Do I have a jamming issue?

Hello all,

I wonder if I am having a jamming issue and need to take some corrective action accordingly (clean up the hot end).

It'll he ironic if I do have a jamming issue b/c it happened while printing parts for hot end fan mount...

My printer was running fine for the first two layers - I had to restart printing a couple of times before that after increasing the current flow to the extruder motor; the gear started ticking instead of spinning and pushingthe filament. At that time I just thought there wasn't enough current to the motor, but now I think it was a sign if jamming?

Anyway after a couple of first layer I noticed that there's no more extrusion of the plastic evev though the gear was turning.

I stopped printing and reversed the filament. I could see that the teeth of the hobbed bolt ate into the filament almost half way in, so the bolt was turning against nothing - nothing to grab on to and push down.

The lower part of the filament was narrow and long, line a hair which is something I've seen before when I took the filament out from the extruder. So, I didn't expect any problem at that point yet.

However, now I can't get the extrudef work again! When I feed the filament in, 5 mm at a time at 20 mm, while keeping the hot end hot, i get to a point where I can see a little bit of plastic comming out of the nozzle. Then the the filament stops moving and thehobbed bolt start digging into the filament.

I tried to push the filament by hand after disassembling the extruder (but still keeping the hot end switched on) and pretty much the same thing happens - I can push it until I see a little bit of extrusion frilom the nozzle but I can't push it any further.

I'm pretty sure the hot end is hot enough to melt the plastic - I am using PLA btw - b/c I even tried it with the hot end temperature set at 220c - well maybe the thermister suddenly went bad?

Or is pushing filament supposed to be take this much force that feeding 3mm filament for 5mm at speed of 20mm simply was something that would cause nothing but the hobbed bolt to dig into the filament, and I can't be done by hand?

There are other reasons I suspect jamming:
1. I didn' t a fan for the hot end even though I was printing with PLA.
2. I Was running my hot end at pretty high temperature - like at 215, some times at 220.
3. When I disassembled the extruder unit, I could see the wooden part where the J hot end is wedged in is chatted - another indication that I've been running the hot end maybe too hot.


Is there any way to check if the hot end has a jamming problem (if the symptoms I have described here weren't enough that is)? And if it indeed is a jamming issue how can I fix it?

Thank you!

I would suggest heating the hotend up to 130C and then manually pulling the filament out. Hopefully that'll get it just hot enough that any contaminants in the nozzle will be pulled out as well. After that, you need to get a fan ASAP and you need a filament cleaner, even if you just zip-tie a piece of lint free cloth to the filament right before it enters the extruder. As for the fan, it's not optional with PLA on most hotends. If you need to jury rig something just long enough to print your fan mount then do it, otherwise just print the fan mount with ABS. Also, your temps sound a bit high but unless you've calibrated them with a thermocouple in the melt chamber, they're meaningless to anyone using a different machine. You'll have to experiment quite a bit before you gain any sort of reliability from your machine (I sure did).

Thanks for the tips. Really appreciate it.

Yes, I guess I am learning it hard way that hot end fan with PLA is a must. Actually, I've been printing a lot of stuff with PLA without a fan past couple of weeks, so I actually have been quite lucky not to have this jamming issue until now. Or, come to think of it, I think I had to gradually increase the hot end temperature, so maybe the melted PLA was building up inside and I just didn't know about it..

I tried to clean up the path with PLA filament while setting the hot end at 130C. I didn't really see any derbies or blobs of plastic coming out. I tried to clean the hot end with a toothpick (I wish the toothpicks were just a little bit longer!), and it felt like the melted plastics are only in the metal part of the hot end, and I tried to scrape any plastic deposits on the non-metal part, but I couldn't feel anything inside.

So, I tried to push the filament with hand again. I could make extrusion happen, but I had to put a lot of force... Should this be a little easier than this? I remember being able to extrude plastic quite fast (when my extruder was working), but for me to extrude the plastic at that speed, it would require a tremendous amount of force. Is this normal, or is it a sign of still clogged in nozzle head?

When you try to unclog the nozzle by pulling out the filament, you should be able to see an imprint of the inside of the nozzle in the filament, if you dont, you probably still have some plastic left in the hotend.

When I want to clean out the hotend, I turn it on at 100 degrees, and when temperature reaches ~60 degrees, I start pulling the filament, and somewhere between 70-90 degrees it breaks loose. Normally the bit of filament that was left in the nozzle oriffice is still attached to the end. But this only works when the hotend is stone cold to start with, if I fail at the first attempt, I have to wait at least an hour before I have a second go.

Well, this may be a dumb question, but I need to have the filament already in the hot end (molded and fit tight) when doing this, right?

