3D printing: Blobs, holes and how to remove them

When using 3D printing, the goal is usually that the result will be strong and nice. To achieve this, one must have a well-adjusted slicer profile. The result of a bad slicer profile can be that the models you print have spots and or holes distributed over the entire model. Removing these blobs and holes is a balancing act of options like the ones below.

Activate retraction

If retraction is not turned on in your chosen slicer, blobs as seen in the picture will most likely occur wherever the print head is stationary, even just a short glance. When the plastic gets hot enough, it will flow out of the nozzle even if the extruder does not push on.

Set the retraction length

Different printers have different retraction needs. Many printers come with a "bowden" setup which means that the printer has the extruder sitting in a more or less stationary place on the printer and has a PTFE tube connected between the hot end and the extruder. When the extruder sits just above the hot end with a very short tube connected to it, it is called "direct drive".

A bowden setup usually needs more retraction to compensate for the excess material inside the pipe. between 3 and 5 mm retraction should work with an extruder of this type.

A direct drive setup needs very little retraction as the filament in the hot end and the extruder are directly connected.

If you set the retraction too high and too fast, the printer will be able to pull plastic back up into the nozzle as if it were a straw. This results in holes wherever the printer makes a retraction.

Clean the nozzle

If your printer's nozzle is covered in molten plastic, it can be pulled off the print and leave marks and lumps. Heat the printhead to about 140 degrees and get out a pair of pliers. You should be able to grab the plastic and pull a lot of it off like was gum. Because of the consistency at that temperature, it sticks to itself and pulls off easy.


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Published: Oct 2020, updated: Jan