A blob is messing up my first layer

Hello,

Everyone here has been extremely helpful so far - you are a great community. I have a new latest problem however.

When the Mini goes to print, it always goes to one specific spot and tries to but down a big glob of filament. Then it goes from there to make the skirt around the item I want to print. I assumed this glob was another type of skirt measure. However, this glob often either sticks to the nozzle, or a strand of filament is dragged over to where the skirt is being made and then this rogue strand of filament messes up the first layer of the print.

What is causing this to happen? What can I do about it? If I am not clear enough in describing I can take some pictures and a video to post as well.

Sounds like the main nozzle prime is what you’re seeing. If you look in the starting gcode (need to be in expert mode). You will see something like this…

;This Gcode has been generated specifically for the LulzBot Mini
;Basic settings: Layer height: {layer_height} Walls: {wall_thickness} Fill: {fill_density}
;Filament Diameter: {filament_diameter}
;Nozzle Size: {nozzle_size}
G26                          ; clear potential 'probe fail' condition
G21                          ; metric values
G90                          ; absolute positioning
M82                          ; set extruder to absolute mode
M107                         ; start with the fan off
G92 E0                       ; set extruder position to 0
M140 S{print_bed_temperature}; get bed heating up
G28                          ; home all
M109 R140                    ; set to cleaning temp and wait
G1 Z150 E-30 F75             ; suck up XXmm of filament
M109 R140                    ; heat up rest of way
G1 X45 Y174 F11520           ; move behind scraper
G1 Z0  F1200                 ; CRITICAL: set Z to height of top of scraper
G1 X45 Y174 Z-.5 F4000       ; wiping ; plunge into wipe pad
G1 X55 Y172 Z-.5 F4000       ; wiping
G1 X45 Y174 Z0 F4000         ; wiping
G1 X55 Y172 F4000            ; wiping
G1 X45 Y174 F4000            ; wiping
G1 X55 Y172 F4000            ; wiping
G1 X45 Y174 F4000            ; wiping
G1 X55 Y172 F4000            ; wiping
G1 X60 Y174 F4000            ; wiping
G1 X80 Y172 F4000            ; wiping
G1 X60 Y174 F4000            ; wiping
G1 X80 Y172 F4000            ; wiping
G1 X60 Y174 F4000            ; wiping
G1 X90 Y172 F4000            ; wiping
G1 X80 Y174 F4000            ; wiping
G1 X100 Y172 F4000           ; wiping
G1 X80 Y174 F4000            ; wiping
G1 X100 Y172 F4000           ; wiping
G1 X80 Y174 F4000            ; wiping
G1 X100 Y172 F4000           ; wiping
G1 X110 Y174 F4000           ; wiping
G1 X100 Y172 F4000           ; wiping
G1 X110 Y174 F4000           ; wiping
G1 X100 Y172 F4000           ; wiping
G1 X110 Y174 F4000           ; wiping
G1 X115 Y172 Z-0.5 F1000     ; wipe slower and bury noz in cleanish area
G1 Z10                       ; raise z
G28 X0 Y0                    ; home x and y
M109 R140                    ; set to probing temp
M204 S300                    ; Set probing acceleration
G29                          ; Probe
M204 S2000                   ; Restore standard acceleration
G1 X5 Y15 Z10 F5000          ; get out the way
G4 S1                        ; pause
M400                         ; clear buffer
M109 R{print_temperature}    ; set extruder temp and wait
G4 S15                       ; wait for bed to temp up
G1 Z2 E0 F75                 ; extrude filament back into nozzle         <-----------------------------------------------
M140 S{print_bed_temperature}; get bed temping up during first layer

The line the arrow points to is pushing filament into the nozzle to try to get things ready to go. Some filaments will string from it, as you mentioned. You could try changing the “E0” part to “E-5” to reduce the amount of filament it pushes in to start up. If you still have a skirt printing, it’s probably fine. You could also create a larger blob, let it cool a bit, then pull away from the “anchor”. I do that with some of my own profiles, got the idea from someone on this forum I think…

That’s the approach I took. All of my profiles end with this:

G1 Z1 E0 F75		; extrude filament back into nozzle
G1 Z1 E6 F75		; extrude a blob to make sure nozzle is primed
G1 Z1 E5.5 F600	; retract 0.5mm
G1 X15 Y15 Z10 F5000	;move up and away from blob
G92 E0		; reset extruder position to 0

The 0.5 retraction is deliberately not countered to prevent ooze, so the skirt doesn’t always start perfectly – but as long as there are at least a few mm of skirt that isn’t a problem.