J-Head jamming every day for 10 days straight

I am angry and I am going crazy. I have printed for about 4 hours a day until my printer jams. I have had to clean out the nozzle every day for the past 10 days. I have started with an acetone bath and a guitar string, but have used a blow torch for the past 2 days. It is become an infuriating inconvenience and I'm spending more time cleaning out the hot end than actually printing. I've disassembled things so much that the wires for the resistor on the J-head are nearing the breaking point from being bent too much.

It's a J-head MK IV-B, printing with ABS.

There are billions upon billions of theories and have exhausted the internet as a resource for possible solutions. I have slashed through what I can but can really only test one a day before the stupid thing jams. Here's some theory:
1.) Just bad machining of the actual nozzle? Answer: Doubtful. Brian was kind enough to send me a replacement. However, I have the same issue.
2.) Need a filament filter? Answer: No. I have been using one since after the first two days of jamming.
3.) Need a fan? Answer: Doubtful. I have been sitting with the prints with a hair dryer on cool recreating the effect. No good. I have only barely been able to print long enough to print out a fan mount which I'm going to be trying anyway once the fans arrive in the mail.
4.) Bad filament? Answer: Possible. I don't know the symptoms other than people randomly spouting "bad ABS" and "stupid chinese crap". There is no reliable criteria for bad source filament so I cannot eliminate this theory.
5.) Temperature too high? Answer: Possible. I do not know. All the factors theorized about regarding firmware, calibration, fluctuation, etc. All I figure I should do is try to set the temperature to the minimum required to extrude the plastic through trial and error. 230 seems correct. However, the temperature fluctuates by ~20 celcius, so how am I to know? Is that fluctuation normal? Is the thermistor bad? How can I tell? I realize if the temperature gets too high the plastic will burn itself into place.
6.) PTFE tubing "problem"? Answer: Doubtful. Another case of not knowing the true criteria. Once again my internet searches merely regurgitate pointless advice of "bad PTFE tubing" and no indication of what is correct. After the clogs, there is no plastic strewn about in the metal housing that would indicate a bad seal near the tip at the hot end. I do not know what significant resistance in the lining would be, but the tip of the tubing is slightly smaller than the rest of it. Is it normal? I have no idea.
7.) Various extruder issues? Answer: No. I cannot push the filament through by hand through the hot end alone (until I clean it out again).

I have to admit that I'm disappointed by the lackluster advice and poorly conceived theory en masse on the internet regarding reprap. Each issue should is solvable by way of eliminating possibilities, and in fact I daydream about a troubleshooting guide that would do just this. However, when I research each problem I have, I end up finding people pitching untestable theories (like "bad filament") that do nothing but give me another factor to consider and another thread of information to track down for identifying correctness. It is almost insurmountable to keep track of these possibilities and sift the good ideas out of the cruft. I know it does no good to complain about human nature, but considering that I've spent so much time chipping away at this problem I can't help but being upset about it. So if you are one of those people to pitch a possibility without a way of testing it, please be aware that I would be in a mood to punch you given how these past few weeks have gone.

Seriously though, what the hell. Should I just buy a completely different type of hot end? All advice I've found say that J-head's great, so I worry other hot ends would be even more of a nightmare. I can only stomach a few more jams before I simply snap and throw this time vampire into the garbage.

Well you are complaining about lake of info but you too are lacking info we need to help.

What brand of ABS? What color? Have you tried other brands/colors?

If it is black ABS and you have only tried Black ABS I would say it is about a 99% chance it is bad ABS and you need to test with other plastic. (Black filament is known to contain scraps which can contain contaminants).

Have you tried cleaning just the nozzle hole to see if it is a clog or do you go straight to taking it apart?

If you over tighten the set screw in the top of the j-head it forces the liner into the taper which makes the hole in the PTFE smaller and cause jams. If you have done this you need to remove the liner and make the hole larger again.


One last thing .Don't complain about things being disorganized when you can't even post your question in the correct section. As the title to this section says (RepRappers "People building or using RepRaps") it is for people to introduce themselves and to talk about themselves not about the machines). I usually avoid answering any questions in this section because it shows that the person asking the question does not pay much attention to what they read.

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20C temperature fluctuation is not normal and is too much in my opinion. I get about 5C variation with a J-head even with bang-bang control and less that 1C with PID.

