odd over extrusion??

[stonemonkee 0]

Hi guys,

new to this forum and new to Cura.

previously been using Kisslicer but moved onto Cura as it seems well develped and supported.

Im currently trying to tweek my printer . its printing ok with some good retraction then all of a sudden it will over extrude on one layer (randomly) it does this on both the support and the body of the object being printed.

oddly it leaves a band on the object a layer thick, further inspection reveals it extends out of both the internal and external side of the print, when it does this my extruder makes a louder sound and then it will carry on prinitng nicely for a while anyway until the next random "fat layer" kicks in.

Any ideas whats causing this?

 

[illuminarti 18]

Welcome, stonemonkee. What sort of printer are you using?

Does the problem always happen at the same point, if you print the same file over again? Or is it random each time you try the same gcode?

A possible cause is that your retractions are sometimes failing - perhaps because you have Cura set to retract too far/fast. If the extruder motor skips steps on the retraction, then when it tries to reverse the retraction, it will, instead just force a bunch of previously unretracted filament out of the nozzle. The skipped steps on the retraction would also account for the louder noise.

If you're printer isn't an Ultimaker, and especially if it isn't Bowden-fed, then you can probably get away with much shorter retraction amounts than the default 4.5mm in Cura. And depending on your set up, you might also want a slower speed.

 

[stonemonkee 0]

hi thanks for the warm welcome and prompt responses

I have read those links and thank you however.I have missed out some important info in my first post.

im using a rostock printer with bowden tube and an airtripper extruder , a 0.35 nozzle 1.75mm ABS.

the other thing is that the filament is not under extruding , quite the opposite and over extruding.

It is random , i can run the same print twice and it happens in different areas.

I have always used kisslicer but prefer Cura and would like to get it working correctly.

im retracting 4mm at 21mm/s any faster grinds my extruder and seems to have a negative effect.

oh by the way the problem is much more pronounced when using support.

I can print a vase with spiral flawlessly

 

[stonemonkee 0]

A possible cause is that your retractions are sometimes failing - perhaps because you have Cura set to retract too far/fast. If the extruder motor skips steps on the retraction, then when it tries to reverse the retraction, it will, instead just force a bunch of previously unretracted filament out of the nozzle. The skipped steps on the retraction would also account for the louder noise.

This has to be the reason..I think you hit the nail on the head.my 4mm retraction was set from my kisslicer settings.I have not tried a lower setting but have tried higher which resulted in the same banding but longer print times.I will try a shorter retract tomorrow

 

[gr5 2,172]

A picture of your part would be nice. If it's a Z screw issue where the bed doesn't move as far as it is supposed to then you get over extrusion on a given layer and then it corrects on the next.

 

[mr.-waldorf 0]

the other thing is that the filament is not under extruding , quite the opposite and over extruding.

 

I am sorry, my mistake. I will delete my previous posts since they aren´t over extruding related

 

[stonemonkee 0]

Well thank you guys, the problem was with my retraction as Illuminarti said, seems the retraction was skipping and then extruding a retracted amount plus the backlog from the skipped layer.Printing sweet as a nut right now.

just printing a new fan head i designed at.24 layer height so we will see how it manages that, but I have printed a couple of test heads and hands and Im certainly getting the same quality Kisslicer was giving ...very happy :-P

BTW i was originally retracting 4mm at 21mm/s had to bring this down to 2mm at 16mm/s ...shocking