This is particularly important for machines that use a Bowden extruder, as the long distance between the extruder motor and the nozzle makes retractions more troublesome. This way the extruder never has to reverse direction and can continue a nice uniform extrusion. The retraction and coasting settings mentioned above can help avoid defects each time the nozzle retracts, however, in some cases, it is better to simply avoid the retractions all together. Typically, a coasting distance between 0.2-0.5mm is enough to have a noticeable impact. Enable this option and increase the value until you no longer notice a defect appearing at the end of each perimeter when the extruder is coming to a stop. Coasting will turn off your extruder a short distance before the end of the perimeter to relieve the pressure that is built up within the nozzle. You can find it right below the retraction settings on the Extruder tab. If the defect does not occur until the end of the perimeter when the extruder is coming to a stop, then there is a different setting to adjust. Adjust this setting until the defect no longer appears when the extruder initially begins printing the perimeter. However, each time the extruder has to start extruding again, it will only push 0.8mm of plastic back into the nozzle. For example, if your retraction distance is 1.0mm, and the extra restart distance is -0.2mm (note the negative sign), then each time your extruder stops, it will retract 1.0mm of plastic. You can reduce the priming distance by entering a negative value for the extra restart distance. If you notice a surface defect right at the beginning of the perimeter, then your extruder is likely priming too much plastic. Right below the retraction distance, there is a setting labeled “Extra Restart Distance.” This option determines the difference between the retraction distance when the extruder is stopping and the priming distance that is used when the extruder is restarting. Click on “Edit Process Settings” and go to the Extruders tab. Does the defect appear the moment the extruder starts printing the perimeter? Or does it only appear later when the perimeter is completed and the extruder is coming to a stop? If the defect appears right away at the beginning of the loop, then it’s possible your retraction settings need to be adjusted slightly. If you start to notice small defects on the surface of your print, the best way to diagnose what is causing them is to watch closely as each perimeter of your part is printed.
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