Lulzbot Mini - Filament Purge Line

Recently I have been using a Prusa I3 MK2. I really like how it does a purge line right before it starts to print at the very front left of the build plate. I think that the Mini would really benefit from this type of command. Even if you preheat a Mini and extrude filament before it is started, by the time it goes through its whole start up process, the filament often times has trouble coming out. This obviously differs in severity by different types of filament, but it seems to be a consistent issue. I think that a purge of filament at the end of the Mini’s startup process would really improve it’s success rate. The heavy duty purge that the Prusa does is way more effective at getting the filament going than the outline skirt that most slicers do.

I looked at the scripts tab of S3D for the Prusa and see the following:

G1 Y-3.0 F1000.0 ; go outside printing area
G1 X60.0 E9.0 F1000.0 ; intro line
G1 X100.0 E12.5 F1000.0 ; intro line

Would it be as simple to add this to the Mini’s script? Would I need to alter it at all?


The lack of sufficient “priming” comes up pretty frequently on the forum. If you search, you should find quite a few posts that include variations of startup script that implement slightly different solutions.

I have a couple concerns about the code you posted. First, going to Y-3.0 could crash into a leveling washer if Z is low enough, unless you first ensure X is greater than about 7 and less than about 152. Second, on my mini Y-3.0 is right at the edge of the glass. That can vary a millimeter or so between machines, so it may not be a problem for yours.

My personal solution is to extrude a small “blob” before the print starts. Here is the last bit of my startup Gcode script:

M204 S2000		; set accel back to normal
G1 X1 Y7 Z8 F5000	; get out the way
M400		; clear buffer
G4 S1		; pause
M140 S[bed0_temperature]	; Set bed temp again
M109 S[extruder0_temperature]	; set extruder temp and wait
M190 S[bed0_temperature]	; wait for bed to finish heating if needed
G1 Z2 E0 F75		; extrude filament back into nozzle
G1 Z2 E6 F75		; extrude a blob to prime nozzle
G1 Z2 E5.5 F600	; retract 0.5mm
G1 X15 Y15 Z10 F5000	;move up and away from blob 
G92 E0		; reset extruder position to 0

Ending with the 0.5mm retract assumes there will be a skirt to finish the job; if you don’t use skirts then after moving up & away I would add a “G1 E6” (before the G92 E0) to counteract that retraction.

NOTE: The [variables] above are specific to Simplify3D; the variable names for Cura are slightly different!

Also… The size of the blob will be different depending on the sequence of events. If you prime the nozzle, then start a print – it really will extrude 6mm of filament when the G1 E6 is executed. But the default ending script retracts -5 to relieve pressure at the end of the print. So if you sequence is “finish a print, start another print” then the “G1 E6” will only extrude a net 1mm of filament.