Introduction: Monoprice Mini: Remove Broken Filament From Nozzle

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About: I'm a Mechanical Engineer turned IT Professional and Author. I came into the Information Technology world because someone challenged me to. But at heart, I'm still a grease monkey with no desire to lose touch …

The Monoprice Mini is an awesome 3D Printer. I've been using it for sometime now and this printer has completely convinced me to stop using my only other printer that I've had over the past 2 years.

However, like with all machines, you will run into rough weather - some of your own making, and some that are part of buggy product designs.

In this case, I got in trouble - one of my own making and midway during the course of a print! Therefore, I had to react quickly to overcome the problem in order to restore my printer back to peak running condition.

In this instructable, we'll talk about how to remove a broken piece of filament from the Hot End of the Monoprice Mini and restore proper filament feed.

Step 1: Before Describing the Problem Statement ...

Before I describe the problem, I will assume that readers are:

  • Familiar with owning and operating a Monoprice Mini 3D Printer
  • Familiar with a Bowden-style feed mechanism
  • Wary enough about working with the hot end heated to high temperatures

SAFETY PRECAUTIONS

These instructions are reactionary in nature and weren't planned in advance. I did not refer to any Monoprice service instructions or manuals before I jumped on the fix. The pictures were captured to make sure that I knew how to reverse the whole process and put the printhead back together.

As a result, I had to work on this printer that was powered ON with the hot end operating at temperatures as high as 205-deg Centrigrade, not to forget the print bed heated up to 65-deg Centigrade. In addition, the extruder fan was ON and spinning at full operational speed as illustrated by the pictures.

Therefore, readers are advised to exercise appropriate caution and proceed only if they feel safe and comfortable with applying the fix discussed in subsequent steps!

HANDLING DELICATE PRINTER COMPONENTS

The Monoprice Mini is a mechanically delicate printer. The parts of the print head are small and light and move on an overhanging arm. All of these components can be easily damaged if proper care is not exercised.

For example, the printer arm can be bent easily if excessive force is applied while working on the print head.

Step 2: The Broken Filament... a Problem of My Own Making!

The Monoprice Mini has a Bowden style extruder wherein the feeding mechanism (extruder) is separated from the nozzle (hot end) by a narrow (Bowden) tube. This design means that the extruder must send a continuous and uninterrupted flow of the filament into the tube for the molten PLA to be extruded through the nozzle.

If by any chance you run out of filament before the part is completely printed, then the filament will cease to flow into the nozzle as soon as it clears past the extruder feed mechanism. Now we have situation where an orphan piece of filament is inside of the Bowden tube. I refer to this as a broken filament (for lack of a better term) because it has been completely detached from the extruder feed mechanism. One quick solution is to feed another roll of filament into the extruder and send it down the Bowden tube so that it continues to push the broken filament down through the nozzle. Theoretically, this solution works. But as I experienced, it partially did until the broken filament left the Bowden tube completely and entered the nozzle. At this point, the contact between the filament fed by the extruder and the filament inside the nozzle is lost, and three things happen as a result:

  1. The broken piece of filament will stop flowing out of the nozzle
  2. It blocks the active filament feed causing the extruder gears to grind and slip over the filament
  3. The printer will continue printing, but as there is no filament flowing out the extruder, you will see an "air print"

The visual attached illustrates the problem of the broken filament.

So why did I end up with a broken filament?

Very simple, I ran out of filament when my printer had progressed about 14% into the print. A while back I had wrapped a smaller sample roll of Yellow filament over a larger roll of filament role of the same color and completely forgotten to take this into consideration before I decided to use this particular roll!

Step 3: Stopping the Print and Moving the Print Head to an Accessible Location

Once the printer is in the "air printing" mode, the only recourse is to stop printing so that filament feed can be restored. In this particular case, I missed to check back on the status of the print in a timely manner. As a result, my print was beyond saving.

