Prusa i3 - Filament goes out only for a while, then the printer prints with air

Hello,

I've been trying to solve this problem for a long time, but I don't know what causes it, so I've decided to ask you.

I've tried to print a test cube a many times and eveytime, no matter what parametres I choose, the printer always stops printing at a similar stage (the photo shows one print, but trust me, it always stops extruding somewhere halfway second layer).

You can see my problem perfectly on those photos:







Does any of you know what can be the cause?

Thank you!

Most likely is your hotend, chinese clone? Take it apart and clean it up completely, if it have a PTFE tube check and see if burn or deformed and change it, clean nozzle and run through a proper size drill bit. Also the extruder might be either to tight or too loose. If your retraction settings are to big the melted filament will get to the cold side and jam. Temperature can cause problems too if too hot specially with PLA will create jamming issues.

The interesting part is that it extrudes pretty well when I press "extrude" in pronterface. Yes, the hotend is chinese, but is it possible, that the nozzle diameter changed and the slic3r prepared the g-code for wrong nozzle? The "original" nozzle was 0.4 mm in diameter, but this one I got from a friend and I'm not sure if the diameter didn't change. Maybe that's the cause? I can't check now, that's why I'm speculating. I will try to configure it in the morning.

Edited 1 time(s). Last edit at 06/01/2016 05:31PM by Diabl0.

That will definitely can cause a jamming problem if you are extruding for a 0.4 nozzle and the one you put is smaller, filament thickness also can create problems, are you measuring it?

Well, I know I should, but I always forget to bring a caliper. You know, the jamming started after I replaced the nozzle, it used to print good before, so the filament shoudn't be a problem. It must be the nozzle... I'll change the diameter in slic3r and see if something happens.

Do yourself a favor and purchase a cheap chinese set of drill bits for the printer, it comes with 0.1 to 0.5 sizes so you can use the right size in the slicer.

That's really good idea, I've never thought that something like this exists.

Well, still nothing. I changed the diameter, it still stops extruding at the same point. I raised the temperature, but still nothing.

Can you check whether the E motor is running or not when the printing stops? If its not running its not your nozzle. I dont think thats the case but just to rule it out. If it is running I am presuming the fillament is not coming through so its slipping. That brings me to the same conclusions as above... Just really weird it only happens after a while and not immediatly..

Unfortunately, I can't check that now, but I will be able to do it on sunday, I will try to rule out those things and we'll see what I'll end up with.

I found some time in the morning to test it. I removed the fan from the extruder to see what's going on inside when the filament stops coming out. The motor works well, it just slips on the filament which is blocked in the nozzle, which for some reason keeps cloging. When it does that, I have to remove the filament, cut out the part that was melted but cooled down and then when I put the filament back inside it goes out normally like nothing never happened. And then it repeats.

Edit: I don't know if it's normal or not, but that's what the filament looks like after I take it out:

http://i.imgur.com/9UiD2pE.png

(sorry for paint, I can't access the actual piece right now).

Edited 4 time(s). Last edit at 06/02/2016 01:39PM by Diabl0.

Yeap, that's the shape of a normal melted filament after pressed against the nozzle. The important part is how long is the melted section and to see if is reaching the cold end of the hotend.

Now you mentioned that you have to remove the fan to see what was happening with the extruder, can you post a picture of it? Does it have an adjustable idler?

One more thing, what's you retraction settings? You might be retracting too much and cooling the melted filament in the cold section of the hotend creating the jam.

If you have a Chinese Mk8 extruder/hotend, you might need as I mentioned before taking it apart and check the PTFE liner for damage.

Edited 1 time(s). Last edit at 06/02/2016 03:01PM by ggherbaz.

Retraction was the first thing I disabled in the slic3r, nothing changed, but maybe there's another settings somewhere in the firmware I don't know about.

Well, I will post a photo of the extruder as soon as possible, but I don't think will be able to do that until sunday evening (the printer is at a different location).

I can show you how the extruder looks using a photo from the Internet:



The idler is adjused with a screw with a nut.

EDIT: I also noticed that originally the bearing was screwed in without any washers, so it couldn't turn freely. I added those, the bearing works great, but that still wasn't the cause of the problem.

EDIT2: The Idler can not be the problem, because when the filament stops extruding, it won't move at all, even if I lift the idler and try tu push the filament in with my hand. It's just blocked. I have to take it out, cut and push back in, then the filament "shoots" from the nozzle and prints normally for short time.

Edited 2 time(s). Last edit at 06/02/2016 04:51PM by Diabl0.

Quote
Diabl0
The motor works well, it just slips on the filament which is blocked in the nozzle, which for some reason keeps cloging.

Slipping filament would be a sign of insufficient idler tension.

Quote

9UiD2pE.png

http://i.imgur.com/9UiD2pE.png

(sorry for paint, I can't access the actual piece right now).

If you could post a photo that would be great. With the proportions you have drawn, that would be a very long transition zone and will cause a lot of friction, in turn requiring a lot of extrusion force to overcome. That length of transition would suggest that your hotend cooling fan isn't working well enough.

Quote
JamesK
Slipping filament would be a sign of insufficient idler tension.

As I said, the idler tension can not the problem, because when it stops, even if I try to force the filament in using my hands it won't go, until I do the ritual I described earlier. Then it goes smoothly.

I will post all photos on sunday evening.

I believe that it's either the nozzle or the pipe with PTFE tube. I think I will try to get new ones, but in the meantime I will try to discover what exactly happens adbd why,

Edited 1 time(s). Last edit at 06/03/2016 04:57AM by Diabl0.

You can't produce a fraction of the force with your hands that a well adjusted extruder will produce.

Ok, good point, but still, I believe the filament shouldn't act the way it does right now.

Id say your fillament is cooling of somewhere, that seems to me the only reason it gets jammed. Maybe try find a way to heat up that part of the extruder somehow.

Well, is it possible, that not the printer is the problem, but the filament? It's been lying around since october in room temperature, in open space. (It's PLA).

It's possible that it's taken on moisture from the air. Could cause it to swell up in the hotend and jam also.

http://reprap.org/wiki/PLA#Moisture_Issues

I have another question

From the drawing, it almost looks like the barrel is too large for the filament.

If you could, you might have to take the extruder arm and gear off, but look down the barrel and see if the hole somewhat larger than your filament.

Generally, for 1.75mm filament, the hole is 2mm so you shouldn't see alot of space around the filament. If there is, there was most likely a PTFE liner that's supposed to be in there that's missing.
If you find that to be the case, your filament's probably just getting pushed into this open space, melting and jamming there. The PTFE liner would constrain it so that the force pushes it out the nozzle.