The Ultimate Guide to Preventing Clogs and Jams on Your FDM 3D Printer

Your FDM 3D printer is constantly clogging and jamming. You haven't been able to print anything useful for months and don't know how to solve the problem. This guide aims to help anyone in this situation. I have had my fair share of clogs and jams and have searched through the dark depths of the internet to find a solution. This guide is a collection of all the knowledge that I have gained through endless hours of unclogging, cleaning and experimenting.


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Step 1: Knowing How Your Printer Works

Before you can solve a problem you have to know why it is there in the first place. Thus, in order to stop clogs and jams, we need to understand why they occur.

The picture above is a cutaway view of an E3D V6 assembly. I shall use it to explain the causes of jams and clogs. The ideas discussed here are applicable to most printers as this is a fairly standard concept.

The assembly is made up of two parts, the hot-end and the cold-end. The hot-end is what gets heated up and it is here that the plastic melts. It is also where the nozzle is attached. This is the lower part of the assembly as seen in the picture. The cold-end is pretty much everything above the hot-end. It consists mainly of the heatsink and fan. The hot-end and cold-end are joined by what is known as the heatbreak which is essentially a small metal tube that screws into both ends.

Plastic is passed into the cold end and pushed through the heatbreak into the hot-end. It then melts and is deposited onto the printer bed through the nozzle.

In the ideal situation the hot-end will be at the temperature required to melt the plastic (eg. 200C for PLA) while the cold-end will be at room temperature.

Step 2: Clog or Jam?

Most people would refer to a clog as plastic getting stuck in the hot-end or nozzle while a jam is plastic getting stuck in the heatbreak or heatsink.

It is pretty easy to figure out if your printer is clogging or jamming. Just heat up the hot-end to the correct temperature for whatever filament is stuck and try pulling the filament out. If the filament comes out easily, you most probably have a clog. If not, then it is probably a jam.

Of course if you want to be absolutely sure then you can always just take apart the assembly and have a look inside.

Clearing the clog or jam is another matter and is not discussed in depth in this guide. However, the most common methods are dissolving the filament away or melting the filament away using a heat gun or lighter. A quick Google search should be all that is needed to know what to do.

Step 3: Preventing Jams

We will start with jams since they tend to be the most difficult to deal with. A common cause of jams is the cold-end being too hot. The assembly relies on there being a sharp difference in temperature between the cold-end and the hot-end.

Before doing anything drastic, check that the temperature that your printer reports is accurate. To do this, simply just stick a thermometer next to the heating element. The heating element is the smallish cylinder that is clamped into the heater block.

If the temperatures don't check out then make sure that your thermistor working correctly and that the correct type of thermistor is set in your printer's firmware. If you have bought a pre-assembled printer then this shouldn't be a problem but it is worth checking anyway.

If the temperatures check out then the cold-end is most probably not being cooled correctly. The heatsink should be cool to the touch when the printer is printing. If is not, then you definitely have a cooling issue.

Cooling issues are most commonly caused by fans running too slowly or inefficient third party cooling ducts.

Start by checking that the heatsink cooling fan is running at full speed. If you are unsure check the fans voltage rating and solder the fan directly to that voltage(eg. If the fan is rated 12V then solder it directly onto the 12V pins of you printer's control board). Most of the fans used for 3D printers are 12V and most 3D printers will have 12V accessible somewhere on their control board.

If you are running a third party cooling duct make sure that it is working correctly and that it is efficient. An easy way to do this is to find other setups similar to yours that use the same cooling duct and look at both the success rate and print quality from these setups. If you are unsure and it is possible to switch back to the default setup that came with your assembly then do so. This will give you a definitive answer as to whether your cooling duct is adequate or not.

Another cause of insufficient cooling is using fans with a CFM rating that is too low(CFM is a measure of how much air a fan can push). This one is pretty easy to fix. Just check the recommended fan CFM rating for your specific assembly and make sure your fan meets it.

It is also possible that the heatbreak is not properly 'thermally connected' to the heatsink. By this I mean that the heat is not being efficiently removed from the heatbreak. The solution is to unscrew the heatbreak from the cold-end, apply a little bit of thermal paste onto the threads and screw the heatbreak back in.

If the issue is not related to cooling then it can become a bit more complicated. Before moving on, make absolutely sure that cooling is not the issue as it is the most common cause for jams.

