Broken Jhead

I have only been printing for maybe 2 weeks at most and out of about 12 attempted prints of actual parts and trying to iron out all my flaws in my prusa i2. Things were going well for about 2 days then out of no where I kept having issues with the filament getting chewed up by hobbed bolt. I thought this was an issue with the bolt itself until I looked down and realized my j head was broken.

This was a brand new hot end I ordered from a reputable supplier so I don't..... or at least didn't think it was a quality issue.

Im pretty sure no type of warrenty will be issued although im not so sure I want to go back with the same hot end.

I can't even seperate the nozzle from the top end due to filament being clogged up inside it. I was going to get it to temperature and try to remove the nozzle that way and see if I could figure out how this happened but upon trying to remove on of the ends on my resistor broke off so now I have to order another one anyway.

Definatly bummed out have you guys seen anything like this before ?

looks like a classic case of too much heat

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The PEEK melted from getting too hot. It melts around 260C. Your hot end probably got too hot due to one of these reasons:

1. The thermistor table selected/loaded in firmware was the wrong one.
2. The PID setting in the firmware is wrong and resulted in large overshoot.
3. The thermistor popped out from the hole in the hot end. (This happened to me.)

The hot end is still usable but you need to replace the PEEK and also the PTFE lining. You can heat it up as you planned if you replace the resistor and then unscrew the hotend. You might also be able to uncrew the hotend even without heating it. Once you remove as much plastic as you can, and also the thermistor and resistor, you can clean it using a blow torch. Here's a youtube video oh how it can be done.

... what brnrd said, not sure where all the text i wrote went .

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I stole it.

I'm pretty sure I selected the right thermistor in my settings I had it set to 230 my prints just seemed to do better at that temp. I will back it down I didn't realize these were pushed so close to the maximum envelope. I went ahead and picked up another one. Hopefully I can get back and running by the end of the week.. I guess I will have spare parts might switch over to pla for a little while so I don't have to set the temps so high

i blame the nargles ...

Edited 1 time(s). Last edit at 03/18/2013 01:08AM by thejollygrimreaper.

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thejollygrimreaper Wrote:
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> i blame the nargles ...

Indeed

The thermistor delivered with the j-head Mk-V from hotends.com might come with a different thermistor than what it used to come with. They used to all come with the #1 thermistor choice in Marlin and Sprinter. But he changed to another type due to supply problems. 230 is a good temperature setting. I usually print between ABS between 220-230. But, did you also tune the PID if you're using Marlin with PID option? Unless you tune your PID setting, you should use bang-bang to avoid wild overshoot.

I was using the all in one file that is sprinter/marlin mix I am not sure yet if the firmware was to blame for the cause of this however it very well could be I spike with makerfarm which is where I got the first one and asked if they would provide me with the correct configuration file for the thermister and resistor that I purchased I'm also going.to see about setting.up a cut off when temp exceeds 240 for future safe gaurds

u can calculate your own look up table from the beta value of the thermistor.

For the J-head from makerfarm they specified B value of 4066 on their website, so there is already a look up table available. EPCOS 100K (B57540G0104F000)

add that to your thermistortables.h and change configuration.h accordingly then u're good to go.

Edited 1 time(s). Last edit at 03/28/2013 01:20AM by ghostling.

hi Tattooedfish

I almost ran into the same problem as you. Was pushed in the right direction for a solution after visiting this forum.

I just posted it "J-head cooling mount"