Monday, August 6, 2012

A Tool to Clear Clogged PrintJets

Scour the hobbyists and consumer 3D printer sites and blogs and you will see that sooner or later most, if not all, 3D extrusion printers will clog for one reason or another.  It comes with the territory.

As more and more 3D printer manufacturers use pre-built hot ends, it becomes less effective to tear a hot end apart to clear the clog.  The Cube falls into this category... as does the much more expensive ($17,000-$22,000) HP 3D printer.  HP has even published a Support Document that deals with how to clear a clog in their printer.

While it rarely happens, when a Cube's tip becomes clogged, a user has two choices.  They can either send the unit back for repair.  Or, they can clear the clog themselves.  Cube time is so precious to me that I have opted for the latter.  And, I want to explain to everyone how I do it.

But, before doing so, we have to say that if you try what I am about to describe that you do so at your own risk.  To clear the Printjet tip, it has to be heated and it can cause a nasty burn if we aren't careful.  Of course, no child should be allowed to do this.  It requires good small muscle control and a steady eye.


The most critical item you will need is piano wire that is under .5mm in diameter.  I use .38mm piano wire (0.015") that can be found in any hobby store.  This wire is inserted into the tip of the hot end to clear it.


While it is not required to have handles, they certainly make it easier.  And, since we have a 3D printer, we can make the type of our choice.  In my case, I printed two different types.  Since I've not had a clog recently, it's not been possible to test either of them.  But, I am certain that both will work well.


The first style is short and the wire is mounted in the center of the handle.  There is a shaft for the wire's exit and a small hole into which the bent end of the wire is inserted.

Short Handle for Piano Wire
Taking some time to discuss the design characteristics is useful not only for this project; but, others.  As always, the first design goal, other than basic usefulness, is NO SUPPORTS.  The objects print FACE DOWN as in the bottom right quadrant of the image.  There are holes in both halves.  And, some posts are printed separately.  These posts will be inserted into the holes to line up the halves.

The reason why the posts are not attached before printing is that it would have required supports for at least one half.  The above arrangement, with external posts, allows us to print without supports and still provide a way to ensure perfect alignment of the halves.

Notice that the holes appear to be considerable larger than the diameter of the posts.  At print time this difference goes away and the posts and holes are very closely sized.  Remember, holes get smaller and posts get larger as we discussed in a previous article.

In like manner, the shaft and hole for the piano wire must be a lot larger than the piano wire's diameter.  Otherwise, the hole will close up.  Here is an image of the completed small wire handle.  A piece of paper is included in the image to help show the wire.

Finished Piano Wire in Short Handle


In the small handle, the wire exits the handle in the middle of the handle.  The large handle is designed to be asymmetric so that we can reach in from the side.  It may or may not be easier.  We'll see if and when we have a clog.

Long Handle for Piano Wire
Aside from the length, the only big change in this design is that the hole for the wire's exit goes through one of the halves and near one end of the handle.  A stabilizing channel is wedged between the two halves.  The posts and alignment holes are the same.

Here is the completed long handle.

Finished Piano Wire in Long Handle


If I get a clog, I will used the "Install Cartridge" option to heat the Printjet hot end.  When I hear the extruder running in reverse to back out the filament, I insert the wire into the tip and hot end and gently press upwards until the wire moves freely up into the print tip about 1/4" to 1/2".  This should push the errant filament out of the bottom tube.  Or, at least that has been my experience in the two times I've used piano wire in the past.


Normally, I would put the designs up on the Cubify Store.  But, liability issues outweigh helpfulness in this particular case.  It's not only possible to burn yourself.  It's also possible to ruin your Cube unless you are careful.  So, I post this article simply to tell you how I deal with the issue and let you decide if you do or do not want to go the same route.  Hopefully, NONE of us will need it.  But, I want to be prepared, just in case.  I don't want to lose a single day of work with my Cube!


There are two things that I have found will CAUSE a clog.  
  •  The first is to pull the filament out too aggressively when changing cartridges.  You do NOT want to break off a piece inside the head.  So, be patient and let the machine do the work of reversing the filament.
  • The second is not rounding the tip of the new filament before loading.
Here is a simple image that shows filament tips trimmed in three different ways. 

Three ways to trim the end of the filament

The cut on the blue filament is too straight.  The edges can bump onto the lip of the bottom tube just below the extrusion wheels.

The cyan filament is cut so that the long tip bends outward.  Filament has a natural curve and the tip of the filament cut like this ends up either hanging on the lip of the bottom tube or guiding itself outside the tube altogether.

