Not an gcode expert... but you can use spiralize from the expert settings in cura to get what you want.... maybe create some using this function .. check first in layer view if its what you want. Then you can also study the generated gcode created by cura..
See the utility in this thread: http://umforum.ultimaker.com/index.php?/topic/5951-calibration-utility-leveling-ringsgcode/
It generates gcode that prints rings for leveling the build platform and should help you understand how the E value is calculated.
I second the suggestion about spiralize in Cura. That should keep you from worrying about learning gcode.
The UM2 can print gcode the way the UMO does or using "ultigcode" method. I'm not sure what triggers the difference but to get ultigcode mode you have to do something special like add the right comment near the top. So you probably are not in ultigcode mode.
The big difference is that in regular mode it's mm of filament (we are talking 2.85mm filament, not 1.75mm filament!) in normal mode and mm^3 of filament in ultigcode mode as anon says above.
There is no way to tell it to "automatically do the E axis". You have to specify how much extrusion for each "line" of filament laid down.
The UM2 expects the string ';FLAVOR:UltiGCode' in the first or the second line of the file. Otherwise the UM2 assumes RepRap-flavor and displays a warning that the gcode is overriding machine presets. But there is also the possibility to run RepRap flavor with volumetric E-values (choose volumetric RepRap flavor in Cura).
I recommend http://reprap.org/wiki/G-code as a great source for which codes should be used and which not. A special list for the codes on the UM2 can be found https://github.com/Ultimaker/Ultimaker2Marlin (you have to scroll down).
Thanks for all the replies! My first problem was that Cura was exporting this instead of GCode:
I thought this was some kind of unreadable, compressed GCode - it turns out it didn't like the model I was using. The instructions for calculating the E value were very helpful and my ultimaker is spitting out the models I want with my own custom version of spiralize.
My last (for now) question is about these lines:
Is the layer number significant? I also wonder if the ;TYPE is changing settings on the UM2 - maybe the SKIRT setting increases the E or Z value perhaps?
I dont know if the firmware recognize the ;LAYER to count progression of the print but basically anything starting with ; is a comment.
Also the layer numbers are splitted by objects. If you use print one at a time every object define its own layer count and reset the layer index.
Comments like ;TYPE:WALL-OUTER can be useful for post-process plugins to perform special actions or Cura to change the display color in layer view.
Hmmm, both the M108 and M101 are probably not appropriate for the UM2.
Disclaimer: I have a UM1 so my info could be wrong.
I believe the E values on the UM2 in ultigcode are in mm3. this makes it easier to calculate than the UM1 as the printer firmware adjusts the feed rate based in the filament size setting in the firmware.
So to calculate the E value, you take the nozzle diameter and assume that will be the line width times the height of the layer times the line length.
So for your first move from 0,0 to X0.025189008959740775 Y0.022321046299000193, the length value is square root of (delta X squared plus delta Y squared) or if my maths is right 0.03365583575334315261683035076938 times .4 for the nozzle times your layer height which looks to be 0.2mm from the above gcode or 0.002692
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