Clogged Extruder Nozzle? – What Causes It, How to Avoid It, and How to Fix It

Nothing can be more irritating, or more intimidating, than a clogged print nozzle. You’re printing a job, everything seems to be progressing nicely, when suddenly you hear a clicking or knocking sound from your extruder motor.

That dreaded clicking sound! 

You look over and see that your filament isn’t moving off of the spool and no material is being extruded from the print nozzle. The likely culprit in this situation is a clogged or blocked print nozzle.

In this article we’re going to deal with the problem of a clogged print nozzle. We’ll look at some of the common issues that cause a clogged nozzle and what you can do to avoid them. We’ll also show you a couple of techniques that you can use to unclog a nozzle that’s already blocked and get you back printing in no time flat.

Common Causes of a Clogged Print Nozzle and How to Avoid Them

A clogged print nozzle is usually caused by one of several common problems. So, even though a clogged print nozzle is one of those “Are you kidding me, really?” issues that everyone dreads, the good news is that the problem can easily be prevented from occurring by simply paying attention to a couple of things beforehand.

Incorrect Nozzle Height

As you probably know, your nozzle has to be at the correct height from your print surface in order for you to successfully print an object. If the nozzle is too high, the print material has to travel a longer distance to reach the surface. This longer distance translates into cooler temperatures. The result is that your material will likely have trouble adhering.

If the nozzle is too low, a couple of undesirable things will occur. First, there won’t be sufficient room between the nozzle and the print surface to allow the material to extrude correctly. This will result in the nozzle smearing the thermoplastic all over the surface. Second, the insufficient room between the nozzle and the surface will begin to cause the retrograde extrusion – the material will begin to back up into the nozzle, ultimately causing a clog.

The easy fix for this problem is to make sure that your print bed is leveled correctly and that your starting Z coordinate are sufficient to allow adequate room for proper extrusion. In general, your Z coordinate should be no higher or lower than the diameter of your print nozzle. This will allow the nozzle to maintain a slight pressure to the top of the extruded filament that will increase adhesion while avoiding retrograde extrusion.

Incorrect Print Temperature

Correct print temperature is critical for both a successful print run and for printer performance. If the temperature of your hot end is too low, your print material will not melt correctly. This can cause the material to begin to adhere to the inside surface of the nozzle. This causes pressure to build up in the print head. Eventually, the extrusion motor can’t feed the filament into the head and a clog forms as a result.

In addition, printing at too high a temperature, especially with PLA, can cause you to experience what is known as “heat creep”. Essentially, heat creep occurs when higher temperatures extend back and upwards from the hot end.

This causes the “melt area” to extend father back as well, softening and melting the print material well before the nozzle end of the extruder. The softened thermoplastic increases the amount of pressure needed for extrusion. As with having your print temperature too low, eventually the extrusion motor can’t keep up and the nozzle gets clogged.

In extreme cases of printing at too higher temperatures - PLA and similar filaments can actually crystallize in the nozzle

You can avoid this problem by always checking to make sure that your printing at the recommended temperature for the material that you’re using. PLA does well at temperatures around 180C and up and ABS likes temperatures around 225C+. Experiment with the material that you’re using and find the “sweet spot” that allows for good adhesion and layering, but doesn’t cause problems like clogging.

In addition, when you are changing materials, always make sure that you’ve removed the previous material completely and flushed it through before changing print temperatures. Failure to do so may also cause a clogged nozzle later on.

Poor Quality Filament

Not all filaments are created equal. Low quality filament is not subjected to rigorous tolerance tests. This can result in an end product that has differing widths throughout the filament strand. Segments of the filament that have a thicker diameter will not only take longer to melt, they will also be more difficult to extrude and may cause a clog.

There is an easy way to check the quality of the filament that you’re using. Take a pair of calipers and check the diameter of your filament at several different points. If you’re finding significant deviation from the advertised diameter specifications, it might be time to start thinking about obtaining your filament from a different source.

It’s not just inconsistent tolerances that can cause issues with cheap and low quality filament – the purity of the raw materials is also a huge, often overlooked issue. Contaminants in the filament, or even just poorly mixed resin (leading to areas requiring higher print temps than others) can cause problems in the extruder.

Dust and Dirt

Despite your best efforts, dust and dirt can still become adhered to your filament and travel with it down into your hot end. Once there, they burn in the heat of the nozzle and start adhering to the inside surface of the nozzle as carbon.

When enough carbon builds up on the inside of the nozzle it can start to narrow the width of the nozzle opening, as well as begin to impede the flow of the print material. The end result can be a clog. We’ll discuss a fix for this problem in the next section.

How to Fix a Clogged Print Nozzle

When you’ve got a clogged print nozzle there are number of techniques that you can use to get it unclogged depending on the material that’s causing the problem. Let’s take a look at some of these methods.

The Atomic or Cold Method

This is a technique that works great if you have a build-up of carbon or carbonized material in your nozzle that’s causing the clog. It also works well if your clog was caused by the switch from a high temperature to a lower temperature printing material.

You can check out the specifics of how to use this method by taking a look at our article on under extrusion problems that can be found here.

Guitar Strings and Acupuncture Needles

Another method to break out a clog is to essentially break through it using anything strong and narrow. A surgical or acupuncture needle or a B or high E steel guitar string all make excellent routers.

Simply heat your hot end up to the printing temperature of the material that’s involved in the clog. Using a pair of pliers, carefully insert the needle or guitar string into the nozzle opening and move it back and forth, essentially breaking through and removing the clogged material.

The Solvent Method

If the material that is causing the clog is somewhat easily soluble then removing the nozzle and soaking it in the solvent in question can provide a solution to really tough clogs. Every FDM printer has a slightly different technique that’s involved when removing a printer nozzle.

Take a look at your owner’s manual for the specific methods that apply to your printer.  Once the nozzle is removed, place it in a container filled with the appropriate solvent. For example, if you’re trying to dissolve a clog caused by ABS, you’d place the nozzle in a glass container filled with acetone. Leave the nozzle in the solvent for 24 hours, agitating it every few hours.

After 24 hours is up, remove the nozzle from the solvent and using a steel guitar string or needle remove as much of the plastic clog as possible. If necessary, repeat the solvent bath for another 24 hours and again attempt to unblock the clog.

An Ounce of Prevention

One of the best ways to fix a clogged printer nozzle is to never have a clog happen in the first place. As we discussed, proper printer settings and high quality filament can go a long way to preventing clogs from happening in the first place.

Another preventative option is to regularly use a cleaning filament to remove any remaining plastic and contaminants that might remain in the nozzle between print jobs. Cleaning filaments operate at a wide range of temperatures. The purging compound in the filament sticks to contaminants and mechanically removes them when the cleaning filament itself is extruded through the hot end.

It’s an easy way to maintain your printer, allowing you to avoid nozzle clogs that can delay your ability to print the objects that you need. You can view our cleaning filament here.

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