Target Image Size and Options

Target Image Form

From this dialog you can set final image size and offset as well as laser speed and modes.

M3/M4 Laser Modes

The laser is enabled with the M3 spindle CW or M4 spindle CCW commands. These enable two different laser modes that are advantageous for different reasons each.

M3 Constant Laser Power Mode
  • Constant laser power mode simply keeps the laser power as programmed, regardless if the machine is moving, accelerating, or stopped. This provides better control of the laser state. With a good G-code program, this can lead to more consistent cuts in more difficult materials.
  • NOTE: M3 can be used to keep the laser on for focusing.
M4 Dynamic Laser Power Mode (new in grbl v1.1)
  • Dynamic laser power mode will automatically adjust laser power based on the current speed relative to the programmed rate. It essentially ensures the amount of laser energy along a cut is consistent even though the machine may be stopped or actively accelerating. This is very useful for clean, precise engraving and cutting on simple materials across a large range of G-code generation methods by CAM programs. It will generally run faster and may be all you need to use.
  • Grbl calculates laser power based on the assumption that laser power is linear with speed and the material. Often, this is not the case. Lasers can cut differently at varying power levels and some materials may not cut well at a particular speed and/power. In short, this means that dynamic power mode may not work for all situations. Always do a test piece prior to using this with a new material or machine.
  • When not in motion, M4 dynamic mode turns off the laser. It only turns on when the machine moves. This generally makes the laser safer to operate, because, unlike M3, it will never burn a hole through your table, if you stop and forget to turn M3 off in time.

For more info, read about laser mode support in grbl v1.1 wiki.

Power Modulation via S-Command

LaserGRBL can process grayscale images to produce power modulated line by line engraving. Power modulation is hardware implemented as PWM modulation on arduino PIN D11, controlled by “S command”.

GRBL’s PWM functionality – How to control a laser or variable speed spindle.

If your hardware does not support power modulation you have 2 choice:

  1. Modify/Hack your engraver to add PWM control
  2. Configure LaserGRBL for pwm-less hardware, unchecking “Support PWM” in settings. Pwm-less support was added in v2.5.1-pre