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Force required on filament to extrude?

Posted by kickinthethroat 
Force required on filament to extrude?
April 13, 2013 09:52AM
Hey all,

I just want to know how much force is normally needed to push a 3mm filament through a .4mm nozzle? I'm using ABS, and it seems like the force required is excessive... turned up the heater to 240C, and it still requires a lot of force.
Re: Force required on filament to extrude?
April 13, 2013 11:09AM
I took off the hobbed bolt and it still requires a lot of force to get a constant flow. I push the filament in with some resistance, get a little flow, but then pushing on it really hard creates no additional flow. Any suggestions?
Re: Force required on filament to extrude?
April 13, 2013 04:11PM
Have you checked that your nozzle is not clogged?
Re: Force required on filament to extrude?
April 13, 2013 04:15PM
Maxx Mayhem Wrote:
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> Have you checked that your nozzle is not clogged?


Thanks for the reply.

Well it does ooze out some before it becomes hard to push. I assume if it was clogged, I wouldn't be able to get any of it to come out?
Re: Force required on filament to extrude?
April 13, 2013 05:40PM
I've heard that it shouldn't require much force to push it through, but I have to push pretty darn hard to get anything to come out (to the point that I worry about stressing the Z couplers or bending the X smooth rods). The motor, on the other hand, has no trouble pushing it through and I can print without problems as long as my idler springs are as tight as they'll go. If my idler springs are the least bit loose, it will skip and grind PLA into my hobbed bolt and ruin the print. I recently installed a "filament cleaner" which is just a piece of lint-free cloth zip-tied to the filament right before it enters the extruder, so I hope that will keep my nozzle from getting clogged and anything that may already be in there will work its way out. We'll see.
Re: Force required on filament to extrude?
April 13, 2013 06:17PM
Yes! That's very similar to me before today... I would have to tighten the coupler until the springs were completely compressed then it would go OK (maybe 2 print attempts total). Today though, I had it so tight the stepper motor was skipping.. So maybe I do have a clog?

I'm thinking about getting a new extruder plastic part... My nut locks are all stripped on the one I have and the nuts sometimes turn as I tighten... I've had to drill out the holes on the idler to get the screws to fit, and i don't think the idler slides on the screw correctly... Even though with the springs fully compressed there isn't much sliding anyway. Maybe it would be easier to go all metal on the extruder?
Re: Force required on filament to extrude?
April 14, 2013 08:16AM
There is an all metal extruder now available, but do you have a fan to cool your upper part of your nozzle. When you retract, if the upper nozzle is too hot, it will prematurely melt your filiment and could cause the issue you are having.
Re: Force required on filament to extrude?
April 14, 2013 09:09PM
Maxx Mayhem Wrote:
-------------------------------------------------------
> There is an all metal extruder now available, but
> do you have a fan to cool your upper part of your
> nozzle. When you retract, if the upper nozzle is
> too hot, it will prematurely melt your filiment
> and could cause the issue you are having.


Thank you so much for this info. I do not have a fan, and I'm using a jhead. Should the fan be aimed at the 'shaft' of the jhead then?
Re: Force required on filament to extrude?
April 15, 2013 10:43AM
When printing PLA, you should actually have two fans, one aimed at the "shaft" to prevent jams and one aimed at the print to help with bridging. I'm just using one right now, but I can definately see where a second fan would help (although I can print the "bridge torture test" just fine without the second fan, it would help with sagging). The fan that's aimed at the "shaft" can just be connected to 12v and doesn't need to be PWM controlled by your slicing software. If you're using a fan on the print, it should be wired for PWM control and you should update your cooling settings in whatever slicing software you're using to get good results.
Re: Force required on filament to extrude?
April 15, 2013 03:29PM
Hi there,
If you try to manually feed filament after a startup from cold, where the insulator (PEEK) hasn't heated, but the hot-end is up to temperature (230deg or so) does the filament push through relatively easily then?
If it doesn't feed manually, when the PEEK is still relatively cool then there are a few things to check.
Have you measured the filament diameter with a digital vernier, checking around it in cast it's oval in shape? I've had filament that was slightly oval and it pushed to 3.2mm in places, and it jammed in my j-head. The PTFE liner in the j-head is 3.2mm max internally.

If it's hard to feed (again when the PEEK is cool) then perhaps the locking hollow set screw at the top of the PTFE is too tight, causing the PTFE liner to compress on to the filament.
Which J-head do you have? The v4 has a taper at the base of the PTFE and too much pressure on the set screw will narrow the taper as it it is forced into the cone in the brass hot-end.

If is a relatively new setup or was it working ok, and then started to worsen?

Cooling the j-head with a fan is a good idea in my opinion, but when printing with ABS it's important that no stray airflow heads down towards the nozzle. It will cause you problems with the first layer sticking if it does.

It only takes firm hand pressure to feed filament through when all is good.

Best of luck with it.
Regards,
NumberSix


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