To begin:

  1. Stop the printing process by selecting the Cancel Print menu item
  2. Then select the Exit menu to go back to the Home screen of the Printer menu
  3. Next, select the Move menu item from the Home screen to go to the motion control panel
  4. Select the X Axis - we want to move the print head to the middle of the printer arm
  5. Based on where the print head is, turn the dial CCW to move the print head right, or CW to move left until it's positioned approximately to the middle of the printer arm
  6. Next, select the Z Axis, and turn the dial CCW to move the arm higher and way from the print bed
  7. At this point, you should have enough working room below and on both sides of the print head


REMEMBER!

  • Do not load the printer arm with the weight of your palms - the arm is delicate and will bend when stressed!
  • Do not power off the printer as we will need the nozzle to maintain temperature to fix the problem

Step 4: Tools Required

You will require only two or three simple tools to fix the problem:

  1. A 1.5 mm Allen wrench
  2. A 3.0 mm Allen wrench (or any wrench that is slightly larger than 1.75 mm PLA filament)
  3. A humble toothpick, or something similar that isn't made of metal or plastic

The Yellow piece in the picture is the print that was abnormally terminated as a result of the issue at hand.

Step 5: Getting to the Broken Filament Inside the Nozzle

First, detach the fan by removing the two clips on either side of print head.

The clip on your right side is located below the Red wires running into the print head and is a bit tricky to get at.

If you can afford to, leave the fan attached to this clip, but take care not to run your fingers or tools into the rotating fan blades!

Next, use the 1.5 mm Allen wrench to loosen the nut and detach the end of the Bowden tube connected to the nozzle

There's no need to remove the screw and the nut entirely, back the screw out just enough to free the Bowden tube from the nozzle

Staring straight down into the nozzle, you'll see the filament stuck inside! The annoying click of the extruder teeth now makes complete sense!

The piece stuck inside is curved and resting against one side of the nozzle. The filament fed in by the extruder is repeatedly slipping over this piece resulting in the extruder teeth to grind against the filament creating an annoying click, and cutting off filament supply.

Step 6: Removing the Broken Filament

With the printer still ON, the nozzle will be considerably hot, but as the printing has been stopped, the temperature will be on the decline.

To get the nozzle up to temperature, return to the Home Screen and select the Temperature menu item.

From the temperature control panel, begin the preheating process by selecting the Start Preheat feature.

Wait for the nozzle to get up to at least 120-deg centigrade.

Take the 3.0 mm Allen wrench and using the long end, push gently on the the filament inside the nozzle.

With the nozzle at 120 degrees, the PLA filament will simply flow out without much resistance!

Finally, use the humble toothpick to clean up the molten filament from the tip of the nozzle and the print bed - the wooden toothpick will prevent damage to the tip of the nozzle.

NOTE

  • Keep your palms off the printer arm when pushing down on the filament to prevent excessive down force
  • There is no need to push very hard on the filament - all it needs is a little push, and the hot nozzle will do the rest

At the end of this step, you should be past the broken filament problem!

Step 7: Restoring Filament Feed

Now that the obstruction has been removed, the next step would be to restore the filament flow.

Return to the Home Screen and select the Move menu item.

From the motion control panel, select the Extruder menu item.

Turn the dial to run the filament down the tube until a small section of it is projecting out of the end of the Bowden tube detached from the print head.

Insert the filament, followed by the Bowden tube back into the nozzle, and hold it in place with your hand.

Use the 1.5mm Allen Wrench to lock the Bowden tube back in position.

Carefully, remount the running fan back on the print head - the clips are easy to put back on and will not require much force.

NOTE

  • Again, do not use excessive force on the Allen wrench or rest your palm on the printer arm!

  • Before locking the tube back on the print head, make sure that there are no gaps between the Brass end of the Bowden tube, the white sleeve in the middle, and the nozzle below the white sleeve

  • From the control panel, turn the dial to move the filament forward and back by a small amount to ensure that there is no resistance to the filament feed

With these steps completed without incident, your printer should be back to printing in no time!

Step 8: So, What Was I Printing?

The print that was interrupted by my carelessness was a bracket that I designed to park the tools that I most frequently use with the Mini.

Ironically, two of them happened to be the ones that I used to fix the problem at hand.

Thanks for reading my IBLE! Happy printing! :-)