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However, if something goes wrong with just one of these layers, it is usually clearly
visible from the outside of the print. These improper layers may appear to look like
lines or ridges on the sides of your part. Many times the defects will appear to be
cyclical, meaning that the lines appear in a repeating pattern (i.e. once every 15
layers). The section below will look at several common causes for these issues.
17.1 Inconsistent extrusion
The most common cause for this issue is poor filament quality. If the
filament does not have very tight tolerances, then you will notice this variation on
the side walls of your print. For example, if your filament diameter varied by just
5% over the length of the spool, the width of the plastic extruded from the nozzle
could change by as much as 0.05mm. This extra extrusion will create a layer that
is wider than all the others, which will end up looking like a line on the side of the
print. To create a perfectly smooth side wall, your printer needs to be able to
produce a very consistent extrusion which requires high-quality plastic.
17.2 Temperature variation
Most 3D printers use a thermistor to regulate the temperature of the extruder.
If this thermistor is not tuned properly, the temperature of the extruder may
fluctuate over time. Due to the nature of how thermistor works, this fluctuation is
frequently cyclical, meaning that the temperature will vary with a sine wave
pattern. As the temperature gets hotter, the plastic may flow differently than when
it is cooler. This will cause the layers of the print to extrude differently, creating