z-axis limits

Adjustable z-axis limits on both sides. Prevents running too low if there have been missed steps by mechanical failure.

Removes issues caused by unreliable z-proximity detector that does not keep its sensitivity stable .

Use normal miniature limit switch (remove the sheet metal cam).

Pins are made of steel  wire. 

90 degrees bend of both rods. Used pop rivets as rod material. 

The interconnection of rods is done using a piece of electrical screw connector block.