Regarding the E-step in Cura I'm using a Delta Wasp 2040 printer equipped with a clay extruder. I'm using Marlin firmware. 

I'm trying to print food (vegetable creams) not PLA filament, but my question is about the setting of some of the parameters. 

As reported in Marlin, the default values for X, Y, Z, E axes are:

* D e f a u l t A x i s S t e p s P e r U n i t ( s t e p s / m m ) * O v e r r i d e w i t h M 9 2 * X , Y , Z , E 0 [ , E 1 [ , E 2 [ , E 3 ] ] ] * /

#define DEFAULT_AXIS_STEPS_PER_UNIT { 80, 80, 4000, 500 }


My questions are below:


The value 500 is intended as mm/min. If so, the actual value should be 8.33 step/mm of filament in a time of 1 s. Is this correct?
It is not clear, in my mind, the E-step that I can change in Cura. This is what I believe:


If I leave in Cura, an E-step=0, then this means that I'm using the default value (500)?
What happens if I change the E-step value in Cura for instance at +0400? Is it changed from 500 to 400 mm/min, or the value on Cura is intended as a percentage of the default value?



Can you explain to me exactly how the E-step changes when modifying its value in Cura.
I can only weigh in on the Marlin side of your question - "The value 500 is intended as mm/min" - uh, no, AFAIK it's steps per mm, just like it says - i.e. with filament, 500 steps per mm of filament fed. Other than not allowing the feedrate parameter to go so high that steps are skipped (which is a different limit) it's time-independent. I suppose with an extruder it would be mm of piston movement, but I don't have an extruder.

In my case, an actual value is closer to 250, and I typically check the calibration with 50 or 100 mm of filament feed so I can make a decent measurement.

I also wonder if your firmware knows it's running on a delta, since mine reports "A, B, C" rather than XYZ and all three towers are the same steps/mm - the "default values" you are looking at might apply to a typical cartesian printer where the Z axis is threaded while the X &amp; Y are toothed belts. 

Assuming it runs correctly you might be seeing irrelevant "default values" and having correct values loaded from EEPROM when the system starts (look at the log window when the control system connects to the printer.)