FAQ and Troubleshooting

µCNC FAQ (Frequently Ask Questions)

These are a few Q&A that I think may be more common while using µCNC.

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• Is µCNC safe to use?
• Is µCNC a direct replacement for Grbl?
• µCNC is not recognized by the software I used with Grbl. How can I fix this?
• Ok I've installed µCNC on my board but nothing is happening. What went wrong?
• µCNC is running veeeerrrryyy slooooowwww?
• My sender software is not working/communicating with µCNC

Is µCNC safe to use?

• In terms of collisions I believe it's has safe has Grbl. By default all boards have been configured so that any unconnected or fault wire trigger the response and get picked UP by the interlocking checking.
• In terms of work production you can use it with caution. This is not a Grbl port or fork. This was built from zero. There are still work to be covered to consider 100% reliable but you can try it. In any case safety precautions should be implemented. Run the code in check mode to check for GCODE errors and incompatibilities. If still not confident, do a dry run on a scrap peace or in the air to see if everything looks ok. Then run your real job.

Is µCNC a direct replacement for Grbl?

• Yes.
• Pinout and settings.
• Grbl startup message is also emulate by default. This is required by many Grbl programs. It, s enabled with option EMULATE_GRBL_STARTUP enabled (cnc_config.h).

µCNC is not recognized by the software I used with Grbl. How can I fix this?

• By default µCNC emulates a Grbl welcome message. Some interface software (like Candle, Candle2, and UGS) expect the Grbl startup message and would not recognize µCNC own start up message. This can be modified with option EMULATE_GRBL_STARTUP (cnc_config.h). This option actually also forces some of the messages of µCNC to be more Grbl compliant, like the report status message for configurations with less then 3 axis for example. OpenCNCPilot for example have no problem with this.

Ok I've installed µCNC on my board but nothing is happening. What went wrong?

• Check if your board is in Alarm mode. You can connect directly to the board with a Serial Terminal like Putty, Termite, PlatformIO/Arduino IDE serial monitor, etc... and talk directly to the board. Send a ? char to query the board status. Is the board in Alarm mode? This can be due to several reasons:
  • If you used a pre-compiled version, as a safety feature all limits and control input pins are pulled high by internal resistors. If µCNC is not wired all limits and control alarms will be active including de Emergency-Stop (ESTOP) input.
  • This means that for safety reasons also µCNC will halt. To go around this question short your ESTOP input pin to GND and reconnect your board. µCNC should respond now. If you don't want to use the ESTOP input and want to get rid of the wire, reconfigure cnc_config.h file to enable INVERT_EMERGENCY_STOP option to invert the signal coming from ESTOP, remove the wire and reset your board. µCNC should be running without the wire. At this point other settings may need adjustment. You can read this in greater detail in the basic guide
  • Since version 1.11 if the settings stored in non volatile memory are invalid or corrupted the machine will be locked in Alarm mode for safety reasons. In these cases the board will reply saying that it requires a settings erase/restore command to allow unlocking. Send the $RST=* command and after that unplug and re-plug your board. This should fix the Alarm lock. If you are having issues with it you can bypass this feature by uncommenting the option in the cnc_config.h file

µCNC is running veeeerrrryyy slooooowwww?

• Older versions had a different meaning for setting $0 that represented max step rate and not step pulse in ms. This has now been modified so this should not happen.

My sender software is not working/communicating with µCNC

• Several things can be happening.
  • Check if the machine is not in alarm mode by following the above checks.
  • Some senders are very strict with the startup message format and expect only the original Grbl message. You can make it emulate Grbl by changing the emulation level to 2 in the cnc_config.h file