Circle not perfect

i don’t understant why i have 2 opposites littles zones not perfect on a circle.

Here you have a picture with the 2 points an the origin of my work.
The size is ok, the is just this problem.

Do you have any idea ?


make sure your belts are properly tightened.

Especially the ‘y’ :blush:

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and remember, you can over tighten belts and cause other issues like excessive drag on stepper motor bearings causing higher loading of the driver and thermal issues.

I tighten mine a little bit and then look closely at the belts as the to into and out of the motor gear drive. I look for ANY deflection of the belt on either side and if I see some I tighten just a pinch more. Some will say tighten until they sing when plucked but I like the a bit less tight than that.

I’m with you on the tightness. Check regularly, not so much that the belts will need adjustment rather for you to get used to the tension when you do need to adjust

thank you all for your answers !

i cheked the belt and it seems to be ok.

I tried to make my circle in a different place on the bed and take a look to the result.
In the top left, my circle seem to be perfect, in the middle, less…

Always the belt ? Or something else ?

Do you see those wiggly lines in the left and right sides of the right-most circle? Looks like a mechanical ringing problem to me.

Hi, by ringing, do you mean an oscillation of some sort ?

Fred, did you check the belt in the four corners and center of the bed. If not, please try and let us know.

Also can you send images of your runner type please.

Also, with power off, if you slide the head all over the bed are there any tight or loose spots, noises, anything not smooth ?

Not only the belt, but also the pulley on the Y axis of the stepper. Those steps are occurring on the reversal of the Y axis. Loose belts can cause this like most people say, but if the pulley on the Y stepper is not secure on the shaft, it can also cause this. OR if the start/stop acceleration is incorrect, you are stepping positive one way, then stepping negative the other way… the reversal could be causing this. The ramp down and ramp up issue in this case would show up more as the faster you ran the axis. The circle doesn’t look smooth in either direction, but perhaps that is an illusion with the media.

what is your machine model? You just named the controller in your profile and that tells us little about the machine. Pictures? When I mentioned the ringing/oscillations what you’re seeing is a mechanical movement which is not supposed to be there and it is likely less than 2mm. Loose belts can cause this, a lose axis slide mechanism(bearing, wheels, etc), a lens which isn’t held in place well and other things like a loose stepper motor mount, belt pulley etc.

You are looking for a VERY small amount of play but the fact it happens more in the center than the edges still looks like belts or maybe a worn linear bearing at the center of the machine. ie if the machine was used in production and the designs were always cut in the middle of the machine then that X and Y axis linear motion guides would be worn there and not at the corners.

What speeds are you seeing this at and I expect your are doing a vector engrave and not raster?

Hi, give me few minutes, an i make a big answer :wink:

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For circles, especially offset fill, you should convert the circle to path first.

Also, if using a cheap diode laser, the laser is usually a rectangle shape and not a circle so the cuts tend to be “off” a little bit. I’m still learning but I think you might be using a diode laser and that’s why it’s offset just barely like that.


first i made the laser myself with the documentation in october 20.

The laser is CO2, 100W.

I have a working area of 1.2m x 1m.

I will add some pictures, it’s not finish at 100% but it’s operationnal.


  • i tested all belts, retighten all screws, change my linear rail and put some grease. I don’t find hard zone on the linear rail or on the others belts.
  • i tried a little circle (2cm) on each corner, and middle. I always have the problem, my circle is like a little lime (where is my mojitooo ?)…
  • i cleaned the lens, change the speed…


I founded some older job (circle key ring), the circle is perfect… I really have no idea…

so you did a 2cm circle at each corner and the center and in ALL CASES you get the unmatched halves of the circle but you grabbed a file from a keyring project and all circles are correct at all 5 locations?

Please post the file which is not presenting a circle.

No, i found the real keyring, made few months ago, and it was ok… the cut is ok. Something changed, hardware or software, but something changed… i dont find what…

I just created a circle in LightBurn, selected it and converted it to a path. then I selected it and changed the layer mode from fill to line and ran the simulation. It starts at one point, moves the laser head around the circle and back to the starting point. Is this what your LightBurn file is doing?

Or did you create 2 half circles. join them and each is burned one half and then the other?

and why are you not just turning down the power and just etching on your scraps instead of burning holes? Save power, wood, etc as to troubleshoot. And if you get your arm or hand in the way and burn yourself it won’t be so bad at low power. :wink:

It’s one circle. The laser cut it in 1 pass.

All files are created on illustrator an i import the AI file…

(i use my scrap to show you example, large scraps ok, but scraps :wink: )

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You really should do a bit of your own troubleshooting, for example eliminating possible failure points like the conversion from AI to LightBurn. Just make a circle in LightBurn and validate your problem still exists.

Earlier you said that it only does this odd misalignment in the center of your work area and later you said that it happens at all 4 corners and the center( same problem). This is inconsistent, please clarify if it has the problem at all corners AND the center or only the center.

This really looks like you overlooked something since this looks so much like a mechanical issue. Check all mirror mounts, all motor mounts, all motor gear drives, all gear idler mounts, all belt tensions and the laser head mechanism and all frame corner/assembly mounts/screws. I would also put my hand on the machine frame while testing to see if you feel anything different at the center as opposed to a corner or side where the odd behavior does not exist.

Since your entire machine is held together with 3D printed parts, can you set your speed to only 10 mm/s and test that it still make a lime shape and it still shows those oscillations on the left and right side of the circle?

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