3D Print Blobs and Zits: How to Get Rid of Them

When it comes to surface defects on 3D prints, there are numerous concerns. For example, we have previously discussed solutions to avoid issues like scars or scratches on the top surface of 3D prints. Today, we are going to solve another defect issue: 3D print zits and blobs. Generally, inconsistencies in extrusion on the surface of printed objects result from mechanical hardware and print setting problems, leaving behind many annoying bumps that can't be ignored. But this is not permanent, and we can also make the surface smoother through post-processing, such as sanding. A more favorable strategy is to prevent it from happening again. Let's explore solutions further.

Why Do 3D Printer Blobs and Zits Occur?

3D Print Blobs and Zits

Zits and blobs in 3D printing look like bumps or ridges on the surface of a 3D print. It is mainly due to inconsistent extrusion, where excess material oozes out of the nozzle, then deposits and forms small accumulations on the print surface. There are many reasons for these print imperfections, and we need to notice when blobs and zits occur during the printing process.

When there are 3D print blobs on the first layer, it's likely that the Z-axis is set too low, causing the nozzle to be too close to the build plate, potentially resulting in a collision with the print layer. Fine-tuning the Z-offset can help improve this issue.

If 3D print small lumps occur at the start and the end point of layers, it's likely Z-seam blobs, and you may need to adjust retraction settings. It's also possible that there are extruder tension issues and print setting problems such as excessive print temperature, speed, or insufficient cooling. The reasons for blobbing on 3D prints are outlined below.

  • 3D printer nozzle is hitting the print.
  • Extruder issues, such as clogs or over-extrusion.
  • Printing speed is too fast.
  • Nozzle temperature is set too high.

How to Stop 3D Print Zits and Blobs?

Method 1: Calibrate Your Printer Extruder

Direct drive extruder

(Direct drive extruder)

When you notice your 3D printer extruding inconsistently or extruder making a clacking noise during printing, it's time to calibrate your printer's extruder tension. This can help prevent issues like blobs and zits in 3D printing. After feeding into the print head, if the filament is subjected to excessive pressure from the extruder, there can be temporary over-extrusion problems. Then, bumps may be left on the 3D printed object. On the other hand, if the extrusion force is not strong enough, the filament can easily slip in the extruder gear, producing debris and causing blockages, which in turn affects the consistency of material extrusion. Therefore, ensuring the correct extruder tension should not be overlooked.

Lowering the extrusion flow rate (or extrusion multiplier) can help improve 3D printing blobs and zits. In slicer settings, the flow is, to put simply, how much filament flows out of the nozzle. Typically, this setting doesn't need to be adjusted every time you slice, but it may vary for changing some filaments with different densities. You can try starting with the default 100% flow rate and gradually reducing it by 5% with each print, and then test on a calibration cube to see if the issue improves.

Method 2: Lower Print Speed and Nozzle Temperature

3D printer is printing

High printing speed and nozzle temperature can cause the print head to move very fast, and the hot end to heat the material quickly. Consequently, the molten filament may uncontrollably drip from the nozzle, leading to the deposition of small or large blobs on the print surface. Therefore, appropriately lowering these two parameters can help alleviate this issue.

When adjusting the printing speed, it's advisable to follow the manufacturer's recommended settings. If you find that most average 3D printers are too slow for your expectations, but at the same time, you don't want to reduce the current machine's speed, you might consider investing in an affordable high-speed printer. Anycubic Kobra 2 Pro is an excellent and reliable high-speed printer. It is under $300 in the US market, capable of completing a standard 3DBenchy print in just 15 minutes. The Kobra 2 Pro can reach speeds of up to 500mm/s, which is several times faster than many conventional printers in the market.

Method 3: Adjust Retraction Settings

Cura Retraction Settings

Activating and fine-tuning the retraction settings in the slicer not only effectively reduces zits and blobs on 3D prints but also prevents common issues like 3D print stringing and oozing. Since the 3D printer has to travel between different print points, there is a risk of molten filament oozing out during this process, causing surface defects.

The retraction settings can reduce filament leakage because the extruder pulls back a small amount of filament from the hot end when the print head performs travel moves. The settings mainly include retraction distance and retraction speed. The former controls the distance the extruder retracts the filament, and you can increase it by 1mm each time. The latter determines how quickly the filament is retracted, and you can increase it by around 25% to see if it improves the 3D print blob problem.

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