Works in Line but not in Fill mode

3D printer (i3 clone)
ZRIB board running Marlin 1.1.x
EleksMaker 2.5 watts connected to Fan 1
New user running trial mode for now.
Running at 100% power and at 20mm/s.

Imprted image and used the Trace feature. When printing in Line, all is good. If I try Fill or Fill+Line, I get nothing on the result. The printer moves but the laser is enabled only about 1% of the time.
Preview looks okay though.

Marlin works, it’s just poorly suited for laser use. The code is incredibly verbose, and it doesn’t do power ramping, so if you’re doing vector marking you’ll get dark spots on sharp turns, as well as start and end points.

You can check that you have set it correctly for laser use here:

You say “connected to Fan 1” - Check that your system is set to use 255 as the maximum PWM value for the fan, or you’ll need to change the corresponding setting in LightBurn to match:

The GCode commands used between Line and Fill modes are basically the same, but you can always try saving the GCode to disk and looking at it to see if anything appears different enough to cause an issue with your specific setup.

Yes I’m using M106/M107. I’ll try to decipher the actual code. That’s what I’m using anyway. I prefer to transfer the code via an SD card.

As you say the settings are/should be similar and it does work in Line mode (tried with different power settings). In Fill, nothing… If I find something, I’ll post it here

If you do a simple shape in Line mode, and another in fill mode, save the GCode for both, and just post the first 30 or 40 lines from each here we might be able to help.

I’ll upload the gcode tonight but at first glance it looks good. The main difference is however that the Line mode is in Absolute and the Fill+Line in Relative (G90/G91).

Continuing investigation.

So the GCode is fine. It’s my laser that is apparently too slow, so that when it gets the signal to turn on and move at the same time, the material doesn’t have the time to be burnt by the laser.

Some plugins in Inkscape have a settings to allow the laser to ramp up, is there such a thing in Lightburn?

You’re asking for a dwell at the beginning of each scan - that would increase the amount of time it takes to run your scan by a huge amount. There must be something else going on here.

The top of your logo at the widest spot looks to be about 4mm. At 20mm/sec, that would be 1/5 of a second, or 200ms. If the laser isn’t on by then, you will not be able to get reasonable results from this - it should be switching on/off in a millisecond or less, and if it’s not, you may have a configuration issue (like the fan speed is ramping up / down maybe?) or a hardware issue.

You have a point there. I’ll try to see if I can measure the voltage change on the pin.

Right now I’m using the VCC driven from the Fan pin. Do you believe that if I change this to have the VCC always powered but control the laser power through the TTL pin instead would help me?

It’s possible, but that would be a very Marlin specific question, and I don’t know enough about Marlin firmware to answer that. It’s possible that Marlin itself isn’t instantly changing the fan speed (depending on config), and it’s also possible that something about the diode you have is lagging.

Ramp up time on the fan pin does not seem to be the issue…

I would check the power to the diode itself next. I know that some diode drivers have an R/C circuit to prevent inrush surge. It would be very strange for an engraving diode to have this, but it’s common on flashlight driver supplies.