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Under or over extrusion?

Posted by IG88 
Under or over extrusion?
December 07, 2015 02:55PM
Attached some pictures of the melting man!

I've just finished building a homemade 3D printer but I'm having some difficulty getting my layers to bond correctly.
My very first prints with ABS had this problem even after trying a myriad of different settings, so i decided to try PLA from Colorfabb, as seems to be an easier medium for beginners.
I secretly hoped i'd lose the disconnected layers... I was wrong!

These new PLA prints really confuse me, as you can see the layers aren't sticking properly, and i could easily tear this man apart.
This leads me to think I'm under extruding.

However when i look at his back and his chin, he's developed alarming amounts of back hair and a funky goatee..
This leads me to think im over extruding (either that or my retraction isn't working properly, even though it was fine with ABS at 60 mm/s)

I'm using an enclosure and print temp is at 190 C.
As it's a homebuilt printer it gets kind of wobbly when i print too fast, so most print speed settings are at 15 mm/s. (for printing small items like this)
Repetier Host + Slic3r. Layer height 0.1mm.

I'm going to print some calibation pieces later to get my Extrusion Multiplier tuned, I'm thinking it's the main culprate.
Can anyone deduce what the main problem is?
open | download - 20151207_203700S.jpg (325.5 KB)
open | download - 20151207_203643S.jpg (339.2 KB)
Re: Under or over extrusion?
December 07, 2015 04:43PM
The enclosure will have an adverse effect if you print PLA. You need to cool the printed parts while printing, or at the very least not trap the heat in an enclosure. PLA will remain very soft and viscous and the result is drooping strings and sagging prints.
Start with calibration pieces, a statue like that is of not much use to get the amount of material right. A simple cube is a good start.

Re: Under or over extrusion?
December 07, 2015 06:38PM
This looks strange... As if it is under-extruding at times and over-extruding at other times. Have you checked the hotend is not partially blocked? If that's the case it would do that, i.e. it would mostly under-extrude but then plastic would accumulate and it would periodically unload it by over-extruding. Also worth checking your retraction settings (seems you may be over-extruding on layer changes) and increasing extrusion width/width to height ratio (for better adhesion).

Edited 1 time(s). Last edit at 12/07/2015 06:38PM by fixerT.
Re: Under or over extrusion?
December 07, 2015 10:25PM
Before you play with settings and mess around to get a better print: Do a proper calibration of all axis and the extruder!
There is no point in compensationg for hardware problems through the slicer winking smiley
Re: Under or over extrusion?
December 08, 2015 11:27AM
Thank you all for your replies!

Ahh thanks for the heads up. I got the feeling i was doing something wrong when i saw the print lurch about with the movement of the extruder.
I'll remove the enclosure entirely with PLA from now on.

That could be true, perhaps some ABS is still in the nozzle, and won't fully extrude away since I'm extruding PLA at only 195 C.
I'll bump up the heat and extrude with manual control, do a couple of 100mm feeds and check for inconsistent diameters of the filament being extruded.

I've calculated X Y and Z and checked them, they're on point.
I thought the calculated E step/mm were right but they weren't, i must have had something in my eye when i checked it before, hah.
Just calibrated the E steps by feeding filament through manual control and marking the length, it's spot on now!
Same problems still persist however.

Can anyone tell me if there's a certain order in which to calibrate different settings? I'm going to go through the following:

Extrusion width - currently all set to 0.35 as I'm using a 0.3 nozzle. (am i better off just putting this back to 0 to let Slic3r sort it out?)
Extrusion multiplier - currently set to 1, I'll find out how to calibrate this
Extruder temp - 195 (advised lower limit of this filament) still flows well, i tried the max advised temp but it didn't create better layer adhesion.
Cooling - Slic3r auto cooling, I'll try it at 'always on'.
Retraction length - 2 mm (is this adequate?)
Retraction speed - 70 mm/s (is this adequate?)

Are there other important settings that are worth a look?

Edited 1 time(s). Last edit at 12/08/2015 11:30AM by IG88.
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