Z Axis Zero Tool works by placing the sensor on your work piece under the cutter, then initiating the cnc software to lower the tool until it touches the sensor, sensing a closed circuit between the tip of a CNC cutting tool and the zero sensor.
The software will then raise the tool away from the sensor and calibrate the job top surface based on the height of the sensor calibrated in the software.
Cheap eBay units have no movement, this is ok for larger end mill cutters etc but the thin long tungsten carbide engravers snap/crumble if the driven into a hard surface.
This will vary on your print and the circuit board thickness used.
I used what I thought would be common scrap box ,garage components.
Spring was from an old bathroom tap cover holder.
and the 29mm copper disc was a piece of circuit board I cut out.
You can use any spring or springs.
Any material like copper, aluminium or stainless for the disc.
making the appropriate modifications to the spring guide to suit.
The disc was super glued to the spring loaded plastic end stop plate.
you can modify the height of the housing to suit the sensor height you require.
After assembly modifications:
Wire placements on disc and path through enclosure.
I would solder the wire more to the outer edge of the disc, or even underneath.
I initially used a knot in the wire to prevent it being pulled out, this restricted the up down movement of the sensor pad so I drilled holes in the cross shaped spring guide and threaded the wire through so it wont get pulled out of sensor.
The parallel accuracy was excellent.
Now I just have to modify my mach3 software and cnc driver to accept the sensor.
This is the video that gave me the idea.