Initial Purge Line question, something to do with G92?  

RE: Initial Purge Line question, something to do with G92?

The informal name is ooze, and one common way to deal with it is to leave the nozzle at a temp slightly less than print temp while the printer runs through all the cals, then raise the nozzle temp just prior to purge.

ps: G92 is not doing anything; it resets the extruder counter to zero.

RE: Initial Purge Line question, something to do with G92?

Hi Tim, 

I am not referring to the tiny bit of filament that oozes out the nozzle. I am referring to the nozzle would park at the bottom left hand corner of the bed, dwell there for a small amount time while doing a purge, after a few seconds then it will start to initiate the initial line purge across the bed. 

Perhaps I should shoot a video to show what I mean? 

cheers

RE: Initial Purge Line question, something to do with G92?

This happens during "Tc" command. You can't change it. It's a firmware thing.

If you want your nozzle to be on a different position at that time, change the "G1" line above the "Tc" command to your desired coordinates and add "G1 X0.0 Y-3.0 Z0.4 F1000.0" after the "Tc" line.

RE: Initial Purge Line question, something to do with G92?

Thank you 🙂 

I will add that line of gcode after command and adjust the Z value. 

RE: Initial Purge Line question, something to do with G92?

Posted by: hwlin85

Thank you 🙂 

I will add that line of gcode after command and adjust the Z value. 

 

Maybe a vertical move after "Tc" isn't ideal. I diagonal move like "G1 X25.0 Y-3.0 Z0.4 F1000.0" should be better to handle the purge

RE: Initial Purge Line question, something to do with G92?

Should I delete the 
G1 X55.0 F2000.0
G1 Z0.3 F1000.0

In starting gcode? 

RE: Initial Purge Line question, something to do with G92?

No. They should stay.

RE: Initial Purge Line question, something to do with G92?

I think you mean the purge bubble bit, I've took that out of my start g-code's now so it only does the line without the initial blob bit as found it was leaving mess on the nozzle.  I can't remember the exact g-code but if you look at the start g-code on the pretty profiles by Chris it has a comment on the line about the purge bubble so you should be able to spot the right bit.

RE: Initial Purge Line question, something to do with G92?

ya it was a mess, I ended up having to clean my nozzle after every print.  
This happens more often with my Mk3s + mmu2s setup then my stand alone mk3s. 

@Miker I am not sure who Chris you are referring to, I am pretty new here.  Are you referring to another post that discusses this purge bubble?

Thanks

RE: Initial Purge Line question, something to do with G92?

I did a little search, i think chris's post is referring to the purge block that the mmu2s setup generates.  

My trouble is something else, just the initial squirt of filament that printer would do at the bottom left-hand corner at the start of every print on my mk3s + mmu2s setup.

RE: Initial Purge Line question, something to do with G92?

Posted by: hwlin85

ya it was a mess, I ended up having to clean my nozzle after every print.  
This happens more often with my Mk3s + mmu2s setup then my stand alone mk3s. 

@Miker I am not sure who Chris you are referring to, I am pretty new here.  Are you referring to another post that discusses this purge bubble?

Thanks

There are some profiles to download called Pretty PLA (and others) created by Chris Warkocki which have comments on the g-code startup lines so you can see what does what as a learner.  You can download them here and import into the slicer. https://github.com/eoprede/prusa_profiles/tree/master/MK3/Slic3r

RE: Initial Purge Line question, something to do with G92?

You are looking for G1 lines with an Exx parameter. The Exx tells it how many mm of filament to extrude. In your sample code, I don't see any extrusions with 0 X or Y movement, so no "bubble". I've added some comments:

;go outside print area
G1 Y-3.0 F1000.0 ; Move to Y-3 (outside print area - standard)
G1 Z0.4 F1000.0 ; Raises Z 0.4mm - not default, but won't cause oozing. Presumably to make purge line easier to lift.
; select extruder
Tc
; purge line
G1 X55.0 F2000.0 ; Moves to X 55 with NO purge
G1 Z0.3 F1000.0 ; Sets Z to 0.3mm (seems high for a purge line but OK)
G92 E0.0 ; Resets extrusion position. Just helps keep subsequent extrusions correct. 
G1 X240.0 E25.0 F2200.0 ; Extrude 25mm while moving to X 240. 
G1 Y-2.0 F1000.0 ; Moves Y to -2 (outside print area adjacent to previous)
G1 X55.0 E25 F1400.0 ; Extrude 25mm while moving X back to 55
G1 Z0.20 F1000.0 ; Set Z to 0.20mm
G1 X5.0 E4.0 F1000.0 ; Extrude 5mm while moving back to X5

I don't use a MMU so I may be missing something, but I really don't see the purpose of what this line is intended to do. You really don't gain anything by printing 2 adjacent lines in terms of ensuring even flow, and I'd rather see a single extrusion to be able to judge evenness. I've got my documented start gcode example here if you'd like to compare. I don't try to avoid any pre-print ooze so much as ensure it will be captured by the my purge line routine. I get very good results with this version. Again, a MMU may require something different.

