Cold pull voor 3D printers

Cold pull technique explained in steps.

How do you unclog your nozzle? Below you can read everything about the commonly used technique, the cold pull.

When printing via the FFF / FDM technique, there is a problem that everyone will encounter at some point. A clogged nozzle. This can be caused by several things. PLA, for example, can burn if left in the hot nozzle for too long. When you change filament type, for example from ABS to PLA, it can happen that ABS remains behind and does not melt properly due to the lower temperature at which PLA is printed. After a while, the nozzle can then become clogged.

The nozzle may also become partially clogged. The material will then no longer flow through the nozzle as well because there are some residues in the way. This will make your prints look like you are suffering from under-extrusion.

How can you solve this problem? The cold pull method below is tailor-made for the Ultimaker 2 but can also be used on other 3D printers.

Cold pull in 5 steps:

  1. Remove the material.
  2. Remove the Bowden tube.
  3. Prepare for the cold pull.
  4. Do the cold pull.
  5. Replace the bowden tube.

Step 1: Remove the material.

To begin with, the material must be removed from the bowden tube. Chances are you already know how to do this. We'll explain it anyway just to be sure.

In the printer menu, go to MATERIAL and choose CHANGE. When the filament asks for new material, press Cancel.

Step 2 Remove the Bowden tube.

Remove the bowden tube from the printhead. When the printer is off, you can move the print head freely for better access.

To release the bowden tube, remove the blue clip. (Be careful not to lose it.) Then push the white collar down and pull the Bowden tube. It should come out easily, you don't have to force it. If you feel some resistance, make sure to push the white collar down. If you apply too much force, you could break it.

Step 3 Prepare the cold pull.

Take a piece of filament and make it as straight as possible, at least 10 cm.

Preheat the printer, (MAINTENANCE, HEAT UP NOZZLE), start at a temperature of 230-240°C. Much warmer is often not necessary. If you have ABS in the nozzle, 240°C is often sufficient to melt it. The temperature can be set at 180-240°C, it should not be too hot because you don't want the clogged filament to burn further.

If you want to be on the safe side, you can also start at a lower temperature and increase the temperature incrementally.

When the temperature is reached you can feed the filament from above. (where normally the bowden tube is.) Gently push the filament through until you see a little filament coming out of the nozzle.

Step 4 Do the cold pull.

Lower the temperature to about 90°C for PLA and 130°C for ABS. (These temperatures may vary by printer and filament.)

You can keep pushing the filament a little while it cools down to make sure it's in the entire nozzle. If nothing comes out of the nozzle, you just have to push further.

Once the temperature has been reached, pull the filament firmly and quickly.

Before the first cold pull, it is helpful to test the temperature by pulling slowly. If nothing moves, it is too cold and you can raise the temperature slightly. If it moves, pull quickly.

The goal is to get a clean, cone-shaped tip on the filament. If the filament is stretched, you are pulling too slowly or the temperature is too high.

If the conical tip is still dirty after the cold pull, repeat the cold pull until you have a clean, conical tip on the filament.

Step 5 Replace the bowden tube.

Put the bowden tube back in. Remember to push the white collar back in and make sure the tube is back in place. The blue clip can be placed back and then you can load the new filament and continue 3D printing.

If the nozzle is very clogged, you can also use a small needle. This needle should be thinner than the nozzle size. Heat the nozzle to a high temperature and try to pick up some filament with the needle. Make sure that the needle does not break!

If you regularly change material, it can be wise to regularly perform a preventive cold pull.

Also check out the "How to unblock nozzles?" video from BASF-Innofil3D