The clunking sound comes from the stepper motor in the extruder head skipping because it’s overloaded - in other words it’s taking too much effort to push fresh filament into the hot-end, melt it and extrude it onto the build surface. This can result in reduced or no extrusion of plastic and a decrease in print quality.

A clunking sound may also be an indicator of wider problems that can damage your printer like an incorrect Z-Offset or retrograde extrusion. It’s worth figuring out what’s wrong to avoid damage to the machine and improve build quality.

Possible Causes

• A blocked nozzle.
  
• The Z-Offset is too low - the tip is being driven into the bed, blocking off the nozzle and preventing extrusion.
  
• Print temperature is too low - fresh filament isn’t melting fast enough in the tip to extrude properly.
  
• Stepper driver power is too low - the driver circuit may not be providing enough power for normal operation
  
• Print speed is too fast.
  

You may occasionally hear a single clunk or two, particularly in a cold environment when extruding the first layer of a part, when printing with higher density plastics or when printing at high speeds and high layer thicknesses. One or two clunks at a time isn’t bad, but consistent misstepping needs to be fixed.

How to Fix it

Blocked Nozzle:

Your nozzle may become blocked with residue from poor quality plastic filament, environmental grit, or residue buildup from repeatedly switching back and forth between different filament types without purging. Try purging some clean filament. If that doesn’t work, you may need to replace your printer nozzle. More information here.

Z-Offset Too Low:

If you’re hearing a scraping sound and seeing the nozzle leave an impression in the print bed as it prints then the Z-offset is too low and you need to re-calibrate your Z-offset. A walkthrough on how to do this is available here. It’s also worth checking your hot end feed tube isn’t loose. Information on that process can be found here.

Low Print Temperature:

Check the manufacturer’s recommended print temperature for the filament (if it’s a range of temperatures we’d recommend starting in the middle). In BuildBee, make sure you are using the correct preset for the material you are using. If you are experiencing issues with the presets, please submit a support request. 

Stepper driver power:

You’ll need to check your wiring, make sure nothing is unplugged, check your power supply, then check the driver for damage or incorrect current limiter settings. This can be a tricky problem, so don’t be afraid to submit a support request.