j head jam

Hi,
when i first used my j head it melted down and jammed.
I opened it and cleaned it from the plastic inside and cut the piece that melted then connected it back.

I added i fan to blow on the head but it keeps jamming after it prints one layer or two, I cleaned it several times but it always happens.

Am i doing something wrong or the j head is damaged and I should replace it?
I am printing PLA at 165C,
I've ordered all metal j head from e3d to avoid these problems in the future, it is supposed to be more durable and can handle mistakes and experiments.

Read this post about J-Head clones.

A few things are probably going on here:

-A badly designed or manufactured nozzle is more likely to build up back pressure, especially with PLA. It's also possible that manufacturing debris or PEEK from your attempts to recover from the meltdown could be causing the clog too.

-The heat break with 4 vent holes is less effective at keeping the incoming PLA cool, leading to possible jams. From the looks of it, your hotend mount blocks the upper 1 1/2 vents. Although not ideal, as long as the fan was running I doubt these are the culprit.

-Even with a clone, the barrel is still PEEK and should survive to ~245C. This shouldn't happen at 165C (which is low for most
PLA). One of the following could have caused the meltdown: wrong thermistor setting in firmware, bad thermistor connection, thermistor isn't thermally coupled to the block enough. If possible, get a thermometer you can jam down the barrel to insure that it's hitting the temps that you're dialing in.

-Not sure how you managed to fix the melted threads... but if you had to shorten the barrel in the process, you need to trim the PTFE to match and make sure not to overtighten the set screw.

I wouldn't spend any more time on this hotend, especially with an E3D on the way.

Quote
pokey9000
Read this post about J-Head clones.

A few things are probably going on here:

-A badly designed or manufactured nozzle is more likely to build up back pressure, especially with PLA. It's also possible that manufacturing debris or PEEK from your attempts to recover from the meltdown could be causing the clog too.

-The heat break with 4 vent holes is less effective at keeping the incoming PLA cool, leading to possible jams. From the looks of it, your hotend mount blocks the upper 1 1/2 vents. Although not ideal, as long as the fan was running I doubt these are the culprit.

-Even with a clone, the barrel is still PEEK and should survive to ~245C. This shouldn't happen at 165C (which is low for most
PLA). One of the following could have caused the meltdown: wrong thermistor setting in firmware, bad thermistor connection, thermistor isn't thermally coupled to the block enough. If possible, get a thermometer you can jam down the barrel to insure that it's hitting the temps that you're dialing in.

-Not sure how you managed to fix the melted threads... but if you had to shorten the barrel in the process, you need to trim the PTFE to match and make sure not to overtighten the set screw.

I wouldn't spend any more time on this hotend, especially with an E3D on the way.

So I have bought a bad hot-end, my fail.
I think you are right, it shouldn't be mounted this way. I was able to print few layer today then it jammed again
I fixed it by opening it and cleaned everything using drill, it was aggressive and I think I made places where the plastic can jam.
[www.youtube.com]
I've ordered E3D-V5 full kit just to avoid the problems I faced. should it be good for PLA? ,some people claim it is not good for PLA and jams a lot.

Edited 4 time(s). Last edit at 06/11/2014 01:46PM by EEstudent.

Quote
EEstudent
I've ordered E3D-V5 full kit just to avoid the problems I faced. should it be good for PLA? ,some people claim it is not good for PLA and jams a lot.

Mine has been through almost a full spool of PLA without a jam on an E3D-v5/Bowden setup. As long as the fan is running 100% at all times, I suspect that you will not have any problems either.....

Quote
vreihen

Quote
EEstudent
I've ordered E3D-V5 full kit just to avoid the problems I faced. should it be good for PLA? ,some people claim it is not good for PLA and jams a lot.

Mine has been through almost a full spool of PLA without a jam on an E3D-v5/Bowden setup. As long as the fan is running 100% at all times, I suspect that you will not have any problems either.....

I am glad to hear that.
I changed the order to get the new E3D-V6 full kit, it is not cheap but it looks great, all assembly problems like how to place the heater/thermistor has been solved
looking forward getting it!