Mountainous terrain on print

I am trying to print a new X end for my Prusa but am getting large blobs on some corners which are mechanically snagging the nozzle and causing missed steps. I am printing this (Improved X ends for Prusa with clamped rods by jonaskuehling) on a Rostock in PLA and this problem doesn't exist on the first few layers, or after about layer 20. The mountains are on the sharpest bends and are about 0.6mm high. Close up side view of a mountain range in the first picture and a top view in the second to show where it is.



I have not seen anything like this before and normal adjustments to flow rate print speed, temperature seem to have no effect. What is specially perplexing is that the problem seems to be limited to a small number of layers.

Thanks for any insight you can give

No idea, oozing can get blobs the nozzle can bump into, but doesnt seem to match your description.

Taking another brief look at this, I see that each "Mountain" is more like a crater with a raised rim. The inner part of the crater is actually below the level of the layer and seems to be melted out. The most prominent crags appear where the nozzle does a reversal of direction with a thin inner perimeter and another close edge - as in the picture Topview.jpg in my earlier post. The nozzle seems to move slowly at these points. The disappearance of the problem after approx layer 20 is perhaps due to the thin slit inner perimeters being discontinued at about this level - although that doesn't account for them disappearing at other corners and sharp bends.

Has anybody any thoughts on this? possibly software or communication stalling?

Mike

Can it be your filament has variable width? And do you think your filament settings are correct? I had the same with filament that wasn't a nice constant thickness..

Nope, the filament is nice and even, 1.7mm +- 0.05mm. I have had some success by droping the temperature - I had only tried increasing it as the extruder was stalling at my initial setting. Whether this has stopped the nozzle jamming on the print will have to wait for this print to finish, but it looks promising.

Mike

Makes sure you bed is level too. If too close on one side you can push filament up like that.

I had this issue with a MakerFarm J-Head, primarily due to the nozzle having a 'nipple'. That your nozzle 'snags', makes me think your nozzle isn't smooth to its surrounding contour where the opening meets the world. The new J-heads / most new nozzles today have no 'nipple'. I can only assume this is evolution at work.

O.K. I think that I have solved it. The "Mountains" were crater rims , the most damaging ones were where there were sharp - like 180 degree turns -the firmware threw in a short pause and this allowed the heat fro the nozzle to melt a small well in the print. Although the effect was tiny, it built up layer after layer and, after a while, the nozzle started picking up PLA from the crater rim and depositing it when it pushed through the next crater rim. Eventually the build up becomes so severe that the nozzle sticks long enough to loose steps --- DOOM.

Later in the print the four 180 degree turns dissappeared -and the wells and crater rims subsided.

For most prints with this roll of natural PLA I have run the nozzle at 215 degrees with beautiful results on vases etc., but this X end needs 200 degrees to avoid this problem.

Mike