If you are using Marlin try the PID autotune.

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[www.hydraraptor.blogspot.com]

Well, I appreciate the response despite my silly tantrum and apparent post in the wrong area. My rage has subsided a bit. I posted here because I saw another post about a similar J-head problem, but I can see that I posted in the wrong area.

It is a 5lb donut of black ABS from MakerFarm (no spool). I think your idea about the black ABS may be spot on. This holds my largest suspicion as well. Do you have a recommended source?

I do not fully understand what you mean by your suggestion of cleaning the nozzle hole. I try a few things before resorting to disassembly: first I try using guitar wire while everything's still fully assembled, although if it's a clog I don't fully fathom how this would help. Then I try pushing in some filament through the top and taking it back out hoping to pull up the clog with it. This has not worked for me. This is when I resort to disassembly of it all and take the metal tip and clean it out (either acetone bath overnight or a blow torch).

I follow what you mean by the PTFE lining so I've been careful about this. The PTFE lining does seem slightly smaller at the tip, but it doesn't seem significant since I can still get filament through it easily. I do not know how to widen this hole, though as you suggest; I would like to re- widen it just to be safe. How would you do this? I could also replace it just to be safe but I don't know how to go about this either.

JohnnyDude Wrote:
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> It is a 5lb donut of black ABS from MakerFarm (no
> spool). I think your idea about the black ABS may
> be spot on. This holds my largest suspicion as
> well. Do you have a recommended source?

I don't know makerfarm so I can not comment on the filament quality. But If you would like to try a filament with known quality and are in North America you could try Makerbot, Makergear or Ultimachine.

> I do not fully understand what you mean by your
> suggestion of cleaning the nozzle hole. I try a
> few things before resorting to disassembly: first
> I try using guitar wire while everything's still
> fully assembled, although if it's a clog I don't
> fully fathom how this would help. Then I try
> pushing in some filament through the top and
> taking it back out hoping to pull up the clog with
> it. This has not worked for me. This is when I
> resort to disassembly of it all and take the metal
> tip and clean it out (either acetone bath
> overnight or a blow torch).

I use a small drill bit (in my fingers) and clean the hole from the outside while it's hot and has some pressure in the hotend so when you break up the clog with the drill bit the pressure oozes out some plastic with the clog.

>
> I follow what you mean by the PTFE lining so I've
> been careful about this. The PTFE lining does seem
> slightly smaller at the tip, but it doesn't seem
> significant since I can still get filament through
> it easily. I do not know how to widen this hole,
> though as you suggest; I would like to re- widen
> it just to be safe. How would you do this? I could
> also replace it just to be safe but I don't know
> how to go about this either.

I use a knife and carefully remove the very edge (tiny tiny amount) that flares inwards. You could also try a 1/8" drill bit to remove the flared edge.

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I know this doesn't help. but I've run over a pound of black abs from makerfarm (and 1/2 pound red & natural) through my j-head (.35 nozzle) in the last few weeks.

My temp fluctuation is less that 5c also.

When I put it together, the resistor was 'loose' so I wrapped it with aluminum foil until it was a tight fit. Could yours be loose? That could explain temp fluctuation.

Okay, I've ordered some plain filament from Ultimachine. I will see if that helps. It is useful to know that some filament from MakerFarm reportedly isn't problematic.

By the way I neglected to mention I have a .35mm tip with my J-head.

Sounds like my ~20 degrees C temperature fluctuation is not normal. I want to resolve this. The resistor is a little loose and I can try some foil. Could someone help me with these questions?
1.) With my first hot end, the thermistor came with tiny plastic tubing for the wires. With the replacement hot end, these plastic tubes were absent. I do not know if these tubes are necessary. What are these tubes? I assumed they must be to keep the wires from touching and causing a short. My best hack to resolve this was to use kapton tape around the wires, although I do not know if this is enough for whatever purpose the plastic tubing was for.
2.) I don't know what PID autotune is exactly. I've looked around and it looks like it's for Marlin firmware, although I have Sprinter (a predecessor?). I'm using Gen6 software. Is this something I could change?
3.) When it comes to gauging the variance in temperature, is it safe for me to have the tip sitting here hot and without extruding? Even if I pull the filament out, there will still be some in the tip. I can spend some time testing and troubleshooting if this is safe to do, but I worry that this will hurt things by baking plastic into the tip.
4.) How much of the filament should be melted when I pull it out of the extruder? I wonder if this would help indicate improper temperatures. When I pull out the filament, there is usually at least 15mm of molten filament, sometimes 25mm or more. That indicates that the plastic is becoming molten before leaving the PTFE. I do not know if this is normal.

