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Leaving filament in printer or not

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mgnbuk14/04/2020 10:45:47
1188 forum posts
71 photos

Very much just getting started with the Anycubic Mega I took delivery of recently & wondered how other, more experienced, users handle filament between jobs.

The Mega has a Bowden tube extruder & after my Benchy print I left the filament in place. The hot end was turned off straight away, and I left the fans running for several minutes before turning the power off. At that point I just had a couple of metres of the sample PLA left, so not leaving a full reel exposed to the atmosphere, which I understand can degrade printing performance due to moisture absorbsion.

Yesterday I managed (eventually - constraints are taking a bit of getting used to) to design a part in FreeCad, sliced it with minimal perimeters/infill to get something to print with the remaining PLA (still not got the 1kg that was part of the order - stuck in Germany according to tracking info) - and the print failed early on. All the hallmarks of a blocked nozzle, but it turned out to be the Bowden tube that was blocked with hardened, shattered pieces of filament. Cleaned out, it then ran the print OK until the filament ran out - very satisfying to make something 3 dimensional from scratch.

So from that it appears that I should empty the Bownden tube at the end of the print ? The filament that had been outside the Bowden tube seemd OK, but the bits that came out are very brittle. Have others had similar issues, or is it possibly just the particular filament that was supplied as a sample (in a vacuum sealed bag) ?

Comments welcomed.

Nigel B.

Rockingdodge14/04/2020 11:01:45
315 forum posts
72 photos

If it's brittle it usually is because it's old stock, I have a reel of white that's unusable due to that.

I have a printer in my spare bedroom, which gets the afternoon sun, and has a one kilo roll of filament permanently loaded. This has no issues but I do run through a couple of centimetres before printing if I haven't used it in a while. I also tend to check bed level before running as well.


Edited By Rockingdodge on 14/04/2020 11:02:49

Edited By Rockingdodge on 14/04/2020 11:06:14

Steve F14/04/2020 11:21:39
93 forum posts
25 photos


It might be the sample that has the problem. Before you use PLA try and break it . If it snaps easy then it's had it. If you then try a little further up you may find its ok from that point. Ive had some total rubbish filament from China that just breaks like spagetti.

I try to put my rolls away in a bag with silica gel when finished. The PETG lives in a dry box as that does like humidity. I now buy by own brand filament from 3Djake in Austria. I have a roll of PLA thats been out since October and tested it and it just bends doesnt snap.

On the subject of hot end. There are 2 fans one for cooling the part the other for the hot end. If you turn the machine off before the hot end has cooled the fan stops and residual heat travels up the hot end thru the heatbeak into the hot end body. This can cause filament in the heatbreak to soften and stick to the heatbreak. That can be difficult to shift because it doesnt get hot. its there to stop the heat



I.M. OUTAHERE14/04/2020 16:44:43
1468 forum posts
3 photos

I had a similar problem and it would even occur if i left it in there overnight and i thought it was moisture doing it .

I mentioned this to a person i knew who has many years of experience with 3D printing ( as a profession) and he said it was one of the funny things with PLA and some brands will do it , others won’t , he also stated it was more likely caused by stress cracks forming as the filament is being forced to comply to a different shape than what it is on the spool which is what it had when made - ie it is being straightened out by the tube .

I had a couple of cheap rolls that did this and changed to a known brand and the problem went away - i still remove the filament when i finish a set of prints as it could be weeks or months before i use it again , this is stored in an airtight plastic box with some moisture absorbent beads .

Martin of Wick14/04/2020 21:33:52
249 forum posts
5 photos

In the past, I used to leave the open spools (PLA) on the printer for months with a feeble attempt to cover/protect from sunlight with old box, paper bag etc.

However, recently noted two issues;

Where the filament run to the hotend had been exposed to sunlight, it had become brittle and snapped like cheap spaghetti, the stuff on the spool that had minimal protection was OK, I just determined the extent of the brittle section and cut it off.

When changing to a fresh spool of PLA of the same make, I noticed that the print made with the fresh stuff was notably better in overall quality than the old material that had been exposed for months.

Unless I intend to be using the printer on a daily basis, I now remove the spools, pack in airtight bag with silica gel and store out of the light.

It seems a bit of a faff at first, but you soon get the removal technique sorted. I did have a free demo reel of PLA that was completely shattered, couldn't even be unwound without disintegrating into tiny fragments. PLA from reputable suppliers has been generally fine unless abused as above.

mgnbuk16/04/2020 20:44:52
1188 forum posts
71 photos

Many thanks for the feedback all. I'll make a habit of leaving it empty & bagging the reel from now on & see how it goes.

Fresh filament supplies have now arrived, so play will resume over the weekend - not going to be going out again it seems.

Nigel B.

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