Z Banding (Z Wooble): Rooting out the Cause and Fixing the 3D Printing Defect

Time is a valuable resource for makers, so it is always frustrating to find that a 3D print job that has taken a couple of hours to produce hasn’t turned out quite the way you expected. Warping, stringing, and poor adhesion to the print bed are all common problems that makers face. But today we are looking to troubleshoot a particular 3D printing issue: Z banding. 

Recommended reading: What Causes 3D Print Warping and How to Prevent It

What is Z Banding?

Z banding, also known as ribbing, is a common defect that occurs in fused deposition modeling (FDM) 3D printing. It is easy to recognize Z banding by simply looking at your 3D printed part. If the outer surface of the part has prominent horizontal ribs or lines instead of a smooth surface, Z banding has likely occurred.[1]

That being said, any object made using an FDM 3D printer will have visible layers. This is due to the nature of the 3D printing process, in which melted filament is extruded layer by layer until a part is made. The difference between a successful 3D print and one that has suffered from Z banding is that the layers will only be slightly visible, not textured, like a ribbed surface. It’s also important to distinguish between Z banding and ringing or ghosting. While Z banding results in straight horizontal ridges, ringing appears as wavy patterns or oscillations on the surface of a printed object, usually caused by vibrations or resonance in the printer's mechanical components.

Fortunately, if you’ve encountered Z banding while using your 3D printer, it is not an insurmountable hurdle. Once you understand what is causing the 3D printing defect, it is relatively straightforward to prevent and fix it. Let’s dive in.

What Causes Z Banding and Z Wobble?

In the FDM process, the cause of Z banding can almost always be traced back to the 3D printer hardware. And while there are many specific things that can be causing the problem, most of them can be categorized into two groups, which we’ll explore in more detail: Z wobble and extrusion problems.

Z wobble and filament extrusion problems are the main causes of Z banding. 

Z wobble

Z wobble is one of the leading causes of Z banding issues. In short, Z wobble is what happens when the 3D printer’s vertical Z-axis is misaligned. In a cartesian 3D printer, the Z-axis is responsible for moving the print head up and down. In the printing process, the print head must be incrementally moved up, as each new layer is deposited. If, however, something causes the print head to rise in uneven increments, even by a fraction of a millimeter, the deposited layers will be affected. Think of it this way, if you are 3D printing a part with a layer height of 1mm, the printhead should be rising by 1mm with every layer. If something causes the printhead to only rise by 0.5mm, the 1mm layer will effectively be squished by the layer above it, causing a ridge.

There are a few different parts of the Z-axis that can be causing the misalignment, such as the Z-axis stepper motor, the motor bracket, the threaded rod coupler, or the threaded rod. If any of these components is defective or not perfectly straight, it can cause inconsistencies and the dreaded “wobble”. 

Extrusion issues

The other main cause of Z banding is related to inconsistent filament extrusion. In this category, there are a few main culprits that disrupt the flow of filament: poor filament feeding, inconsistent filament, and a clogged extruder nozzle. If the filament you are using is not being smoothly fed into the hot end, there is a risk that it will cause a slight pull on the printhead, which will result in misalignment. As the filament then comes through, the printhead will go back into position. The repetition of this process can cause ribbing in the 3D print and lessen the overall print quality.

Variations in filament diameter can also contribute to inconsistent extrusion. Most 3D printers rely on a consistent filament diameter to accurately calculate the amount of material needed for each layer. If the filament diameter varies significantly, the printer may extrude an incorrect amount of material, resulting in Z banding.

The other extrusion-related cause for Z banding is a clogged nozzle. If your 3D printer’s nozzle is clogged even a little bit, it can cause filament to extrude unevenly, which disrupts the consistency of layers as they are deposited. As one can imagine, this can cause some deformities in the final part.

An easy way to determine whether your Z banding is caused by Z wobble or poor extrusion conditions is to look for consistency. That is, if your printed part has a consistent ribbed pattern, it is more likely that it was caused by Z wobble. If the surface defects are more random, it could be due to a problem with your filament feeding or nozzle.

How Do You Fix Z Banding in 3D printing?

If you notice that your 3D prints are plagued by Z banding, the good news is that there are ways of troubleshooting the problem. First, if you don’t want to toss the 3D printed part, you can minimize the effects of the ribbing using manual post-processing techniques, like sanding and smoothing. But that’s only a one-time solution. It’s also important to get to the root of the Z banding problem and fix it at the source. 

Recommended reading: 3D print post-processing steps: supports, sanding, smoothing, more

Ensuring all 3D printed Z-axis components are aligned can reduce the risk of Z banding

Fixing Z Wobble

If the cause of Z banding is Z wobble, you will first have to figure out which component or components of the Z-axis are causing the misalignment. To start, check the stepper motor. If the motor shaft that connects the stepper motor to the shaft coupler is not completely straight, it could be causing Z banding and must be replaced. 

If you see that the stepper motor is moving at all during the printing process, the motor bracket could be the source of the problem. Simply try tightening the bracket to see if it secures the stepper motor or, if all else fails, replace it with a new one. (You can find many bracket models to 3D print on Thingiverse, just be sure the bracket is printed at a high quality level.) 

The shaft coupler, also known as the rod coupler, which connects the stepper motor to the threaded rod, can also cause Z wobble. If you suspect the coupler is the culprit, take it apart from the stepper motor and rod and reassemble them while ensuring every component is well aligned.

