3D Printer Blobbing: Tips to Prevent Zits and Blobs

Print quality issues can significantly affect a 3D print’s strength, shape, dimensional accuracy, and appearance. One common issue, 3D printer blobbing , refers to the presence of zits or blobs that manifest as irregular bumps, ridges, or accumulations on a model’s surface. These defects are especially critical for items where aesthetics are important, such as cosplay equipment. Moreover, blobbing can cause problems for functional components that need precise fitting, and it can negatively impact the dimensional accuracy of a print.

In this article, we’ll explore the causes of 3D printer blobbing, discuss methods to address them, and offer tips for prevention. By understanding and mitigating these issues, you can improve the quality and functionality of your 3D printed models.

Considerations

Before proceeding, it’s important to note that we’ll assume you are using a default 3D slicer profile. These profiles are generally reliable and work well with most printer and material combinations. However, they are quite general and do not account for the unique elements of your printer, such as the extruder configuration. As a result, they often require some tuning to achieve high-quality prints.

While this article will cover how to prevent zits and blobs on prints, it is also helpful to know how to remove these defects from already printed models. Unfortunately, there aren’t many methods for this, but post-processing options such as sanding and acetone smoothing can be effective.

The Causes

To prevent 3D printing complications, you first need to identify the source of the issue and determine how to solve the problem. Here are some common causes of zits and blobs on 3D prints.

Before moving forward, it’s crucial to tune and calibrate your printer to avoid mistaking other problems for zits and blobs. This includes leveling the bed, calibrating the extruder (E-steps), ensuring the nozzle is clean and tightly secured, correctly setting the Z offset, and using appropriate temperatures for your filament. Additionally, make sure your filament is dry before printing.

Here are some common causes of zits and blobs:

Retraction: Retraction is when the extruder pulls back a small amount of filament to relieve hot end pressure. While this can help prevent stringing, incorrect retraction settings (too small, large, slow, or frequent) can lead to zits and blobs. Extrusion: This describes how filament is extruded or printed. Zits and blobs often result from inconsistent or over-extrusion on the model's exterior. Nozzle Temperature: The nozzle temperature affects extrusion and filament melting. Too high a temperature can cause the filament to ooze excess material, even when the extruder isn't pushing filament. Printing Speed: This is how fast the printhead moves while depositing material for the infill, walls, and first layer. Frequent speed changes and excessively high speeds can cause quality defects, including zits and blobs. Cooling: Proper cooling is essential in the FDM 3D printing process, as the filament needs to cool before a new layer is added. Inadequate cooling can cause zits and blobs because melted material is more prone to form unwanted features when another layer is added. Tip 1: Fix Incorrect Extrusion

As mentioned previously, extrusion can cause printing issues like zits and blobs. Therefore, tuning your printer’s extrusion is crucial. If your printer isn’t extruding material consistently and in the right amounts, printing issues will arise.

To tune your printer’s extrusion, start by calibrating your extruder if you haven’t done so recently. Next, check that your flow, or extrusion multiplier, in your slicer profile is set correctly. The flow setting controls how much filament your printer extrudes.

Additionally, clean or change the nozzle to address any partial clogs that may cause inconsistent extrusion. You can also use Linear Advance, a feature in firmware programs like Marlin, to further improve extrusion. This feature tells your printer to extrude a specific distance of filament per every 1 mm/s of print speed, helping you predict and counteract hot end pressure that can cause zits and blobs.

Tip 2: Lower Temperature & Speed

To address zits and blobs, consider lowering your nozzle temperature and print speed, as both affect your printer’s extrusion.

A high nozzle temperature can cause over-extrusion, leading to zits and blobs as excess filament flows out. Adjust your nozzle temperature in increments of 5 °C to find the optimal setting, but avoid going too low to prevent layer adhesion issues. Always start with the manufacturer’s recommended print temperature.

High print speeds can also reduce print quality, giving the material less time to settle and cool before the next layer is added. Rapid filament delivery to the hot end creates extra pressure, making it harder to control filament flow. To improve print quality and prevent zits and blobs, reduce your printing speed by 5-10 mm/s.

Tip 3: Adjust Retraction

To prevent zits and blobs on 3D prints, adjust the retraction settings in your slicer profile. Retraction pulls back filament from the hot end to relieve pressure, preventing unintended extrusion. Retraction settings, including frequency, distance, and speed, significantly impact the appearance of zits and blobs.

Z Hop Settings: Consider adjusting Z hop settings, which control how the printhead travels over the design without the nozzle touching it during retraction. Retraction Minimum Travel: To minimize zits and blobs, try reducing the number of retractions by increasing the minimum retraction travel distance. This setting determines the shortest distance the nozzle can travel before a retraction occurs, reducing retraction frequency and potentially lowering the number of zits and blobs. Retraction Distance: Adjusting retraction distance is another effective method. This setting controls how much filament is pulled back during each retraction. If the distance is too short, excess material may extrude, causing zits and blobs. Conversely, if the distance is too long, air may enter the nozzle, leading to blobs and bubbles. Start by increasing the retraction distance and then reduce it if blobs or zits persist. Retraction Speed: Finally, optimize retraction speed, which determines how quickly filament is pulled back and reintroduced to the hot end. Insufficient retraction speed can result in oozing and material buildup. Increase the retraction speed by around 25%, up to a maximum of 65 mm/s, to prevent these issues. Tip 4: Increase Cooling

To prevent zits and blobs on 3D prints, increase your printer’s cooling. High nozzle temperatures can cause over-extrusion, leading to these defects. Proper cooling ensures layers solidify correctly, preventing oozing and surface flaws.

In addition to lowering the nozzle temperature, enhance cooling by increasing the fan speed in your slicer settings in 10% increments until the issue is resolved. If your fan is already at maximum speed and cooling is still insufficient, consider adding an extra fan, such as the 5015, or using a more powerful one to ensure adequate cooling for your prints.

Tip 5: Use Coasting

To prevent zits and blobs, activate coasting in your 3D slicer program. Coasting stops extrusion a small distance before a print move ends, utilizing the residual pressure in the hot end to continue extruding material.

This pressure can unintentionally push filament out even after the extruder stops moving. By predicting this pressure, coasting helps prevent over-extrusion and the formation of zits and blobs.

Most slicer programs, like Cura, have this feature. Simply activate it and adjust the settings based on its effectiveness. Increase the coasting distance until defects disappear when the extruder stops at the end of a perimeter. Typically, a coasting distance between 0.2-0.5 mm improves print quality noticeably.

Tip 6: Adjust Shell Settings

Lastly, adjusting the shell settings in your 3D slicer program can help prevent zits, blobs, and similar problems like Z seams and infill bleeding. These settings control how the exterior of your model is printed, significantly impacting the final appearance.

Here are some useful shell settings in Cura:

Wall Ordering – Outside to Inside: This setting prints the outer wall before the inner wall. Since inconsistent extrusions are more likely to occur later in the layer, printing from outside to inside helps hide any printing issues within the model's interior. Outer Wall Wipe Distance: This setting moves the nozzle a certain distance after printing the outer wall, helping to hide visual defects. It is particularly useful for concealing the Z seam, which appears as an alignment of inconsistent extrusion along the print's side. You can also adjust other settings, such as Z seam alignment and position, to further minimize this issue. Enable Ironing: Ironing smooths out the top layers of a print, squishing down any over-extrusions (zit or blob-like features) on the model's top exterior areas. This experimental feature is available in Cura and PrusaSlicer and can significantly improve surface quality. By fine-tuning these shell settings, you can enhance the overall appearance of your 3D prints and reduce the occurrence of zits and blobs.

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