In other words, if I am trying to clean the hot end out but do not have a filament in there, I first need to heat up the hot end, insert the filament all the way in (until I see some extrusion, I would assume), let the hot end cool down completely, turn it up to 100 degree, and so on...



Ralf Wrote:
-------------------------------------------------------
> When you try to unclog the nozzle by pulling out
> the filament, you should be able to see an imprint
> of the inside of the nozzle in the filament, if
> you dont, you probably still have some plastic
> left in the hotend.
>
> When I want to clean out the hotend, I turn it on
> at 100 degrees, and when temperature reaches ~60
> degrees, I start pulling the filament, and
> somewhere between 70-90 degrees it breaks loose.
> Normally the bit of filament that was left in the
> nozzle oriffice is still attached to the end. But
> this only works when the hotend is stone cold to
> start with, if I fail at the first attempt, I
> have to wait at least an hour before I have a
> second go.

Yes that's right.

This is how the filament should look like, if you succeed..

Ralf,

Thank you for the picture! I tried your trick twcie. Each time I got something similar as what you showed in your picture. I attached a picture of one of them.

It seems like I may have pulled it too hard that about 10mm from the bottom of the filament, there's a section which is a bit stretched out. I think I was pulling it so hard that I ended up stretching the filament, when it got soft enough to be stretched but still a little too cold to be detached from the hot end and come out.

Also, both time, I wasn't able to pull it out until my temperature reading got to 115 - 120C - this is actually I was pulling it hard - since I was expecting to come out at between 70-90C like you suggested, I applied a little more force thinking maybe I wasn't pulling it hard enough.

At this point I really wonder if my thermistor reading is way off. Like 30-40C off. As I have stated in my previous post, it's very very hard to push the filament and make extrusion at 185C. When it's set at around 210C, I can squeeze out the plastic from the nozzle with a reasonable amount of force...

Now that I think the hot end is clean, I tried to print some test piece with hot end temperature setting at 205C. I know 205C is a bit too high for PLA, but then again, I didn't want to try any lower temperature because I was afraid the extruder hobbed bolt would eat into the filament because of the too much resistance.

The print quality is actually pretty good (I stopped in the middle so there's a little bit of blob) - I've attached a picture of this test piece. It was printed with 0.2mm layer height and 0.5mm extrusion width.

Oh, I also strap on a fan to the extruder (third attachment). I know its aim is not really optimal, but I figured it would be better than nothing, so I will use it until I can print fan mount part.

Tour temperature isn't necessarily off, it also depends on the heat propagation in the hotend, and the length of the melt zone, when you can pull out the flament. As Scheck wrote, the best way to be sure thar the temperature is ok, is to stick a thermocouple down the hotend.

It sounds like the filament gets stuck in the tube, I had the exact same issues when I switched from ABS to PLA, the first layers printed fine, and then things got stuck. Cooling of the tube, to shorten up the melt zone resoved that issue.

I dont have an awfull lot of expeirience in hotends, that I have not build myself, as I have been having very satisfactory results with a design, very much like the E3D hotend

Man... I don't believe this. My extrude is jammed again!!!

It was about 80-85% done printing the last part of the fan mount unit, and started pumping out no plastic! LOL

I have attached a picture of this 85% finished part - just to share my frustration!

Now I wonder... what should I do? I do have some fanning for the hot end body, until I can finish printing this fan mount kits, which I am having problems because of jamming, this is the best I can do for cooling.

This actually was the third attempt since the cleaning of the hot end.

In my first attempt the part got knocked out of the heated plate when it was about 75% done. There were just too much warping and build up from overhangs, and the extruder head literally knocked the object out of the place.

In my second attempt, about half way in, one of the lower layers de-laminated. It was the basically the same issue - build up from the overhang causing it, but this time since I put extra amount of hair spray on the plate, the bottom hold up to all the knocking but one of the layers in the middle couldn't take the banging any more and decided to come apart...

In my last attempt, I just changed the extrusion width back tot he default 0.53mm - until then I had it set to 0.4mm, which is the same as the layer height.

I seemed like going well... until about 85% completion.. then the extrusion stopped. The hobbed bolt probably has digged far into the filament - when I realized it was not pumping out anything, it already has gone through several layers, so there was more than enough time for the hobbed bolt to grind out a good portion of the filament.


I had temperature setting at 205C.. well, but now I know I don't know the exact temperature at the tip of the hot end where the plastic gets melted.

What should I do? Should I try to increase the hot end temperature? I think higher temperature does make it easy for the extruder gears to push the filament in... but then now I may end up having melted plastic in the non-metal body of the extruder, and have a true jamming. So, does that mean I should try with lower hot end temperature?

