and that they had wobbles too. They said I should try engraving below 15 mm/s.

So I need some expert opinions. Is it normal for straight lines to be perfect but for curved lines and circles to be wobbly? Is 30 mm/s too fast to engrave curves? Is 5-15 mm/s a reasonable speed for engraving or is OMTech just not able to figure out how to fix the problem? Am I overreacting and these wobbles really are normal?

The examples here are cut at 30-35 mm/s.

Note that I’ve read through these 3 forum posts and have tried their suggestions but have still not been able to fix the wobble.

  1. Wavy vertical lines
  2. Circles are cutting rough after latest update

Thanks for the help! Please let me know what questions you have.

Here’s the third forum link. I wasn’t able to post more than 2 links.

  1. Help - Laser cutting shakey wobbly lines

To me, it looks like the “wobbles” correspond to the grain variations in your wood. Possibly at (x) power the grain variations don’t burn the same due to minor density differences. I dunno, sounds good in my head😁

What do you have your curve tolerance set to?

I have an OM tech 50 and a 60 watt machine…neither does that wobble thing. Both cut nice circles…and I don’t agree with their speeds. 30mm a sec is slow…not butt slow but it sure isn’t fast. I engrave anywhere from 120 to 250 mm a sec depending on what it is and I engrave some dinky features that would get ruined by excessive wobble.
Does it only do it circles but not on a square? I am curious if it is an issue when you move x and y simultaneously. How about a triangle where two side only move one axis but the hypotenuse is an x y move but in a line.

The fact that it looks fairly repeatable would indicate more of a mechanical issue. I know you said you have looked at everything but go back and start with the mirrors at the laser side and verify that nothing is jiggling or that you have anything that is vibrating the unit.

One way to try and narrow it down would be to cut a circle in each corner quadrant of the machine and see if it is still repeatable. That may help you narrow down what may be causing it.

Even though you haven’t found anything loose, you may want to look at the cabling and see if it is pulling or tugging in a certain way when you are in that 1:00 to 4:00 cutting area. Also see if it is repeatable if you cut the circles in the opposite direction.

Keep us informed and we will do our best to get you operational.

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I can give you a few suggestions 1: Check your X,Y axis machinery. Whether parts are loose, or mechanical clearance
2:This can also happen when the X,Y, and axis Settings in your RDWORKS software don’t match. Probably more on your X.Y. stepper drive subdivision, you can try to make this X and Y axis subdivision bigger, it will help you

Thanks. I’m using lightburn software. How can I check the X and Y axis subdivision?

Thanks for your response. It doesn’t seem to be a factor as I see the same wobbles when engraving on acrylic or powder coated metal.

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Thanks for your response. My curve tolerance is set to 0.025 mm, which I believe is the default setting. Should I change that?

Thanks for the feedback. I thought that was unreasonably slow. I took your suggestion and you’re correct. It is anytime the X and Y are moving at the same time. A perfect square comes out fine. But on the triangle, you clearly see the same wobble as in the circle.

I agree that all signs point to mechanical. OMTech just refuses to believe that. Today the tech told me that the wobble really isn’t that bad.

When I cut in all four quadrants, they all appear to be the same. When I reverse the circle, I still have wobbles but seemingly on the mirrored side. So you can see below the top circle is the reversed cut. The wobble moves from the bottom left to the bottom right. Yet more evidence of a mechanical fault.

If you create a 6" diameter circle, and set curve tolerance to .025, and export a GCode file, you end up with 288 lines that approximate the circle.

If you create a 6" diameter circle, and set curve tolerance to .10, and export a GCode file, you end up with 144 lines that approximate the circle.

I would try setting the curve tolerance to .10, and see if anything changes. If it is more jagged, there probably is something wrong mechanically.

Thanks, I’ll try that tomorrow.

Additionally, I’ve found that there is a squeak coming from the roller on the left side of the x axis gantry. Not the roller with teeth, the smooth one on the other side, where the tensioning screws are. So here’s my questions:

  1. Does that sound like it could be what’s causing the wobble?
  2. Do you know what’s causing the squeak and how to fix it?

Here are to pics of a circle done on my OM tech 60 watt. The settings are in the photo. I cut around 30 mm sec on average but could be a bit faster or slower depending on wood type…thickness etc.
Now you see the circle is decent at 40mm sec but jagged at 180 mm sec which is stupid fast to cut so I would never use that fast and I would expect to see this result anyway at this speed. Usually due to, I would guess, at non optimized accels and decel settings for that speed but again…don’t cut that fast and never would . But you can see what you should be getting at 40mm sec. thats about as good as I would expect and I have no issues with it.

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And before someone tells you to check your belt tension…and most people are way wrong on this actually but they don’t listen. Your X axis belt is a toothed timing belt. They are not supposed to be tight…just taught enough so the belt doesn’t jump a tooth. But read this sentence or two on belt tension from the actual manufacturer of timing belts.

Timing belt installation should be a snug fit, neither too tight nor too loose. The positive grip of the belt eliminates the need for high initial tension. Consequently, a belt, when installed with a snug fit (that is, not too taut) assures longer life, less bearing wear and quieter operation. Preloading (often the cause of premature failure) is not necessary.

O.k….so there you go. I know this anyway as I was a field engineer for a few years on high end robotics and we had to be taught proper timing belt tensions. People, including myself, tended to set them too tight. So I doubt any belt is too loose…actually I can almost guarantee it. It’s a red herring around here it seems unless it is so slack it jumps and that is so loose you would easily see it….easily.

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I read a majority of the responses and didn’t see anyone mention your laser head?.

  1. Is the mirror seated properly and no “giggling” around?

  2. Is the laser head secure?

When things like this happen I stop and think logically…“If the lines are straight when I do a square, what’s the difference when I do circles?”. I then write down some of what I think can be and start checking off my list. Usually, I can figure it out and what I can’t figure out I visit FB groups or do what you are doing, asking questions here.

Try “RDWorks” to see if it shows up…if it does, then maybe it is the software, if not, then it might be something mechancially.

Could it be any sort of backlash? Does the circle start and end point line up? That may be be the root cause of the waviness but might point you in the right direction.

It’s either mechanical or a controller setting mst likely. Check the head to make sure everything is tight, including the lens, nozzle, and housing. Also, check the other mirror housings and make sure they are all adjusted and tight (I found a loose mirror bracket that was vibrating that didn’t help my output. Have you tried taping a smooth piece of paper down on the bed and test that to eliminate substrates? Could they be moving during print (vibrations for example]?

Also worth checking and cleaning the lens. Perhaps the issue is exacerbated when cutting non square images.

I dont have any knowledge of this laser, only the Ortur LM2. I had similar problems with mine. It turned out to be the eccentric nuts on the inside of the rail wheels. These tighten or loosed the wheels to the rail. Mine were too tight on the x axis so when i created a circle i had the same issue you are having. Not the bolts holding the wheels in place but the ones actually next to the wheels.
I dont know if this helps at all or if your machine even has eccentric nuts.
Cheers

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The most common reason for wobbly lines is a loose lens inside the laser head, if your laser has air flow inside the head this can cause the lens to move about. I put a rubber o ring against the lens as something to tighten against and to stop any possible looseness.