Feature Request: Simple Arithmetic with variables in start/end gcode?

[lordofhyphens]

I'd like to be able to issue a M190 command in the start Gcode so that it waits until the bed is 1 or 2C lower than [first_layer_bed_temperature], then issue a M140 to let it heat up the rest of the way while my hotend gets up to temp.

Near as I can tell, this behavior isn't supported in Slic3r.

[lordofhyphens]

I think I can get a workaround by postprocessing the gcode through a perl regexp looking for the M190 command, but it's not very pretty.

's/M190 S([0-9]+)([+-][0-9]+);/"M190 S".($1+$2).";"/e'

[lordofhyphens]

Yeah, I've got workaround in the form of a sh script that calls perl with that regexp. It supports the format S[temp]-offset, and addition too.

entire script:
#!/bin/sh
perl -p -i -e 's/M190 S([0-9]+)([+-][0-9]+);/"M190 S".($1+$2).";"/e' $1

[alranel]

I have considered implementing arithmetics. I have also considered implementing custom variables that you could associate to print and filament presets, so that you could call them in your Start G-code like [my_custom_temporary_bed_temperature].

[simonkuehling]

Yes, that is a beautiful idea, @alexrj!
This would enable us to set a custom "chamber_temperature" in filament presets to use in the start gcode - a feature that isn't needed for the majority of the other 3D printers and therefore probably won't justify its own native parameter.

I really like the custom variable idea - sleek solution that can integrate well into the UI

[lordofhyphens]

Implemented as per https://github.com/slic3r/Slic3r/wiki/Conditional-Gcode-Syntax-Spec in #3390