E value Calculation of the G code in Prusa Slicer
 

E value Calculation of the G code in Prusa Slicer  

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Vick
 Vick
(@vick)
New Member

Hi, I am wondering does anyone know how to calculate the E value (the amount of extrude from the start to the endpoint ) in the Prusa Slicer? I am trying to test the performance of my adaptive slicing (non-uniform layer height) f0r my research, but not sure how to adjust the G-code ( E ) of Prusa slicer based on my given length and height. Many thanks 

I have tried to use the formula below, but it does not match the E of Prusa Slicer. 

Posted : 26/06/2020 11:57 am
karl-herbert
(@karl-herbert)
Illustrious Member
Posted by: @vick

Hi, I am wondering does anyone know how to calculate the E value (the amount of extrude from the start to the endpoint ) in the Prusa Slicer? I am trying to test the performance of my adaptive slicing (non-uniform layer height) f0r my research, but not sure how to adjust the G-code ( E ) of Prusa slicer based on my given length and height. Many thanks 

I have tried to use the formula below, but it does not match the E of Prusa Slicer. 

if you want to know how Prusa calculates this in the slicer, you can browse the source code of the slicer:

https://github.com/prusa3d/PrusaSlicer/releases

I you want to calibrate the extruder, look here:

https://mattshub.com/blog/2017/04/19/extruder-calibration

Statt zu klagen, dass wir nicht alles haben, was wir wollen, sollten wir lieber dankbar sein, dass wir nicht alles bekommen, was wir verdienen....
Posted : 26/06/2020 12:57 pm
Vick
 Vick
(@vick)
New Member

@karl-herbert

Thank you very much. 

Posted : 26/06/2020 3:11 pm
Sanglae Kim
(@sanglae-kim)
Active Member

I'm currently working at same page(Calculating E value in G-code from prusaslicer), but I couldn't find some functions in source files..

Also, I'm not expertise in coding.

 

The only thing I found was

The related functions and variables which is "m_E(to stack when it's absolute coordinate), dE", etc..

All functions are pointed each other, so that there is no direct calculation formula there..

On the other hand, I also looked a "Flow math" at slic3r. The calculation for my E value isn't correct

 

I have 2 questions for this.

First, E value calculation, What is wrong with my formula?

(This is some part of G-code from prusaslicer)

; external perimeters extrusion width = 0.45mm
; perimeters extrusion width = 0.45mm
; infill extrusion width = 0.45mm
; solid infill extrusion width = 0.45mm
; top infill extrusion width = 0.40mm
; first layer extrusion width = 0.70mm

 

(This is somewhere between top, bottom layer, just to avoid compensation for first, last layer)
G1 X115.996 Y179.003 E0.86610
G1 X115.996 Y160.225 E0.90316
G1 X118.961 Y154.015 E0.33096
G1 X120.077 Y151.147 E0.14800
G1 X120.766 Y148.109 E0.14984
G1 X120.996 Y145.038 E0.14811
G1 X120.996 Y64.964 E3.85132
G1 X120.766 Y61.893 E0.14811
G1 X120.077 Y58.855 E0.14983
G1 X118.961 Y55.985 E0.14809

form X120.996 Y145.038 to X120.996 Y64.964, (I made it bold)

 

extrusion at nozzle

from "Flow math" the width(w) : 0.45, layer height(h) : 0.3

cross section area from nozzle = h*h*0.25+w*(w-h) = 0.11568582

the extrusion length will be 80.074(=145.038-64.964).

total extrusion volume = 9.263426

 

At the same time, for filament

the 1.75*1.75*PI*0.25=2.4052813(cross section area for filament)

 

So my conclusion is to 9.263426/2.4052813 = 3.851286

It is not even close to 3.70389(=3.84993-0.14604)

It seems I'm missing something, for sure.

 

Second, 

Some parts of G-code has same value of E or even minus or less then before, even they are still extruding

Is there any method that I'm missing..?

 

 

Giving any small hint would be thankful..

Thanks,

This post was modified 2 months ago by Sanglae Kim
Posted : 17/01/2021 8:21 am
misan
(@misan)
Moderator

@sanglae-kim

a hint: https://manual.slic3r.org/advanced/flow-math

but you do not tell if Linear Advance if in use, that may affect too.

This post was modified 2 months ago by misan
Posted : 17/01/2021 8:54 am
Sanglae Kim
(@sanglae-kim)
Active Member

@misan

So, the E value that I calculated was not wrong!

I'll look for it right away

Thanks for the advice!!

Best regards,

 

(PS, for those who are struggling with,

the effect of advanced linear - )

This post was modified 2 months ago by Sanglae Kim
Posted : 18/01/2021 12:30 am
misan
(@misan)
Moderator

@sanglae-kim

By modelling the pressure inside the hot-end, Linear Advance may cause different extrusion values for the same length of the extruded line. So expect some non-obvious differences if you monitor the length of extrusion for a given line length if LA is active.

Posted : 18/01/2021 8:38 am
Sanglae Kim
(@sanglae-kim)
Active Member

@misan

Yes, thank you so much for reply.
I'll work on that part, see if LA was the missing point

Thanks a lot!
Best regards,
Posted : 18/01/2021 9:35 am
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