Changing filament by going forward, not reversing out?
 

Changing filament by going forward, not reversing out?  

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john.a
(@john-a)
Eminent Member

I saw this technique talked about in another 3D printing forum, but I think it was a different type of machine. I was wondering if it might work for the Prusa i3 Mk2?

When changing spools of filament, instead of unloading (reversing) the old filament and loading the new filament, some folks were suggesting this:

1. With the printer heated to working temperature, cut the filament off just above the feeder input hole.
2. Prepare your new filament and square-off the end.
3. Then manually run the extruder, pushing the new filament in right after the end of the old filament.
4. Continue running it through until you see your new filament emerge.

This avoids the possibility of leaving gooey filament in your Bowden tube when you back it out. The printer just thinks it is printing one continuous strand of filament.

Would this work for the Prusa? Does it need to know when a spool of filament is changed? I'd like to try this, but I'm a newbie and I would hate to screw something up (especially since I just got it printing again after about two weeks of down-time).

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Posted : 27/10/2016 10:23 pm
PJR
 pjr
(@pjr)
Antient Member Moderator

John

The PTFE tubing within the extruder body is not a "Bowden Tube"; that is the PTFE tubing employed to carry the filament from a remote extruder motor to the extruder body, as in the new multi-filament upgrade.

Your suggestion can work; it can also on occasion go horribly wrong when the filament misses the PTFE tube because it is not pointed. I did use this method on a Chinese clone but it has proved less successful with the "Original" and I no longer attempt to change filament using this method.

Peter

Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…...
Posted : 27/10/2016 10:53 pm
john.a
(@john-a)
Eminent Member

The PTFE tubing within the extruder body is not a "Bowden Tube"; that is the PTFE tubing employed to carry the filament from a remote extruder motor to the extruder body, as in the new multi-filament upgrade.

Ah, thanks for the clarification, Peter. I'm afraid that is my newbism showing--I have been using those terms interchangeably.

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Posted : 28/10/2016 1:15 am
MrMik
(@mrmik)
Honorable Member

I tried something similar today and it did not work.
I cut the old PLA filament off, then dialled "Load filament" and stuck the new one in. No success. Then I cut the new filament squarely, it still did not work.

I had to unscrew the spring loaded screws and pull the old filament out with long nosed pliers.

Next time, I might try to melt the two filaments together, then use Settings>move axis>extruder to gently move the fused filament into the extruder.

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Posted : 28/10/2016 9:54 am
PJR
 pjr
(@pjr)
Antient Member Moderator

Michael

The problem with using the "Load Filament" option is that the first stage is too fast to push the filament in the extruder body out of the nozzle. You need to do this slowly; it really is far better to unload then load.

Peter

Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…...
Posted : 28/10/2016 10:32 am
patrik.r
(@patrik-r)
Reputable Member

When we are on the topic of unloading. Am I the only one who have the problem with the unload filament process being to quick?
If I just choose "unload filament" the feeder spins really quick but not long enough to get the filament out.
I have to either do the unload filament process twice in a row, or with my fingers gently "help" the filament to unload at the same time as I let the feeder wheel do its thing.

This works fine for me but it is an issue when using the "change filament" function. If you're not helping the filament to be unloaded your'e pretty much stuck, and the only thing you can do is to answer YES on the question, load the filament again, let it start the print for a few seconds and then repeat the "change filament" function but make sure that you help gently pulling out the filament when the feeder starts to spin.

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Posted : 28/10/2016 4:14 pm
JohnOCFII
(@johnocfii)
Estimable Member


I have to either do the unload filament process twice in a row, or with my fingers gently "help" the filament to unload at the same time as I let the feeder wheel do its thing.

I've been in the habit of helping it unload, and also feeling the filament as it loads.

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Posted : 28/10/2016 7:57 pm
stephan.k
(@stephan-k)
Reputable Member

When we are on the topic of unloading. Am I the only one who have the problem with the unload filament process being to quick?
If I just choose "unload filament" the feeder spins really quick but not long enough to get the filament out.
I have to either do the unload filament process twice in a row, or with my fingers gently "help" the filament to unload at the same time as I let the feeder wheel do its thing.

Same problems here. I turned to "helping" as well.

In some very rare instances the molten end of the filament is deformed and gets stuck in the hole up there, forcing me to unscrew the extruder and pull it out that way.

I also have problems loading filament if I forget to cut the tip at the proper angle when loading.

And while we're at it: its not that good for flexible filaments either

Overall, i am not terribly thrilled with this extruder. If i wasn't waiting for the 4 color upgrade anyway, i'd be starting o look for a replacement, maybe try to fit a E3D Titan or somesuch.

Posted : 30/10/2016 12:40 pm
peter.j3
(@peter-j3)
New Member

I have a Original Prusa 3d Printer MK2 and when I unload the filament most of the time it only pulls back maybe 1cm, and I have to repeat the unload several times before the filament finally comes out
This is ok, except that sometimes it comes out all the way on the first try, but that makes me wonder if I'm doing something wrong.

It also affects the "Change filament" option, because if the filament doesn't come out all the way on the first try, there is no option to repeat the unload again.

So the question is:
1) what can be stopping the unload from ejecting the filament totally on the first try
2) is there a way in the "Change filament option to repeat the unload part of it until all the filament is out

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Posted : 02/11/2016 6:51 pm
PJR
 pjr
(@pjr)
Antient Member Moderator

Peter

Sounds as though you may need to tighten the tensioners a little.