RE: Initial Purge Line question, something to do with G92?

I think the main reason the MMU has such a long purge is to ensure any traces of the colour/material in the nozzle at previous unload are gone. Remember it auto-unloads at print finish so there isn't a way to cold-pull or get rid of nearly all that black when you want to print white again....

RE: Initial Purge Line question, something to do with G92?

I think @hwlin85 is talking about the blob at [X0; Y-3; Z0.4]. Before the purge starts.

RE: Initial Purge Line question, something to do with G92?

Posted by: Peter S.

I think @hwlin85 is talking about the blob at [X0; Y-3; Z0.4]. Before the purge starts.

 

Yes, I was addressing Bobstro's comment on why the MMU purge line was different/what it's intended for.

RE: Initial Purge Line question, something to do with G92?

Posted by: vintagepc

I think the main reason the MMU has such a long purge is to ensure any traces of the colour/material in the nozzle at previous unload are gone. Remember it auto-unloads at print finish so there isn't a way to cold-pull or get rid of nearly all that black when you want to print white again....

I have no experience with the MMU. I just wanted to explain what the gcode is doing. In OP's case, I don't think the startup gcode is the cause of the problem being described. Your explanation makes sense and I'll defer to anybody on MMU specifics.

RE: Initial Purge Line question, something to do with G92?

Posted by: Peter S.

I think @hwlin85 is talking about the blob at [X0; Y-3; Z0.4]. Before the purge starts.

Those 2 lines are just movement though. There is no extrusion (E parameter) going on. They've moving outside the print area, so you probably don't want to get rid of those moves. In other words: I don't see anything in the OP that is causing extrusion without moves to form a blob as often seen in custom startup routines. All extrusion is occurring during moves. It sounds like OP has something causing extrusion (or ooze) before the startup gcode even starts. Temp related perhaps.

RE: Initial Purge Line question, something to do with G92?

there is a chance of bit of extrusion during the MMU load sequence ( not in the G code) . the load sequence starts the motor feeding, feeds filament from mmu till ir sensor detects filament in bondtech, releases mmu, feeds filament to hot end , retracts filament almost back to bondtech, tests that the filament is still in the bondtech,  then starts the purge

RE: Initial Purge Line question, something to do with G92?

here's the actual startup from a stock 2.1.0-alpha1 prusaslicer install

M73 P0 R116
M73 Q0 S118
M201 X1000 Y1000 Z1000 E8000 ; sets maximum accelerations, mm/sec^2
M203 X200 Y200 Z12 E120 ; sets maximum feedrates, mm/sec
M204 P1250 R1250 T1250 ; sets acceleration (P, T) and retract acceleration (R), mm/sec^2
M205 X8.00 Y8.00 Z0.40 E1.50 ; sets the jerk limits, mm/sec
M205 S0 T0 ; sets the minimum extruding and travel feed rate, mm/sec
M107
M115 U3.7.2 ; tell printer latest fw version
G90 ; use absolute coordinates
M83 ; extruder relative mode
M104 S215 ; set extruder temp
M140 S60 ; set bed temp
M190 S60 ; wait for bed temp
M109 S215 ; wait for extruder temp
G28 W ; home all without mesh bed level
G80 ; mesh bed leveling
G21 ; set units to millimeters

; Send the filament type to the MMU2.0 unit.
; E stands for extruder number, F stands for filament type (0: default; 1:flex; 2: PVA)
M403 E0 F0
M403 E1 F0
M403 E2 F0
M403 E3 F0
M403 E4 F0

;go outside print area
G1 Y-3.0 F1000.0
G1 Z0.4 F1000.0
; select extruder
T0
; initial load
G1 X55.0 E29.0 F1073.0
M73 Q0 S117
M73 P0 R115
G1 X5.0 E29.0 F1800.0
G1 X55.0 E8.0 F2000.0
G1 Z0.3 F1000.0
G92 E0.0
G1 X240.0 E25.0 F2200.0
G1 Y-2.0 F1000.0
G1 X55.0 E25 F1400.0
G1 Z0.20 F1000.0
G1 X5.0 E4.0 F1000.0
G92 E0.0

M221 S95
G92 E0.0
G21 ; set units to millimeters
G90 ; use absolute coordinates
M83 ; use relative distances for extrusion
T0
M900 K30 ; Filament gcode
G1 Z0.200 F10800.000
;BEFORE_LAYER_CHANGE
G92 E0.0
;0.2

G1 E-0.80000 F2100.00000
G1 Z0.800 F10800.000
G1 Z0.200
;AFTER_LAYER_CHANGE
;0.2
M900 K0
G1 E-2.20000 F2100.00000
G1 Z0.800 F10800.000
G1 X233.000 Y125.000
G1 Z0.200
G1 E3.00000 F2100.00000