Your extrusion width should not be the same as your layer height. Think about it, if width=height then the extrusion is cylindrical. That means that you get the absolute minimum contact between layers so it's almost gauranteed to delaminate. Even 0.56/0.4 is a bit low. I'd try 0.66/0.3. As far as the extruder failing towards the end, check your filament path into the extruder and make sure the extruder can physically pull in the filament and it isn't binding or pulling back against the idler springs. At higher Z height the filament might be at an odd angle to feed the extruder. Once the hobbed bolt begins to chew up filament, the teeth begin to get clogged and it becomes a snowball that eventually ends up with no extrusion.

I had this jamming issue. The whole pull-it-out-when-luke-warm trick didn't work so well for me. I ended up modding my hotend by rigging up a stainless steel heating element holder, with some copper washers and aluminum foil for makeshift cooling fins. I haven't had the problem since (although I also haven't tried extruding PLA again since either). But if you can't get the fans working, you could try adding aluminum foil fins... conduct the heat out away from the extruder rather than convection via fan.

Side note - Is the PLA jamming issue caused by poor heat distribution?

Status Update

I just completed printing a small test piece (oozebanetest). I printed it at the lowest temperature I've ever used as far as I can - 185C hot end 110C heated bed for first layer, and 180C hot end and 105C heated bed for the others. Funny thing is that, this is the best printing quality I got with this particular piece in terms of blob and ooze control (and I printed this same shape a lot of times - like 20 or 30). I've attached a picture - it was printed with 0.4mm layer height.

The unfortunate thing is that I have no idea why it's working again. I did disassemble the J head and cleaned the inside, but as far as I can tell there was nothing really to clean. I still went ahead and scrape imaginary derbies and particles using wooden toothpicks while keeping the hot end at 230C. After it cooled down I also blew out invisible gunk and dust with compressed air.

I attached a few pictures of the inside of the nozzle - this was BEFORE I did any cleaning. I took these pictures to visually inspect the inside of the nozzle.

The only thing I could suspect as the cause of the jamming was.. the seam between in PTFE liner and the brass nozzle. I wonder if there was a gap into which the melted plastic got in and somehow (I don't know how, honestly) interfered with the filament movement.. There are a few other unlikely scenarios I can come up with, but they are all basically causing more friction on the filament movement and making the extruder gear not to be able to push the filament and start digging into it instead.

I've collected quite a few filament pieces which I had to pull out by hand - I let the hot end cool down to about 50-60C and then heat it up again to 120C and pull the filament out. I actually wondered why there always is a "waist" - a portion near to the bottom which is a bit narrower than its original 3mm thickness. It turned out that its starting location, the distance from the bottom is exactly the same as the thickness of the nozzle head, and that's also where the PTFE lining starts. In other words, where this "seam" is.

I've attached a picture of those filaments. I wonder if this is an indication of anything, or this is what everybody would see when they pull out their PLA filament after heating up the hot end to 120C from the room temperature.

Anyway, for any of my theories to be true, this extrusion mechanism must be a very delicately balanced operation... Just a ted bit more of friction and no extrusion.

I know I am also using a lower temperature than I normally do, but I did try to print the same piece at 185/185 just yesterday (before the disassembling the J Head and cleaning inside) and had a jamming issue. I don't think 185/185 is that different from 185/180, and if 5 degree of temperature difference can make it or break it, again this extrusion process is a really delicate one...

Another thing I did differently today is that I rearranged the wires to the heating resistor. During the cleaning I've noticed that the resistor's leads get very hot, most likely due to heat conduction. Until now these leads and the wires were tightly taped around the J Head PEET body. Well, I even installed a fan to cool that area of the J Head, so it didn't feel right to place the leads/wires there. So, I let those wires come out to the front, where the fan mount is. I wonder if has resulted in better cooling of the J Head body, and ultimately prevented the jamming...


Oh well, I need to print some more before I can safely declare myself done with this jamming issue. I just thought I should post a status update, at a risk of jinxing myself I really thank everyone who has responded with valuable information.

Well, I guess I can officially close this issue - I have printed a more complicated piece which took well over an hour (I didn't time it actually) and it printed without any jamming. This actually is the very piece with which I started having a jamming problem last week. So, I can confidentially say I no longer have a jamming issue... at least for now and until I have another one. LOL

Like I said in my previous posting, I don't know what resolved the jamming issue, and also I can only make some guesses on why I have a slightly better printing quality and much much better ooze and blob control. It probably is a combination of slightly lower temperature and hot end cooling fan; I installed the half way finished fan funnel - the other unfinished half was a fan for the printed object. Now I have printed a complete set of funnel, I'm anxious to see how much difference in printing quality I am going to have to the second fan.