Hotend jams - not blocked

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Genaforge
Posts: 8
Joined: Thu Aug 29, 2013 6:20 am

Hotend jams - not blocked

Post by Genaforge »

I've been having some hotend jams recently that I haven't been able to find a solution for (by my own trial and error, and via searching the forums).

The printer works fine for the first 10-15 layers. But it jams suddenly for some unknown reason. I've tried four different filaments with no difference between them (all PLA - different colours). I've tried printing at temperatures between 195 and 230 with no difference in performance. I've purchased a set of miniature drills and can clear out the nozzle with no benefit. I've adjusted the tensioner between 'barely grasping' and 'death grip' with no real difference.

Once the print head jams, I can pause the printer and reduce the tensioner (to nothing), yet I still can't push filament through by hand (if I wriggle the filament about inside the hotend, it will eventually flow through again). Generally, I remove the filament, cut the length that's been inside the hotend and reinsert. Then the filament will flow through nice and smooth. I can push through a good 20cm of filament like this with no issues, but when I retighten the tensioner and start printing, it quickly jams.

One hypothesis I have is that the extrusion and retraction of the filament during printing is causing a buildup of unmelted filament in the print head (potentially by scraping against one of the internal pieces). This eventually causes a blockage that resolves itself when I remove the filament to trim it; any excess unmelted filament in the hotend would then get the chance to melt and fix the issue.

What I need is some idea of how to stop this blockage from happening. I have some ideas, but it would come down to me hacking the print head, which I don't want to do unless I have some idea that it's going to work.

I should add that there seems to be some pressure buildup within the print head. Prior to his problem, during a print, when the filament retracted, the hotend would stop producing filament. Now, no amount of retraction will stop this. I can push filament through the hotend to produce a nice flow, and retract the filament entirely (by hand), and still have a decent amount of filament flow out of the print head. If I don't retract the filament, it will continue to flow a steady smooth stream for over 15 seconds.

I'll add that this is a fairly new print head. I've only done about 15 prints on it. I've pulled the print head appart, and inspected the individual sections, but haven't been able to see anything that's amiss. I did note that it was difficult to pull filament out of the heatsink; this is where I noticed that 'retracted' filament was scraping off against the edge.


Any help would be greatly appreciated.

Hugues
Posts: 270
Joined: Thu Apr 04, 2013 5:36 pm

Post by Hugues »

I was battling with similar symptoms last week-end,

have you unscrew the top part of the print head from the Peek ? There is not much in there to block the filament, but it takes 5 minutes to look. My problem was not there.

The filament was not guided properly. The little bearing that keeps the pressure on the filament was not aligned properly and the filament ended up on the side of the bearing. I removed one washer from the back of the bearing and it worked out, i could print a big part, 9 hours printing none-stop, no issue.
Hugues
Regards from Switzerland

Saamec
Posts: 157
Joined: Fri Jun 21, 2013 9:28 am

Post by Saamec »

Drill a hole in PEEK in diameter of 6 mm, take fluoreplast the puck with an outer diameter of 6 mm, and inner 2 mm, thickness of 2.5 mm When the Assembly to place it inside PEEK. The whole problem of jams in the fact that to PEEK plastic sticks. I long ago made the sleeve inside the extruder fluoroplast and forgot about jams forever....

http://forum.felixprinters.com/viewtopic.php?f=9&t=729 Here is my work, but all do not want to notice it.... the Problem was solved. Have printed out not a single coil plastic, no jams. All printed just need to click on the START button...

Hugues
Posts: 270
Joined: Thu Apr 04, 2013 5:36 pm

Post by Hugues »

Saamec wrote:Drill a hole in PEEK in diameter of 6 mm, take fluoreplast the puck with an outer diameter of 6 mm, and inner 2 mm, thickness of 2.5 mm When the Assembly to place it inside PEEK. The whole problem of jams in the fact that to PEEK plastic sticks. I long ago made the sleeve inside the extruder fluoroplast and forgot about jams forever....

http://forum.felixprinters.com/viewtopic.php?f=9&t=729 Here is my work, but all do not want to notice it.... the Problem was solved. Have printed out not a single coil plastic, no jams. All printed just need to click on the START button...
Interesting Saamec, some questions:
- can we use teflon instead ? easier to find for me today at the hardware store
- you say O.D. = 6 and I.D. = 2, so that leaves 4, divided by 2 i get 2 on thickness (unless i'm still sleeping). So why you say 2.5 thickness ?

thanks
Hugues
Regards from Switzerland

Saamec
Posts: 157
Joined: Fri Jun 21, 2013 9:28 am

Post by Saamec »

Teflon and PTFE, it is one and the same))) the Only thing different brands, different thermal characteristics. I used Teflon working up to 240 degrees.
Dimensions are not essential. The main thing to get rid of the partitions in the PEEK. PEEK will play the role of the coupling. But fluoroplastic will play the role of a cutoff of heat. 2.5 mm > 2 mm. It is necessary to ń ring tightly in contact with aluminum. 2.5 is the height)))) Partition PEEK in approximately equal to 2 mm

This is the way out of the problem without reshaping the extruder or manufacture of a new. This idea came up after the tests of the new Hotend. And this will work. The only thing, if you plan to print the ABS, it is better to replace the fan at 12 V. Because fluoroplastic works to 240 degrees. Taking into account the continuing forced cooling at a temperature of heads 250 degrees is ń ring has a temperature of about 200 degrees. Of course performed by the rod-shaped and not ring cooling is much better.