The best way to trim the end of the filament is to trim it in multiple directions so that the pointed tip is roughly at the center of the filament.  Also, make sure that the filament is as straight as possible.


  1. Hi, Tom:

    Good info, thanks! It got me thinking.

    I recently bought some 0.015" piano wire after reading your earlier post about unclogging. Haven't had to use it, yet.

    This post made me think about how to hold it. Both of your handle ideas are sure WAY better than trying to hold the wire by hand!

    For me, if I ever have to use the piano wire, I'd take a short length of it and put it into a "pin vise" that I already have. That's a small hand-held drill-chuck type of thing, but designed to handle very tiny wire diameters while giving us fat-fingered humans something we can hold on to.

    With that I assume I can set the amount of wire that sticks out to a safe amount -- 1/4" at the start, then trying it with more if that isn't enough. That would help keep me from going too far into the nozzle with the wire and possibly damaging things.

    The short wire sticking out of the pin vise should be stiff enough that I won't feel the need for my fingers to be near the hot nozzle to guide it.

    That's my plan, anyhow. I haven't unclogged a nozzle that way while you've actually done it, so my ideas are completely untested.

    I like your idea of creating or having some sort of handle to keep fingers AWAY from that hot nozzle!

    I've already accidentally touched the print BED (MUCH cooler than the print NOZZLE) for an instant with one finger, and had a quite red and sore finger afterwards. I don't want to even THINK about what touching the nozzle would be like. A serious burn, for sure.

    Another thought: How to cut piano wire and get a clean end? I did a Google search and the consensus seems to be to use a Dremel cut-off wheel. WITH GOGGLES -- NO exceptions!! And it appears piano wire is hard enough to damage the usual diagonal cutters used to cut electrical wires.

    I sure hope I never have to try this, but your experience with doing that and your discussion about clearing clogs has made me think about it and gather the necessary materials in case I need to do it that way.

    Thanks again!

    1. I trust you won't have to use a wire either. But, your idea of the pin vise is a great one. In fact, it's a better idea than making a plastic handle. I like it. :)

      It's a bit like carrying a lug wrench in the trunk of your car. 99% of the time your tires are fine. But, when that 1% flat hits you sure are glad you have it! :)

    2. I have to admit, one of my attempts at inserting the filament when I first got the Cube looked pretty much like your example on the right -- a diagonal slash of an end. Looking back on it I can only wonder what I was thinking.

      I think you're right on target about how the tip should look, and that the filament should be straight, which I hadn't considered until you mentioned it.

      Actually, I've got all of your comments about avoiding jams printed out and sitting on the spare cartridges I have, to be consulted before switching filament colors.

      I thought I had a brainstorm yesterday about preparing the filament tip: Since it's about as thick as a wooden pencil lead, why not try putting it into a turn-the-crank pencil sharpener? I thought it might come out with a nice-looking tip like a freshly-sharpened pencil.

      Unfortunately, the results were not pretty. What a tangled mess of filament and what a chewed-up end! Oh, well. If I ever see a powered, faster-spinning sharpener I might try the experiment again.

      I have a good small flush-cutting wire-cutter that I've tried using to shape the tip, with pretty erratic results. How do you shape your filament ends to be as you've shown in the center example?

    3. Your post prompted me to go into some of the methods I've used to shape the tip. I keep a Dremel, with a grinding tool attachment in it, next to my RapMan 3.2 printer all the time. I first used it to smooth areas connected to supports and raft. But, also use it to dress the end of the filament before loading.

      I've also used a variety of abrasives like emery boards and sheets of sand paper.

      When using the flush side cutter, the shaping is a bit less precise. But, I use the ones meant for jewelers, from Rio and craft stores. They work relatively well. But, not as well as the Dremel.

  2. I learned that the gap between tip and platform is very important for not clogging the unit. Since we set the gap when the machine is cold it is going to change when it worms up. Leave the gap slighty bigger than 2 sheets of printing paper.
    The seccond tip is the temperature of the room. Do not try to run the machine in over 80 degree F. It will cause overheating of the machine. The glue may give up and the part may warp meanwhile is printing. All this may cause oposite preasure in the filamnet and make the head clogged.

  3. Thank you Tom, your declogging method just saved me!

    1. I am REALLY happy to hear that. Being able to service the machine without having to send it in is a big deal!

      Nice job!

      Check out Albatros3D's hints, above, about some causes of clogging.

      Glad you were able to keep on printing. :)