Problems feeding flexible filament

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Toby
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Problems feeding flexible filament

Post by Toby » Sat Apr 26, 2014 8:46 pm

I'm trying to use some flexible filament (Flex Polyester) and running into problems feeding it.

The manufacturer recommends 205-225, so I started at 225 for the v3b It went in ok for about 30-40 mm, but then the gears started skipping and I never got anything to extrude. When I retracted it was ok for about 20-30 mm but then started skipping again. I could go forward and backward in that range without skipping but that's it.

Eventually I managed to pull it out and then the gears ran ok. I tried to feed it by hand without the filament tube, but the same thing happened. Then I I tried to run some PLA through it (bright idea #1), but the gears skipped almost immediately. The filament showed a decent bite at first but now when I try to feed it won't go in at all.

The gears sound fine when there's no filament, but otherwise they just skip and don't pull it in. I'm pretty clueless about where to go with this- any ideas?

Edit: I shut it off and had a look at the gear- some of the flex filament was coming out of the front. I pulled out a string of it that must have been wound around the gear in back. So it looks like it never made it into the hot end.

But I'm still having problems feeding PLA. It goes in a ways but then gets stuck and either won't go any further or else the gears start skipping again.

I took off the new hot end and there doesn't seem to be anything in there. I can feed PLA into it about as far as you'd expect it to go cold.

Is there some trick to making sure the hotend lines up with where the filament exits the extruder? I just pushed it in as far as it would go. There was no "click" or anything.

I'd like to run some filament through the extruder with the hot end off so I can see what's happening in the gear. I know I have to send some gcode or other to allow the firmware to extrude cold, but is it a bad idea to do that for some other reason?

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Tim
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Re: Problems feeding flexible filament

Post by Tim » Sat Apr 26, 2014 9:12 pm

Are you printing at the VERY slow speeds required for flexible filament, like 25mm/s, which is what Jim recommended to me?

Toby
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Re: Problems feeding flexible filament

Post by Toby » Sat Apr 26, 2014 9:32 pm

Tim wrote:Are you printing at the VERY slow speeds required for flexible filament, like 25mm/s, which is what Jim recommended to me?
I'm not at the printing stage yet. I haven't been able to get it to feed into the nozzle to the point that I can extrude. Do I need to slow down the feed rate even when I'm just loading the filament for the first time?

The situation now is that I can see there's a bit of the flex filament caught in the extruder gear but I can't get it out with tweezers. The gear turns fine and I can feed PLA through it, but I'd rather clean it out. Is there something I can do short of taking the extruder apart that will increase the chance I can pull that bit out with tweezers? My guess is it's wound around the back of the gear.

Toby
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Re: Problems feeding flexible filament

Post by Toby » Sat Apr 26, 2014 10:37 pm

So I took the extruder apart and cleaned the gear out. I'm now experimenting with the hot end off and seeing if I can get a sense of the best way to extrude this stuff. It's so soft that it seems impossible for it not to go limp and back up eventually.

I notice what looks like a tensioner on the right hand side of the extruder mount. Does that make a difference for soft filament?

I wish I could feed the filament into the hot end by hand before putting the hot end back on, but I can't see a way to do that.

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jimc
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Re: Problems feeding flexible filament

Post by jimc » Sun Apr 27, 2014 4:13 am

Flexible stuff can be tricky. On an occasion i have gotten the filament all wrapped up around the gear. Only thing to do is remove the filament drive and clean everything out. Usually when the peek is put all the way back in the groove then the hole should line up. Pull the peek out letting the hot end hang. Turn the heat on and jog the extrude to feed the filament. It should come out the bottom hole of the filament drive. Once you get it there jog it back up so it just disappears into the fildrive. Grab the peek gently with a pair of pliers and put it in the groove. Hit extrude and feed it into the hot end. You should be good at that point. Once you get it to extrude put the fans back on.

