- Tension on the filament clamp spring(s) too strong
- Tension on the filament clamp spring(s) too weak
- Tension on the filament itself (ie. Not unwinding/feeding freely)
- Extruder motor malfunction
- Hotend not hot enough
- Hotend too hot
Each of these situations can and will cause issues with extrusion, however we've missed one insidious possible cause of error: the hotend nozzle being too close to the print bed. Betcha didn't think of that one! The reason why this is such a pain in the ass is because with the way I troubleshoot, I generally go through the above checklist first before checking the nozzle to bed distance. This is a problem is because it doesn't allow the filament to freely escape the nozzle, which results in the hobbed bolt chewing up the filament, the nozzle grinding the print bed, and a lack of extrusion. The solution to this problem is to recalibrate your Z-stop and to make sure your print bed and X-carriage are level. If you've already calibrated everything else, and you are definitely too close to the print bed, you more than likely only need to recalibrate the Z-stop.