how do I calculate the E-parameter for Start G-Code

axiom

If I want to enter a first line of 595mm in the starting G-code...how do I calculate the E-parameter?
Here is my current startup G-Code that I would like to adapt:

G28 ;Home
G92 E1 ;Reset Extruder

G1 Z2.0 F3000 ;Move Z Axis up
G1 X5 0.5 Z0.3 F5000.0 ;Move to start position
G1 X600 Y0.5 Z0.32 F1500.0 E50 ;Draw the first line
G1 X600 Y2.0 Z0.32 F5000.0 ;Move to side a little
G1 X5 Y2 Z0.32 F1500.0 E100 ;Draw the second line
G92 E1 ;Reset Extruder
G1 Z2.0 F3000 ;Move Z Axis up

and here my driver parameters from config.g

; Drives
;M569 P4 R-1 ; Treiber 4 deaktivieren
;M569 P3 R-1 ; Treiber 4 deaktivieren
M569 P0 S1 ; physical drive 0 goes forwards
M569 P1 S1 ; physical drive 1 goes forwards
M569 P2 S1 ; physical drive 2 goes forwards
M569 P3 S1 ; physical drive 3 goes forwards
M569 P4 S0 ; physical drive 3 goes forwards
;M584 X0 Z2 E1 ; set drive mapping
M584 X0:4 Y1 Z2 E3 ; set drive mapping
M350 X16 Y16 Z16 E16 I1 ; configure microstepping with interpolation
M92 X80.00 Y80.00 Z640 E322.58 ; set steps per mm
M566 X900.00 Y900.00 Z100.00 E120.00 ; set maximum instantaneous speed changes (mm/min)
M203 X6000.00 Y6000.00 Z300.00 E1200.00 ; set maximum speeds (mm/min)
;M201 X500.00 Y500.00 Z20.00 E250.00 ; set accelerations (mm/s^2)
M201 X500.00 Y500.00 Z40.00 E250.00 ; set accelerations (mm/s^2)
M906 X1900 Y2300 Z1800 E1600 I30 ; set motor currents (mA) and motor idle factor in per cent
M84 S30 ; Set idle timeout

; Axis Limits
M208 X0 Y0 Z0 S1 ; set axis minima
M208 X750 Y640 Z1220 S0 ; set axis maxima

fcwilt

@axiom

You could create a simple 3D model, say, a rectangle of 595mm by 10mm by 10mm, convert it to STL, process that with your slicer and examine the generated print code.

Perhaps this STL file will work for you:

595x10x10.stl

Frederick

droftarts

@axiom the current move is 600mm, with 50mm of extrusion. Changing it to 595mm is a difference of less than 1%, and will be barely noticeable in extrusion, especially as it’s a purge line. I’d say leave as is. Or change it to 50 x 0.99 = 49.5mm.

Also, this move needs a ‘Y’ in it:

G1 X5 0.5 Z0.3 F5000.0 ;Move to start position

Ian

OwenD

@axiom
I do a similar thing using this macro, which I call from the slicer (Prusa Slicer)
It's overkill for doing a trivial thing like a prime line that probably won't change, but I did it as the basis for doing dynamic generation of some test files I was working on.
The line you're interested in is

var amount = ((var.d*var.height*var.l) + (pi*pow(var.height/2,2)*var.l)) / (pi*pow(var.FD/2,2)) * var.SF

I can't guarantee if the way I calculate the extrusion amount is 100% correct as compared to a slicer, but it works well enough for a purge line and means I can change the length of the line easily.

You must pass the following parameters.
S = extrusion factor
D = nozzle diameter
F = Filament diameter
O = Origin X and Y points as an array
L = Line length

e.g. in Prusa Slicer / Super Slicer I use the following after homing etc.

G1 X0 Y{"{move.axes[1].max}"} Z0.6  F1500 ; Move to back corner while heating
M568 P{current_extruder} R{"{heat.coldExtrudeTemperature+5}"} S{first_layer_temperature[current_extruder]} A2 ; (set standby and active temperatures for active tool.  Standby is 5 degrees above cold extrude temp )
M118 P3 S" Waiting for temps..."
G4 S1 ; Wait 1 Second
M116 ; Wait for all temps to stabilise
G1 X0 Y{"{move.axes[1].max -5}"} Z0.26 F1200 ; move to edge to wipe any oozed filament
M98 P"0:/macros/print/doPrimeLine.g" S{extrusion_multiplier[current_extruder]} D{nozzle_diameter[current_extruder]} F{filament_diameter[current_extruder]} O{"{1,0}"} L150; does prime line with calculated extrusion amount
G10 ; Retract
G1 Z0.1 ; lower head
G1 X{move.axes[0].machinePosition + 50} F1200 ; wipe
G1 Z10 ; raise head
G92 E0 ; reset extruder

note that in order to pass an array as a parameter from Prusa Slicer you have to enclose the array in double quotes O{"{0,10}"}