Toby
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Re: Problems feeding flexible filament

Post by Toby » Sun Apr 27, 2014 7:35 pm

I'm about ready to give up on this stuff. With the hot end off I can get it to feed through the filament drive. But as soon as I put the hot end back on it just ends up winding around the gear instead of feeding into the hole.

I measured the filament diameter and it doesn't look consistent. I get anywhere from 1.77 to 1.91. So maybe that's it.

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ednisley
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Re: Problems feeding flexible filament

Post by ednisley » Sun Apr 27, 2014 8:51 pm

Toby wrote:winding around the gear
Back in the day, several folks made dual-sided drives that gripped the filament on both sides, rather than mashing it against a smooth bearing. Stacking the two drive splines:

http://www.thingiverse.com/thing:27654

probably isn't any better than a single spline, but somewhere in the Thingiverse pile I saw one with opposing drive shafts ("hobbed bolts") capturing the filament between them. IIRC, it was unstoppable and tended to not strip the filament. I vaguely recall a pair of outboard gears driving the shaft gears from a common stepper motor, which would allow center-to-center distance adjustment over a reasonable range; you couldn't do that with two directly linked gears.

Perhaps an extruder specifically built for bendy filament would make it less annoying?

Toby
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Re: Problems feeding flexible filament

Post by Toby » Sun Apr 27, 2014 10:07 pm

ednisley wrote:[Perhaps an extruder specifically built for bendy filament would make it less annoying?
Sounds good based on my experience so far. It seems that the stuff is so soft that when it goes through the gear the tip gets mashed and then when it tries to enter the hot end the slightest interference makes it buckle. There's not much space from the gear to the hot end, but something that would reliably guide it into the hole might help.

I wouldn't mind threading it by hand just to get it to print, but I can't see how given the way the hot end slides in from the front.

Edit: I think I just found a way to get it started. That cylinder that presses the filament against the gear (sorry don't know what it's called) can be removed. So I think I can take off the filament guide, thread the filament through it and into the hotend, then pull the filament back into the empty space left by the cylinder enough that I can re-install the filament guide over the gear and press the cylinder back into place and Presto! It's through the gear and into the hotend.

So much for theory... I'll try it later tonight and see what happens.

Toby
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Re: Problems feeding flexible filament

Post by Toby » Mon Apr 28, 2014 4:59 am

After taking the filament drive apart and trying to feed the flex filament by hand it's pretty clear what's going on: the hole into the hot end is not perfectly aligned with the hole exiting the filament guide. It's close enough for PLA to be forced to go through, but not for this soft filament, which just buckles. When I remove the hot end and feed the filament into it by lining it up by sight, it goes in no problem. But put the hot end back on the filament drive and it doesn't go.

So right now I'm annoyed with the filament drive housing. Being 3D printed on an M2 isn't accurate enough for this case. I think that's the only problem here.

Maybe it would work to send the filament drive housing STL out to a high-accuracy printing company? Or is there a better design that I can print that would solve this particular problem? It's hard to see how to make sure the holes are perfectly lined up just by a design change. It needs to have the accuracy built in I think.

I'm tempted to widen the hole in the hot end just at the very top, but would I risk ruining the hot end by doing that? I have a dremel I could use on it that I assume would do the job in some fashion.

jsc
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Re: Problems feeding flexible filament

Post by jsc » Mon Apr 28, 2014 5:22 am

Toby, try rsilvers' filament drive (http://www.thingiverse.com/thing:267137) and see if it works better for you. It has increased coning and filets on the bottom hole to allow more leeway for getting it to feed. I have been using it happily, although only for PLA and ABS (there was nothing wrong with my stock drive, I just wanted one in red).

When I look through my stock guide, I can visually sight through the hole, so I don't think it is an alignment issue. The gear does tend to push the filament off from true. Two other things I can think of to try:

1. loosen the tension adjuster all the way before feeding, then retighten (untested supposition).
2. feed the filament off the gear into the hot end, then mount it. A friend with an M2 has done this successfully.

But really, try the alternate drive, it should help....

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