grbl-LPC-CoreXY/doc/markdown/laser_mode.md

Grbl v1.1 Laser Mode

DISCLAIMER: Lasers are extremely dangerous devices. They can instantly cause fires and permanently damage your vision. Please read and understand all related documentation for your laser prior to using it. The Grbl project is not resposible for any damage or issues the firmware may cause, as defined by its GPL license.

The main difference between traditional Grbl operation and the laser mode is how the spindle/laser output is controlled with motions involved. Every time a spindle state M3 M4 M5 or spindle speed Sxxx is altered, Grbl would normally come to a stop, allow the spindle to change, and then continue. This is the normal operating procedure for a milling machine spindle. It needs time to change speeds. However, if a laser starts and stops like this for every spindle change, this leads to scorching and uneven cutting/engraving.

Outlined in this document is how Grbl alters its running conditions during the laser mode for both improved performance and enforcing some basic user safety precautions.

When laser mode is enabled:

• Grbl will move continuously through consecutive motion commands when programmed with a new S spindle speed (laser power). The spindle PWM pin will be updated instantaneously through each motion without stopping.

  • Example: The following set of g-code commands will not pause between each of them when laser mode is enabled, but will pause when disabled.

    G1 X10 S100 F50
    G1 X0 S90
    G2 X0 I5 S80
    

  • Grbl will enforce a laser mode motion stop in a few circumstances. Primarily to ensure alterations stay in sync with the g-code program.

    • Any M3, M4, M5 spindle state change.
    • A S spindle speed change when M3 is active and there is no motion programmed.
    • A G1 G2 G3 laser powered state change to G0 G80 laser disabled state when M3 is active and there is no motion programmed.

• The laser will only turn on when Grbl is in a G1, G2, or G3 motion mode.

  • In other words, a G0 rapid motion mode or G38.x probe cycle will never turn on and always disable the laser, but will still update the running modal state. When changed to a G1 G2 G3 modal state, Grbl will immediately enable the laser based on the current running state.

  • Please remember that G0 is the default motion mode upon power up and reset. You will need to alter it to G1, G2, or G3 if you want to manually turn on your laser. This is strictly a safety measure.

  • Example: G0 M3 S1000 will not turn on the laser, but will set the laser modal state to M3 enabled and power of S1000. A following G1 command will then immediately be set to M3 and S1000.

• Grbl supports two different laser modes with the M3 spindle CW and M4 spindle CCW commands. These are both advantageous for different reasons.

  • M3 enables 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: Use M3 to keep the laser on for focusing.
    • For a clean cut, you generally want to add lead-in and lead-out motions around the line you want to cut to give some space for the machine to accelerate and decelerate.

  • M4 enables dynamic laser power mode. Dynamic laser power mode will automatically adjust laser power based on the current speed relative to the programmed rate. It'll 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*.

    • NOTE: 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.

• A S0 spindle speed of zero will turn off the laser. When programmed with a valid laser motion, Grbl will disable the laser instantaneously without stopping for the duration of that motion and future motions until set greater than zero..

  • M3 constant laser mode, this is a great way to turn off the laser power while continuously moving between a G1 laser motion and a G0 rapid motion without having to stop. Program a short G1 S0 motion right before the G0 motion and a G1 Sxxx motion is commanded right after to go back to cutting.

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###CAM Developer Implementation Notes

TODO: Add some suggestions on how to write laser g-code for Grbl.

• When using M3 constant laser power mode, try to avoid force-sync conditions during a job whenever possible. Basically every spindle speed change must be accompanied by a valid motion. Any motion is fine, since Grbl will automatically enable and disable the laser based on the modal state. Avoid a G0 and G1 command with no axis words in this mode and in the middle of a job.

• When using M4 dynamic laser power mode, the only force-sync condition is changing M3 M4 M5 spindle states. There are no others because dynamic power mode automatically disables the laser whenever it is not in motion.