Oval Circles (kinda) when engraving. Why?

I am running some test cards and have ran into a problem I have not seen before. When engraving circles the engraving goes beyond the edges (at the top of the material), BUT it is still a circle deeper in the engraving. See image.

This test is using a Line Interval of .1mm. Looks like I may need to adjust that, but I would not think that that would cause this issue.

This is on a 90W CO2 with a Ruida controller. I know there is no overscan setting to change for Ruida controllers so I am not real sure why this is happening and what I need to do to fix it.

Try the same pattern with Bi-Directional engraving disabled
Will it fix the problem?

If it does you have some slack in the X axis somewhere

I will give that a shot. Thanks

Meaning belt tension? What else could it be on a brand new machine with linear rails? I guess I could check all the pulleys and make sure they are tight.

I would not be the best person to help with the mechanics of a Co2 machine. I only know the basics
However, I know the test above will at least put you in the right directions and might help others help you :slight_smile:

Run a filled rectangle with a larger line interval, something like 1mm and using bi-directional. This will confirm the diagnosis of scanning offset.

Causes of scanning offset can be either mechanical or electronic.

If mechanical this would be caused by backlash. Most typically this would be seen in improper pulley installation or from wear. Improper belt tension can also cause this.

If you have removed any potential mechanical backlash then you can correct for this using “Scanning offset adjustment” in Edit->Device Settings.

More information on how that works here:
Scanning Offset Adjustment - LightBurn Software Documentation

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I was able to set some Scanning Offsets and now the engravings are looking better.

BUT now I need some help figuring out why the Cut circles are weird shaped.
This is from the front

This is from the back

I notice that the odd shapes are not necessarily consistent.

What do you guys think is going on? And what do I need to do?


I really think you need to review your machine belts/gantry

the circles at the bottom to me really are telling.

I would follow the manufacturers guide to check for belts tension and squareness of the Y and X

Unfortunately my laser did not come with a manual from the factory. I bought it from a dealer here locally. He imports and sells them. He is not a very helpful person. He rarely responds to any of my communications. So I am gonna have to work through this without it.

I did a quick feel check on the belts and all but one feel about right. The drive belt (from the stepper to the pulley shaft) for the X axis was quite loose. I tightened it up. I have not ran another test yet.

Also I did some calibrating my X/Y axes. I was able to get them pretty close. But measuring from corner to corner on some test squares show it is skewed slightly. On a 4"x4" square, it is out .01" corner to corner. Do I correct this by loosening one of the belt pulleys on the drive shaft and turn it slightly and re-tighten? Then re-check?

i thikn you are pretty dang close.
What i would do is run machine a good while, run a few jobs
Let machine settle in. then in a couple weeks recheck

Unless you need higher precision than what you have now, i wouldnt get into the rabbit hole of persuing the last 1%.

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I don’t think I do. I will run some more tests and jobs see what happens.

Thanks for the help

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If you need a more help post pictures of your machine, a lot of Co2 users here some will for sure have a similar machine and can provide more exact help

You almost certainly have mechanical backlash in your system. This may in fact be the cause of the scanning offset. By using the Scanning offset adjustment you’re just masking the underlying issue.

Check all pinion gears and junctions. Make sure they are properly secured.


Gonna do some more testing over the weekend and see what I can figure out.
Here are some pics of my machine. If you happen to have a similar machine and have had similar issues I would appreciate your input.


In addition to the belts & their mounts …

Grab the laser head and give it a good wiggle in all directions: the mounting bolts / brackets / doodads can be loose or, in some cases reported around here, screwed loosely into stripped threads.

Take the laser head apart and verify the lens is secure in its holder. The little knurled ring compressing the silicone washer can work loose.

Make sure all three mirrors sit snug snug in their mounts. You’ll need a pin wrench to test / tighten the lock rings.

It’s also possible, although unlikely, that the linear rails aren’t firmly screwed to the frame & gantry.

So many places to check! :grin:

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Chinese give you a good potential product at a good price. Once you completely dismantle clean and reassemble.

One issue you haven’t had yet: bending over that thing is gonna wreck your back.

I hoisted mine up on furniture risers using a combination of levers and a floor jack:

Yours might not have the same legs, but the risers have a cup on the top for the caster, so it won’t roll off.

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I will be checking all these. Thanks

I agree completely. I had hoped that by purchasing from a local business that has been importing from the same supplier for many years that a lot of these things would have been addressed up front. At least that is what I would do if I was selling them, BUT that was not the case. So I guess I have to go through the entire machine. I could have saved a ton of money ordering from an online dealer but oh well.

YES! I love this idea. I will be keeping this in the back of my mind for a future upgrade for sure.

Thanks everyone!

Well I spent some time today checking all the screws and bolts and was surprised to find the laser head mounting bolts (mounts to linear guide) were completely loose. They weren’t even finger tight.

After making sure everything is tight I reran the test card and my circles are actually circles :metal:

Thanks AGAIN guys! Much appreciated!

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I’m beginning to lose faith in the “Trust” part of the “Trust, but verify” adage. :hammer_and_wrench:

Especially when you purchase from a business that imports and sells lasers. I realized when I bought mine and he came out to set it up that he does nothing but deliver the laser as it came off the boat without doing any adjusting/calibrating/fixing. Very disappointing. But I guess I am learning more this way :face_with_spiral_eyes: