Mendel User Manual: Extruder

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Extruder is a bit problematic. Some times it blocks and needs cleaning. Also the temperature used vary with the type of plastic and a wrong temperature give problems. Read the next typical problems and solutions.

Extruder jams with melted filament at the end of the brass barrel, starts to flow backwards

Try and increase the temperature of the extruder heater. If the temperature is too low, not all the plastic can melt and only the plastic touching the barrel gets enough hot to melt and do a back flow.

Read more here: Extruders Pt. 1: Backflow and Bench Experiments

Final printed piece have a kind of displacement on XY axis, and when I see extruder going against ooze, then it gets that XY displacement

Try to build the Spring_extruder, it automatically flexes when it goes against ooze or something blocking its path, and then it returns to where it should be. Alternatively, try increasing the current going through the steppers so it needs more force in order to slip.

The stepper motor stalls and can't move the filament

You might try increasing the gap between the splined shaft and the tension wheel. Particularly with hard plastics like PLA, you can get problems if you try and push it though too small a hole. If the extruder design allows, using a spring to allow for varying filament sizes can work well.

It takes a long time after the extruder motor stops before the flow of molten plastic stops

Its possible the temperature is too low, so the excessively viscous plastic takes too long to escape through the nozzle. Try increasing the temperature, or you can experiment with reversing the stepper instead of merely stopping it. [LINK NEEDED]

The temperature reading fluctuates by more than a few degrees, or the viscosity of the plastic appears to vary greatly

It may well be that the thermistor/thermocouple isn't well attached to the nozzle. Check the body of the sensor is actually touching the metal of the nozzle, and as near as possible to the tip. Its also possible that the high currents in the heater/stepper wires are inducing a current in the sensor wires, messing with the readings. Experiment with moving the sensor wires further away to see if it helps. Finally, its possible the voltage across the thermocouple amp is changing, particularly if you're powering it off the same PSU as the steppers/heaters. The 5V from a usb port is far more stable, try powering the circuit from there if you can.


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