Laser starting early or motion starting late?

[Steveb48 (Steve)]

I have a Lowrider 3 with a Neje A40640II controlled by and SKR Pro running Marlin.

If I run at 10mm/s or below, life is grand! If I start speeding up, I’m seeing gaps a the end of lines. These gaps grow as speed increases. It also appears that the start of the line is darker than the main part of the line. If I draw a 100mm x 100mm square, the gap is at the end of the line in both X and Y, regardless of direction. The image contains 3 identical squares. I’ve noted the direction of travel which is the same on each. The gap at 20mm/s is about 1mm increasing to 4mm at 40mm/s.

Any clues?

Thanks,
Steve

; LightBurn 1.7.08
; Marlin device profile, current position
; Bounds: X0 Y0 to X83.5 Y31.5

;USER START SCRIPT
M203 X900 Y900
M03 I
;USER START SCRIPT

G21
G91
; Cut @ 1200 mm/min, 20% power
M8
M05
G0 X25 Y0 F6000
; Layer C00
G1 X-25F1200 I S51
G1 Y31
G1 X25
G1 Y-3.79
M05
G0 Y-0.5 F6000
G1 Y-26.71F1200 I S51
; Cut @ 1800 mm/min, 20% power
M8
M05
G0 X28.5 Y0.5 F6000
; Layer C01
G1 X-25F1800 I S51
G1 Y31
G1 X25
G1 Y-31
; Cut @ 2400 mm/min, 20% power
M8
M05
G0 X30 Y-0 F6000
; Layer C02
G1 X-25F2400 I S51
G1 Y31
G1 X25
G1 Y-31
M9
M05
; return to starting pos
G0 X-83.5 Y-0.5 F6000

[ednisley]

@Steveb48

a Lowrider 3

So it most likely has achingly slow acceleration.

This Troubleshooting section seems relevant:

Corners Are Too Dark, Too Light, Or Missing - LightBurn Documentation

You can try cranking up the acceleration, but you may be stuck with very low speeds due to the combination of large moving mass and small-ish motors.

[Steveb48 (Steve)]

You may be right. I started cranking the acceleration up and as I did, the gaps got smaller. I’m suspecting that 40mm/s is more that my machine can handle mechanically as I was getting some ringing at that acceleration rate. 20mm/s looks very doable. Thanks!