Finally, a misaligned Z-axis rod (aka lead screw) is a common cause for Z wobble. The threaded rod is essentially the pillar that carries the print head up and down, so if it is not perfectly straight, it will cause the printhead to move inconsistently. To check if it is aligned, remove it from the 3D printer frame and roll it on a flat surface. If the rod doesn’t roll smoothly and straight, it has been bent.[2] In this case, it is often easiest to replace the lead screw, though it is possible to fix it using special alignment tools. Once you’ve reassembled your 3D printer’s Z-axis, do a test print to see if the Z banding has stopped. 

Worn-out lead screws, which are responsible for converting the rotational motion of the stepper motors into linear motion along the Z-axis, can also contribute to Z banding. As the lead screws wear down, their threads can become uneven or damaged, causing inconsistent movement along the Z-axis. This inconsistency can result in horizontal lines on the printed object. Additionally, debris or dirt buildup on the lead screws can cause similar issues, as it can impede the smooth movement of the Z-axis components.

Fixing extrusion issues

As we saw in the previous section, there are three main ways in which inconsistent extrusion causes ribbing. The first is due to inconsistent filament feeding. If, for example, your spool of PLA isn’t feeding into the 3D printer smoothly, you can remedy it by ensuring there is nothing obstructing the filament’s path to the extruder. You can also encourage smooth feeding by installing a simple filament guide on your 3D printer (these too can be 3D printed). 

For issues related to filament quality and consistent diameter, simply using high-quality filament with consistent diameter can help mitigate this issue. You can check your filament’s diameter by using calipers to measure the filament at various lengths. 

If a clogged nozzle is causing inconsistent extrusion, you have two routes: cleaning the nozzle or replacing it. (We should also note that high-quality nozzles made from hardened materials will be less prone to clogging.) There are several techniques for cleaning a nozzle to remove clogged filament. For example, you can heat up the nozzle to print temperature and use a brass brush to remove any melted filament that has stuck to the outside of the nozzle. To clear out clogged filament inside the nozzle, you can jab a needle into the nozzle to break up the filament, which should be pushed out the next time you extrude. Alternatively, you can buy a dedicated cleaning filament.[2]

In general, a good way to prevent Z banding is to maintain your 3D printer regularly, checking for alignment issues, tightening screws on the X-axis, Y-axis, and Z-axis, cleaning your extruder nozzle, and taking the time to achieve proper calibration. Other best practices for 3D printing can also make a difference. This includes using good quality filaments, ensuring the right nozzle temperature is being used, and a stable print environment is provided.

Recommended reading: How to Clean 3D Printer Nozzles and Prevent Clogs

Conclusion

While it’s never encouraging to see a print ruined due to Z banding, with this knowledge you can easily identify the cause and fix it. Keeping the alignment of your Z-axis in check and ensuring your filament feeding and nozzle are running smoothly are key to preventing Z banding and ensuring successful 3D prints. If you are encountering other common issues, such as stringing, the problem could be related to your 3D printing materials and moisture. We’ve covered that topic as well, here. We also have troubleshooting guides on issues like under extrusion and over extrusion.

Frequently Asked Questions (FAQs)

Q: What is Z banding? 

A: Z banding is a relatively common 3D printing defect that appears as prominent horizontal lines or ridges on the surface of a printed object. Depending on the cause of the Z banding, these ridges can occur at regular or irregular intervals along the vertical Z-axis.

Q: What is the difference between normal layer lines and Z banding?

A: FDM 3D prints are known to have visible layers. This is a product of the 3D printing process, where melted filament is deposited layer by layer onto the build platform. The key difference between normal layer lines and Z banding artifacts is that the layers will only be slightly visible, they will not be textured or ribbed.

Q: What causes Z banding? 

A: Z banding can be caused by mechanical issues, like a worn out or bent lead screw, as well as inconsistent extrusion, or a clogged nozzle.

Q: How can I prevent Z banding? 

A: Preventing Z banding involves addressing its underlying causes through regular 3D printer maintenance, alignment checks, extruder calibration, nozzle cleaning, and proper slicer settings.

Q: How can I fix a 3D print with Z banding

A: If you don’t want to throw out printed part with signs of Z banding, it is possible to smooth the surface of the print using sanding and other post-processing techniques. Note that the sanding process can influence the dimensional accuracy of your print, which can be an issue if tight tolerances are required.

Q: What are some hardware upgrades that can help reduce Z banding? 

A: Upgrading to high-quality Z-axis lead screws and linear rails can help reduce Z banding by improving the smoothness and consistency of the Z-axis movement. A higher grade nozzle can also reduce the risk of clogging.

References

[1] 3D Print Knowledge, 2022. “Common 3D Printing Terms and Abbreviations”. [Internet] https://3dprintknowledge.com/common-3d-printing-terms-and-abbreviations/ [Accessed March 7, 2022].

[2] Tech2C, 2015. “3D Printer - Improve Z-Axis Print Quality”. [Internet] https://www.youtube.com/watch?v=HySgeiDD8AA [Accessed March 8, 2022].

[3] 3DSolved. “Ender 3: How to clean the nozzle (Unclog it)!” [Internet] https://3dsolved.com/ender-3-clean-the-nozzle-unclog-it/ [Accessed March 8, 2022].