The only reliable way to verify temperature is with a thermocouple on a meter.
Having said that my experience is the thermistors are usually accurate with the correct firmware setting.
20 degrees is a lot of swing, I use PID to drive mine and variation is < 1 degree.
Marlin has an option to try and auto tune the PID settings M303, I don't think sprinter has an equivalent.

If your hot end is holding temperature, there is no harm in leaving it on, the plastic in the nozzle wil leak out.
The plastic tubes are just to stop the wires shorting, tape should be fine.

JohnnyDude Wrote:
-------------------------------------------------------
> 5.) Temperature too high? Answer: Possible. I do
> not know. All the factors theorized about
> regarding firmware, calibration, fluctuation, etc.
> All I figure I should do is try to set the
> temperature to the minimum required to extrude the
> plastic through trial and error. 230 seems
> correct. However, the temperature fluctuates by
> ~20 celcius, so how am I to know? Is that
> fluctuation normal? Is the thermistor bad? How can
> I tell? I realize if the temperature gets too high
> the plastic will burn itself into place.

230 C is very much on the cold side for ABS. Many people print ABS as high as 260-270 C.

In any case, 20 C fluctuation is guaranteed to cause problems. Either you're using Gen6 electronics or some of the stepper or heater wires are running too close to the thermistor wires. (Or there's something more esoteric wrong, such as noisy power supply, but those two are the most common causes.)

You definitely need to look at your thermistor wires. If they are touching each other or the hot end body, you will get a short.

I cemented my resistor into the hot end with muffler putty and then wrapped the leads with kapton tape to keep them separate.

The thermistor leads were also wrapped individually. I did this by ensuring the leads were separate and then placing a piece of tape between the leads as close to the thermistor body as possible and then wrap one lead and then leave a small ( 3mm) space between the leads and wrap both leads leaving the 3mm gap between wires.

Then i soldered extensions to these leads and wrapped these soldered leads in the same way. The thermistor is then wrapped to the hot end with more kapton tape and all leads are wrapped together to ensure the thermistor cannot move or break.

Pronterface needs feedback from the thermistor to set the temp. If this signal is incorrect pronterface will raise or lower the temp to compensate.

It sounds like the temp is getting too low and the printer is still trying to extrude causing a jam. I had the same problem with my first hot end. I wrapped the thermistor badly and the leads were touching each other and the extruder body.

Here are the PID settings I use with a J-head MK IV-B

    #define  DEFAULT_Kp 34.19
    #define  DEFAULT_Ki 2.47  
    #define  DEFAULT_Kd 118.19

They are what the Marlin auto tune command generated. I don't know if they are portable to Sprinter but they might be.

If you leave the hot end hot for a long time with air in it then the plastic remaining will start to go brown and hard.

It is normal for the plastic to melt in the PTFE. The brass is at say 230C but ABS melts at 105C. The PTFE will have a thermal gradient along it so a significant length will be above the melting temperature.

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[www.hydraraptor.blogspot.com]

ttsalo Wrote:
-------------------------------------------------------
> 230 C is very much on the cold side for ABS. Many
> people print ABS as high as 260-270 C.
>
> In any case, 20 C fluctuation is guaranteed to
> cause problems. Either you're using Gen6
> electronics or some of the stepper or heater wires
> are running too close to the thermistor wires. (Or
> there's something more esoteric wrong, such as
> noisy power supply, but those two are the most
> common causes.)

Seconded. I had a similar problem with my current run of natural ABS from ultimachine - J-head jamming and filament stripping. Ramped up to 240 from 230 and no more jamming/stripping of any kind. Gone through about 3 lbs so far without issue.

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- akhlut

Just remember - Iterate, Iterate, Iterate!

[myhomelessmind.blogspot.com]

This is all very good to know, thank you for the help!

I will work on eliminating possible thermistor wire shorts, although all I have that would survive the high temperatures is kapton tape. I'd rather not use cement given how often I have been cleaning out the tip and I rather like how thorough the blow torch method works. I think I will order more of that tubing stuff since it did the job well and is pretty well guaranteed to give insulation. I don't know the name of it but I can probably find it.

I have Gen6 electronics. Is that a known culprit for temperature problems? Is it a lost cause? All I was really aware of was that it doesn't have heated bed control (well, and it's loud).

I don't think I tried higher temperatures for a while, actually. I was too scared of thermistor inaccuracies putting me at the burn limit. Once I'm more confident I've got the themistor safely set up I'll give it a try.

JohnnyDude Wrote:
-------------------------------------------------------
> I think I
> will order more of that tubing stuff since it did
> the job well and is pretty well guaranteed to give
> insulation. I don't know the name of it but I can
> probably find it.
>

I think it is probably PTFE tubing. Have a look on Ebay, I have found good deals on it there.

Bad ABS or bad temperature control, or both. I confirm that all of my thermsistors are accurate with a cheap infrared thermometer every day. My bed thermsistor is about 10c off so I have to make sure that my temp is set to 90c to get 100c. My J-Head thermsistor hasnt had any issues with temperature control, although I do notice that sometimes my filament does come out burnt if the temp is set at 230c. If you live in the US, I would buy replacement thermsistors from makerfarm and maybe some of their filament($15.80/lb isnt that bad). They also make J-Heads so maybe you can ask them about this issue.

Edited 1 time(s). Last edit at 06/22/2012 10:39AM by Zimtower.

Are you using any thermal compound in the resistor and/or the thermistor? Something insulative, or something without decent thermal conductivity would cause wide termperature swings.

I had a recent bout of blocking in my J-head, but it was contaminants in the Plastic - if you think you have a blockage, push up a pin while applying pressure to the filament while its at temperature, if material starts to come out, then you probably have something blocking the nozzle inside. - just check it's not ball bearings! - http://richrap.blogspot.co.uk/2012/06/jammed-frggn-nozzle-30doc-days-1518.html

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[richrap.blogspot.com]

They looked more like glass beads than ball bearings to me.

I recently had a blockage caused by black ABS. When I dissolved it out with acetone there where some black flakes that did not dissolve. I.e. they were something other than ABS so presumably they didn't melt either.

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[www.hydraraptor.blogspot.com]

I dissolved the hot end's abs in acetone as well. There were a lot of black flakes that did not dissolve. I don't know if all the plastic should dissolve just sitting there, however. And, in my situation I think the temperature may be burning the abs. I could try this experiment again with some abs directly from the source.

Things I have done since the failures:

1. Added a fan mount to the X-axis carriage to blow onto the hot end
2. Switched to "natural" ABS filament from Ultimachine.
3. Re-wired the 4 wires to the hot end, using teflon tubing to guarantee that the wires are not producing any shorts.
4. Cleaned out the hot end with a blow torch, again.
5. Prayed to the gods of plastic

The extrusion is working fine again, thanks to the blowtorching. I am ready to print again, however the temperature continues to fluctuate to an obnoxious degree. When the printer is sitting here at a target of 230, I get fluctuations from 215 to 240.

I am going to try to print again anyway, but I'm convinced I need to do research into different firmware, because the temperature fluctuation is abhorrent.

Even with bang-bang control, your hotend shouldn't be varying by more than +-5 degrees C. I had no problem with my J-Head using bang-bang control at around 220 deg C. With my new J-Head MK VB and PID control, I have variations of less than 1 deg C.

Does Sprinter have PID hotend control? Look in configuration.h and see if it is there. If so, enable it and use nophead's values that he posted.

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Hmm. Well. It seems the mystery may be solved. I printed for a good 10 hours yesterday. Even without a fan on the hot end (because it was cooling my build platform too much, I'll have to readjust). I'm printing again now.

The new "natural" ABS from Ultimachine seems to be the key. The prints are a little less rough as well. I think the black ABS I had used previously was the issue. Thank you very much for the tip that black ABS may be the culprit!

I decided to go ahead and print because I noticed that the temperature was constant enough while printing (~8 degrees C). I had heard the temperature behavior is slightly different with a constant stream of plastic feeding through. I cannot fathom why exactly, but it's stable enough. I'll still look into better temperature control sometime, probably. Currently it is using "bang bang" control with sprinter.