Ender 3 Dual leadscrew Mechanical Gantry Alignment Endstop

Just print 2 of those and snap on the top of the printer. Now you can bump the gantry on them to mechanically align your gantry.

You will also need 1 T-Nut and equivalent screw.

Ideal for Enders with 2 leadscrew but just 1 stepper driver controlling both motors. For Marlin you have to recompile firmware to enable Mechanical Gantry alignment. For Klipper you can use the following macro:

[gcode_macro MECHANICAL_GANTRY_CALIBRATION]
gcode:
   ### SET THIS DEFAULT CARFULLY - start really low
   {% set my_current = params.CURRENT|default(0.3)|float %} ; adjust crash current on the fly :D
   ###
   {% set oldcurrent = printer.configfile.settings["tmc2209 stepper_z"].run_current %} ; TODO: Find runtime current settings
   {% set z_max = printer.toolhead.axis_maximum.z %} 
   {% set x_max = printer.toolhead.axis_maximum.x %} 
   {% set y_max = printer.toolhead.axis_maximum.y %} 
   {% set fast_move_z = printer.configfile.settings["printer"].max_z_velocity %}
   {% set fast_move = printer.configfile.settings["printer"].max_velocity %}
   
   {% if "xyz" not in printer.toolhead.homed_axes %}
       G28       #Home All Axes
   {% endif %}
   G90 ; absolute
   G0 X{x_max / 2} Y{y_max / 2} F{fast_move*0.8 * 60 } ;put toolhead in the center of the gantry

   G0 Z{z_max} F{fast_move_z*0.8 * 60 } ; go to the Z-max at speed max z speed
   
   SET_TMC_CURRENT STEPPER=stepper_z CURRENT={my_current} ; drop current on Z stepper
   
   G4 P200 ; Probably not necessary, it is here just for sure

   SET_KINEMATIC_POSITION Z={z_max - 10} ; Trick printer into beleiving the gantry is 12mm lower than it is

   G1 Z{z_max} F{fast_move_z*0.5 * 60} ; try to move 10mm up
   G4 P200 ; wait
   G1 Z{z_max*0.2} F{fast_move_z*0.8 * 60} ; move 4mm down
   G4 P200 ; same as the first one
   
   SET_TMC_CURRENT STEPPER=stepper_z CURRENT={oldcurrent}

   G4 P200 ; same as the first one
   G28 Z ; we MUST home again as the ganty is really in the wrong place.

[gcode_macro G34]
gcode:
   MECHANICAL_GANTRY_CALIBRATION