What causes these blobs on the top layer?
I just assembled and calibrated my mk3s. I printed the prusa logo for my first print and it printed fine, but on the top layer there are "blobs" in the letters. They look like they are at the start or end of a filled area.
The gcode is the standard Prusa logo gcode from the sd-card ("MK3S_PLA_Prusa_200um_20M"). I printed with the included silver PLA. I printed on both the smooth and the textured sheets, and the result looks similar with the blobs in the same places.
Oddly I don't think there were any blobs during the printing of the lower layers, they showed up on the final top layer(s).
RE: What causes these blobs on the top layer?
This looks like slight over extrusion...
did you slice this or is it the pre sliced model from Prusa?
If you sliced it, try re slicing with 0.95 extrusion multiplier!
if this is a pre sliced model, try reducing the flow on the LCD (Tune menu) it's probably already at 95, drop it to 90...
this line in the 'Start G code' within prusa slicer
M221 S{if layer_height<0.075}100{else}95{endif}
sets the flow value to 95% if the layer height is above 0.075mm
regards Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK
RE: What causes these blobs on the top layer?
This is the pre sliced reference gcode included with the printer. It's the one recommended as your first print.
Prusa support suggested I try a higher z-offset, so I raised it by 75 um. That resulted in exactly the same blobs, but an overall worse print.
I looked closely during the print and could see that the blobs formed when the nozzle lifts up after finishing an area. It would fill in a letter, lift up and move to the next letter. And each time the nozzle lifted it left a blob behind.
Regarding your suggestion: Does the flow need to be tweaked depending on filament or other factors?
RE: What causes these blobs on the top layer?
Printing is an art, rather than a science,
If the filament is slightly too large, you will get over extrusion.
If your Bondtech idler is too tight, or too loose, you will get different levels of extrusion, IIRC, too loose extrudes more too tight extrudes less
Hard filaments extrude more, soft filaments extrude less, flexible filaments tend to extrude least of all...
Rather than worrying about it at the moment, try a fresh print with reduced flow...
regards Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK
RE: What causes these blobs on the top layer?
Ok, thanks for the explanation, it makes sense.
Someone else had seen the same thing on this very print and suggested that it could be caused by the printer doing a z-hop to fill in the last corner of the letter and for some reason going too low and making an indent in the print
RE: What causes these blobs on the top layer?
@farbrormartin
it's the wipe before the Z hop... but the real problem is probably over extruding!
regards
Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK