Common issues & fixes

Last Update: 4 December 2020

This part of the resources covers common issues and fixes for the LongMill. If you run into an issue with your machine, we hope that this can help you diagnose and fix problems to get you milling as quickly as possible. If you can’t find the answers here, please feel free to get in touch with us.


Motor and controller issues

My controller is not turning on

After switching on your controller and flipping the power switch, your machine remains unresponsive

  • If the red LED lights on the drivers (visible through the grates on the underside of the controller) are on, then you are getting power to the controller. You may be having issues with connecting your machine to the computer.
  • If the red LED lights flicker momentarily before turning off when the power switch is turned on, you may have a faulty switch. Please contact us.
  • Is your power supply connected properly and providing power? There is a green LED that should be turned on when your power supply is plugged in. Check if your AC cable is pushed in all the way into the socket of the power supply.
  • Make sure that the polarity of the wiring is correct. Switch the wires around if need be.
The wire on the left should be white, and the wire on the right should be black.

One of my motors does not move/moves erratically

When jogging or running the LongMill, one of the motors does not move correctly or at all.

  • Check that both the plugs on the controller side and the motor side are connected properly. We recommend completely disconnecting the plug and plugging it back in.
  • Check that all of the wires on the plug are connected and secure.
  • If your motor does not move at all, try switching and testing if it is working correctly by plugging it into a different axis on the motor controller. If the motor moves on a different axis, then you can confirm that the motor is working correctly and identify that there may be an issue with the controller.
  • Check that the light on all of the drivers inside the control box are illuminated. If you have a driver that is not illuminated, please contact us for additional support.
  • Check that all of the DIP switches are properly seated in the correct orientation. If the switch is only part of the way on or off, the driver may not operate.
  • Make sure your Arduino is fully seated in your control board. You can typically use a non-conductive tool to push it into the socket if it is starting to come loose.

My machine isn’t moving in the correct direction

  • Ensure that all plugs and cables are fully seated and connected properly.
  • Check the color pattern of each wire coming from the motor and connected to the LongBoard. Is the pattern all the same with each motor? If not, change the order of the wires to match.
The wiring color pattern should be blue, yellow, green, red.

My machine is not moving the correct amount when I jog a certain amount

  • The microstepping on your drivers may not be set correctly. Check the drivers under your machine and make sure that they are set to 1/8″ microstepping by ensuring that the DIP switches are in the correct position.
  • Your coupler may be slipping. Ensure that the screws on your coupler are fully tightened.
  • Try restarting your g-code sender.

My motors are stalling

  • Make sure that you have not overtightened the Delrin anti-backlash nuts on your machine. Loosen the two M5-25mm screws that hold the nut in place and see if that helps.
  • Make sure that all of the motor wires are seated properly.


My cuts are not coming out accurately

  • You may have a loose component. Make sure that all of your fasteners are tight and your eccentric nuts and Delrin anti-backlash nuts are tensioned correctly.
  • Your motor or lead screw may be slipping inside the coupler. Ensure that the coupler is fully tightened and pressed firmly against the flange bearing to eliminate movement axially.
  • Try reducing your speeds and feeds, or use a different cutting tool.

My cuts on the Z-axis are not the correct depth

  • Ensure that the set screws on the two pulleys on the Z-axis assembly are tight and the belt is tensioned
  • Ensure that the LongMill has enough travel on the Z-axis for it to cut deep enough. It may be bottoming out.
  • If your LongMill is bottoming out, lower the position of your router or use a longer end mill. The LongMill comes with two set of holes on the Z-axis gantry plate for placing the router mount (upper and lower), and using the lower mount position on the Z-axis may work better.

My lead screws wobble excessively

  • Loosen the two M5-25mm screws that hold the Delrin anti-backlash nuts slightly for the axis which the lead screw is on and run the machine back and forth. This will align the lead screw and the nut. Retighten the screws once the wobbling as gone away.
  • Check that the lead screw is not bent. You can check by rolling it along a surface that is very flat and seeing if it rolls evenly.

The machine moves really really slowly or not at all when I jog it

  • If you are jogging your machine for the first time, your feedrate may be set to 10mm/min. This means it will only move 10mm in one minute (really really slow). Try increasing the speed until it is perceptible. 1000mm/min is a good place to start.
  • If you are running code or a job, make sure that your feedrates are set correctly.

