Hi, this is my design for a Z-Axis opto sensor mount for the Orca 0.3. It is much more secure than the cable tie method, and follows on from my X-Axis Opto Mount. (http://www.thingiverse.com/thing:14155).
The parts position can be adjusted easily, just slacken off the nut and bolt, move it to where you want it, and tighten back up.
v2 - uses method similar to orca 0.40. One bolt adjusts, the other bolt and the 8mm bar guides. The spacers are used to tighten the bolts with nuts to stop them moving. I am using extruder springs and they seem to work well. The bolts are M4x40 cap heads.
The picture is different to the current stl, i've modified it since fitting the one in the picture.