# Gobs of filament during initial movement of extruder

I have successfully printed a few models on my Maker Select V2 (Wanhao Duplicator i3) including 3D Benchy, but I'm seeing a consistent problem with a model that I've sliced with Cura.

The extruder starts by doing a little filament wipe at the origin, then moves to the center of the build plate where the part should be printed. During this move, it extrudes a big burst of filament (PLA), several centimeters worth, which completely ruins the print.

I debugged the initial G-code that Cura uses, and am able to reproduce the problem with this:

M104 S200 ; heat to 200 C
M109 S200 ; wait to reach temperature

G21 ; metric values
G90 ; absolute positioning
M82 ; set extruder to absolute mode

; move to home
G28 X0 Y0
G28 Z0

G1 Z15.0 F120 ; move up 15 mm
G92 E0 ; zero the extruded length

; problematic!
G1 F200 E6 ; extrude 6 mm of filament


What this is doing is moving to the origin position and pushing some filament through the extruder.

• As a note and information, G28 X0 Y0 and G28 Z0 are not completely correct G-code commands, substitute the 2 lines for G28 instead or just use the axis flags solely. The digits after the axis flags are ignored. – 0scar Mar 20 at 23:04

The G-code you posted indeed extrudes a blob of filament at the origin (6 mm). During this extrusion pressure is build up in the nozzle/heatbreak, if you command a move after this prime blob, the nozzle will leak filament releasing the leftover back pressure, it is normal to include a retraction before moving to the start of the print, e.g.:

; problematic!
G1 F200 E6 ; extrude 6 mm of filament
G92 E0
G1 F1500 E-1
... ; End of start G-code, move to skirt/brim etc.


An example Cura start G-code could look like:

G21 ;metric values
G90 ;absolute positioning
M82 ;set extruder to absolute mode

G28 ; Auto Home All AXIS

M117 Heating bed 1st...
M190 S{material_bed_temperature_layer_0}
M117 Heating core 1st...
M109 S{material_print_temperature_layer_0}

M117 Priming...
G1 X0 Y0 F2500
G1 Z2
G92 E0
G1 E15 F250
G1 Z4.0 F500
G92 E0
M117 Wiping...
G1 Y5 Z4.0 F500
G1 Y10 Z0.2
G1 Y15 Z0.2 F500
G92 E0
G1 F200
G1 E-3

M117 Printing...

• Thanks. The start code does have the G1 F1500 E-1 actually, but it does not put the genie back in the bottle, so to speak. Is there another improvement I could make? For instance, this extrusion happens at Z=15mm, perhaps I could do it closer to the build plate so the blob sticks to the plate first? – rgov Mar 21 at 20:28
• @rgov raise to 2 mm, then it should stick. Personally, I also do a wipe afterwards, then you are certain the nozzle is clean. – 0scar Mar 21 at 23:19