Knocking noises from the extruder stepper motor are usually caused by the stepper motor actually jumping up and down slightly and tapping on the mounting block causing the noise.

This happens when the machine is having feeding difficulties that basically result in the drive wheel turning and “pushing the filament” but the filament not moving

forward down the extruder.

This can be caused by:


On Loading Filament:

1. The filament curving so that it misses the barrel and taps into the mounting block. (Fig 1.1)

Solution : unload filament, straighten it with your fingers and load again


2. There is a small broken piece of filament stopping the new  filament from loading – this WILL happen if you ever allow the  machine to run out of filament mid print. (Fig1.2)

Solution : remove front fan and heat sink. You will now be able to see around the barrel and remove broken piece. If still on barrel run load and then use pliers to pull the piece up once warm and load in new filament. You can do this with the fan off just make sure it is hanging in such a way as to not damage blades. Make sure when replacing fan that air blows back towards the extruder (there is usually a sticker on the back with fan specs)



When Printing:

1. A blocked nozzle

How to diagnose : run load and watch the filament flow.

A partial blockage will cause filament to want to come out at 30-45  degree angles

Solution :If you think the nozzle it blocked completely, see “cleaning and replacing your nozzle” Under solutions at


2. A bulge (or swollen part) in the filament that stops it from fitting in the barrel. (Fig 1.3)

How to diagnose : unload filament and look at its width consistence from different sides (a bulge may be only evident from one side)

Solution : Cut out bulge, check along filament for 30-60 cm for not more and start again.


3. A Damaged or faulty thermo cable that is providing false messages

to the mother board resulting the filament not being heated properly

How to diagnose/solve : please see solution on



BilbyCNC hopes you found this helpful. Please visit if you need further assistance