Cura: Start gcode isn't at the start

[ntoff]

What were you doing?

Changing my start gcode

What did you expect to happen?

That Cura would add my start gcode to the start of the exported gcode

What happened instead?

Cura added a bunch of other stuff before my start gcode which would cause the printer to malfunction.

Cura version

2.4.0-Beta - Windows10

Notes

My printer needs M80 to be the very first line to turn on the power supply, thus my start gcode is this: https://gist.github.com/ntoff/699213b39abb74c195385dfc34b07d36 which works in cura v15.x but in 2.4 it adds its own temperature lines before my start code (excerpt from a saved gcode file under 2.4): https://gist.github.com/ntoff/d87b47f6ee1ac6b1845b8031f3926f14

Obviously also the temperature parameters don't seem to be the same as 15.x but the main concern is that M80 is never the first line.

[Ghostkeeper]

Normally the start g-code has a lot of stuff like priming that needs the nozzle at printing temperature. Not all though.

If you put M109 S{material_print_temperature} in the start g-code, or anything with {material_print_temperature}, CuraEngine won't put the temperature before it.

So by default it puts the temperature there because it's easy for many printers (e.g. those without any special start g-code). But if your printer requires a special procedure at start you can place the material pre-heat in the start code yourself as well. Anything in brackets gets replaced by the value of the setting between the brackets.

[Ghostkeeper]

Your start g-code already has such lines but we renamed the setting key in 2.3. I think your start g-code would become something like this:

M80                                 ; turn printer on
G21                             ; metric values
G91                                 ; Relative Positioning
M82                             ; set extruder to absolute mode
G1 Z+10                         ; makes sure the nozzle isn't going to hit the bed when it homes
G28 Y                               ; home y
G90                             ; absolute positioning
G1 Y190                         ; move bed away from e3d fan of death
M190 S{material_bed_temperature}    ; heat bed
M104 S{material_print_temperature}      ; start heating
G28                                 ; home
M109 S{material_print_temperature}      ; finish heating
M107                            ; start with the fan off
G92 E0                              ; reset extruder
G1 X5 Z0.5 F2500                    ; move up and across
G1 Y55 E10 F150                 ; extrude some material to prime the nozzle
G92 E0                          ; reset extruder
G1 F{speed_travel}
;Put printing message on LCD screen
M117 Started at {time}

[ntoff]

But if your printer requires a special procedure at start you can place the material pre-heat in the start code yourself as well.

Yes, I figured that part out but (thanks) the issue still stands that I would have assumed start gcode would be the absolute first thing added before anything else in there.

Also is there any list of those parameters? I googled for a bit but didn't find anything and just resorted to sifting through the source code to figure out what they were renamed to.

[Ghostkeeper]

Yes, over here: https://github.com/Ultimaker/Cura/blob/master/resources/definitions/fdmprinter.def.json

You can use all keys of all settings. Just the print temperatures are special in that they prevent the print temperature from being put in front of the start g-code.

I wonder, by the way, what would happen if you were to include the {machine_start_gcode} key... 😄

[ntoff]

I wonder, by the way, what would happen if you were to include the {machine_start_gcode} key...

Don't know but I'm willing to try for science since cura 2.4 isn't my main slicer (cura 15.04 is), I don't mind if I break it.

edit: It just includes the start gcode twice, no infinite gcode

[Ghostkeeper]

In short, this is expected behaviour because it's just handy that the temperature gets inserted there, and the print header also gets included before the start g-code because it usually requires information that is unavailable in a start g-code.