MatterSlice adds certain automatically generated code before and after your custom custom start G-Code. This normally where your temperature settings would be applied. MatterSlice will wait for the bed to warm up first, then begin warming the extruder, then run the custom start G-Code, and finally wait for the extruder to finish heating before continuing.
If MatterSlice detects that you have any extruder heating commands (
M109) in your custom start G-Code, it will remove these from the automatic G-Code. Likewise for bed heating commands (
Here are some examples of the automatic G-Code:
; automatic settings before start_gcode G21 ; set units to millimeters M107 ; fan off M190 S95 ; wait for bed temperature to be reached M104 T0 S210 ; start heating extruder 1 T0 ; set the active extruder to 0
; automatic settings after start_gcode M109 T0 S210 ; wait for extruder 1 to reach temperature T0 ; set the active extruder to 0 G90 ; use absolute coordinates G92 E0 ; reset the expected extruder position M82 ; use absolute distance for extrusion