3D Printing Tech Tip: Clogged FDM extrusion tip – why it happens and how to fix it

Article by Pierre Hart updated April 12, 2017


FDM extrusion tips can occasionally become clogged due to various issues. Continue reading to learn why this happens and how to fix a clogged FDM tip on your own 3D printer.

Why Do Clogs Happens?

The most common reasons for a clogged FDM tip are:

  • Moisture in your material: Moisture in the material will vaporize inside the extrusion tip making the plastic ‘sticky’. This causes the material to stick to the inside of the extrusion tip – causing a blockage. Moisture in the material can be seen as tiny bubbles in the purge material or build (see figure 1) and will sometimes cause sputtering as material is extruded from the tip. If you are seeing tiny hairs (see figure 2) of material on the build, this is an indication of moisture as well. Material that has moisture in it can be sent back to Stratasys for replacement. Contact your service provider or Stratasys for information on how to RMA faulty material.
3d printer tip clog

Figure 1: Rough build from bubbles due to moisture in the material

3d printer tip clog

Figure 2: Strings/hairs in build due to moisture

  • Extrusion tip too close to the build: If the extrusion tip is too close to the build due to a poor z calibration or a part that has warped, the additional back pressure can cause the tip to clog. Care must be taken when doing the z calibration. Calipers are necessary to ensure that this calibration is done accurately. The z calibration must be even more accurate with 0.005” and 0.007” layers, as additional back pressure on the tip will cause mushrooming at the tip entrance. This mushrooming can ultimately cause a clogged tip. See figure 3 below for a part that had warped at the corner resulting in tip drag marks on the part. Eventually this would lead to a tip clog. If you are having issues with parts warping, reference the following curl management best practices document to prevent part warping.
3d printer tip clog

Figure 3: Flat plate part warping at corners causing tip drag marks on the part and poor surface quality

  • Not using ‘Sacrificial Tower’ when printing with Nylon: Nylon is an inherently ‘sticky’ material and can cause tips to become clogged. When printing with Nylon use the ‘Sacrificial Tower’ functionality in INSIGHT to prevent tip clogging and to achieve the best surface quality. Refer to the ‘Nylon Best Practices Document’ for more information about ‘Sacrificial Tower’.
  • Head motor failure: As the head motor ages, it loses torque and can have issues feeding or retracting the filament from the extrusion tip, resulting in a clogged tip. Failure of the head motor encoder can cause ‘following errors’ which cause the head to feed material when the tip is not ready – resulting in clogging. Typically, this can be verified by confirming head motor following errors in the machine .CFG file.
  • Tip damage or using a tip beyond its recommended life (mileage): Damage to the end tip of the extruder can cause a blockage. Using a tip beyond its recommended life/mileage can also be the cause of clogging.
  • Dried air system failure: The F360/380/400/450/900 machines have a dried air system that feeds dried air to the material delivery systems, keeping moisture out of the material. If this system fails, the material could become exposed to moisture resulting in a clogged tip.
  • Bad z zero position: The z zero position is the position of the first layer placed on the build sheet. If the tip z zero position is too close to the build tray the tip can become clogged due to the increased back pressure. If you are consistently getting tip clogging on the first few layers of printing it could be related to this.
  • Improper processing in INSIGHT: INSIGHT allows you to modify tool paths and roads widths and allows you to ‘overfill’ a part. This is done to improve surface quality, improve xy strength and to attempt to make a part water tight. Care must be taken to not overfill too much, as this can result in tip clogging. If a tip consistently clogs at or around a specific layer, check the tool paths and road widths in INSIGHT.

How Can I Tell If My 3D Printer Has a Clogged FDM Tip?

After material has been unloaded from the tip, a clogged tip will have resin right to the top (or even a little mushroom on the top) as shown in Figure 4 on the left. Unclogged tips will be clear of resin at the top (see Figure 4 on the right).

3d printer tip clog

Figure 4: Tip on the left is clogged, tip on the right in not clogged

You can also tell if you have a clogged tip by examining the end of the filament after it has been retracted from the tip, after the material has been unloaded.

As can be seen below (Figure 5) the filament on the right is from a clear tip since it has a ‘dairy queen’ on the end. When a filament is retracted from a clear (unclogged) tip, the filament separates somewhere in the middle of the extrusion tube and pulls from the remaining resin creating the ‘dairy queen’ end profile. The system is designed so that the filament breaks in the middle of the extrusion tube when unloading, keeping the entrance open so new material can be loaded into the tip. When the filament is retracted from a clogged tip it will break or shear at the top and have a square end profile, as shown below in Figure 5 (on the left). The entrance to the tip will look like figure 4 (on the left) and when new material is loaded it won’t enter the tip.

3d printer tip clog

Figure 5: Filament on left side is from a clogged tip, filament on the right is from a clear tip

Another indication of a blocked tip is if you see a mushroom surrounding the filament when it is loaded (see figure 6 below). This can happen when there is too much back pressure on the tip causing material to come out (mushroom) from the top of the tip.

3d printer tip clog

Figure 6: Mushroom forming at extruder tip entrance

In systems that have APD (auto purge detection) the machine will register an auto purge detect failure if you have a clogged tip. When a tip is clogged it won’t purge at all or it will purge a very weak stream, and will cause an APD failure.

How Do I Unclog a Tip?

Dimension, uPrint and the Fortus 250 3D printers have a process for unclogging tips. Essentially, the head is placed into maintenance mode and the drive wheel is manually reversed to retract the filament from the tip. If the tip is still clogged after retraction, the blower that cools the entrance to the tip can be de-energized causing the tip to overheat. When the tip overheats, the resin inside starts to bubble and mushroom out of the top of the tip and can be removed. Refer to the user guide of your machine for this process.

With Fortus machines (F380mc/F450mc/F900mc) there is no manual way to unclog the tips when they are loaded into the machine, but any clogged tip (including uPrint and Dimension) can be cleared using a 1/16” drill bit. Carefully drill out the first ¼” of the blocked tip entrance and, as long as the tip is still under its recommended life, you should be able to re-use it. Take care while drilling out the tip that you don’t come into contact with the sidewalls.

Blocked tips do occasionally happen during normal operation but if it is happening consistently it could be an indicator of a bigger problem. Lastly, remember to unblock your blocked tips if they are still under their recommended life!

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Pierre Hart