J-Head MK5 hard to extrude

I have a problem with J-Head MK5 (3mm filament, 0.35mm nozzle). I can't get it to extrude reliably past 60mm/min (that's the speed of extrusion, i.e. 60mm of filament go in a minute). Even when pushing filament by hand, without hobbed bolt, it takes considerable amount of force to extrude anything. This is happening with white ABS, nozzle temp at 240-260.

What I have tried:
* Dismantled and cleaned the nozzle (with propane torch- so I'm sure nothing is blocking the nozzle) multiple times.
* Checked the PTFE liner- it looks good. Molten filament is not leaking anywhere.
* Tried cranking temperature to 270- it gets a little bit easier, but I couldn't reliably extrude at 100mm/min.
* Verified thermistor calibration with a thermocouple- temperature inside melt chamber is what I think it is.

What temperatures other J-Head nozzle users use for ABS? What extrusion (not print, but extrusion itself) speed is common?

Actually, I made a few calculations, and it seems that when printing at 0.25mm layer height, 1.5 WOT (0.375mm line width) at 60mm/s, the actual extrusion rate is lower than 60mm/min- ~48mm/min. However, I can only achieve such extrusion speed at 260*C- is that normal with J-Head nozzles?

My J-Head MkV is much easier to extrude with than for example an Arcol V4. The J-Head I have does 75mm/s at 0.3 layer height and 0.6 track width just fine, at 230 C and 3mm reprapworld.com ABS filament. Is yours from hotends.com or somewhere else? There have been some poor quality clones around...

Just purging mine will do 150mm/min with 190c pla quite happily. I'm sure it will go higher, but I have no need.

Print speeds of 150mm/s are possible although I do loose massive quality for other reasons then!

My J-Head does com from hotends.com. At 230 *C I can extrude a few mm of filament until it starts stripping the filament. My ABS filament comes from GRRF.de.

how sure are you about the temperature? at 260 you should be melting the peek insulator.

I'm fairly certain about temperature- verified thermistor's readings with thermocouple and a multimeter. Measurement with thermocouple inside the melting chamber shows a difference of 1-2 degrees from the temperature I have set extruder heater at.

ok, is your nozzle partly blocked maybe?

As I said- I have cleaned it thoroughly- by heating it with propane torch until it glows- and I'm sure there is no contamination there.

I'm now suspecting, that this cleaning with blowtorch may be the culprit of this problem, as the brass surface inside the nozzle is oxidated- maybe that's what's causing excessive friction. Googling tells me that brass can be cleaned with lemon juice and baking soda- will have to try that out.

I have a j-head that was blocked because I tightened it so much the PTFE sleeve was crushed up against the nozzle and restricted flow.

Just saying.

Roy

I agree with Roy. The Mk-V less prone to the PTFE constricting around the feed if you tighten the set screw too much compared to the Mk-IV, but it will probably still happen if you tighten enough. The symptons fest is getting is consistent with constriction in the PTFE tubing.

@fest - After putting the hot end together, did you try to push a filament into it while it's cold to make sure that it's not restricted? One test to confirm that it's not the nozzle is to push the wrong end of the right size drill bit (around 3 mm) and push with it. If you're able to push with it but not with the filament, then it's not the nozzle and the problem is likely in the PTFE-hotend junction.

Did you get your Mk-V from hotends.com?

Edited 1 time(s). Last edit at 03/12/2013 06:13PM by brnrd.

fest Wrote:
-------------------------------------------------------
> As I said- I have cleaned it thoroughly- by
> heating it with propane torch until it glows- and
> I'm sure there is no contamination there.

It's possible for the nozzle to be partially clogged by some foreign particle that does not burn with a blowtorch...

I have never had the problem with the J-Heads, but the Arcol hot-end I have clogs easier and I just had to unclog it yesterday. I used a method someone else described: heat the hot-end, push the filament in, let it cool to 140 C and then pull the filament out. This should pull all the plastic out along with the contamination. Combined with pushing a thin copper wire through the nozzle aperture from the outside this seemed to clean things up without disassembling anything.

konwiddak Wrote:
-------------------------------------------------------
> Just purging mine will do 150mm/min with 190c pla
> quite happily. I'm sure it will go higher, but I
> have no need.
>
> Print speeds of 150mm/s are possible although I do
> loose massive quality for other reasons then!

What layer height, what track width? Giving just the speed doesn't tell anything about the actual output volume per second...

What is the maximum feed rate when extruding in the air?
I cannot go higher 100mm/min with my diy 0.5 J-head-v1
And it means that with thick layers you cannot go faster 45mm/s

@brnrd, yes, my J-Head comes from hotends.com. When it's just cleaned and heater isn't on, filament can be pushed in without resistance all the way down to the nozzle. PTFE sleeve isn't crushed (or at least I think so- I tightened the grub screw so it's pressing against PTFE just a little bit (tried tightening it more- no effect).

@ttsalo, when heating the nozzle until it's red, the orifice is visible quite well, and it looked like a nice and round hole without any particles.
I also tried to pull back filament when hotend has cooled to 130-140 *C, but the filament always snaps off where brass barrel starts.

Frustrated with previous (failed) attempts to clean the nozzle, I drilled it with a 0.5mm drill today. I miss being able to print 0.1-0.2mm layers, but hey, I can at least print something now (at 230*C, which really helps with overhangs vs 260*C I printed earlier).

Why do you think you can't print 0.1 or 0.2 mm layers with a 0.5 nozzle? Many people have done that quite successfully.

Greg, you may be right. I think I simply got lost in labyrinths of my mind :>

blow torch will not clean crystallize pla it will make it hard as rock, take a tiny drill bit like a 0.25mm shaft size, and work it thru on a heated hot end. if it is blocked you will see a build up puss out after the blockage is removed.

Blow torch will burn pla off the nozzle. I've done it. I followed spacexula's youtube video and went through a few cycles of burning and dunking in rubbing alcohol.

The other way that I've cleared a nozzle is by sticking a small needle into the hole while it's hot.

I had similar problems with my Mk5 until I mounted a cooling fan from an old CPU beside it so that it blows across the cooling vents. Now it works like butter at 230 degrees. If you go hotter than that, you actually cause more friction because the ABS crystalizes in the Peek part. The cooling fan keeps the filament solid right down to the nozzle so it can push the short melt zone out easily. Without the cooling fan, especially at 260 degrees, the filament is soft the whole length of the PTFE and it is like trying to push the melted plastic out with a wet noodle. I epoxied the fan to the side of the carriage and I attached a square piece of paper with double sided tape to the bottom of the fan to direct the flow across the cooling vents and prevent it from blowing on the nozzle and heat bed.

> konwiddak Wrote:
> --------------------------------------------------
> -----
> > Just purging mine will do 150mm/min with 190c
> pla
> > quite happily. I'm sure it will go higher, but
> I
> > have no need.
> >
> > Print speeds of 150mm/s are possible although I
> do
> > loose massive quality for other reasons then!
>
> What layer height, what track width? Giving just
> the speed doesn't tell anything about the actual
> output volume per second...

Fair enough,150mm/s PLA 0.2mm layer 0.6mm width @180C - square object where it definitely is getting up to speed. I don't really print at this speed because quality suffers, but enough plastic seemed to go down. So yes there is something funky with your nozzle (but I think you already realised that!)

+1 for cooling fan

Edited 1 time(s). Last edit at 03/15/2013 07:20AM by konwiddak.