failed prints from blobs of filament  

0.6mm nozzle ... when you changed it did you pay particular attention to the diagrams at the bottom of this page:

https://help.prusa3d.com/en/article/changing-or-replacing-the-nozzle-mk2-5s-mk3s-mk3s_2069

Cheerio,

RE: failed prints from blobs of filament

Blobs: 1. Incorrect nozzle assembly, filament oozing down the heat break and heater block onto the print. 2. Crud accumulated on the nozzle and/or heater block. Clean with a soft wire brush and keep clean between prints. 3. Damp filament. Dry it. But those blobs don't look like they're falling down.

RE: failed prints from blobs of filament

yes, i can take it apart and try again. 

ok i just did, yup it was leaking out of the top of the heater block,  thanks!

RE: failed prints from blobs of filament

I was just about to post a question on this same subject when I saw JD's post.  I have been having a similar problem printing PET-G (see attached photo). I've been keeping the print nozzle and surrounding heater block clean, and I don't see any evidence of filament oozing down from the heat break.  The first blob usually does not appear until the print has been underway for a while - say 15 minutes.  I have yet to actually observe the event.

So - wet filament? Is there a phenomenon where water vapor pressure builds up behind the nozzle until it suddenly forces out a blob of plastic?

RE: failed prints from blobs of filament

PETG Clings to the nozzle if the nozzle ploughs through already printed filament, then drops off at the most inopportune moment, 
try reducing your flow rate a little, maybe 5%, Please be aware that prusa slicer already sets flow rate to 95% for layer heights of 0.075 and above

regards Joan

RE: failed prints from blobs of filament

Is this an observable phenomenon? If you watch the print will you see the material build up on the nozzle?

Yours is a different problem to the OP.  @joantabb's explanation is very likely to be the issue - one cause can be poor first layer adhesion allowing the print to warp and lift off the bed at one end so the nozzle collides, scoops up some plastic, melts it and drops it elsewhere on the print.

Cheerio,

RE: failed prints from blobs of filament

if the problem is happening, yes,
at the top right of your picture, it looks like the nozzle has been ploughing the printed filament, PLA gets pushed out of the way, petg seems stickier  and can build up on the nozzle.

the other common cause of dribbles, is incorrectly changed nozzles, 

Good luck, Joan

RE: failed prints from blobs of filament

yeah its leaking out of the top of the heater block not the nozzle, thats why i never understood where it was coming from, i mean its so much.. when i took mine apart, the top had a lot on it..  sooo much better now. 

RE: failed prints from blobs of filament

Joan, thank you for response; I'm trying some prints with reduced flow now.  I examined the print that I posted the picture of and looked more carefully at the feature you pointed out.  It seems to occur at the end of every row, and the "ploughed" region is longer when the row is longer.  I'm speculating that it is consequence of the head reversing direction - so it if it is trailing a small blob of molten plastic it smears through it when it reverses direction.

RE: failed prints from blobs of filament

That could be a linear advance issue. Joan