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

I just switched from a basic home made hot end (that actually worked great!) to a J-Head Mk IV-B with a .5 nozzle and it's giving me a bit of trouble.

Im printing in PLA and it seems to be requiring a LOT of force to extrude and is causing my stepper to miss steps.... It usually happens when doing infill probably because im doing infill at 60mm/s as opposed to 30mm/s on perimeters.

What happens is that after doing infill at 60mm/s for more than like 5 seconds a lot of pressure seems to build up in the hot end, then I hear my motor skip a few steps and the big gear on the cold end will spring backwards a bit.

I have experimented with different temperatures and currently find 195c to minimize this problem the most. I have also read that this hotend requires a small fan to blow over the cooling vents at the top but it doesn't seem to help much... I actually seem to be getting better results without a fan. I presume the purpose of the fan is to cool the top so the PLA doesn't get soft and create more resistance... but i also wonder if because the melt/molten zone of the hotend is so short that it can't melt the PLA fast enough.

Also, even at slower speeds like 2mm/s if i try to manually extrude a long distance like 50mm eventually pressure or resistance seems to build, then the extruder motor skips.

I believe this buildup of pressure is also giving me problems with ooze/strings/retraction, even when retracting 1.5mm at 10mm/s it will still immediately begin to ooze when moving from one place to another. Im pretty sure this is due to the large pressure build up in the nozzle that even a normal amount of retraction cant overcome.

Has anyone else had issues with this? What did you do? Are there just some inherent limits to this hot end that I am exceeding? Or am i just doing something wrong?

I have the same problem using ABS with a J-Head i bought a couple weeks ago. 0.5 mm orifice.


Roy

I am using the J head MK IV-B 0.35mm nozzle and have experienced it once when I had my extruders idler bearing pinch too tightly against the hobbed bolt. So thats what I would check first. I print ABS the faster I print the hotter the hotend has to be to keep up. I can easily print at 100mm/s with the J head at 220C but it will start to drop to 216 once it reaches 100mm/s. Not that I would print ABS at that speed but just saying its doable.

I dont think its the Jhead thats giving you issues but more so the mechanics, if you took the idler off the extruder can you push the filament through the tip with ease? or is a ton of force required.

---

___________________________________________________
Kreativ-e
Tinkerine Studio

Hey ECSuyu, i don't think the problem is with my idler pinching too tightly, i have loosened it all the way until it starts to strip the filament and it still has the same problem.

I also took off the idler and tried pushing it by hand (which i have done before) and it is VERY hard to push... i basically push as hard as i can and it still comes out REALLY slow.

So i do feel like it has to be something with my hot end... either somehow there is excess resistance in there (maybe due to the fliament getting too soft too early), or the melt zone is so short that it can't melt the plastic very fast, or somehow my thermistor is bad, or i have the wrong thermistor table choosen in my firmware (Marlin firmware with thermistor #1 choosen which is the 100k thermistor). I doubt my thermistor table is wrong though because it matches exactly the one listed here [reprap.org] unless i have a different thermistor than i was told i have.

Ok, so this is super embarrassing, but I just realized that my J-Head Mk IV-B ACTUALLY has a .35 nozzle, haha!

I could have sworn when i ordered it from here [www.reprap-usa.com] it said it had a .5 nozzle, but i just measured the fillament extruded into air and it comes out anywhere between .37 and .41, so it would have to be a .35 nozzle. And I double checked the description on the website and it says a .35 nozzle is included.

SOOOO, the fact is that it STILL takes a lot of force to push the filament through by hand, but maybe that makes more sense with a smaller nozzle.

I am mostly using Slic3r to generate my gcode and have the nozzle size set to .5, so would that cause gcode to be generated that would try to push out plastic quicker than is possible for a .35 nozzle?

Any other thoughts now that we know i have a .35 nozzle?

Edited 2 time(s). Last edit at 03/12/2012 01:39AM by daufhammer.

with the 3 J-heads I've used, there has been no problem and they are all 0.35mm. The calculation for the extruder generated by slic3r would have been thrown off due to the 0.5mm nozzle input.

When taking off the idler and free pushing the filament in by hand, there should be some resistance but it shouldnt require a tremendous amount to start to see the filament coming out the tip of the nozzle in a constant flow.

PLA does get soft fast. and without a fan at the flutes on the MK IV-B PLA will get way too soft to extrude and jam up. Even with ABS I am printing with a fan on the flutes

---

___________________________________________________
Kreativ-e
Tinkerine Studio

Thanks ECSuyu, that makes sense. I will also have to try a fan again over the cooling flutes i imagine that will help stop the PLA from softening higher up on the hot end and decrease the resistance i am getting.

I changed my nozzle size in Slic3r to .35 and things seem a lot better! I tried a part with a long runs of infill and my extruder motor isn't skipping steps anymore, so it seems like the problem definitely was my nozzle miscalculation and before the change the extruder was trying to push too much fillament out too small of a hole too fast!

My parts do seem a bit overfilled on 100% infill on the top and bottom layers. I probably need to go and re-calibrate things again.

I ordered a 0.5 mm nozzle to use with 1.75 mm filament, my filament measures out at 0.60 mm through the J-Head. I have tried 5 different hobbed bolts in two different extruders, both loose and tight on the idlers. I have pushed the filament by hand and it is more difficult to push through than my 0.50 mm Budaschnozzle. When it does work for a few minutes, it eventually puts a kink in the filament and that stops it from flowing all together.

Not sure what else to try so I ordered another Budaschnozzle.

Roy

Hi, I'm using the J-4B head and I have no problems, I'm happy with it, but I can not make overhangs provided air layers fall, not subject, I am printing at 210 degrees Celsius, with ponterface and skeingforge, I can do?

