Mendel User Manual: Extruder

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Revision as of 19:42, 23 March 2010 by Casainho (talk | contribs) (Added a link to my blog message about extruder backflow problem/solution)
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Getting a reliable extruder to work can be a bit problematic. Sometimes it blocks and needs cleaning. Also the optimum temperature varies with the type of plastic and an incorrect temperature gives problems. This page lists some 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:

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.

Printed objects show brown/beige discolouration.

The temperature is probably too high, try reducing it. If the discolouration only occurs sometimes, especially when the extruder isn't doing much, it probably means that your temperature sensor isn't well attached to the tip of the nozzle. It can help to put a bit of insulation around the barrel to keep the temperature a little more even if this is the case.

The stepper shaft grinds through the filament instead of gripping it.

Try moving the tension wheel closer to the stepper shaft, or slowing down the motor. If this happens only from time to time, it may be that your filament isn't even enough, which can be remedied by adding springs to the tension wheel to compensate. It may also be that whatever method you're using to add friction to the shaft (splines, teeth, gears) isn't good enough. Cutting a worm thread with a lathe appears to be the most reliable method if you have the tools, but there are some alternatives. [LIST SOME]


This are links to blog messages, forum messages, etc. WARNING: not all things written may be correct: