Not able to cut a simple circle :(

[Mykeul]

Hello,

I have a very annoying problem with my laser, when working with vectors, I am not able to just finish the cut/engraving of a simple circle.
The result gives a circle where the end point does not touch the beginning point, so I get about a half millimeter not cut.
It is very annoying, because I have to recut every single round manually after. When I engrave a raster image, I do not see this problem.

I did tighten the belts, clean the rails, change gcode generating and sending software, change image, change GRBL version etc ...

Here is a example to understand :
Attachment 1 is the picture (vectorized and elements are correct) in Lightburn

Attachment 2 is the result when I use Lightburn (0.9.0.7 with GRBL 1.1e and driver GRBL-M3) where I modified GCODE to keep the laser ON, so that I see the travels, and I see that the errors happens when the laser start a new shape

Attachment 3 is the result on a paper with horizontal lines (software is Laseraxe CNCC 2019 v1.25c using GRBL 0.8)

Attachment 4 is another more finer & complex cut, where you can see again the problem.

Thanks in advance for your help, I tested all I know and I really do not know what to do.

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[fixtureman1]

What controller are you using. Have you tried lightburn to run the laser.

[Kenny Duval]

You lost me at simple circle. There's nothing simple about getting a multi axis machine to work well enough to cut a perfect circle.

[Mykeul]

Hello,

@fixtureman1: yes, I did try with 2 software, including Lightburn as shown in first attachement. The Controller is a Laseraxe mini running GRBL 0.8 when using Laseraxe software, and running GRBL 1.1e when using Lightburn (Configured as GRBL-M3). I cannot upgrade to GRBL 1.1f+

@Kenney Duval: It is not really about having a "perfect" circle, the point is that ANY vector shape is not finished, half a millimeter is missing on each one. It is a real pain.

Thanks

[Kenny Duval]

If you try to produce a square do you end up with gaps? That may point to perhaps which axis is either setup incorrectly or is losing position/steps due to something mechanical. Is it possible that a mirror alignment is off? You mention you see it happen when the laser fires perhaps there is a voltage drop happening upon firing the laser.

[Mykeul]

Hello,

Thanks for your reply, sorry I was doing tests on it and I was a bit sick too.
When I cut squares, there are no gaps, they are correct.
I do not know what a mirror alignment is, would it be that Y motor 1 and Y motor 2 are not working equally ? Mechanically, everyting is levelled and all is squared, I verifiied many times. X motor is alone, so I do not understand why it happens on X but almost not on Y. I have nema 17 (42x42x34mm, 26Ncm) motors, may I change them for stronger ones like 42x42x47, 59Ncm ?
The voltage drop is a good idea, especially because I took the most powerful laser head for their product, which is 15w. I should maybe change the power adaptor from 12V - 4A to 12v - 6A (for example, I do not know current values, I will check this evening) ?

Regards

[Kenny Duval]

Mirror alignment -

[Mykeul]

Oh ok ... my bad, I do not have the chance to have a CO2 laser, it is a simple 15w diode laser like seen in this attachment, so there is no mirror, just a focus pillar to get the tiniest light dot possible.

[Mykeul]

Hello,

I thought your idea about the voltage drop when laser at the moment the laser is lit was very good, so I did remove the laser head and replace it with a pencil.
Here is the result, in attachment.
Basically it gives the same problem at the same places ... AND it highlights an interesting thing : at the end, the laser goes back to origin, and we see that it is NOT at the same place. I think it confirms missing steps, but I do not know for which cause.
I did order 1 stronger motor and a new GRBL controller board, to test each.

Thanks for your help