Why Do 3D Prints Get Zits and How to Prevent Them

3D printing often encounters various surface quality issues, and imperfections such as zits or small spots on the surface of the printed part are one type of them, especially when pursuing a smooth effect. These zits not only affect the appearance, but also impair the function of precision parts. In this article, we will explore the reasons why zits appear in 3D prints and how to eliminate or reduce them.

Source: https://www.reddit.com/r/3Dprinting/comments/g1gjfo/whats_causing_those_blobszits/

Common causes of zits in 3D printing

zits are small raised material spots that appear on the surface of 3D prints. They are usually caused by uneven deposition due to excessive material extrusion or improper print head movement. The size and frequency of zits can vary, depending on factors such as materials, slicer settings, and printer hardware.

1. Retraction settings

The retraction settings control how much filament is pulled back to the nozzle when the print head moves between different parts of the model, helping to prevent rashes in the print. But incorrect retraction settings can cause filament oozing, resulting in zits when the nozzle starts printing again.

2. Extrusion inconsistency

Nozzle blockage, poor extruder calibration, or filament diameter fluctuations can all cause extrusion inconsistency. These inconsistencies can cause filaments to burst suddenly, resulting in zits.

3. Printing speed

Printing too fast can cause new layers to be deposited on top of the underlying material before it is fully cured, so the underlying material may be over-extruded and deformed, resulting in zits.

4. Too high nozzle temperature

If the nozzle temperature is too high, it can cause the filament material to become too fluid, making it more likely to ooze out and form zits.

5. Incorrect layer starting point

Slicing software often starts new layers at a specific point, which can cause a lot of zits at the seams if not optimized.

How to prevent zits in 3D printing

1. Adjust the retraction setting

Properly increasing the retraction distance can effectively reduce the possibility of oozing out, because when the nozzle stops extruding, the retraction action pulls the filament back a certain distance, reducing the pressure in the nozzle, thereby limiting the outflow of excess filament. It should be noted that excessively increasing the retraction distance may cause blockage or delay re-extrusion, so it is recommended to adjust the amplitude between 0.5-1mm each time until the best setting is found.

Increasing the retraction speed allows the filament to quickly retract into the nozzle, thereby reducing exudation. It needs to be adjusted gradually, for example, starting from 40mm/s, gradually increasing to 60mm/s, and observing the printing effect. Make sure the retraction speed matches the printer performance.

2. Calibrate the extruder

Ensure that the actual amount of filament extruded is consistent with the slicing software settings by calibrating the extruder. You can use the 100mm ruler command to test the extrusion length. If you find that the extrusion length does not match the command value, you need to adjust the step value (E value) in the firmware. Accurate calibration can significantly improve printing accuracy and reduce exudation. In addition, regular nozzle replacement can prevent extrusion blockage.

3. Optimize stroke movement

Try to minimize the distance the nozzle moves in the non-printing area by adjusting the path optimization option in the slicing software. This not only helps reduce exudation, but also shortens printing time. Software such as Cura or PrusaSlicer usually provide path optimization functions, and users can choose the shortest path or avoid cross-model movement options.

4. Reduce the printing temperature

The melting degree of the filament is directly related to the nozzle temperature. Too high a temperature may cause excessive filament flow, which may cause exudation problems. Gradually reduce the temperature by 5°C each time until the best balance between exudation control and layer adhesion of the filament is found. Note that too low a temperature may cause poor interlayer adhesion.

5. Modify the starting point of the layer

Setting the starting point position of the layer to "random" mode in the slicing software can allow the starting point to be distributed in different areas of the model surface to avoid acne-like marks being concentrated in one place. Slicing software such as Cura provides a seam hiding option that can align the layer starting point to the edge, corner or inconspicuous area of ​​the model, such as the bottom edge. This setting can effectively cover up acne marks and make the model surface smoother and more beautiful, especially for prints with strong display.

6. Use the glide function

When the glide function is enabled, the nozzle will stop extrusion in advance when the printing path of a layer is about to end, and use the remaining molten filament in the nozzle to complete the last part of the path. This can effectively avoid acne or exudation problems caused by excessive extrusion at the end. It is recommended to start with a sliding distance of 0.1-0.2mm and adjust it to the optimal value according to the printing results.

JLC3DP provides professional post-processing services, including fine grinding, painting and oil spraying, which can avoid acne problems on the surface of 3D printed parts to the greatest extent and further improve the appearance and texture of the printed parts. Whether it is a customized post-processing or a mass production demand, JLC3DP can provide a full range of solutions to ensure that customers get a final product that meets high standards.