Blobs and Zits

All troubleshooting pages are a work in progress.

Identifying Blobs and Zits

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Blobs and zits are little imperfections the shells of your print. These little blobs are extra deposits of filament that stand out from the otherwise smooth layer lines. Sometimes these lines are aligned vertically in a straight seam, other times they’re scattered all along your print. Blobs and zits are not found on the top or bottom-most layers of your print.

Causes

Blobs and zits are caused by filament oozing out of the tip of your nozzle. Unlike stringing, however, blobs and zits are formed when ooze happens on the shells of your print instead of between islands on each layer.

Solutions

Temperature

Lower your temperature

Retraction

Increase retraction distance and speed

Z-Hop Tuning

Decrease Z-Hop distance

Temperature

Filament ooze is usually caused by overheated filament, which is less viscous. The best printing temperature for you depends on your HotEnd, accuracy of your temperature sensor, and the filament type that you’re using. If you’re printing too hot, filament will ooze more, leading to more stringing.

Experimenting with one of the numerous temperature calibration tests will help you see what printing temperature is right for you. Typically lowering your printing temperature by 5-10° can be a good first step to test.

  • Some materials have very stringent temperature guidelines for printing. For example, PVA should not be printed above it’s recommended temperature range, as it is liable to burn and clog your HotEnd.

  • Remember to be mindful of your HotEnd’s maximum temperature!

  • Trying to print with low temperatures can increase the risk of grinding your filament, due to extra back-pressure in your HotEnd.

Retraction

Retraction is the most common defence against blobbing. Removing filament from the HotEnd while traveling helps reduce ooze, and in turn eliminates blobbing effectively. Tuning your retraction settings for your HotEnd and printing material can take some time but will lead to much higher quality prints.

While conventional wisdom is to always increase your retraction distance to remove blobbing, this isn’t always the best solution. Depending on your HotEnd, there is usually a maximum amount of retraction that is useful, and going above that value can cause clogging (filament will be retracted into the cold part of your HotEnd, expand, and stick to the walls).

It is a good idea to experiment with different amounts of retraction. Usually, printing several retraction tests can help you find a retraction distance that will work for your HotEnd and filament. Don’t forget to try out different retraction speeds as well, as faster retractions can help eliminate ooze too.

Flexible materials are frequently printed without retraction to help reduce buckling.

Z-Hop Tuning

If your printer’s Z-axis moves very slowly, having a large amount of Z-Hop can leave a lot of time where your extruder isn’t pushing filament. During that time, filament can ooze and so you might notice extra blobbing as a result.

If possible, increase your Z-axis movement speed, but make sure that you don’t accidentally hurt your print quality by moving too fast. If it isn’t possible to speed up your Z-axis, you can lower the amount of Z-hopping either by reducing the Z-hop height, or by limiting Z-hops to only happen before larger travel moves (making them more infrequent).