Miguel Angel

I have to admit that I did not try a fan on the flutes of the JHead. with temps at 230-240 C, it was hard to push the filament through by hand and turning the big gear by hand although it would push the filament through. Purging using the motor it would eventually kink and jam.

Roy

Did you use the aluminum mounting plate that he's also selling in hotends.com? I wonder if this plate would be enough of a heatsink to dissipate the heat even without the fan. Another thing that might be worth doing is to wrap a heatsink around the PEEK above the flute.

I tried it with a homemade mounting plate, made from a fender washer... with a hinged extruder and then with a non hinged I printed an extruder that had a clamp to hold the PEEK onto the extruder... NO mounting plate.

My thought was that the fender washer might have sucked too much heat away from the nozzle, so I thought I'd try without any extra added metal.

Both had a difficult time feed the filament through and the filament kinked which caused the jam up.

Did you replace the PTFE liner with an appropriate sized liner for use with 1.75mm filament? J-Heads only come with 3mm liners....

Just a thought.

Yes, I replaced the liner.

Brian saw this thread and he is going to send me another nozzle to see if that is the problem.

Thanks everybody for your suggestions.

Roy

Where does the filament kink? The feed path should be about 2mm all the way up to the where the hobbed bolt meets it. There shouldn't be room for it to buckle.

---

[www.hydraraptor.blogspot.com]

It kinks just below the hobbed bolt, just enough to stop the filament.


Roy

Is this with a standard Wade's extruder?

---

[www.hydraraptor.blogspot.com]

Standard and hinged, both.

For what it's worth I have a jhead mk4 .35mm and I had the exact same problem, very hard to push filament through manually an extrusion issues. I heated up the hot end, stuck a filament of wire in the nozzle and wiggled it around a bit, cleaning out the nozzle. It now extrudes with almost no force at all manually and I have no issues extruding. It does seem to ooze a lot, however.

PastaRocket848, that's helpful to know, I'll have to try sticking some thin wire up the nozzle to see if things were a little clogged up. I didn't even think to check if my nozzle was clogged/partially clogged or not because it was still extruding (i figured it would either extrude or be jammed, didn't think there could be middle ground).

I was also thinking about how to determine how much force is "normal" to push the filament through the hot end because i have been struggling with whether or not the force I need to apply to manually extrude from my hot end is "normal" or if there is something wrong... I figured as the nozzle hole gets smaller, the force to extrude the same amount will have to increase, if the speed and temperature are kept the same.... If you think about it as a percentage it may help gauge how much force is "normal"....

So say you had 3mm filament, and a 3mm nozzle hole (crazy i know), but that would take 0 or no force to extrude... if you decrease the nozzle size to half that, so a 1.3mm hole, that would require 50% more force. So just doing the math, 3mm filament pushed through a .35mm hole would require 88% more force than a 3mm hole with no resistance.

So as i push my filament through by hand, it seems the force that i am needing to apply feels about right when i think about it in those terms. I know this is all relative (and probably too idealistic by not factoring in how quickly the plastic can melt, etc), but i think it has helped me determine there is probably nothing wrong with my hot end.

Does that logic sound right or am i way off here?

The pressure to push the plastic through the nozzle exit actually goes up with inverse fourth power of the nozzle diameter. However, a lot of the force to push the plastic is actually at the transition zone where the diameter is bigger but the plastic is much more viscous.

---

[www.hydraraptor.blogspot.com]

I was going to use one of my 0.5mm drill bits to clean out the nozzle. I bought 10 of them off of eBay a few months ago, they came in this minuscule little tube. The tube was so small, no I cannot find it

I should be getting the replacement nozzle from Brian today or tomorrow. I will report back my results.

Roy

i dont know what is "normal"... but with my 3mm filament and 0.35mm nozzle the weight of my hand is nearly enough to push the filament through. i don't have to push on it barely at all.

My experience with normal non clogged extrusion is the same as pastarocket. hold onto the filament going into the extruder and just rest my arm and let gravity do the work. That alone is more then enough to start extruding.

---

___________________________________________________
Kreativ-e
Tinkerine Studio

This can be done quantitatively by either using a force gauge or weights on top of the filament. One can measure the minimum force required to extrude at a given temperature. This way, it would be easier to make an objective comparison of different hot end designs.

Roy,

Did the new nozzle help things out? I am having the same issue. Lots of force required to push filament through.

Using the J-Head Mk IV-B .35mm with 3mm filament.

Might I ask for those who are having J-heads that are hard to extrude. Did this happen at the beginning? or did it gradually become hard to extrude. I find out of the 3 J-heads I use I have to clean the nozzle every once in a while (few months with it printing 8-12 hrs daily) to keep it going strong. That's to say, taking it off and dipping it in acetone for a few days. I dont know the cause of this, but it might have to do with the ABS I'm using

---

___________________________________________________
Kreativ-e
Tinkerine Studio

Mine was hard to extrude from the beginning.

ECSuyu: I haven't received the new nozzle yet, I bet it arrives today.


Roy

Edited 2 time(s). Last edit at 03/15/2012 08:26AM by roygpa.

i ran into extrusion problems yesterday while using a fan to cool the pla (weird, right? wouldn't extrude with the fan.. shredded the filament). i found that my nozzle had become difficult to push filament through once again, as i suspected due to the extrusion issues. i did the same old trick... a filament of wire up the heated nozzle, and it was back to normal in no time. once again it requires nothing more than the weight of my hand to push the filament through.

it may be worth doing as routine maintenance on the smaller nozzles. works like a charm for me.

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.