Old filament can also be a cause for jams. Most filaments that are used for 3D printing are polymers and therefore absorb a fair amount of moisture from the air. PLA is particularly good at this. Filament that has absorbed a lot of moisture often has an inconsistent diameter and melting temperature. To check if your filament has absorbed too much moisture, bend a piece about 20mm long in half. If it snaps then your filament has a high moisture content and will not print well or cause jams.

Baking the filament in an oven at around 40C for a couple of hours will dry out the filament and hopefully fix the problem. Alternatively, just use a new roll of filament. If you want to look after your filament then store it in a closed box filled with silica gel packets(or rice if you are a cheapskate;)).

The next thing to check is your retraction settings. Too much retraction will pull hot filament into the cold-end where it will instantly solidify and get stuck. Testing this is not as simple as disabling retraction altogether because if the printer is left idle at high temperatures then some filament from the hot-end may ooze back into the cold-end. This usually does not happen as the filament tends to ooze out of the nozzle but it is still something to consider.

For direct drive setups it is not advisable to retract more than 2.5mm. Bowden setups are more complicated as the retraction distance is related to the length of the Bowden tube. For most setups however, about 6mm is a decent amount. Some experimentation is required here and it can be quite tough to get a good setting. If you are experiencing large jamming problems then I would tend to sacrifice print quality in order to get more reliability.

Another consideration is the amount of friction in your system. Of course, the more friction your system has, the more likely it is that a jam will occur. Friction is more commonly a cause for jams with Bowden setups as the Bowden tube adds a lot of friction to the system. Often the inside of the heatbreak of cheap assembly clones are not polished sufficiently which can cause pressure build up inside the heatbreak and lead to jams. I have seen some people try to combat this by coating the filament in lubricant but I have never done this myself. The solution to the problem is to stop cheaping out on parts and just buy the original assembly.

The final consideration is your extruder calibration. Under-extrusion can sometimes lead to jams but most often does not. Over-extrusion however, can be a consistent cause for jams. Checking that your extruder motor is calibrated correctly is not too difficult. Simply make a mark on the filament next to a fixed reference point. For Bowden setups, the entry to the Bowden tube is a great place to make this mark. For direct drive setups, it is a little more difficult and depends on your setup. You will have to use your brain a bit to find a good place.

Once you have made this mark then simply extrude a minimum of 10mm of plastic. The more you extrude the better as this will reduce the error in your measurement. Then make another mark at the same reference point and measure the distance between the two marks. From here, you can adjust the steps per mm of the extruder motor based on your measured and expected distances. Repetier is a good tool to do this although many printers have the option to do it without having to connect to a computer. If you are unsure of exactly how to do this then a quick Google search should give you an answer.

Step 4: Preventing Clogs

Clogs are almost always in the nozzle. Since the nozzle typically has a very small diameter, even small pieces of dust and debris can cause a full or partial clog.

If your printer has been sitting doing nothing for a while then it is possible that some dust has got stuck in the nozzle and is stopping the plastic from passing through.

More commonly, dusty filament carries small dust particles into the nozzle and gradually this dust build up can cause a clog.

Some cheaper filaments tend to do weird things when they heat up or contain small solid particles which can easily get stuck in the nozzle.

Of course the solution is to use high quality filament from reputable sellers and keep your filament in good condition in a dust free enviroment.

How one goes about looking after their filament depends on the type of filament and so is not discussed here.

Other then that there is not much else that can cause clogs in the nozzle. Luckily, clogs tend to be really easy to clear and generally do not stop prints altogether.

Step 5: That's It. That's All I Know.

Well, that's everything that I've tried and read about. If your printer is still jammed or clogged at this point then I'm afraid I can't help. However, if you find a way to fix it that isn't in this guide please let me know so that I can add it.

Happy printing!

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    3 Discussions

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    2 replies

    Hey there

    Maybe instructables was the wrong place to post something like this but I have recently been having issues with clogs and jams on my 3D printer and I couldn't find one single place that listed all the ways in which to solve the problem. I understand that good, clear pictures are helpful but it is quite difficult to get such pictures for something like this (first, your printer has to jam and second it is not easy to get a clear picture of the jam). The goal of this post was more to provide a summary of all the ways in which one could prevent clogs and jams on their 3D printer. I would argue that the post is complete in what it is trying to achieve but I am open to criticism. However, since I cannot see what I should change(even after reading the instructable that you have linked), I was wondering if there are any specific examples of things that I could add or change.



    The current publishing guidelines require at least one picture for each step. But it just needs to be enough to roughly illustrate what happens in each step. It doesn't need to be anything specific. Just do your best to illustrate your points.