Speed slows on X-axis

I am new to LightBurn but not laser cutting, I noticed that my cuts were not going through on the y-axis and burning thru on the x-axis. I cut some rectangles to show the issue, these are 80 x 20 mm rectangles in three positions; vertical, tilted 45, and horizontal, all cut at the same time. The x-axis (horizontal) always cuts through but the vertical does not. Watching the machine closely and listening, it slows down as it moves along the x axis and speeds up along the y axis.

Here is a picture of the front and back of my test cuts.

In lightburn I set my feed rate to 10mm/s.
Any ideas on what could cause that, and how to correct it?

I am running a win 64 machine with Lightburn 0.9.11, My CNC is Shapeoko 3, here are my GRBL settings


thanks for the suggestions

Assuming you’re using a diode laser and you de-focus it, which is the longer direction? X or Y? Higher power diodes don’t focus to a single spot, but a rectangle, because they use multiple emitters in an array, and that can mean the cutting power is much different along the direction in-line with the array.

Yes, I am using a 5w laser diode. I will adjust the focus and see what that does.

Oz I see what you are talking about now with the array. I did a few more tests.
I re-focused the laser to get the smallest point possible. I had to really squint to see the point (goggles on of course), it looks completely round, so small the rectangle looks like a point.

I re-ran the rectangle cuts, with the same result, through cuts on the horizontal but not on the vertical.

For the second test I rotated the laser 90 degrees, and the problem followed.
Through cuts on the vertical now, but not on the horizontal. In both tests the rectangles at 45 degrees cut evenly on all sides. Ahhh, it all makes sense.

For now I will leave the laser at 45 degrees on the spindle, this should give me consistent cuts along both axis.

BUT is there a trick to getting the beam to focus on an even tighter point.

Easily? No. But it’s possible to use asymmetrical optics, like a cylindrical lens to focus the wide beam to a point. They aren’t cheap. :slight_smile:

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