Sincerely, Ilya.

Genaforge
Posts: 8
Joined: Thu Aug 29, 2013 6:20 am

Post by Genaforge »

Thanks for the replies. I've had another look at my print head, and using details from the comments above, I think I may have found the cause of the issue.

The PEEK (at least I think that's what it's called, based on the comments above) is overheating. Plastic is melting in here rather than in the hotend itself. This is resulting in a buildup of plastic in the PEEK which isn't directly flowing down into the hotend; this creates a pressure buildup, which pushes against the extruder. Once the filament stops going into the PEEK, the molten filament will empty from the hotend, and the PEEK will cool enough for the filament to solidify in it; creating my blockage.

At least, this is what I think is happening.

The simple solution is to use a better fan over the PEEK. I would assume the near 40 degree days we've been having here are the culprit for my issues.

I'm currently printing a piece to test my theory.. and so far, it's working well. I'll provide some more details once the job is done.

Saamec
Posts: 157
Joined: Fri Jun 21, 2013 9:28 am

Post by Saamec »

When extruder does the reverse movement plastic, at the moment of transition of the head to another coordinate happens sticking of plastic inside the extruder, brown coupling (PEEK). Exacerbated by the position of not precise sizes of holes. Plastic as if clinging to the walls. This problem in the transition Aluminum - PEEK - Aluminum. I got rid of it. I have now the transition Teflon - Aluminum. Plastic glides. Cling to do so.
Of course you are right. A more powerful fan provides a solution to the problem but not 100%. Sometimes all it will be repeated. And it is very sad, after 12 hours of printing, model is not done just a little bit. A bunch of plastic been spent in vain.

Guys, I just wish that you would just printed, and always high quality, without any jams.

Sincerely, Ilya

Hugues
Posts: 270
Joined: Thu Apr 04, 2013 5:36 pm

Post by Hugues »

Genaforge wrote:Thanks for the replies. I've had another look at my print head, and using details from the comments above, I think I may have found the cause of the issue.

The PEEK (at least I think that's what it's called, based on the comments above) is overheating. Plastic is melting in here rather than in the hotend itself. This is resulting in a buildup of plastic in the PEEK which isn't directly flowing down into the hotend; this creates a pressure buildup, which pushes against the extruder. Once the filament stops going into the PEEK, the molten filament will empty from the hotend, and the PEEK will cool enough for the filament to solidify in it; creating my blockage.

At least, this is what I think is happening.

The simple solution is to use a better fan over the PEEK. I would assume the near 40 degree days we've been having here are the culprit for my issues.

I'm currently printing a piece to test my theory.. and so far, it's working well. I'll provide some more details once the job is done.
funny enough, i'm also battling with similar issues since last night :-(

to test your theory a little bit, you can remove the extruder, unscrew the top part (heat sink) from the Peek (plastic part), then manually push your filament in the peek. Then try again without the Peek, you can unscrew it from the hot end, be careful not to burn yourself. Then push filament into the hot end. YOu can then compare the behavior and test your theory, and also have a ..peek... inside the peek.
Hugues
Regards from Switzerland

Genaforge
Posts: 8
Joined: Thu Aug 29, 2013 6:20 am

Post by Genaforge »

Saamec, I have a feeling that I'll end up needing the advice you've given. But at the moment, I've got it working nicely with minimal changes. In honesty, I moved the printer into the main living area so I could run tests on it more easily... and it mostly fixed itself (as it was moved to the air conditioned area of the house). So long as it keeps working, I'm going to be happy.

Thanks for the details Hugues. I did try this, and you're right. The filament goes through nice and easily without the Peek. I was a bit surprised at how easily. It seems there is some friction between the filament and the Peek itself, which may account for some of my issues.

But now that I've got this thing in a cool area with a better fan, I've been able to get some prints off with no blockages.

And now I can finally get this large item I've been working on printing. There was no way I was going to try a 50 hour print before. Now I'm more optimistic.

Hugues
Posts: 270
Joined: Thu Apr 04, 2013 5:36 pm

Post by Hugues »

i think i found the origin of my problem,

as the estimated printing time was 11 hours, i decided to increase the speed from 120% to 150%. From that moment i could not print anymore. I think this filament feeding rate is too high and the plastic overflows into the peek and finally jams.

I changed the speed back to 120% and I've been printing non-stop for 4 hours now.
Hugues
Regards from Switzerland

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