Blob of plastic at random points

omega42

Sidewinder X1 V4

I'm having trouble with my prints failing at random points in the print because a blob of pla forms at the top layer. Its not the print file as its happening at different times and at different parts of the build.

I've changed the PLA, leveled the bed

My temps are 200 - 70 and extruder size 0.42mm



any suggestions

TIA

bryan06

omega42 wrote: »

Sidewinder X1 V4

I'm having trouble with my prints failing at random points in the print because a blob of pla forms at the top layer. Its not the print file as its happening at different times and at different parts of the build.

I've changed the PLA, leveled the bed

My temps are 200 - 70 and extruder size 0.42mm



any suggestions

TIA

Any pictures of what's happening? I've never heard of that before.

Overheal

bryan06 wrote: »

Any pictures of what's happening? I've never heard of that before.

/I see this being a real shortcoming of the vBulletin setup here, PITA to upload img's.

Blobbing tends to occur because there is a disconnect between the gcode and the tangible mechanism: for example, the ultimate volumetric flow rate doesn't match with the flow rate the program expects, blops or gaps can happen, depending on whether the net difference is high or low. Parameters that can largely affect that:

true diameter of the filament vs. diameter in slicer vs. diameter in mfg spec
true diameter of the nozzle vs. specified diameter by the manufacturer vs. slicer (especially with brass nozzles, which wear (and that bronze erosion disappears into your prints), the diameter can change over time).
True shape of the nozzle, ie. its circularity, this also changes over time
retraction settings, bridge settings, overrun settings
Part curling, which can apply backpressure to the nozzle and hotend. If plastic is in the hotend with nowhere to go, and its being sqeezed from the extruder and from the print surface, then heat and pressure will rise in the hot end until that pressure disappates, such as when the hotend next does a retraction or moves away from a curled area, at that point it can simply squirt out, and I've seen that behavior recently during attempts to reload filament into a jammed hotend: once I stuck a piano-wire size needle up into the hot end I got a volcanic-like burst of purple molten plastic and hot gasses.

Loads of other factors may also play a part, like the thermal steadiness of the hotend and how well it holds its setpoint. but if you notice irregular deposition (ie. less plastic put down in places than expected) alongside blobbing symptom I'd look at it as a hotend overpressure issue ultimately. I would do a flow rate calibration: https://3dprintbeginner.com/flow-rate-calibration/

2PiDesign

I've had this issue when the first layer height was slightly too low, the nozzle was ploughing through the first layer & would deposit blobs on the print a few layers in, everything seemed to snowball from a bad start.