Cura generated temperature commands are ordered incorrectly

[b-morgan 1]

 

On 6/21/2017 at 2:56 AM, ahoeben said:

CuraEngine checks if the start gcode contains commands to heat up the hotend and bed before the print is started. If the start gcode does not have command to do that, CuraEngine adds the three lines (M190, M104, M109) before your start gcode just to make sure that the hotend is not cold before starting the actual print.

If you don't want Cura to add these lines, make sure your start gcode contains lines which have {material_print_temperature} and {material_bed_temperature} in them respectively.

 

The order of these three lines is incorrect. An M104 (heat hotend, no wait) followed immediately with an M109 (heat hotend, wait) is exactly the same as the M109 alone (i.e. the M104 is essentially a no-op). If however, the M104 was first followed by the M190 (heat bed and wait) and then the M109, then that combination would cause both heaters to be working at the same time.

[burtoogle 515]

Maybe their logic is the following: as some beds take a lot longer to heat than hot ends, the ordering is OK as it minimises the amount of time that the filament is static in a hot nozzle while waiting for the bed to heat.

[AbeFM 35]

I've also heard it is for limiting current draw on marginal machines.  I like your explanation better.

 

If I'm really in a rush, I hit "preheat PLA" before a print.

[b-morgan 1]

On 6/8/2018 at 10:02 AM, smartavionics said:

Maybe their logic is the following: as some beds take a lot longer to heat than hot ends, the ordering is OK as it minimises the amount of time that the filament is static in a hot nozzle while waiting for the bed to heat.

 

This might make sense if there were just the two commands, M109 followed by M190. Since there are three commands...