Eliminate 3D Print Zits and Blobs: 8 Easy Fixes

Mario De Lio

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A 3D printed cylinder with visible zits and blobs and an ender 3 v2 in the background

Zits and blobs appear as irregular bumps or ridges on the surface of a 3D print.

Though these slight imperfections may seem minor, they can significantly detract from the aesthetic appeal. In some cases, zits and blobs affect the functional integrity of a 3D-printed object.

This article delves into the causes and solutions for 3D print zits and blobs, offering a comprehensive guide to understanding and preventing these pesky issues. Drawing from a wealth of expert advice and proven strategies, we provide actionable tips and tricks to enhance the quality of your 3D prints.

Causes of 3D Print Blobs and Zits

3d print over extrusion causing zits and blobs on two cubes
(Source: u/donnysaysvacuum via Reddit)

The most common cause of blobs and zits is too much filament accumulating on the print’s surface, also known as over-extrusion. Over-extrusion during the 3D printing allows the excess filament to accumulate on your print’s surface, creating small bumps on the print’s exterior.

Here, we delve into the various factors that contribute to the occurrence of zits and blobs.

  1. Over-Extrusion: Over-extrusion occurs when the printer dispenses more filament than needed. The excess material accumulates at certain points, forming blobs and zits.
  2. Incorrect Retraction Settings: Retraction is the process by which the printer pulls back the filament at the end of a print move. If the retraction settings are not calibrated correctly, it can result in extra filament oozing out of the nozzle, forming zits and blobs at the beginning or end of a print path.
  3. Printing Speed and Temperature: Both high printing speeds and temperatures contribute to this issue. High speed doesn’t give the filament enough time to cool down, causing it to bulge. Similarly, if the printing temperature is too high, the filament stays more liquid, making it more likely to form blobs.
  4. Nozzle Issues: Inconsistent flow due to a partially clogged nozzle can lead to irregular filament extrusion, causing zits and blobs.
  5. Filament Quality and Humidity: Poor quality or moist filament leads to irregular extrusion. Filaments absorb moisture from the air, leading to bubbling and popping during printing, which results in imperfections.
  6. Cooling: Inadequate cooling can prevent the filament from solidifying quickly, causing it to ooze and form blobs.

How to Fix Zits and Blobs

A 3D printed rocket with print defects from leaving the filament in the 3D printer for too long. The print has zits, blobs, under extrusion, gaps, and stringing

There are several ways to fix and prevent zits and blobs in your 3D prints. By taking the time to calibrate your 3D printer, you can eliminate zits and blobs from your prints.

Lower Print Temperature

Printing with a nozzle temperature that’s too high can cause over-extrusion as the filament material becomes too runny. The blobs and zits form as excess filament oozes out of the extruder nozzle.

The ideal print temperature varies by material, brand, and color. There are three ways to find the perfect print temperature:

  1. Check the Filament Roll: Filament manufacturers include recommended printing temperatures on the filament packaging and the side of the filament spool. The manufacturer’s recommendations are the best starting point.
  2. Print a Temperature Tower: The temperature tower on Thingiverse helps you find the perfect print temperature. Each section of the print uses a different temperature in 5°C increments. Examine each section to determine the best 3D printing temperature. I recommend printing a temperature tower when using a new filament.
  3. Trial and Error: Lower your nozzle temperature in 5°C increments until you find an optimal print temperature.

Be careful not to lower the print temperature too much. If you reduce the temperature too much, you’ll face issues with under-extrusion.

Lower Print Speed

When your print head moves too fast, the filament doesn’t have enough time to set before the next layer is added.

Imagine your printer like a car on a road. If it goes too fast around a corner, it might skid or not follow the path correctly. The same thing happens with your printer – if it moves too quickly, the filament can skid off course and make a mess.

High print speeds make it more difficult for the hotend to control filament extrusion as your print head zips around the print bed.

Lower your print speeds in 5-10 mm/s increments. The slower print speed gives your filament more time to cool before adding the next layer. Additionally, your print head can better control filament extrusion at slower speeds.

Adjust Retraction Settings

A 3d printed pikachu with print imperfections like stringing, zits, and blobs caused by wet filament

Adjusting the retraction settings on your 3D printer is another smart way to tackle the problem of zits and blobs. The retraction settings tell the extruder to pull back the filament from the hot end and reduce pressure when moving from one section of your print to another.

