Inconsistent engraving depths

Hi,

Having trouble engraving on 3mm clear Perspex on my K40+, I ran a material test and 250mm/s at 15% power came out the best. But when I tried to engrave the engraving it’s inconsistent, its deep in specific areas if that is on text or a design. Left, top and right seem to be affected. Engrave around the edge also doesn’t seem very smooth.


Bed is level, belts don’t seem overly tight.

Tried different speeds & powers, it’s always the same. Interval 0.100

Thank you.

Have you measured and applied the Scanning Offset Adjustment?

If not, do those tests & measurements on cardboard over a wide range of speeds, fill in the table with half the measured offset distances, and see if that improves the situation.

Thanks, I tried to run the tests, it warns it maybe out of bounds and then it does 1 line and stops

ok

Starting stream

Layer C00

X_LIMIT

ALARM:3

Reset while in motion. Grbl cannot guarantee position. Lost steps are likely. Re-homing is highly recommended.

On or near line 0:

Job halted

Stream completed in 0:00

Reset while in motion.

Grbl cannot guarantee position.

Lost steps are likely.

Re-homing is highly recommended.

ok

Grbl 1.1h ['$' for help]

omtech

[MSG:Check Limits]

[MSG:'$H'|'$X' to unlock]

[MSG:Caution: Unlocked]

ok

If I turn off scanning offset off on the tests it works??

If you’re trying to do the measurements on the original design or haven’t set the origin correctly, then it’s entirely likely the overscan region extends beyond the machine boundaries.

Assuming the machine homes properly and you’re using Absolute Coordinates and you’re making measurements on a small square in the middle of the work area and the line interval is around 0.5 mm, then it should work.

1 Like

I moved the start point further from the edge and it ran this time.

I ran tests at 50/100/150/200/250/300mm/s with the below overscanning and interval settings

Looks quite good to me??

Thought I’d try it on black acrylic so it shows better



Not a CO2 laser guy, but your images start looking crappy as you move away from the center of the burn. Mirror alignment?

Spent all day testing mirrors and made very small adjustments seems perfect now, just tested it and still doing the same in the exact spots.

You clean them too? I can imagine a fingerprint causing that pattern.

With the Scanning Offset settled, other problems come into play … :grin:

Are the designs for those ornaments simple outlines on a Fill layer? Or are they something more complex?

The irregularities echo the outer perimeter of the shape, which suggests trouble with the laser turning on after traversing the overscan region. What are the layer’s speed / power / overscan settings?

If you engrave a simple octagon (drawn as a LightBurn polygon) of about the same overall size with those settings, what does it look like?

Thanks, doing some tests turning on scan offset fixed both issues I was having.