I'm new to PLA. Please help me out here...

My printer has been in the garage all summer because I print ABS which makes for some potentially unhealthy fumes, and because the machine is pretty loud. It's getting cold outside, so I just moved the printer back into my basement workroom which has no ventilation. I decided to try printing with PLA, hoping it might be a little less hazardous to my health.

No problem- I loaded the filament and it printed fine at 190C on a room temperature print bed covered with blue painter's tape. I got perfect results, as usual.





Then the trouble started. I decided to put a spool of ABS back on the machine. I heated up the extruder and retracted via the LCD panel and the PLA got stuck tight in the hot-end. For the first time since I put the hot-end and extruder on my printer last December, I had to take them apart to get the PLA filament out. What's the proper technique for changing filament with PLA?

Thanks!

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

I just cut it off, right above the cold end and feed the ABS through until the PLA is gone.
If possible at slightly lower temps to prevent the PLA from burning black.
Never actually tried removing the filament to get the new filament in.

That's not going to be good. There's no way for me to reach the entrance to the hot-end except to take the extruder off the machine then separate the extruder and hot-end. Ugh!

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

What might have happend is that the retract was so slow that the soft PLA hardened and formed a blockage befor it was completely free. If you have an option to release the idler and pull the filament by hand you might try that. If it is a bowden setup try to pull it through fast in one go.

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[www.bonkers.de]
[merlin-hotend.de]
[www.hackerspace-ffm.de]

On my current hot end, pulling PLA back out (e.g. to change colour) sometimes causes it to jam. After a bit of trial and error, I found that pushing the PLA down to extrude a bit, then quickly pulling it out works.

If you can't go through you go back
As Frankvdh said, a quick pull usually frees the filament.
With my bowden system I used to heat the hotend while already slightly pulling on the filament, as soon as it started to moove I pulled really fast.
This way the filament has no real time to heat up and most of the plastic should come out in one piece.

I've been printing ABS for almost 3 years and had no idea that people who were printing PLA had to do this sort of stuff just to get the filament back out of the hot-end. Hmmmm. This sounds like an engineering challenge...

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Quote
the_digital_dentist
I've been printing ABS for almost 3 years and had no idea that people who were printing PLA had to do this sort of stuff just to get the filament back out of the hot-end. Hmmmm. This sounds like an engineering challenge...

It's really quite easy. The main thing to remember is not to retract and unload the filament at printing temperature. Use 100 to 120C instead.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

That was the first thing I tried and it jammed. I think the retract speed may be too low when using the menu selection on the LCD panel. I'll have to see if there's a way to change that speed. Thanks!

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

I experience exactly the reverse, I have no problem retracting pla all the way out of the bowden tube but abs always seem to get stuck after 10mm retraction. Could it be that the nozzle cavety or melt zone has a slightly bigger diameter than the heatbreak? I can remove it by decoupling the bowden tube and use pliers on the top of the extruder clamping the filament and rotate up the pliers resting its mose on the extruder for leverage. When pulled out a thickened blob is clearly visible, the size of the nozzle cavety. It's a bit more hessle but I've learned to live with it.

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Kind regards
Imqqmi

NFAN CoreXY printer:
[reprap.org]

I'm using an E3D v6 hot end and the heat break tube goes down to the nozzle as one fixed diameter. The hot end mounts on the extruder (BullDog XL) making it hard to access the top of the hot-end directly. I'll try pulling the filament with pliers from the top of the extruder. Thanks!

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Quote
the_digital_dentist
I'm using an E3D v6 hot end and the heat break tube goes down to the nozzle as one fixed diameter.

I have been told by an E3D distributor that the inside of the E3Dv6 where the Borden tube stops is chamfered, so the Bowden tube end should be tapered too. I mean to try this soon. It will hopefully avoid leaving an area where a bulge can form You can taper the end of a piece of PTFE tubing using a pencil sharpener.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

@DC42: thanks for the tip, I use a pencil scharpener on my filament to get it through all the obstacles, and one was the entry into the cold end. Good idea to chamfer the bowden tube

@TDD: I use the E3D V6 bowden too, here are some pictures what the 'plug' looks like:

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Kind regards
Imqqmi

NFAN CoreXY printer:
[reprap.org]

Great quality photos! That ledge would certainly explain some difficulty in extracting the filament from the hot-end. I'll try pulling the filament again and take a closer look at the end of the filament and the pieces in the hot end. Thanks!

Edited 1 time(s). Last edit at 11/21/2015 01:51PM by the_digital_dentist.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]