Enabling retraction prevents the extra filament from leaking out and forming those small bumps or blobs.

Here are the ideal retraction settings based on our experience:

  • For Bowden tube 3D Printers
    • Retraction Distance: 6 mm
    • Retraction Speed: 50 mm/s
  • For Direct Drive 3D Printers
    • Retraction Distance: 0.8 mm
    • Retraction Speed: 50 mm/s

If you want to dial in your retraction settings, this Retraction Test on Thingiverse is a good start for a test print.

The retraction settings are one of the most challenging settings to calibrate. Take your time, and use the test print above until you find a combination of retraction speed and retraction distance that produces excellent results.

Adjust the retraction distance in 1 mm increments and the retraction speed in 5-10 mm/s steps. Only change one setting at a time to measure the impact on print quality.

Enable Coasting

Coasting works by stopping filament extrusion just before the print head finishes its path. It’s like taking your foot off the gas pedal before you stop your car.

When coasting is enabled, it allows any built-up pressure to be released in a controlled way. Coasting minimizes the chances of extra filament oozing out when the printer moves to a new spot, which often causes zits and blobs.

Increase Cooling

Close up of the sprite direct drive extruder on a CR M4 with the volcano syle hot end, cr touch auto bed leveling and the 3d printed fan shroud

Cooling is imperative for achieving optimal FDM prints. We know that zits and blobs are formed when filament can’t cool before adding the next layer.

Enable cooling or increase fan power to help your filament solidify before adding the next level.

If you think cooling is your issue, print several test prints, increasing the fan speed by 10% each time. Compare the test prints to see which cooling setting creates the best surface finish.

If your fan is set to maximum speed and you’re still unable to cool the filament, you can always add a second fan or upgrade the existing fan.

Ambient air temperature may also play a role in cooling your 3D prints. If you’re printing in a warmer climate, you may need to add a couple of powerful fans to your 3D printer.

Enable Wiping

Wiping is like giving the nozzle a quick clean between moves. When you enable wiping, the printer’s nozzle ‘wipes’ itself on the last part of the print before moving to a new section. The back-and-forth motion removes excess filament that might be sticking to the nozzle.

Think of it like wiping a paintbrush on the edge of a paint can before moving to a new area of your canvas.

Wiping prevents drips of filament from oozing out when the print head stops and starts.

Using the wiping feature, you can help keep your prints smooth and free of those small, bumpy zits and blobs, leading to a cleaner, more professional final product.

You can enable wiping settings in Cura by clicking “Wipe Nozzle Between Layers.”

Editor’s Note

As a bonus, Wiping also helps remove issues with Z seams in your 3D prints.

Tune Printer Extrusion

Checking the flow rate using a test print and digital caliper
(Source: petrzmax via Thingiverse)

Tuning your printer’s extrusion is crucial in eliminating zits and blobs from your 3D prints. This involves two key adjustments: calibrating the extruder’s steps per millimeter (E-steps) and adjusting the flow rate.

Calibrating E-steps: E-steps are basically how many steps your printer’s motor needs to take to push out a precise amount of filament. If your E-steps are off, your printer could push out too much or too little filament. When your printer pushes too much filament, the over-extrusion leads to zits, while too little extrusion leads to gaps and weak prints. To calibrate 3D printer e-steps, measure a set filament length, instruct your printer to extrude a specific amount, and then measure how much was used. The difference between the expected and actual length lets you adjust the E-steps until they’re just right.

Adjusting Flow Rate: The flow rate is about fine-tuning how much filament is extruded. It’s a percentage adjustment in your slicing software that either increases or decreases the filament extruded during a print. If you notice zits and blobs, reducing the flow rate can help, as it decreases the filament flow. Adjusting the flow rate is especially useful if you’ve already calibrated your E-steps but still see issues.

Both of these adjustments require a bit of trial and error. You may need to print a few test objects and tweak the settings until you get the perfect balance.

By ensuring your printer extrudes the exact amount of filament, you can significantly reduce imperfections and achieve smoother, higher-quality prints.

Clean Your Nozzle

Using a needle to clean a 3D printer nozzle from partial and full clogs caused by filament residue, dust, and debris

A dirty nozzle in your 3D printer causes zits and blobs in your prints when the built-up residue inside the nozzle disrupts the smooth flow of the filament, causing irregular extrusion. The excess filament deposited results in unwanted zits and blobs.

