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Filament extrusion Failed.. Need help

Posted by dwonh 
Filament extrusion Failed.. Need help
September 23, 2013 03:59AM

I've been building my own 3d printer from the scratch.
Now, I managed to build up everything and did filament extrusion test.
Unfortunately is did not work well.
Extruder alone seems to work well to see pull filament with quite a torque(subjectively of course) while holding filament with hand
And as for the hotend, if I push filament with hand it extrudes ABS filament well.

I was trying to figure out the cause and also did disassemble/assemble again to check any wrong inside hotend.
I'm guessing torque of stepper might not be enough for direct drive (2.3 kgf.cm / 33 oz.in), but I choose this motor because someone using it with direct drive motor also.

Could you give me a any clue for me to solve this problem?
I'm completely stuck now.

Here are the spec of my printer and test numbers.

- extruder motor: NIDEC KH42JM2-901 (2.3kgf.cm)
- driving gear: MK8 (from reprap.me)
- hotend: J-head (1.75 / 0.35 orifice)
- bowden style.
- ABS 1.75mm
- Temperature: 240 degree
- firmware: marlin
- host-software: repetier-host
- feed rate: 50mm/min ~100mm/min at the manual control menu of repetier.

Any help would be very appreciated!

Thank you in advance.
- Dongwon
open | download - IMG_1093s.JPG (205.9 KB)
open | download - IMG_1094s.JPG (200.2 KB)
Re: Filament extrusion Failed.. Need help
September 23, 2013 06:57PM
That's a nice looking printer. However, 2.3 kgf*cm is not enough torque on the motor for direct drive. You want a motor that is rated for 4 to 5 kgf*cm.

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Re: Filament extrusion Failed.. Need help
September 23, 2013 08:57PM
Thanks Cameron,

Yes, I assume torque is the problem.
But, 4~5 kgf*cm isn't overkill for 1.75mm filament?
I saw qu-bd extruder motor is around 2.8kgf*cm. Design of my extruder is same as qu-bd's
It is very hard to source over 3.5kgf*cm NEMA 17 motor here in Korea.

Edited 3 time(s). Last edit at 09/23/2013 09:08PM by dwonh.
Re: Filament extrusion Failed.. Need help
September 23, 2013 09:42PM
Detach it from hot end --- see how well it feeds the filament in the same curve.
If that is OK -- hook it backup -- crank up the temp maybe 225deg C
Extrude and measure current motor drawing
Tweek up drive electronics voltage
"The Vref signal is accessible as the "VREF" pin on the carriers with voltage regulators,
as the through-hole via on the carriers without, and also as the wiper on the trim pot itself on both carriers."
Adjust pot for proper voltage, If motor is buzzing increse or decrease pot

Decrease the temperature to your working temp
and do above again

Then again the Hobbed gear may be bad or idler pressure on gear not enough
I don't see any way to adjust idler
What brand of coldend / hotend extruder?

Have Phun
Re: Filament extrusion Failed.. Need help
September 23, 2013 11:12PM

Thank you for your kind reply.

Extruder feeds filament well enough without hotend (extruder + bowden cable only).

And when I push filament with hand directly through hotend(240C) it extrude ABS well, though it is tough.

I made extruder based on qu-bd or Makerbot design, and use 'ball plunger' to push filament towards gear.
It works quite well, it can pull filament with quite force while I'm holding filament.

I'll check the current setting like you said, and I'll try another high torque motor if fail again.
3.6kgf*cm stepper is best that I can buy here. hopefully it works.
Re: Filament extrusion Failed.. Need help
September 24, 2013 12:19PM
The ball plunger doesn't work well.
Replace it with a idler roller with an adjustable spring tensioner.
Consider a different hobbed gear

SeeMeCNC has a good one


and the SeeMeCNC Ezstruder great

Re: Filament extrusion Failed.. Need help
September 25, 2013 05:34AM

The ball plunger is bad because too much friction against filament?

I tested with new motor which is 1.5 times stronger than previous (3.6Kgf), only failed again.
Drive gear is slipping when filament reaches near melting zone of hotend. Actually it shaves off the filament.
I guess torque of motor is enough.

I think I'd better go for spring hinged extruder, coz I don't know what to do next.

Thank you.
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