Z Axis Optical Fine Adjustment

After making my own version of a compact Z axis adjustment, I upgraded Marlin and started using Mesh Bed Leveling. As MBL allows for height adjustment both above or below Z MIN, I was concerned about depressing the end stop limit switch beyond its limit. Using an optical sensor allows depth below 0 without harm.

The knob was created using the same knurled geometry from the MakerBot Knurled Surface Finishing Library Nut and Bolts. https://www.thingiverse.com/thing:9095 The first photo shows the optical configuration and second photo the earlier non-optical version installed on my printer (nearly identical). To prevent the screw from turning I increased the height slightly and added a hex rib inside the upper plastic part for a nylon locknut. A regular 3mm nut is used inside the knurled knob. There is also a bed leveling spring installed to maintain pressure.

While waiting for my optical end stop to arrive, I completely re-configured my cooling fan and added an experimental yet q