J-head problems

I've been trying on and off to get my reprap working since Xmas... but the hot end is really defeating me. I "gave in" and just bought a J-head hot end preassembled, thinking it'd solve all my problems.

... it doesn't.

For the record this is with 3mm PLA filament. I have a 40mm cooling fan with a little shroud that focuses it onto the heat sink slots on the Jhead body.

The problem is... it jams. Instantly. Every time. If I heat it up to 200C and then introduce the filament I'll get a drop, a lone dribble, from the nozzle and then the filament jams. I remove the hobbed bolt and most of the extruder so I could try pushing the filament by hand and it jams HARD, I can't even force it in with all my might.

Thoughts?

How sure are you that 200C is really 200C?

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- akhlut

Just remember - Iterate, Iterate, Iterate!

[myhomelessmind.blogspot.com]

I haven't verified it independently. But like I said, its hot enough to melt a drop or so. Also if I kick it up to 230C then it will also squirt out a squit of gas and bubbles. Seems like its hot enough...?

if you are sure your temperature is reading correctly
i would turn the temperature up, and try again, but do it by hand , you should be able to push it through... like butter with a hot knife , is probably the best description

I did just notice an interesting symptom... when the indicated temperature jumps by 6C whenever the hotend resistor turns off...???

i would increac the temperature in 10 degree steps and try again sounds like the temperature reading is off

amaurer Wrote:
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> I did just notice an interesting symptom... when
> the indicated temperature jumps by 6C whenever the
> hotend resistor turns off...???


I'd be checking for shorts if I saw that.

If it's Marlin and the 100K Epcos table it could be because there is a 5C jump in the table around 200C. I reported it and it got fixed very recently.

I

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[www.hydraraptor.blogspot.com]

Sounds like you have something clogging the extruder nozzle (tiny chip of metal from the machining process, or broken hobbed bolt tooth perhaps)

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www.Fablicator.com

I dont have any experience with the J-head but i had similar problems with my Makergear hot end. My problem was the heat was soaking up into the top end of the hot end and swelling the PLA high up in the nozzle which caused a plug. If i let it sit anywhere near extruding temps while not extruding it would jam it up everytime. Then when it went to print it just spit out a blob or two and that was it. My problem was solved when i installed a fan to point at the extruder and upper end of the hot end which runs all the time whether the temp is on or not, also i set the g-code in slic3r to set the temp to 120C after printing so it doesnt just sit there heat soaking the filament when not printing. Dont know if any of this will help with your issue but it also could be to much heat causing the same type of problems. Try turning your hot end on without any filament in it, set it to a low heat setting like 150C, then feed in the filament and see if you can extrude any by hand, if not then go up about 5C at a time until you can. Then try running it at that temp setting and see what happens.

what have you set your thermistor in firmware to ? should be 6 if marlin

other thing to try see if hotend it hot enough get a bit of filiment and press the bottom of the hotend with it. if it dont melt there then somethings wrong

Enlightx Wrote:
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> what have you set your thermistor in firmware to ?
> should be 6 if marlin
>
> other thing to try see if hotend it hot enough get
> a bit of filiment and press the bottom of the
> hotend with it. if it dont melt there then
> somethings wrong


Um.... Actually I emailed Brian s few weeks back just to ask this question and this was his response.

Quote

Hello,

For Sprinter, the thermistor setting is 1. I believe it is the same for Marlin.

Regards,

Brian

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The labelling in Marlin is terrible. "100K" and "Epcos 100K" are meaningless. It either needs the full part number or state the beta and the hot end manufacturers should be giving the part number or T25 and beta.

I chose 6 because it looked like an Epcos part but it was 25C too hot.

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[www.hydraraptor.blogspot.com]

i use 6 and have tested and am okay but i ordered from creativemachines.co.uk who seem to stock mostparts from another supplier and they list there thermistors as epcos and im pretty sure if its a small glass type its epoc.

just what works for me only way to be sure i suppose is to order your own from farnell