Slic3r artifacts/blobs on corners - anyone else had?

Hi,

I've attached a couple of images of blobs I keep getting regularly on both netfabb/meshlab processed and unprocessed files when sliced by Slic3r (running through Sprinter). The blobs accumulate at the corners of builds - and on the last one so much filament was deposited that it stopped the Y axis moving over it (even with z axis retraction it couldn't clear in) and offset the rest of the print.

I'm just curious if anyone else has had them before - I haven't been able to find any mention googling them (or at least the versions I seem to have)? They're reproducible and I've watched the printer purposely print them (it comes back to that spot and extrudes a blob and then moves on) so I know it's not improper retraction settings or anything.

Any ideas?

Matthew


EDIT: in one image the blobs appear as a protrusion around the left hand edges of the tear/ water drop shapes and in the other the stick out from the corner to the right, with a gap in the Z height - they're not as consistent

Edited 2 time(s). Last edit at 03/03/2012 06:10PM by mattnedgus.

I've managed to get a toolpath image from Repetier Host if that helps explain what's going on - on the left hand side of the hole you can see how the corner looks to be made of 2 layers of extrusion? This is the point at which it's laying down (sometimes) significant amounts of filament.

I had similar problems. Experimentation showed that my retraction speed was set too high.

Seems like I could extrude at the default speed, but not retract reliably. So when the g-code tried to hop from one object to another, it failed to retract, then moved, then squirted out a blob that would have exactly compensated for the retraction that didn't happen. I couldn't find an option for 'do not compensate', so I had to slow down my retract speed.

I used pronterface's 'extrude' and 'retract' buttons to work out what values my makergear mendel prusa with brut-head extruder could accept, in milimetres per minute, then converted them to mm/sec to enter into Slic3r's 'retraction speed' field.

Problem (mostly) solved. I still sometimes have an issue with ooze, especially when I use natural PLA, which is very soft and extrudes at much lower temperature than pigmented PLA.

Arghh. Sorry. That was a fix for a completely different problem - blobbing at the start of lines. Oh well, maybe it'll help someone else.

Thanks for your suggestions tho :-) Anything that helps me try and understand why it's deciding to inject blobs in certain places is most welcome.