[Prusa i3] Too much extrusion, only on edges

[awanegenebayo]

Hello,

I'm having an issue while printing, hopefully you can see it on this video :

https://www.youtube.com/watch?v=MIov9xAa5Es

This happens on "complex prints", it prints pretty fine on simple objects (like a cube).

I don't think it is over extrusion, i spent quite a long time calibrating this, and it is only on SOME edges...

I'm out of ideas, can anyone help me ?

Thanks a lot !

[CaptainObvious]

Which slicing software did you use?

[awanegenebayo]

Hello,

I'm using slic3r, with Geeetech repeiter host.

[CaptainObvious]

Hello,

I'm using slic3r, with Geeetech repeiter host.

Which version of Slic3r? There's a bug in version 1.2.9 that can cause over extrusion, try 1.1.7 to see if that gives better results.

[printbus]

Back to add that there's another trick that I sometimes apply on overhangs. I try to be in the area when I know a print is getting to a tricky overhang, and have a metal blade like a putty knife handy. If I see a soft edge or the unsupported edge starting to curl up, I'll quickly and gently rest the metal blade on the curl to flatten it; touching the extruded filament with the cool metal pulls heat out of the filament and hardens it flat. Sure, this can be tricky depending how quickly the nozzle returns to that same area of the print, and too much pressure with the blade can compress the soft material that leads to other problems. But I figure it's worth a shot if I'm likely to have to scrap the print anyway.

I'm ready to do this even though I'm usually using my print cooler blower. Print coolers typically blow in air from one side. That means not all sides of the print will get the same cooling. Due to heat from the hot end, the part of a print downwind from the hot end can end up with less cooling effect. Edges that are in-line with the airflow direction get more airflow exposure than edges that are perpendicular to it.

[awanegenebayo]

Actually i was on an old version of slic3r when recording this video ( i think it was 1.1.7), i then upgraded to 1.2.9 and had the exact same issue...

[printbus]

Looks to me like you're trying to add new layers on top of material that isn't firm enough.

Is this PLA filament? If so, adding print cooling airflow would help.

[awanegenebayo]

Yes it is PLA.

What do you mean exactly by "print cooling airflow"? I already have the fan always on

[printbus]

If you don't know what print cooling airflow is, you probably don't have any. This isn't the fan that is typically mounted on to the hot end to cool off a heatsink. Print cooling airflow usually involves a separate fan (or small blower) with a duct or shroud that provides a stream of ambient airflow onto the print right below the hot end nozzle.

PLA can be problematic in that it retains heat for quite a while, remaining fairly soft for a long time. The video isn't the greatest, but it seems to show the print shifting underneath the nozzle. This is a classic sign of trying to print fresh material onto layers that are still soft. Print quality almost always suffers when that is happening. On overhangs (like on your print), the overhang will tend to curl upwards. 90-degree corners tend to end up rounder than they should be.

PLA print thermal management can involve a number of factors. You don't want to print PLA on a bed any warmer than necessary. You don't want the nozzle temperature any higher than it has to be. You can set up a minimum layer time in the slicer which can help, at least to an extent. You can print multiple copies or multiple designs at a time. As I mentioned, adding or increasing the amount of airflow specific to cooling off the printed material will usually provide the most significant way to minimize issues with residual heat in the extruded PLA. This blower-based cooler is specific to my MakerFarm i3v printer, but it'll give you an idea what I'm talking about - http://www.thingiverse.com/thing:461014

[hernejj]

awanegenebayo,

I have struggled with this EXACT problem for a year. What causes this, as far as I can tell, is very aggressive overhangs. It happens to me on every overhang where a significant portion of the flesh filament (PLA) is extruded over the air and it has very little to bond to. I tried everything, including cooling to no avail. I was finally able to overcome most (but not all) of the issue by significantly increasing my extrusion temperature. I was printing at 193 and had terrible overhangs just like yours. After a few experiments I found that 210 and even 215 work much better. I tried to go higher (220) but started experiencing jams.

What temps are you printing at? Please try bumping up your temp and let me know how it works for you!!