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Using a thermoplastic MDF printer with a 0.4mm extruder nozzle, I frequently have trouble with the nozzle getting clogged.

I am not sure what's causing the clog, but my guesses are dust and/or burnt filament (from leaving the hot end on without extruding).

What can I do to prevent, or at least minimize, the extruder nozzle getting clogged?

Bonus question: What other common causes of clogs are there? (ie what should I watch out for besides dust and leaving the hot end on?)

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    $\begingroup$ Perhaps include the brand/make of hotend, printing temperature, type of material and color? $\endgroup$ – Tom van der Zanden Jan 13 '16 at 20:59
  • $\begingroup$ Hello @Martin Carney, I noticed your question has been up for a while now. Have any of the answers below been able to solve your question? If so, would you mind accepting the appropriate answer. If not, what is missing so that we may help you further? Also, if you have figured it out on your own, you can always answer and accept your own solution. Thank you. $\endgroup$ – StarWind0 Feb 7 '17 at 19:16
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Different types of hotends and extruders can lead to different problems associated with clogging. Based on my personal experience the leading causes of clogs and jams are the following

  1. Foreign material in the nozzle (dirt, dust, low quality filament)
  2. Mixing materials in the hotend (running ABS at 220 then switching to PLA without purging the nozzle)
  3. Excessive retraction or "heat soak" in PLA (PLA expands when heated if your retraction is set to high you can actually push the expanded PLA high enough that it cools down and can no longer flow)

To solve these issues I recommend using one type of filament, preferably decent quality (typically $40 per kg), if you swap materials be sure to completely purge your nozzle of the higher temperature material. Set your retraction as low as you can trying to minimize ooze (try .4 mm for all metal hotend or 2-3 mm for makerbot style). To minimize carbonized plastic in your hotend don't leave your hotend's heater on for extended periods of time. One way to keep dust from accumulating on your filament is to cover your rolls when you aren't using them, I personally use hairnets, you can buy a 12 pack for a couple of dollars and they last for a long time.

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Lubricating the filament is the most common solution I've heard of to stop filament jams and clogs. Lubricating makes for a smoother ride through the print head. While you're at it, make sure that the filament is clean. The best way to stop jams from dust is to get rid of the dust in the first place.

Some people recommend canola oil, which I've heard works reasonably well for both ABS and PLA (though especially for PLA). You can even 3D-print dust filters/lubricators, if you think this could be a serious issue.

I personally try to clean the print head regularly, after every couple prints or even after each print, if I have time. Something sharp, like tweezers, can pick off bits of filament near the tip of the nozzle. I haven't tried other utensils yet, but there are certainly other tools that would work. I've also heard of people regulating temperature with a fan, in order to prevent partially melted bits of filament clogging up the inside of the nozzle, but I don't know if that's effective.

In some cases, the problem could even be as mundane as a support issue. I once set up a spool of filament, only to have a jam when the support for the spool failed, leaving the line of filament tugging at the nozzle and clogging it. Taking steps to prevent this from happening can be simply and effective. Whatever the cause, preventative measures are always my choice.

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  • $\begingroup$ Does the oil not cause problems when it's heated along with the plastic? Or does it just get absorbed / mix in? $\endgroup$ – Martin Carney Jan 13 '16 at 23:34
  • $\begingroup$ @MartinCarney I can cause problems if it's applied thickly. A very, very light coating should not affect the composition of the final product too much. In general, it gets mixed in. $\endgroup$ – HDE 226868 Jan 13 '16 at 23:36
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As general advice, regardless of your printer, extruders tend to clog if: [Some of them might not apply to every printer, but they should be as general as possible]

  1. you let the filament run out mid print, most extruders have a "dead zone" between the grinding wheel and the hot end, in which if the filaments stays stuck there, your only option is to open the extruder
  2. you let a filament create knots with no one present to readily fix the knots, or the grinding wheel will saw the filament, leading to (1) plus a clogged grinding wheel: more often than not the quality of a filament brand is measured by the presence or absence of knots.
  3. you let the hot head stay hot without printing for too long, it will fill of melted filament leading to risk of it carbonizing inside the extruder, leading one again to (1)
  4. you use flex or rubber material which have the added complexity of grinding against the common plastic guides of the filaments feeders: depending on the material used, you might decide to avoid using the guides and feeding the extruder directly
  5. you print at higher qualities (e.g. 0.1 mm) leads to lower filament throughput that can become stuck if the nozzle is too wide (and the grinding wheel goes too fast)
  6. you never clean (i.e. blowing will suffice) the grinding wheel: filament dust sticks there increasingly over time.
  7. you let the extruder is too close to the plate: if the filament is not free to fall on plate as it should (settings-wise) it will fill the hot end back up leading to clogs
  8. you print wood, brick and derivate filaments: they are highly unhealthy for the extruder since they are plastic/resin charged with wood powder. The powder tends to a) burn and b) stick to the internal walls of the extruder.

If I can think of more I will add them.

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First, you don't.

To reduce the likelyhood, use good plastics without contaminations.

Do not over heat the plastic, causes faster carbon build up.

Buy hand drills, mini drills to clear it.

Don't switch materials around a lot. Low temp plastic residue will cook when you switch to high temp plastic. Again carbon.

Last will come to your extruder is self. Use a hardened extruder tip, less likely to wear. All metal should help a lot too, PTEF tubes often get baked in a jam situation.

Or do what I do. I use a giant 1mm nozzle. I have printed at least 20 lbs of plastic on the same nozzle.

The other solutions say put oil etc.. I will just say that is not a great idea. First you will have terrible bed adhesion, second it just seems wrong. Not to mention it will be out of the extruder within one KG?. The only time its okay to use oil is if you have a bowden setup.

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