Air in PLA?

[kolia 31]

Hi there!

I've been trying to print some earrings (http://www.instructables.com/id/3D-Printed-Spiral-Earrings/) for a while but it's always failing at some point: PLA stopping to come out. I'm not in front of machine all the time, not sure what happens.

So, I came back to another print that I've already done successfully in other color, and here is what I get:

I saw the lowest "dotted line" happening and applied some more pressure manually on the filament at that time and it kinda recovered. Then I left. The print finished but it seems the same phenomenon happened a few more times.

Is that what happens when there is air bubbles coming out? I'm pretty sure other few prints failed because of that, where the filament totally stopped to come out.

Now, I also got some good long prints with this same (chinese-low-cost) PLA...

But I waste so much time that if it's a PLA problem, I will just move to another roll and stop getting crazy

Thanks!

PS: I printed at 230C, 50mm/s, with retraction disabled, hence the terrible stringing I guess.

 

[calinb 11]

I can't tell much from your photo, but you'd have to have some pretty big bubbles in your filament to cause that defect (and you'd hear them "popping" during extrusion, I think). It seems like the PLA is not extruding well in the faulty areas. I mostly print ABS (though I've been enjoying the relative ease of printing PLA lately) but I think your problem could be caused by the resistance of a partial jam in the hot end. 230 is getting up there for PLA, unless you are printing fast (which you probably can't do with the earrings). Try dropping the temp to 220 or even 210 or so for your 50mm/sec print speed.

Also, your filament feeder might not be supplying full feeding force. Are there any signs of filament grinding on the feeder drive stud? Is the pressure supplied by the "foot" or roller adjusted correctly? Is the filament being driven by the deepest and "best" knurling on the feeder drive stud?

 

[gr5 2,172]

I'm 90% sure I know what the problem is and it's easy to fix. This is a new problem that we've been seeing on these forums with the latest Cura. So not too many people recognize it yet from pictures but I'm starting to be able to spot it better now that I've seen it on my own prints.The latest Cura basically has a bug in the infill where the infill comes out through the walls (skin) under certain conditions. You can verify this by looking at the gcode view and you will see those dots line up perfectly with the infill.

There are several solutions. The simplest and probably the best is to make your skin thicker. You want at least .8mm skin if not maybe 1.2mm. That usually completely fixes the problem. I did a print today at .8mm skin and you could still see the problem but it was much better.

Alternatively you could set your infill overlap to -50% or so - look at the traces in cura to see what's going on before trying this.

Or you could turn off infill completely.

Or you can go back to Cura 13.04.

 

[kolia 31]

@calinb : I think my feeder is fine, even holding back the filament manually I can feel how strong it's pulling it up. But you are right that 230C and slow speed is not the best idea and might cause the heat to go up and mess up. Now, for this print I needed low speed, and under 230 it wasn't fluid enough I felt, especially at the beginning of the print. I will reconsider this thanks!

@gr5 : You are perfectly right, it was using the latest version of Cura, and now that you mention it, it seems most of my recent problems are linked to it. And I didn't think of it because I didn't expect much core difference between 13.04 and 13.06... and a terrible bias concerning chinese quality made me blame it a bit too fast... shame on me.

I'm not sure what you mean by "looking at the gcode view"? The gcode itself or the layers display?

Last question: is what you call "skin thickness" what is named "shell thickness" in Cura? The pictured print was done with shell thickness 0.8mm, I will go up.

Many thanks,

 

[gr5 2,172]

sorry, yes "shell", not "skin". And "layers" view which shows you the gcode graphically/visually.

 

[gr5 2,172]

More info about the bug here:

http://umforum.ultimaker.com/index.php?/topic/2501-is-this-slicing-settings-or-hardware-problem/?p=17683

It's still quite possible that you have a different issue but this is the most likely in my opinion.

 

[bdb 0]

Dear filament printers,

I think you arte all doing fatastic.

There are some basics you must know before you "melt" plastics.

There are "plastics" who you can recycle.

Frome this group there are 2 very diverent streams.

1. the types you who are not hygroscopic, like PP, PE, PS ecetra.

2. Who ARE PLA, ABS, PA, PC. ect.

The normaly procedure te work with these materials is to dry them!

Drying temp is type related.

For pla is tha 70-75 degrees celcius for 3 hours.

The fac is that so many people has not the air bubble problem is due to the fact the material produced so slowly the moister migrades out. New fresh material is dry when correctly packed.

For any questions about manufactoring/producing plastics/products....

Greeting from a plastic engeneer/designer.

BdB

 

[calinb 11]

Well--every filament is different (even from color to color) so that's good to hear. I've been printing Ultimachine blue translucent PLA lately at low speed. I was printing my first layer so slowly that I had to reduce the nozzle temp from 220C to 210C for just the first layer.. The layer took too long long to print and I was getting a jam from heat migration up the filament.

 

But you are right that 230C and slow speed is not the best idea and might cause the heat to go up and mess up. Now, for this print I needed low speed, and under 230 it wasn't fluid enough I felt, especially at the beginning of the print. I will reconsider this thanks!