Peter

Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…...
Posted : 02/11/2016 7:08 pm
peter.j3
(@peter-j3)
New Member

Hi Peter, thanks for your suggestion. I tried tightening the tensioners a bit more, to about 9mm and it did not make a difference.

Observing the extruder motor pulley I noticed that it was only turning 1/4 to 1/2 turn each time I selected Unload Filament and making a grinding noise too. Once the filament was remove, after several unload operations, the motor turned about 2-3 full revolutions at what seemed to be a higher speed. That was with no load (no filament). I tried the to unload with the "High Power" setting, although I don't know if that applies to extruder motor as well.

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Posted : 03/11/2016 4:13 pm
PJR
 pjr
(@pjr)
Antient Member Moderator

Yes, there is a slight increase in motor power when using high power mode; probably won't make too much difference.

Peter

Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…...
Posted : 03/11/2016 5:12 pm
john.a
(@john-a)
Eminent Member

Since I had to disassemble the extruder carriage to clean out the PTFE tube, I've been really careful about not trying to change spools of filament when the nozzle is fully heated. Also, I have tried to minimize the number of times I change filaments, to the point where I have printed things in colors and materials I would have preferred not to--but I didn't want to have to change the spool. So I think I have only changed spools a total of three times in the past three weeks.

And now, despite all that, I seem to have another hard blockage in my PTFE tube, so now I get to take it all apart again. I tell you, I have just about had it with this design. This just clearly doesn't work. 😡

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Posted : 09/11/2016 7:29 pm
PJR
 pjr
(@pjr)
Antient Member Moderator

John

There must be something which is peculiar to your setup.

The new multi-filament upgrade will work on the same principle of extracting the filament at printing temperature; it has to work reliably every time

I would also add that I have not experienced any issues when changing filament - which I have done many times using ColourPrint (M600) GCode again at print temperature (although I do remember one user having issues).

In your instance I would suspect the PTFE tube is not square internally or it is not fully homed int the hot end.

Peter

Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…...
Posted : 09/11/2016 7:36 pm
john.a
(@john-a)
Eminent Member

I really don't know what I am doing wrong. Like I say, I changed the spool a maximum of three times before it clogged up. Three weeks ago when I had the extruder taken apart, the tube looked fine--exactly the way it does in the manual. I'm really at my witzend.

The multi-filament upgrade is certainly one I will not waste my money on. If I can't even keep just ONE filament running...

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Posted : 09/11/2016 8:47 pm
john.a
(@john-a)
Eminent Member

My printer has been idle for about a week now, because I just haven't had time to tear the extruder carriage apart to get to the PTFE feeder tube to try to clear it. But then I just had an idea--I was wondering if this might work.

I was thinking of getting a stiff steel wire that is smaller in diameter than my filament (maybe 1.25mm), and notching it down by the end, so that it has edges that can grab (like a fish hook). Then I hold a butane lighter over the end to heat it up to around 200 C degrees, then run it down from the top of the tube until it sinks into the plastic plug obstructing the tube. Allow it to cool, then pull UP with pliers to try to remove material out the top. Would that work, do you think?

I guess one concern I have would be scratching the interior of the PTFE tube, but I do have a 30cm length of replacement tubing, so it wouldn't be the end of the world...

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Posted : 14/11/2016 6:22 pm
Omikron
(@omikron)
Estimable Member

My printer has been idle for about a week now, because I just haven't had time to tear the extruder carriage apart to get to the PTFE feeder tube to try to clear it. But then I just had an idea--I was wondering if this might work.

I was thinking of getting a stiff steel wire that is smaller in diameter than my filament (maybe 1.25mm), and notching it down by the end, so that it has edges that can grab (like a fish hook). Then I hold a butane lighter over the end to heat it up to around 200 C degrees, then run it down from the top of the tube until it sinks into the plastic plug obstructing the tube. Allow it to cool, then pull UP with pliers to try to remove material out the top. Would that work, do you think?

I guess one concern I have would be scratching the interior of the PTFE tube, but I do have a 30cm length of replacement tubing, so it wouldn't be the end of the world...

It might work, but there's enough unknowns in that plan that your'e setting yourself up for more heartbreak I think. I agree it's a huge pain in the ass to tear everything apart, but at least that is a known procedure that will take a known amount of time.

Perhaps others who have had more experience with blockages can share their thoughts. When I had my blockage I ended up unscrewing the cold end from the heat break and pulling out the offending material with pliers.

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Posted : 14/11/2016 8:02 pm
bastian.m
(@bastian-m)
Trusted Member

Hey there,

i've actual the same problem with changing the filament.
I'm printing a cupholder for my car with ABS (at 240°). Its the second time i tried the ColorPrint-Feature (the first time, i tried it with PLA - it works).
This time, it goes wrong: As the others said, the printer unloads the filament (maybe 2cm?), but it stucks. I can't remove it manually and only be able to say "yes, color not clear and ... the third option".
So i had no other choice: Selected yes and finished the print with the same color.
It would be nice, if you could select "Unload again" in the menu.

Today, i tried it a second time - printed a 20mm cube, colorchange after 10mm Z: Same problem. Then i tried to change the filament manually over the menu; same problem - the filament "stucks" still in the Extruder, no way to remove it.

When i remove filament (abs and also pla) i select "unload filament", additionally i pull the filament out of the extruder.

Maybe, its time to use PETG instead of ABS, as patrik suggested in another post... :-/

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Posted : 28/11/2016 6:28 pm
david.b14
(@david-b14)
Honorable Member

Just as a data point, people having issue, did you order the kit or factory built?

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Posted : 13/12/2016 7:31 am
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