What Is It?

3D printing can be a fun hobby, but sometimes you experience seemingly inexplicable issues. Many of such problems reduce print quality and cause irregularities to form on prints, such as ringing or stringing. Luckily, almost all of these problems have simple solutions, ranging from tightening the belts to changing the nozzle.

Z banding, sometimes known as ribbing, is an issue sometimes seen on 3D prints from FDM printers. It refers to the appearance of obvious lines on the exterior, typically occurring in regular intervals. This print quality defect is relatively rare but is no less important to fix. Besides potentially ruining a functional print, no one wants layers that are even more visible than what FDM printers already produce.

In this article, we’ll go over what causes Z banding as well as steps you can take to fix and prevent this problem from occurring.

Causes

Before we get into the causes, it’s important to clarify what Z banding is and what it isn’t. Importantly, Z banding is the result of other issues – in other words, a symptom – so you can’t eliminate Z banding without first resolving what’s causing it.

Z banding is primarily caused by two different phenomenons: Z wobble and inconsistent extrusion. While Z banding is perhaps one of the more likely results of these two issues, both Z wobble and inconsistent extrusion can also lead to other print quality problems.

Z Wobble

Z wobble sounds similar to Z banding, but they’re not the same. Z wobble refers to the condition where a printer has a tilted or crooked Z-axis movement component, such as the Z-axis rod, or lead screw. Ultimately, this leads to incorrect movement in the printhead.

With a bent or crooked lead screw, the rotational flaw translates to the printhead moving back and forth in repeated layer shifting. Instead of generating a continual drift, as in regular layer shifting, the rotation of the lead screw brings the bulges in and out of the surface of a print, which forms Z banding lines.

Although Z wobble is commonly associated with a bent lead screw, it can also occur due to a crooked Z-axis stepper motor or a loose rod coupler, which connects the lead screw to the stepper motor.

Inconsistent Extrusion

The other potential cause of Z banding is inconsistent extrusion. As the name suggests, this is the non-uniform deposition of material from the nozzle. Inconsistent extrusion is usually caused by either a partially clogged nozzle or abnormal temperature variations, especially when conditions lead to regularly-dispersed effects. (Nozzle temperature might, for example, rise and fall in cycles.)

While a fully clogged nozzle may entirely block extrusion, a partially clogged nozzle can cause material extrusion to be erratic. If your problem is inconsistent extrusion, you may also see signs of over or under-extrusion in certain areas of your print.

Which One?

To determine if Z banding lines are caused by inconsistent extrusion or Z wobble, simply look at the pattern of the lines. Z wobble typically results in more predictable banding lines with an equal interval between them. On the other hand, inconsistent extrusion is a little more, well, inconsistent and the banding lines are more erratic.

Prevention & Fixing

In the next two sections, we’ll go over solutions for both Z wobble and inconsistent extrusion, which should fix your case of Z banding on prints. The first three fixes relate to Z wobble and securing the Z-axis stepper motor, rod coupler, and lead screw. The last two are for inconsistent extrusion, but don’t be afraid to try all five solutions!

Already-Printed Parts

Before we start looking at solutions, it’s important to mention that there are a few ways to lessen the appearance of Z banding on already-printed parts. If you’re dead set on not printing a piece again, you can minimize Z banding’s visual appearance using post-processing. Specifically, you can sand and, after that, layer smooth the surfaces of your print to reduce the bulges’ appearance on the sides.

If your print is beyond saving, and you want to prevent the same issue from happening again, the best way to do this is to eliminate the source of the problem.

Z Wobble Solutions

Stepper Motor
To start, make sure that your Z-axis stepper motor isn’t jolting when your printer moves up and down, as this indicates that the motor isn’t securely fastened to the printer’s frame.

To check this, tell your printer to move up 30 mm and then immediately down 30 mm, and before sending the command, place one hand on the motor and then begin the sequence. If you feel any movement, shift, or jolt from the motor, especially during a direction change, use a screwdriver or Allen key to tighten the stepper motor.

In fact, you can do this even if you don’t feel anything, as the motor and bracket can never be too tight. If your printer came with a weak stepper motor bracket, you can also 3D print a new one.

Rod Coupler

Next, make sure your rod coupler, which is the cylindrical piece that connects the motor shaft to the lead screw, is tight and not tilted in any way. For this, you may want to remove it using an Allen key to take out the two tiny grub screws from the coupler. Then, separate the coupler from the motor and the lead screw from the coupler. Finally, reassemble everything, ensuring that the parts are straight and secure.

Lead Screw

Our next fix for Z wobble is to check up on the Z-axis lead screw, which is the motion system that most FDM printers utilize to move the printhead (or bed) up or down. To do this, once more, remove the lead screw from the coupler and try rolling it on a flat surface. If the screw doesn’t roll smoothly, it’s probably bent.

If it’s significantly bent, you can attempt to bend it back into shape, but it’s likely a safer choice to just purchase a new one. You can find lead screws online or at a local hardware store, as threaded rods are fairly common.

If the lead screw is only slightly bent or you want to further ensure that your screw is straight, you can use an alignment or stabilizer part. This hardware aligns the top of the lead screw with the bottom by restraining the screw’s top position. Alignment pieces usually involve a bearing (where the inner hole goes around the rod) attached to a base that mounts to your printer’s frame.

With a stabilizer part, you can adjust the top of the rod’s position to make sure that it’s centered with the bottom. You can purchase one of these online, like this injection-molded one, or you can 3D print one, such as this bearing fit model.

Inconsistent Extrusion Solutions

Replacing or Cleaning the Nozzle
A clogged or partially clogged nozzle is never a good thing to have on your 3D printer, and it can cause inconsistent extrusion, potentially resulting in Z banding. Luckily, there are two easy ways to fix a clogged nozzle: replacing or cleaning.

Replacing a nozzle is a very simple process as long as you’re using a printer where you can easily access the part. All you need is a couple of tools and a new nozzle. To be on the safe side, we recommend finding an instructional video for your make of printer.

Make sure that your new nozzle is made of high-quality conductive material, as lower-quality nozzle tends to clog faster. Also, don’t forget to fasten your new nozzle tightly onto your hot end so that no material oozes out.

You might also try cleaning your nozzle, which you can do using a small needle and pushing it through the hole in your nozzle. Alternatively, you can extrude cleaning filament through the nozzle or perform a cold pull.

PID Tuning the Hot End

Lastly, PID tuning the hot end should reduce temperature variation in prints, which can prevent Z banding through inconsistent extrusion. PID tuning is the process of re-programming your printer’s method for heating the nozzle to make it more efficient and less subject to over-or under-heating.

PID tuning can be done by sending a few commands to your 3D printer through a G-code terminal. The commands instruct the printer to heat the hot end a few times while the printer takes measurements to determine a better way to heat the component.

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By: Jackson O'Connell

Z Banding & Z Wobble: How to Prevent It