To clean a dirty 3D printer nozzle, there are several methods you can try:

  1. Use a Needle: Heat the nozzle to your printing temperature, then use a fine needle to poke through the nozzle opening and remove any blockages gently. Ensure you remove any filament before inserting the needle.
  2. Cold Pull Method: Cold pulling filament involves heating the nozzle and inserting filament until it melts. After allowing the filament to cool, it takes the shape of the nozzle’s interior and bonds with debris. When you “pull” the filament, it removes residue and clears the nozzle path.
  3. Use Cleaning Filament: Specialized cleaning filament is designed to help clean the nozzle from the inside when extruded through it. Cleaning filament is expensive, so I recommend trying a cold pull before using special filaments.
  4. Brush Cleaning: Use a small wire brush to scrub the outside of the nozzle, removing any external debris.
  5. Replace the Nozzle: If the nozzle is too clogged or damaged, replacing it might be the best option.

Remember, regular nozzle maintenance and cleaning can significantly improve your 3D printing results and extend the life of your printer. Keeping the nozzle clean ensures consistent, high-quality prints free from zits and blobs.

Keep Your Filament Dry

Drying white pla filament in a Sunlu filament dryer

Printing with filament is a common cause of zits and blobs in 3D printing. 3D printing filaments like PLA absorb moisture from the air. Water molecules trapped inside the plastic filament create problems during the printing process.

The moisture becomes steam as the wet filament passes through the printer’s hot end. The steam causes the filament to expand. You’ll often hear hisses and pops as the moisture looks to escape the printer’s nozzle.

The hisses and pops spit out molten filament, creating zits and blobs on your print.

To avoid these issues, it’s crucial to dry your filament correctly.

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SUNLU Filament Dryer Box
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There are various methods for drying filament, including using a regular oven set to a low temperature, food dehydrators, and special filament drying boxes.

Filament dryers are our preferred choice as they are made explicitly for drying filament. Filament dryers are better and more consistent at drying filament spools than the other two methods.

Proper filament storage is equally important to prevent it from absorbing moisture in the first place. Storing filament in a dry, airtight container with desiccant sachets is recommended.

Proper storage keeps your filament dry and prevents moisture absorption.

Removing Zits On Final Prints

Preventing zits and blobs in your 3D prints is the best start. But what do you do if you need to remove zits and blobs from your finished objects?

Here are some practical methods for cleaning up your prints:

1. Sanding: Sanding is an easy method for removing zits and blobs. Start with coarse-grit sandpaper (80-120 grit) to remove the larger imperfections, then gradually move to finer grits (up to 400 grit) to smooth out the surface. Sanding requires patience and a gentle touch to avoid damaging the print. A small file or a piece of sandpaper wrapped around a matching curved object can be helpful for intricate or hard-to-reach areas.

2. Trimming with a Craft Knife: For smaller zits or blobs, a sharp craft knife can be used to trim them carefully. This method works well for prints with small imperfections or in areas where sanding might be difficult. Working slowly and carefully is essential to avoid cutting too deeply into the print. And always work away from your body to prevent injury.

3. Using a Heat Gun or Soldering Iron: Applying gentle heat to the affected area can help soften the material, making it easier to smooth out. A heat gun set to a low temperature can be used to go over the surface lightly. Alternatively, a soldering iron can be used to melt down the zits or blobs carefully. Caution is advised with this method, as too much heat can warp or damage the print.

4. Chemical Smoothing: Certain filaments, like ABS, can be smoothed with chemicals like acetone. Acetone smoothing involves exposing the print to acetone vapor, which slightly melts the surface, smoothing out imperfections. This method should be used cautiously and in a well-ventilated area, as acetone is a strong solvent. As a bonus, acetone smoothing creates a glossy finish on your 3D prints.

6. Using a Rotary Tool: A rotary tool with a sanding or grinding attachment can speed up removal, especially for larger prints. Use a low speed and continuous movement to prevent heat and friction from damaging your print. For large objects like cosplay items, you can use a palm sander.

Each method has advantages and is best suited for different prints and imperfections. In some cases, a combination of techniques might yield the best results.

Always wear appropriate safety gear, like gloves and a dust mask, when working on your prints.

Article by

Mario De Lio

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