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[PRUSA I3]: Direct extruder

Posted by aj.moreno 
[PRUSA I3]: Direct extruder
January 14, 2014 05:16AM
Hi,

I have built a direct extruder similar to this (http://www.thingiverse.com/thing:147705/#files), but I am using a j-head extruder and PLA filament. My problem is that, when I start with the extrusion, this makes fine the first two extrusion commands, but then the extruder motor starts to vibrate and it does not extrude. the sensation is as the motor does not have enough force, but I have seen other direct extruders with the same motor NEMA 17 and they works fine. I have modified extrusion speed, extruder motor (NEMA 17 3.4kg/cm2 and 4.8kg/cm2) and pololus driver adjustment, but I have no success.

Please some help! Thank you very much!
Re: [PRUSA I3]: Direct extruder
January 14, 2014 06:40AM
is it a genuine jhead?




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Re: [PRUSA I3]: Direct extruder
January 14, 2014 06:47AM
Sounds like you need increase the current using the trim pot on the driver. Do it slow and in small increments until it works reliably. Then keep an eye on it for a while to make sure nothing is getting too hot.
Re: [PRUSA I3]: Direct extruder
January 15, 2014 07:29AM
Hi,

thank you very much for your answers. I just read this post from [www.thingiverse.com], which is probably the problem: the strengh is not enough:

Hi,
I am even not going to test 3mm filament with Nema17 smiling smiley.
My rationale is that: average max torque of nema17 motors if ~0.45Nm, even with small drive gear with 7mm diameter we would have max theoretical torqe ~13KG. From my experience with 3mm filament and geared extruders torque ~20KG is needed, so when we substract gear train inefficiencies,..., and friction ~10% (because of direct drive extruder has no such gearboxsmiling smiley ) we will have ~18KG. So it is why I have designed Nema23 version, you can easly get 0.6Nm which is not so heavy ~ 0,6kg, which fullfill such requirement.
Re: [PRUSA I3]: Direct extruder
January 15, 2014 04:22PM
So, in short, you're trying a 3mm filament extrusion with a Direct Drive? Because anyone knows that that doesn't really work out with a NEMA17 stepper..
Re: [PRUSA I3]: Direct extruder
January 15, 2014 09:19PM
Of course direct drive extruder works with 3 mm feed. I use a direct drive NEMA17 extruder that i designed paired with a Mk IV J-head to print with 3mm ABS routinely. When the j-head is working well, it can extrude at up to 150 mm feed/min. The trick is to use a small diameter filament drive. I use an 8 mm bolt that has been knurled with a v-groove mounted on the motor shaft which should be equivalent to the MK8.

Edited 2 time(s). Last edit at 01/16/2014 03:49PM by brnrd.
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