Jamming continues...

I had less than 24 hours of joy after fixing the jamming issue I had all week... and it came back.

I printed a pretty complex object with PLA without jamming, then changed to ABS filament (maybe I shouldn't have?) and printed another fairly complex object without any issue. Then I switched back to PLA (maybe I really really should never have?) and start having the same jamming issue.

I did everything I tried before, including disassembling the hot end and cleaning inside - there were no debris or clogged up plastic or foreign objects - the passage was clean as far as I could tell, but I still scraped inside with toothpicks, just like what I did when I fixed the last jamming issue.

Well, the difference is that even after disassembled hot end clean up, it is still jammed.

What's interesting is, however, that extrusion works fine with both PLA and ABS when I send extrusion command from Pronterface, with various distances from 1mm to 10mm and various speed ranging from 10 mm/min to 60 mm/min. It's only when I start printing, I no longer see any extrusion or very little of it, and I can hear hobbed bolt eating into the filament (I heard it so many times now, I can recognize hobbed bolt chewing the filament by the sound ).

This jamming issue is like a herniated disc or ACL injury. Once you got it, it keeps coming back. I never had any jamming issue until last week, but all of sudden, once I had one it keeps coming back. Is my J Head ruined forever? I actually have another J Head (with smaller nozzle size)... should I just try that one, and use it until it starts having a jam issue?

Edited 1 time(s). Last edit at 08/13/2013 07:33PM by Yamster.

Did you check the nozzle hole? It might be blocked by something.

Yes, I ran a bare 26 AWG wire (0.40386mm diameter) through it to make sure there's nothing clogging up the hole. I did have to clear up some plastic, but I believe it was just a little chunk of plastic left behind when I pulled out the filament to clear jamming.


Now I am actually suspecting the PTFE liner. I had so many jamming, b/c I kept on trying again and again, and as a result I had a lot of filaments pieces laying around me, most of which I pulled out form the J Head after jamming.

Some of them have a section near to the bottom swelled up a bit. I believe that's a part in J Head which is not hot enough to completely melt the plastic, but still warm enough to make it expand/swell up. I just happened to run one of those filaments with swelled up bottom through the J Head (through the PTFE liner), and I realized that even with swelling I didn't have any problem running it through the upper portion, but it almost got stuck at the lower section - the very same section where the filament would expand.

I understand the filament will be a lot softer when it warm enough to be expanded like that, so it may move through more freely.. but maybe not. If it's soft, it will be more likely to be squeezed (but the extrusion gear pushing the filament down from the top) and it will become even fatter. Come to think of it, maybe it was not really an expansion, but rather a compression which caused this section of the filament to become "fatter".

Anyway, for whatever reason the internal passage in the lower section of the PTFE liner is slightly narrower than the upper one, and that difference is big enough to "grab" a swelled up (and cold) filament or let it pass through.

Well, at least that's one theory, and I am not even sure if it really makes sense or not. However, this was enough for me to decide to try to replace the PTFE liner. The liner is cheap - my favorite vendor, from whom I got my J Head, only charges $4 for the replacement PTFE liner, and it's even cheaper if I buy raw material from McMaster-Carr and cut it myself (dirt cheap).

where did you get your jhead from?

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Can you hand feed it?

I got it from MakerFarm. I believe it's original J Head, not a clone. It's a J Head Mk IV B, not V, though

thejollygrimreaper Wrote:
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> where did you get your jhead from?

No. There actually were times (I had so many instances of jamming) I was able hand feed, but the last time, just before I totally disassembled my J Head and decided to replace the PTFE, I was not able to hand feed it.

It took a lot of strength to squeeze out maybe a millimeter or two (not the distance the filament pushed, but the length of the extruded plastic ), then I could not push it any more.

nechaus Wrote:
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> Can you hand feed it?

Is this before or after updating to the new thermistor?

Since I put a fan on the cold side of the extruder, I have yet to get a jam.
(knock on wood of course!)

I guess its caused from heat-creep... after a bit of running, the melted filament creeps back up the tubes
and causes the jam... the fan keeps the cold end cold, and prevents this...

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Curious as to what temperature you were printing the PLA at and when you switched over to ABS, what temperature was that?

I haven't gotten the thermistors I've ordered yet. But I finally found the thermocouple prongs for my multi-meter the other day, and confirmed the temperature reading is fairly accurate.

Actually, it was somewhat interesting how much the temperature difference was on a different point in the brass nozzle.

1. The tip of the nozzle (where the plastic comes out) is good 20c below. At first it was trick to hod the thermocouple tip still for a steady reading, but I managed it by putting the J Head upside down and taping the thermocouple on the tip.

2. On my nozzle, there is a small indentation right next to the hole where the thermistor is inserted. Temperature reading from that spot was almost right on - I got the same reading (or very similar) between the multi-meter and LCD.

3. I was crazy enough to insert the thermocouple into the nozzle - from the top, just like the way the filament is inserted. The temperature reading was actually 10+ C higher! At that time there was some clogged plastic (white ABS), so the tip of my thermocopule was buried in it (I could feel that I was pushing it into something soft and also the tip was covered with white ABS when I took it out). I wonder if that has contributed to the higher temperature reading, or if that's just the way it is.


Anyway, so I have dismissed a wrong thermistor configuration and wrong temperature reading (and setting it on a wrong temperature as a result) from the possible root cause.


iquizzle Wrote:
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> Is this before or after updating to the new
> thermistor?

