What is Going on with My Print?? Under/over Extrusion after First Half of Print.

[Spencer_Webber]

Hey everyone, I have a prusa i3 with a bowden E3d hotend that has produced many high quality prints (img attached).

I am currently attempting to print a PLA piece with 3 tall pillars and as soon as the printer starts on the pillars the extrusion gets very inconsistant (img attached). I have tried the print 4 separate times changing extrusion temperature, extrusion multiplier, retraction settings and even enclosing the printer to try and prevent fluctuations in nozzle temp and nothing has helped. I am very lost as to what may be causing this problem.

Any suggestions?

[dkightley]

I think this is an easy one.......hopefully.

You have the symptoms of overheating when printing small sections....which can hopefully be cured by setting on the Speed override Adjust printing for layers below...with a value of say 15secs and a down to of say 20%

You'll need to experiment on the values first using the s[eed indication in preview mode.

[gwhite]

I've also found it useful to add cooling to small features like that. Basically, the plastic is still melted when the next pass comes around, and it just makes a mess.

[Spencer_Webber]

Thanks for the reply Doug,

I checked my settings and it seems like I already have the speed override enabled, reducing the speed of prints under 15sec by 20%. Also my default print speed is 40mm/s which I believe is quite slow.

The thing that I am most concerned about is that when I watch closely, the printer nozzle seems to be under-extruding on some layers(almost laying out no plastic sometimes) and then over-extruding on others. This happens regardless of the temperature of the nozzle( have tried between 200-220 degrees C) So when I take the print off the bed the pillars break apart very easily because of what I assume is the under-extrusion.

[dkightley]

Its very frustrating telling you how to cure your problem and you don't try it ...and you don't believe me!!

Forget about under/over extrusion. That's not the problem here! Its printing on top of a layer that's still too soft to take anything on top of it!

I had to cure the EXACT issue with this and around a hundred other similar small building:

The chimneys are 1.75mm x 2.75mm and they will print exactly as per your photo if I don't slow the print speed waaaay down. Look at the colours!

This is printing in PLA...and I have 100% cooling throughout the print.

[Spencer_Webber]

I have made the changes you have suggested. I have tried various different speed and cooling settings but I still get the inconsistent extrusion and small gaps in between the layers(I circled one of the gaps in the print in yellow).

Here is a example:

On this print for layers below 30.5sec I reduced the speed to 1%. I also reduced the default print speed to 30mm/s to further slow down the printer.

Print with gaps.jpg (14.05 KiB) Viewed 8718 times

[dkightley]

Attach a factory file for the part as printed in these photos...ie including the exact settings used for that print...and I'l take a look at what your settings are.

Factory file. File menu==>Export Factory File. The file will have an extension of .factory....not .fff

[Spencer_Webber]

Here is a factory file for that exact print:

TourbillonCageFront.factory

(40.48 KiB) Downloaded 398 times

[airscapes]

I have a direct drive extruder so not sure if coasting and wiping are something needed for bowden style but I would uncheck both those options. I also would set minimum infill to .01, Speed outline underspeed to at least 70%, infill under speed 80% and on last page uncheck everything under ooze control and check retract only when crossing open spaces.. but that is how I have things set up from for my setup.. which is different. You are printing tiny little parts you don't need to be coasting and wiping and retracting should only be needed during non print moves. I am interested to see Doug's response as he has a lot more experience than I do.

[Spencer_Webber]

Hi Airscapes, I made all the changes you suggested but the print comes out pretty much the same(Except for a bit more blobbing). I have also tried printing the part with 3 walls instead of 2.... This only made the under extrusion worse. Some layers barely printed at all.