Info request - single heater with multiple extruders
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Over in Cura universe we're just discussing adding an option that lets Cura know that multiple extruders share one heater. At the moment, Cura will set a tool's temp to zero once it has been used for the last time in a given print. This obviously fails for single heater, multiple extruder setups.
The question was asked that as the printer firmware knows that multiple tools are using the same heater, can't it just ignore the lower of the set temperatures for the two tools? What's RRF's approach to this scenario? Thanks. -
The best option is probably to let RepRapFirmware do the tool temperature management when tool changes occur. RepRapFirmware supports separate active and standby temperatures to handle the case of tools with independent heaters, where you want the standby tool to be maintained at a lower temperature.
In machines with separate heaters for each tool, setting a tool's temperature to 0 is OK for an IDEX-style machine, but it is probably a bad idea fo machines with dual nozzles on a single print head. A nozzle that is heated to standby temperature may skate over small protrusions in the print, whereas a cold nozzle is likely to ram into them.
Don't forget that you can have machines with both mixing nozzles and a separate nozzle for support material or high-speed infill. We have a printer like this. So assuming that the machine has either a mixing nozzle or separate heaters for each tool doesn't cover the more general case.
IMO the real problem is that other 3D printer firmwares don't handle multiple tools in a flexible way or abstract the details of a tool (e.g. heaters used) away in the way that RepRapFirmware does. Slicers shouldn't need to know about tool heaters, only about tools. it's daft to have to configure both the printer firmware and the slicer to know what the mapping between heaters and tools is.
The logical solution to your question is that if you want to turn off tool heaters early, the slicer should send a "finished using this tool" command to the printer, and the printer firmware should decide what if anything to do about it.
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Thanks @dc42 for your comprehensive reply. I will copy it into the Cura conversation.