Mogal Wrote:
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> Since I put a fan on the cold side of the
> extruder, I have yet to get a jam.
> (knock on wood of course!)
>
But, I had a fan when I got the latest jamming...

I've actually ordered a fan with higher airflow rating, thinking that maybe my fan wasn't doing its job - I was using a cheap $4.99 fan with <5 CFM.

Come to think of it, I'm ordering quite a few parts here and there because of this jamming issue. Man, this jamming is costing me and I hope my wife never sees this posting! LOL

One question for you... Do you have your fan running when printing with ABS, too?


> I guess its caused from heat-creep... after a bit
> of running, the melted filament creeps back up the
> tubes
> and causes the jam... the fan keeps the cold end
> cold, and prevents this...

kburr Wrote:
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> Curious as to what temperature you were printing
> the PLA at and when you switched over to ABS, what
> temperature was that?

I had the temperature setting 185/180 for PLA and 220/220 for ABS. Actually, it might have been 225/220 for ABS - I am getting old, and the frustration from this jamming issue sure is accelerating my aging!

Anyway, those were the temperature settings at the time of jamming, but the same temperature settings I'd used before the jamming - when I was able to print fairly complex objects both with PLA and then ABS...

Okay... I was gonna say that I no longer have the jamming issue, but.. in order not to jinx myself, let me just say I was able to print a couple of object without jamming. I used my old trusty PLA,

It will be interesting to switch back and forth between PLA and ABS, which is exactly what I did when I got myself into the second (the latest) jamming issue, and see what happens. Yeah, and remembered as the stupidest RepRapper who just couldn't learn his lessons. LOL

I did a couple of things.

1. I got the PTFE liner I've ordered yesterday. To save money, instead of ordering the replacment part from my vender (at $4 a piece), I've ordered a couple of feet of the same material from another supplier for less than $4. I was able to replace the existing liner with it, after cutting it into a right size. It wasn't hard, but it definitely was not as simple as I thought it would've been.

Not gonna get into the details of this PTFE liner replacement (because it will be boring.. maybe some other time), but the thing is that now I got a new, clean PTFE liner inside.

However, I didn't get to try this repaired hot end until today, because yesterday I was dealing with another jamming issue (LOL) with my other, brand new, hot end. I made another posting on that jamming issue, and I actually was able to print with that hot end after switching back to PLA from ABS.

2. The higer CFM fan I've ordered got here yesterday, too. I started using the new fan right away (with the other hot end). It's twice as thick, so I just assumed it would pump in more air.

Well, guess what I have found out today...

I was lazy when I installed the fan I had - I just connected its wires to to one of the unused plugs out of the PSU. But today, I decided to connect it to the main power of the RAMPS, like my build instruction shows.

Man.. after that the fan started spinning a lot faster.. I realized I had my 12V fans connected to 5V (I think it's 5V) plug coming out of PSU all along!!

Now I am actually thinking about going back to my old fan, 'cause I think this new fan is a bit of overkill. It now takes some extra time for the hot end to reach the printing temperature (185/180). In the past, hot end temperature went up really quick, but now I can see it's really working hard to get up to 185 c after around 170-175 c point. I'm pretty sure it's the fan which keeps cooling the hot end down.



Anway, with the newly replaced PTFE, and plenty of air flow into the hot end, everything seems to be working fine (at least for now).

I can't really close the book on my recent jamming issues quite yet because there are so many questions I still don't have an answer for, but for now I am happy. I missed printing so much.. and there are a ton of parts to print, like a new extruder for my new hot end (I have been swapping the hot ends on one extruder until now). You know, I am still relatively new to this game, so I'm in that stage of "printing stuff to make my printer better".

However, after I made all the parts I needed, after I got a new batch of ABS from a more reputable vendor, and if I had some spare time and got board, I may actually be going to try to replicate some of the issues I have had. Hopefully by then, I would have another 3D printer, which is perfectly tuned and fully operational. LOL

Thank you everyone who has shared their wisdom and knowledge with me in their kind responses!

Edited 1 time(s). Last edit at 08/16/2013 04:34PM by Yamster.

For ABS I can only think that you would want the thermal break with air flow, but not the print. Same for PLA, but you should cool the print as well.

Glad you have it running nicely

The reason I was curious about the temperatures you were printing at between the 2 plastics is because if you have PLA residue and you load ABS into the hotend above 230ish it will start to crystallize and cause issues. I haven't experienced it myself as I only print with PLA on my current machine, but it is something I've been told before.

Edited 1 time(s). Last edit at 08/19/2013 09:05PM by kburr.

kburr,

Thank you for your concern. I didn't know about the crystallizing of PLA, so I'm glad you told me. I actually was worried a little bit when switching from ABS to PLA, because of higher melting point of ABS - if I have some ABS left over in the hot end, I won't be able to melt them with PLA printing temperature - but didn't know going from PLA to ABS can also have its own share of problems.

I've learned my lesson (hard way) that now whenever I change the filament or need to pull it out, I let it cool completely, and then heat up the hot end again, not to the operating temperature but about half to that point, and pull the filament out. I've learned it from some other posting (maybe it was you? LOL).

Anyway, now I get a filament of which tip is a shape of the bottom of the hot end (most of time including a short 0.5 mm diameter extrusion at the very end) every time I pull it out. I can sleep better I probably have gotten all the plastics out of the hot end this way.

In the past, I sometimes impatiently pulled the filament out while it's still hot.. and I often got those long stretched hair lines. The most of time that may not have caused any issue - especially if I didn't switch from one material to another - but why risk it, right?