Ulti-Evening: Maintenance

Contributed by
Korneel Bullens

For the Ulti-Evening of September 2015 we invited community member Korneel Bullens to show and tell something about the maintenance he does on his Ultimaker 2's. Korneel has many hours of print experience - his printers are running 24/7 - and thus he got valuable insights on how to shape your Ultimaker in its best condition and make sure to keep it like that.

In this article you can read Korneel's tips on maintaining your Ultimaker, especially focused on under extrusion.

Print quality

Your Ultimaker 2 is capable of making great prints! It is however hard to diagnose if your print was great or not. You can use the following guidelines to determine the quality of your print. A successful print should have these characteristics:

  • Smooth lines (no gaps or stutters)
  • Overlapping lines
  • Smooth tops
  • Straight and “glassy” bottom

After a lot of printing there is however a high chance that your prints will start looking like shown in the below picture. This is the result of under extrusion and is shown as gaps in the layers.


How to diagnose under extrusion?

Although under extrusion can be seen easily on the print itself, there's also a way to diagnose it before the Ultimaker starts printing. At the beginning of each print the print head moves to the front left corner of your printer, after which it will start the heating procedure. When this has finished a little bit of filament will be extruded from the nozzle. This extrusion process is the perfect indicator to verify if your printer will work correctly.

The material should flow smoothly into a nice round build up of material. The result should be like pouring a soft-ice into a cone. If it doesn't come out like this, you can check material flow to figure out what is going wrong:

  • A stuttering flow tells you that there are intermittent issues with the material flow. This is most likely caused by a dirty feeder.
  • If the material is not flowing in a concentric figure (remember the ice cream), there is debris in the nozzle, which means it needs to be cleaned.
  • If the flow is very slow either the PTFE coupler is damaged or nozzle is dirty.

Checking the PTFE coupler

The first thing to do when suffering from under extrusion - after having done the regular checks - is taking a look at the PTFE coupler. Damage on the PTFE coupler is not visible from the outside, but it’s easy to remove the PTFE coupler from the print head to check it.

Once you have removed the PTFE coupler, take a smooth piece of the filament and push it through. This should go smoothly, without interruption. If there is any friction, your PTFE coupler has reached the end of its life.


The lifespan is different each time and is based on retraction, heat and pressure from the spring. A PTFE coupler can last for 100's of hours, but can also be worn within 50 printing hours when put under extreme use. A good indicator is a burned bottom side, as shown in the picture on the left. You can also test the PTFE coupler by inserting a small screwdriver into it and feeling for a little ridge inside. A broken PTFE coupler will look like the below right picture from the inside (when cut through). If your PTFE coupler feels/looks like this it needs to be replaced.


Cleaning the nozzle

If the material flow at the beginning of the print is bad and the PTFE coupler has turned out fine, it's time to clean the nozzle. Although this might have been done by the Atomic Method already a "Nylon Cold Pull" seems more effective in this case.

What you need for this is a piece of nylon filament (e.g. Taulman Nylon 645) and a piece of bowden tube (approximately 10 cm) or something with a similar length and inner diameter. The piece of bowden tube is not required, but will greatly ease the process.

  1. Remove the filament from the printer, place the print head in the front left corner and take the bowden tube out of the print head. To do this you can follow step 1 and 2 from the Atomic Method.
  2. Place the small piece of bowden tube in the print head, all the way down into the PTFE coupler.
  3. Heat up the nozzle to its maximum temperature (260 degrees) and wait till it has reached the temperature.
  4. Insert the piece of nylon filament and push it through the nozzle. You might need to apply some extra pressure with a pair of pliers to get it through the nozzle. You will see small black spots in the extruded material.
  5. Keep feeding the nylon filament until you feel that steady pressure produces a smooth extrusion.
  6. Turn the nozzle temperature back to 30 degrees and keep applying pressure to the filament until it has reached a temperature of 150 degrees. You will notice that the nylon stops extruding from the nozzle at a temperature of approximately 180 degrees.
  7. Once the nozzle has reached the temperature of 30 degrees wait for 2 minutes.
  8. Use a pair of pliers in a leverage motion on the thumb screws of the print head (this is important to not bend anything, make the leverage do the work). You will notice the nylon will pop out.

Note: Don’t put with too much pressure on the filament while feeding; this might damage the axes. For this reason the print head needs to be positioned in the front left corner.

The nylon that comes out should look as on the picture below. The nylon should be nice and clean and you can see the shape of the inside of the nozzle in the front. If there is any black junk in the top of the nylon, this is cleaned debris. Cut the portion off and keep performing the same process until the nylon comes out clean.