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Treating Print Rash

3D Print Zits – Tips & Tricks to Avoid Blobs

Picture of Christian Schmied
by Christian Schmied
Jan 31, 2019

3D Print Zits – Tips & Tricks to Avoid Blobs

Everyone sees it, but no one likes to talk about it -- the rash on their 3D print, also known as zits or blobs. Here you'll find all the facts: What they are, how to prevent them, and how to get rid of them!

3D Print Zits and Blobs Where Do They Come From?

A closeup of some blobs.
A closeup of some blobs. Source: Simplify 3D

Zits and blobs can be found on many 3D prints and are mostly distributed over the whole object. On closer inspection, we see that one blob belongs to one layer. But what causes it to form in the first place?

A blob is created because the filament is still under pressure in the print head when a layer is finished. This results in a short burst of over extrusion: a blob, also know as Z-scaring or Z-seam.

However, it can also happen, at the beginning of or within a layer, that a blob is placed if the retraction or some other settings are not selected optimally and the nozzle oozes slightly during travel moves.

3D Print Zits and Blobs How Can They Be Prevented?

Z-seam.
Z-seam. Source: AprintaPro

The first rule is to print slowly and as coolly as possible as well as to set all speeds to the same value. For example, many slicers print outer walls at a slower speed than infill. Due to the constant changing of speeds, slight over- and under-extrusions occur again and again, which then become visible as blobs and zits on the object.

Another option is the “coasting” setting in your slicer. This will stop extrusion just before the ends of layers so that the layer is finished with the remaining pressure in the nozzle.

With retraction settings, you can also avoid nozzle oozing. Simply make sure that retraction is enabled in your slicer, adjusting the retraction speed and distance, if necessary. If the filament is pulled back too slowly or not far enough, the material may come out of the nozzle and create a blob.

Blobs at the beginning of a layer are often difficult to control. A workaround would be to manually move the starting point of the layer to a position where it’s no long problematic, like a sharp edge or the back of the object.

Check out our articles on Cura and Simplify 3D if you need more information on all the settings.

3D Print Zits and Blobs How Can They Be Fixed?

Sanding sticks.
Sanding sticks. Source: mightynozzle / Thingiverse

If your print comes out in zits, unfortunately, only careful sanding can help. When sanding PLA, be sure to sand wet and slow. Otherwise, the friction heat will cause crumbs on the surface.

Positioning the Z-seam at a certain point helps a lot with manual reworking and saves time.

For more information on sanding, check out our article on post-processing your 3D prints and print some of these helpful sanding sticks.

License: The text of "3D Print Zits – Tips & Tricks to Avoid Blobs" by All3DP is licensed under a Creative Commons Attribution 4.0 International License.

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