About this 3D model

This is an experimental Z height probe using a hall effect sensor wired to a spare analog input port. Sliding the retract bar drops the probe below the nozzle tip. Before a print, a gcode will probe the bed and set the Z height. After probing, when the nozzle approaches normal print height the magnet will automatically pull the probe up into it's storage position. A Z end stop is no longer used and the probe will automatically adjust Z height to varying bed heights. After configuring Marlin, just add this Gcode start sequence: G28 X0 Y0 ;Home X and Y ONLY G29 ;3 Point bed Probe G1 Z.5 F200 ;Force probe retraction Source: http://reprap.org/wiki/CrashProbe