startup: heat up only extruders that are getting used

[QuantumKittens 0]

I've been writing a startup gcode for a custom dual extrusion printer. This is the part of the code that heats up the extruders:

M104 S{material_print_temperature, 0} T0   
M104 S{material_print_temperature, 1} T1
M104 T{adhesion_extruder_nr} S{material_print_temperature_layer_0, adhesion_extruder_nr}

I works fine, but will always heat up both extruders, even if the current print uses only uses one of them. The same issue also happens if one extruder is disabled completely via the enable extruder checkbox, since material_print_temperature will always return something (even for disabled extruders, a bug maybe?).

Does anyone know if there is a way to heat up an extruder only if it is actually going to be used in the current print?

[QuantumKittens 0]

Update: I found a partial workaround: If I don't include any commands for heating up in my startup gcode then Cura will add its own ones before my code. It appers that this correctly takes into account if an extruder is used (even if it stays enabled).

However, it might be benefical to run my own code first, to allow the preheat process to occur in a specific location and to set various values. Is there a way to achive this or can I somehow include the code Cura generates as part my own code? Where does Cura take the code it inserts from?

[gr5 2,172]

@ahoeben I believe understands this pretty well.  Maybe he can explain.

[ahoeben 1,948]

As you have found out, you can either put your own heatup sequence in the start gcode, or CuraEngine can put it before your start gcode for you.

 

The pattern replacement you can do in the start gcode snippet is fairly "dumb"; it literally just replaces the {}-pattern with the value of the setting. There is no logic applied whatsoever, only simple replacement. It does not "understand" gcode in any way, so it does not realise you are adding a heatup line that refers to a disabled extruder. There are no "conditional" lines. Just replacing a pattern by a value.

 

Ofcourse the slicer itself is more intelligent than that. So if you tell it a certain extruder is disabled, it is smart enough to construct a heatup sequence that excludes that extruder.

 

So the logic is as follows:

If the user has specified a heatup sequence, just do a dumb pattern replacement on it. No further logic possible.

If not, created a heatup sequence from all the settings specified by the user, taking into account the number of enabled extruders and which extruder will be used first.