My machine randomly stops and starts

  • Check if your power supply and all of the connectors are secure and properly attached.
  • Check for sources that may be causing electromagnetic interference (EMI). This could be vacuums, motors, and other electronics nearby that could be sending EMI to the control board.
  • Check if your drivers are excessively hot. The drivers should not exceed 80C.

My machine stops cutting / loses connection on long jobs

Loss of connection on a long job can happen if your computer or USB port ‘fall asleep’ on you. If you plan on running long, intricate cuts on your CNC you’ll have to change your computer power settings so that it ‘stays awake’ while cutting:

  • Click the Windows icon at the bottom left corner of your screen and start to type “control panel” to bring it up


  • Once you’ve clicked to open it, go to Hardware and Sound  then Power Options
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  • Now, whichever plan you have currently selected (circled in the picture) will be the one that you want to click Change plan settings


  • Go to the second drop-down and set it to Never, save the changes to ensure that your computer never dozes off on its own. An additional step can be to stop your USB ports from ‘sleeping’ by clicking Change advanced power settings


  • In the separate window that appears, you’ll want to Expand the USB Settings, then USB selective suspend setting, and finally change this drop-down to “Disabled“. Click to Apply these new settings.  **Sometimes on a Windows update these settings will be reset, if you want to make sure you’ve got all your bases covered, be sure to check back on these settings on occasion if you want to feel confident while running long jobs.**



I cannot connect to UGSPlatform or any other g-code sending software

  • Try restarting your program or computer.
  • If you have other programs that are open that may be connecting to your Arduino (especially Arduino IDE) that they are closed.
  • Try installing the latest version of Java.
  • You might not have drivers installed. You can install Arduino drivers by installing the IDE for your computer.
  • Check your computer’s drivers. Update or reinstall them if necessary.
  • Try a different USB port and USB cable.
  • If you are using UGSPlatform, make sure to refresh and check the dropdown box for all of the ports that have devices connected to them. Try each one until you can connect.
Click on the refresh button and try other available ports.

I have an issue with Java when opening UGSPlatform

  • If USG is still not able to open due to a Java access error, then there is another program on your computer blocking UGS from opening properly. UGS is usually able to automatically detect where Java is located on your computer, but since this detection is being blocked the way to fix this is to explicitly inform UGS where Java is. First you’ll need to locate Java. You can usually find it by going to the Windows file explorer under ‘This PC Windows (C:) Programs Files Java jre### or ‘This PC Windows (C:) Programs Files (x86) Java jre###. Once inside the ‘jre’ folder, left-click the navigation path at the top of the file explorer then right-click the selected text and left click the ‘Copy’ option to copy the path.blank
    Once the path is copied, navigate to where you downloaded UGS; this will normally be located inside your ‘Downloads’ folder. Once there, go to: ‘ugs-platform-app-2.0-SNAPSHOT ugsplatform etc’. In this folder should be a file called ‘ugsplatform.conf’. Opening this with a text editor like Notepad, you’ll want to find the line which says: “#jdkhome=”/path/to/jdk“, delete the ‘#’, then replace the text within the quotes with the Java path by right-clicking and selecting ‘Paste‘. The completed edit should look like this: blankTo confirm the changes, click ‘File‘ in the top bar and ‘Save‘. With all this done, once you go back to the UGS .exe launcher you should now be able to get UGS to start up without any errors.

My machine won’t move and says it’s in an ‘ALARM’ state

  • Something’s happened during the operation of the machine which was unexpected so it’s decided to lock itself just in case.
  • In some cases, your EEPROM settings (the machine settings have changed). Make sure they are correct by referring to the default EEPROM settings.
  • To bring it out of the alarm state, press the “Soft Reset” button followed by the “Unlock” button and that will put the machine back into its ‘IDLE’ state.
  • If it continues to go into an ALARM state under similar conditions in the future, check that no wires or hardware have come loose and that there’s nothing externally affecting the movement of your machine.


When sending gcode created from Carbide Create, the machine stops/reports an unknown command

Carbide Create uses M6/M06 codes that are used for tool changes. Because the LongMill does not have a toolchanger and does not use tool change commands, it will pause when the M6/M06 command is used.