ER11A Zero Probe

A simple to assemble version of the [ER11A Z axis probe](https://www.thingiverse.com/thing:4776984) that screws onto an ER11A spindle. It has indicator LEDs and can be used to measure and compensate for a bed that isn't flat when engraving, for example a PCB or a curved surface. I use it for my Stepcraft CNC. This design uses "Pogo" type pins to retain the sense tip and make contact with the stationary part of the switch. The front guide section just screws on and can be opened for cleaning if anything doesn't work.

It is very sensitive and repeatable. I measured the spring force to sctivate the switch to be about 55g. Repeatability is 4um (0.00015") on a sample of 11 measurements taken at the same spot but that's really down to the repeatability of my Z axis, readings were just changing between 2 values.

Pogo pins I used are 16mm long, 1mm diameter and the end is rounded so it can slide on the washer. They were called P75-J1