grbl Alarms & Errors

The grbl firmware has a whole list of Alarms and Error codes that you can encounter when running your CNC. gSender will always display a question mark when there’s an alarm which you can hover over for more information about why it happened and errors will appear as a hovering box in the bottom corner of the visualizer.

You can close an alarm by clicking on the button that appears next to it in the visualizer. Most alarms can also be handled by typing “$x” into the ‘Console’ tab and hitting the ‘Run’ button.

Useful Commands

• $   reminder of all grbl commands
• $$   lists all Firmware settings and their values
• $rst=$   resets all your EEPROM settings to the default Firmware values
• ?   reports any active inputs plus some other useful info
• $i   tells you information on your board Firmware Version
• $#   all the currently stored machine offsets

Alarms

Errors

Error 1, 2, 20, 24, 26, 28

When any of these errors appear in gSender, it can typically be traced back to 3 sources:

1. The g-code file has errors in it: if this is true, then
   • Keep the file loaded
   • Go to gSenders Settings ➜ Safety ➜ to make sure ‘Warn if invalid line detected’ is turned on
   • Next to the ‘Load File’ button on the main screen, you’ll see another button that says ‘Verify Job’ (previously ‘Test Run’)
   • Click this button and it will go through your g-code file, and if the same errors pop up then it’s likely that the file is bad. Go back and check your design software or post processor to make sure it’s all been set up correctly and then try re-generating the file.
2. You have an unstable connection to your CNC: if the file didn’t have errors, then this is the next most likely issue. You’ll want to
   • Check if your USB cable is loose or if other ports or connectors on your CNC board are loose.
   • Try another USB port on your computer, and if you’re using a USB hub try skipping it to connect directly to your CNC.
   • Don’t use a USB Stick, make sure the files on are the hard-drive of your computer.
   • Try running the same job in the air with your router/spindle and dust collector turned off to see if the same errors appear as when you run the job. If they go away then try running the job with full cutting again in some scrap material just to confirm the errors come back. Once confirmed, you’ll want to look to see if your equipment isn’t properly grounded, could have improved electrical shielding, or try using another computer. An example of this is to put your controller and computer on a separate power circuit than the router/spindle and dust collector.
3. Some gSender versions can have bugs: this is the least likely cause, but a couple gSender versions have been known to make errors appear that aren’t actually happening. If you’ve already tried everything else, you should first double-check that you’re connected to the “grbl” firmware if you’re using a grbl board like the LongBoard, or to “grblHAL” for boards like the SLB. After checking that, try installing and using a different gSender version.

Error 33

Can pop up as “Motion command target is invalid” and usually comes from issues with G2 or G3 arc/curve movements in the g-code. If the target is invalid you might want to verify the file again in gSender or regenerate it in CAM with the right post processor.

For example, there have been many reports that if you use the inch post processor in Vectric, Carveco, or Fusion 360 then they won’t add enough decimal places to satisfy arc curve calculations – which will cause an Error 33. The best solution is to just use a mm post processor to get more accurate movements, or for Carveco use UGS grbl.

If this isn’t the cause, then refer to the steps shown for Errors 1, 2, 20, 24, 26, 28 shown above.