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Nozzle temp turns off before end of print! firmware look-ahead issue?

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Only some files on my UM2+ are turning off my nozzle (like a M104 S0) before the print is done. It's like the firmware is using some look-ahead and executing the "M104 S0" immediately before all the buffered "G" movements are done. So what happens is the nozzle temp drops resulting in grinding and under extrusion.


So far I am only noticing it on very simple files (only about 120 lines total) AND ONLY if a second layer and fan are needed.

(FYI-warning  these files are for a 2.0mm nozzle , so if you try to print with a smaller nozzle you will have trouble -  in cura line_width=2.0mm)

EXAMPLE goodMixC-L0-C0_Noz20_6C.gcode = this files prints fine , only has 1 layer and does not use the fan.


EXAMPLE trouble - MixC-L1-C0_Noz20_6C.gcode = this file turns off nozzle about half way through. has 2 layers and uses the fan. NOTE based on the gcode the nozzle should not turn off before the fan, but the fan does keep running the the nozzle goes to zero.


These are just two files from a set of 14 gcode files that make this print, all 7 files that are single layer-nofan work great all 7 that are 2 layer-fan fail in the same way.


UM2+ extend (firmware May 11 2016 13:14:11)

CURA 2.3.1 (windows 7)


What can I do to stop this? Any suggestions are appreciated. I am considering commenting out the fan off command and manually turning that off at the end of the job.

Edited by peetersm

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46 minutes ago, peetersm said:

Only some files on my UM2+ are turning off my nozzle (like a M104 S0) before the print is done.


No - all your files do this.... ?

Marlin has a motion buffer of (up to) 16 line segments. And if printing these buffered line segments takes long enough, this can happen. It's just a coincidence that there are a lot short moves at the end of the other half of your files, so that it doesn't hurt that much...?


The obvious solution is to remove the "M104 S0" from the end of the files. An additional "M400" right before this line would also help.

Where does the M104 come from? Does Cura 2.3 insert these line or have you added this yourself to the end-script? Cura 3.5 does not add this line (anymore?).

  • Thanks 1

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thanks! I just noticed on the file I thought was good that the nozzle did turn off before the motion was done, but it did not matter since the last several moves only took a ~2 seconds.


Cura 2.3.1 is putting that M104 command in the gcode. I did comment that out and things are working better.

I like the idea of the M400 suggestion, this would come in handy in a lot of other contexts too.


FYI  -  Changing my CURA version is a HUGE undertaking that I fear going through.

Edited by peetersm

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