Please help with my J Head

Hi,

I'm using a j head 5-B (1.75 mm with .35mm nozzle) with an airtripper bowden style extruder. My main problem is that, while my extruder can push/pull the filament, once the filament is at the brass hot end, it cannot push further, and the motor starts skipping. I've already set the temperature as high as 250 (i'm using abs). All I get is the slow oozing out of material. The oozing out is too slow for any prints to be feasible. Has anyone had this problem? Do you think that my j head is defective? I wish I knew what was going on inside that J head. Can I get a vise and just untighten it like a soda bottle?

Tips please.

PS. I eventually tried to do it by hand.. I placed a piece of plastic through the bowden tube, and tried pushing the ABS in with my hands.. Before I can see some sort of extrusion, I have to apply a large amount of effort with my hands. Is that normal?

-Noob

No, not normal. You should be able to push it through with your hands.

Have you verified the temperature you are reading is correct?

My first guess would be your thermistor table might not be accurate.

Sounds like a squished PTFE tube on the end closest to the head.
That happened to mine.
Fixed that and then it worked OK.

Take it apart, ream out the PTFE. I cut mine a little shorter and more pointed on that end.
Roy

I too have had a similar problem. I upped the temps and pushed really hard at one point. Now I'm printing at 230 and the flow is better. Still I have random jams which require a little manual push to get started again. Really annoying to have my hours long print ruined by a stupid jam. I haven't a clue what the problem is but am considering taking apart my J-Head. I would appreciate knowing the best way to do it though...can I just use a proper sized wrench to hold it and 'lefty loosey?'



- "Natrual" color ABS from the eBay seller in the Czech Republic
- Sampling filament revieals consistant diameter of 2.6mm - 2.8mm
- Extrusion temp 230deg
- J-End .4mm nozzle
- 0.25mm layer height
- Printbot with Wades setup and hobbed bolt from Ultimachine
- TIGHTLY sprung counter bearing on filament
- Plastic ooses from tip upon heating

I'm pretty sure printing with 1.75mm filament in a J-Head is considered experimental at this time.

The bowden extruder adds another layer of possible issues. If it is possible to push filament directly into the hot end with the bowden cable removed, compare the ammount of force required. This may give some indication as to how much additional force is being required simply to push through the cable itself.

Don't take your hot end up to 250, or even 240°C. This is beyond the melting point of PEEK, and will eventually result in the failure of the PEEK insulator, if it has not already.

The usual modification made to a J-Head, to adapt it to 1.75 is to take 1/4" PTFE rod, and drill a 2mm hole through it. This PTFE liner is then held inside the PEEK usinga small flat washer, and hollw set screw. If you tighten this set screw too much, the hole at the bottom of the PTFE will narrow when the rod heats up. Inspect the PTFE, and make sure this has not happened.

I had a similar problem and what I found is you want to heat up your nozzle clean before any plastic enters for the first time. Put the filament so the motor just grabs it and eat to your extrusion temp. Then test extrude slowly until it makes it to the nozzle. This was night and day for me with my 0.35mm nozzle. So You may need to clean out your nozzle and try that.