how center bed with start gcode?

hello how can i center bed, only with start gcode?
i have a Ender 3
slicer Cura 3.5
start gcode
Ender 3 Don't save on EEPROM

M92 X80.482 Y80.889 Z404.04 E94.256 ; STEP/MM ESTRUSORE
G28 ;Home
;  G1 Z15.0 F6000 ;Move the platform down 15mm
G92 E0
G1 F200 E3
G92 E0

Send: M503
Recv: echoteps per unit:
Recv: echo:  M92 X80.48 Y80.89 Z404.04 E94.26
Recv: echo:Maximum feedrates (mm/s):
Recv: echo:  M203 X500.00 Y500.00 Z5.00 E25.00
Recv: echo:Maximum Acceleration (mm/s2):
Recv: echo:  M201 X500 Y500 Z100 E5000
Recv: echo:Acceleration: S=acceleration, T=retract acceleration
Recv: echo:  M204 S500.00 T500.00
Recv: echo:Advanced variables: S=Min feedrate (mm/s), T=Min travel feedrate (mm/s), B=minimum segment time (ms), X=maximum XY jerk (mm/s),  Z=maximum Z jerk (mm/s),  E=maximum E jerk (mm/s)
Recv: echo:  M205 S0.00 T0.00 B20000 X20.00 Z0.40 E5.00
Recv: echo:Home offset (mm):
Recv: echo:  M206 X0.00 Y0 Z0.00
Recv: echoID settings:
Recv: echo:   M301 P21.73 I1.54 D76.55

i try

G28
M206 Y8.22
G28

but use the same position for homing

Edited 3 time(s). Last edit at 10/07/2018 09:59AM by enricosx.

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Creality Ender 3

Size of the bed is set in firmware. You cant change it (hopefully its correct, you wont be able to reach the far right and far back positions if its wrong.)

After you home x0,y0 needs to be at x0,y0 on the bed
If its is not zero you can change that in start gcode

eg after line G28 ;Home
G1 X{realhome_value} Y{realhome_value} Z5 F6000 ; Move to real X0,Y0,Z5 position, insert real values here.
G92 X0 Y0 ; Set current position to X0,Y0

x0,y0 is now at 0,0 on the heated bed, this is not the only way to do it...

I've never played with M206...

the other thing you need to check is that the slicer has the correct bed dimensions, if this is wrong It will center the code incorrectly.

Edited 2 time(s). Last edit at 10/07/2018 10:37AM by Dust.

thank you so much!

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Creality Ender 3