Preventing and Fixing Zits and Blobs in 3D Printing

Print quality issues can impact the strength, shape, accuracy, and appearance of 3D prints. Zits and blobs, for instance, are surface defects that appear as bumps or ridges on printed models. While often cosmetic, these flaws are significant for visually critical items like cosplay props.

However, they also pose challenges for functional parts, especially those requiring precise fitting, as they can compromise dimensional accuracy. This article explores the causes of zits and blobs, provides solutions for fixing them, and offers tips to prevent them, ensuring higher-quality prints with improved aesthetics and functionality.

Elements

Before proceeding, note that we're assuming you're using a default 3D slicer profile. These profiles work well for most printers and materials but are quite general, often requiring adjustments for optimal print quality, especially considering your printer's unique features, like the extruder configuration.

This article focuses on preventing zits and blobs, but it's also helpful to know how to remove them from printed models. While options are limited, post-processing methods like sanding and acetone smoothing can help eliminate these defects.

The Reasons

To avoid 3D printing issues, it's essential to first identify the source of the problem and then determine the appropriate solution. Zits and blobs on prints can have several causes, and below are some of the most common ones.

Before diving into these causes, ensure your printer is properly tuned and calibrated to avoid misidentifying other issues as zits and blobs. This includes leveling the bed, calibrating the extruder, cleaning and securely attaching the nozzle, setting the Z offset, using the correct filament temperatures, and ensuring your filament is dry before printing.

Now, let's explore the causes!

Retraction is when the extruder pulls back a small amount of filament to reduce hot end pressure, preventing stringing. However, if the retraction settings are too small, large, slow, or frequent, they can cause zits and blobs.

Extrusion, which involves how filament is printed, is another key factor. Inconsistent or excessive extrusion can lead to zits and blobs on the model’s surface.

Nozzle temperature also plays a role; if too high, it can cause filament to ooze out, even when the extruder isn’t active.

Printing speed, especially with frequent changes or overly high speeds, can create defects like zits.

Cooling is essential for proper layer bonding. Insufficient cooling leads to blobs as melted material may shift when new layers are added.

Now, let’s explore solutions!

1. Correct Extrusion Errors

As extrusion is a common cause of printing issues, tuning your printer’s extrusion is essential for preventing zits and blobs. If your printer isn't extruding material consistently, problems will arise.

Start by calibrating the extruder, especially if it hasn't been done recently. Next, check the flow or extrusion multiplier in your slicer profile to ensure it’s correctly set. This setting controls how much filament is extruded.

If extrusion is still inconsistent, clean or replace the nozzle to resolve any clogs. You can also enable Linear Advance in firmware like Marlin, which improves extrusion by compensating for hot end pressure, reducing zits and blobs.

2. Decrease Temperature&Speed

To prevent zits and blobs, try lowering your nozzle temperature and print speed, as both impact extrusion.

A high nozzle temperature can cause over-extrusion, leading to blobs as excess filament flows out. Lower the temperature in 5°C increments, but avoid going too low, as this can affect layer adhesion. Always use the manufacturer's recommended temperature as a starting point.

High print speeds can reduce quality, as there’s less time for the material to settle and cool. Lowering the speed by 5-10 mm/s can help prevent pressure buildup and improve print results.

3. Modify Retraction Settings To prevent zits and blobs, adjust your retraction settings in the 3D slicer profile. Retraction pulls filament back from the hot end to avoid excess material extrusion. The frequency, distance, and speed of retractions can impact the appearance of zits and blobs.

Additionally, consider Z hop settings. These control how the printhead moves over the model during retraction without the nozzle touching the surface, helping to prevent unwanted marks and improving the overall print quality.

Minimum Retraction Distance To reduce zits and blobs caused by retractions, the best approach is to minimize them. Activate or increase your slicer’s minimum retraction travel distance, which defines the shortest distance the nozzle must travel before a retraction occurs. By increasing this distance, you reduce the frequency of retractions, which can help minimize the occurrence of zits and blobs on your prints.

Pullback Distance While avoiding retractions can help reduce zits and blobs, it may lead to more stringing in your print. Fortunately, there are other ways to fine-tune retractions to prevent these issues. One key setting to adjust is the retraction distance, which controls how much filament is pulled back during each retraction event.

If the retraction distance is too small, not enough filament will be pulled back, leading to excess material and resulting in zits and blobs. On the other hand, too large a retraction distance creates a gap between the filament and the nozzle, allowing air to pass through and causing blobs and bubbles. To resolve this, start by increasing the retraction distance and then gradually reduce it if the blobs or zits persist, achieving the right balance for cleaner prints.

Pullback speed The third setting to adjust is retraction speed, which controls how quickly the filament is pulled back and pushed through the hot end. If the retraction speed is too slow, the material won't be effectively pulled away from the nozzle, leading to oozing and resulting in blobs and zits. To prevent this, increase the retraction speed by about 25%, with a maximum of around 65 mm/s. This will help ensure the filament is retracted quickly, reducing the chances of print defects.

4. Enhance cooling

To prevent zits and blobs, increase your printer’s cooling. High nozzle temperatures can cause over-extrusion, as the filament stays melted too long, leading to defects. If layers aren't properly cooled, they may ooze, creating surface imperfections.

In addition to lowering the nozzle temperature, increase the fan speed in your slicer by 10% increments until the issue is resolved. If the fan is already at maximum speed and cooling remains insufficient, consider adding an additional fan, like the 5015, or using a more powerful one for better cooling.

5. Coasting

To prevent zits and blobs, consider activating coasting in your 3D slicer program. Coasting stops the extruder from extruding material a small distance before the print move ends. This helps address hot end pressure that can cause excess filament to ooze out even when the extruder stops, preventing over-extrusion and surface defects like zits and blobs.

Programs like Cura offer this feature, and it’s easy to activate and adjust. Gradually increase the coasting distance until you no longer see defects at the end of a perimeter. In most cases, a coasting distance of 0.2-0.5 mm will significantly improve print quality by preventing unwanted oozing.

6. Modify Shell Parameters

Finally, shell settings in your 3D slicer program control how the outer surface of your model is printed. Since shells form the exterior, adjusting these settings can help prevent or hide defects like zits, blobs, Z seams, and infill bleeding.

Here are some shell settings in Cura that can reduce zits and blobs:

Wall Ordering – Outside to Inside : This setting prints the outer wall first, followed by the inner wall. Since extrusions tend to be inconsistent later in a layer, printing the outer wall first helps hide mistakes on the interior of the model. Outer Wall Wipe Distance : This feature moves the nozzle a set distance after printing the outer wall, helping to conceal visual defects like the Z seam, which appears as inconsistent extrusion lines on the side of a print. Enable Ironing : This setting smooths the top layers of a print, flattening over-extrusions (such as zits or blobs). It’s an experimental feature available in Cura and PrusaSlicer. For more Creality 3D Printer, you can click the related articles as follows:

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