; doPrimeLine.g
; example of calling from Prusa Slicer
;M98 P"0:/macros/print/doPrimeLine.g" S{extrusion_multiplier[current_extruder]} D{nozzle_diameter[current_extruder]} F{filament_diameter[current_extruder]} O{"{0,10}"} L150; 

if state.currentTool = -1
	abort "No tool selected"
var ThisHeater = tools[state.currentTool].heaters[0]
if {heat.heaters[var.ThisHeater].state != "active"}
	abort "Heater " ^ var.ThisHeater ^ " on " ^ tools[state.currentTool].name ^ " not active"
if  {heat.heaters[var.ThisHeater].active < heat.coldExtrudeTemperature}
	abort "Heater " ^ var.ThisHeater ^ " on " ^ tools[state.currentTool].name ^ " set below min extrude temp"
if !exists(param.S)
	abort "no ""S"" (extrusion factor) parameter sent to macro in M98"
if !exists(param.D)
	abort "no ""D"" (nozzle diameter) parameter sent to macro in M98"
if !exists(param.F)
	abort "no ""F"" (filament diameter) parameter sent to macro in M98"
if !exists(param.O)
	echo "no ""O"" (Origin) parameter sent to macro in M98.  Defaults will be used"
if !exists(param.L)
	echo "no ""L"" (Length) parameter sent to macro in M98.  Defaults will be used"

echo "wait for heaters"
M116 ; wait for heaters to settle
echo "heaters done"
G4 P500
echo "set height"
var height = 0.2 ; create a variable then set it depending on slicer commanded position prior to calling this macro
if move.axes[2].machinePosition <= 0.4
	set var.height = move.axes[2].machinePosition
else
	set var.height = 0.3
echo "move to Z" ^ var.height
M400
echo "check extrusion percentage"
var SF = 100
if param.S <=1 ; check if slicer sends percentage of 1 or 100
	set var.SF = param.S   ; extrusion multiplier as a percentage of 1
else
	set var.SF = param.S / 100
echo "check filament dianeter"
var FD = 1.75 ; set filament diameter
set var.FD = param.F
echo "calculate distance and extrusion amount"

var startPos = {0,move.axes[1].min + 10} ; create a default start point
if exists(param.O)
	set var.startPos = param.O
var start = var.startPos[1]
var end = {move.axes[1].max - 10} ; extrude line end default position
var l = var.end -  var.start ; default line length
if exists(param.L)
	set var.l = param.L
	set var.end = var.start + var.l
	; do a sanity check to ensure we're within bounds
	if var.end > move.axes[1].max
		set var.end = move.axes[1].max
		set var.l = var.end - var.start
var d = param.D*1.00 ; nozzle diameter that is passed to macro as paramater
var amount = ((var.d*var.height*var.l) + (pi*pow(var.height/2,2)*var.l)) / (pi*pow(var.FD/2,2)) * var.SF ; calculate how many mm of filament to extrude - Owen's calculation
echo "flow rate value " ^ var.SF ^ " with " ^ var.d ^ "mm nozzle, " ^  var.FD ^ "mm filament dia over " ^ var.l ^ "mm length = E" ^ var.amount ^ "mm"
M83 ; set relative extrusion
G92 E0
echo "moving to X" ^ var.startPos[0] ^ " Y" ^ var.startPos[1] ^ " Z" ^ var.height
G1 X{var.startPos[0]} Y{var.startPos[1]} Z{var.height} F1200 ; move to edge to wipe any oozed filament
M400
G92 E0
echo "Move and extrude to Y"^var.end ^ " E" ^ var.amount
G1 X{var.startPos[0]} Y{var.end} E{var.amount} F600; move and extrude
M400
G92 E0
echo "move over one nozzle width"
G1 X{var.d} ; move by one nozle width
M400
G92 E0
echo "Move and extrude - other direction"
G1  Y{var.start}  F600 E{var.amount}; move and extrude
M400
G92 E0
echo "retract"
G10 ; retract
M400
G92 E0
echo "exit PrimLine"
G4 P500

axiom

@OwenD Thaks a lot!!!