J-Head Mk IV-B needs a lot of force to extrude

I have used a couple J-Heads and never had a problem. With PLA though, you HAVE to cool the thermal barrier. Also, because the melt zone is so short, the extruder temps have to be much higher. In fact, I have to run my J-Head at 40 degrees hotter than with a MakerGear extruder for the same filament to run at 60 mm/s. I have no issues with difficulty to extrude, even after running one for a couple months. This is all with PLA, btw.

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It's ultimachine pla, black. It's only clogged twice, once before I believe was the result of stripping the filament and little chunks of plastic getting down in there. Both it's happened have been shortly after stripping the filament on accident. the weird thing is that my jhead won't extrude pla with a fan on it at all. The extrusion becomes thin and sparse an it eventually strips the filament. Take the fan off, it's fine. I repeated it several times to confirm that was causing it, and it clearly was. Very weird behavior considering the wiki says you need a fan for pla with a jhead...

Wrote:
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> PastaRocket848: Where did you get your PLA? Could
> it be that there are stuff in your feed that's
> clogging the nozzle? The other possibility is that
> you may be overheating the plastic causing it to
> decompose and clog the nozzle.

You would have to prevent the fan blowing on the heater block or it will simply freeze the plastic.

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nophead Wrote:
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> You would have to prevent the fan blowing on the
> heater block or it will simply freeze the plastic.

Not at all. I have the heater block wrapped in a couple turns of kapton, and a small fan that blows across the whole hot end. It reaches 240 deg C in only a couple minutes, and could easily go hotter. I do sometimes use a duct to prevent air flow across the printed parts and heater block when I print larger objects.

BTW, I always use a heated bed. The fan doesn't affect the heating of the bed either, though it is not a high-powered fan. The only issue is that it causes warping on larger prints, which is where I use the duct.

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If your large parts are warping with the fan on, the it is affecting the heated bed. You're also wasting some energy heating your nozzle and your bed and then blowing a fan over them. It's a tricky business.

Looks like my problem was operator error on my part. Yesterday I took the J-Head completely apart and it sure looked like I compressed the nozzle end of the PTFE into the nozzle so much so that it nearly plugged itself, or at least narrowed the hole to almost closed. I cut off the plugged area, reamed the PTFE out with a drill bit, found my 0.50 mm drill bits that I put away in a safe place and forgot where I put them. I then cleaned out the 0.50 hole on the nozzle. I reassembled everything today and it works like it was intended. Now I need to contact Brian and apologize for being a dumb ass and send the brand new nozzle back to him... or pay for it and keep it... Hmmmm.

Anyway... Just so everyone knows. It was my fault not a defective J-HEAD!

Sorry Brian for making you think you made a bad J-head.

And thanks everybody who gave suggestions!

Roy

Edited 1 time(s). Last edit at 03/18/2012 02:46PM by roygpa.

I extrude 15mm of filament or more to free space before I start printing. That gets rid of the high force caused by heat buildup in the extruder head. If you leave the extruder on for a long time before you print the end of the filament expands and becomes hard to extrude. Try to start printing with the head .1 from the surface in that state and now you will create an extruder stall and dig a groove in your filament with the hobbed bolt.

Turn up the temp to 225 and pull the filament out of the top of the extruder and you will see how big the end gets.

Flowing to fast also causes a deep cut groove in the filament. Set your temperature and see how fast you can print to free space before the motor skips. Now back the flow rate down and try to print backing the flow rate down if the motor skips.

Hope this helps someone