Start with the endmill in the machine, move to where you want the reference for Z zero to be, then lower until you can get a repeatable setting. Methods to use:
- use a touch plate: Shapeoko CNC Router, Rigid, Accurate, Reliable, and Affordable (Carbide 3D will be releasing one soon)
- use a piece of paper: Shapeoko2 - First Job
5.Lower your Z-axis so the tip of the end mill mounted in the spindle just touching the material. A good way to gauge is to lower it down onto a single sheet of paper. As the bit gets close to the paper, try moving the paper around slightly. When the bit prevents the paper from moving, then you’re at the right height! This also usually works out to leaving a paper-thin thickness connecting the cut-out part to the balance of the material.
- use a cylinder of known diameter — jog the endmill against it, then incrementally lift and jog until the endmill just passes over the cylinder — this is a good way to set Z-zero when you want to reference off the bottom of the material and material thickness is a bit variable, say when woodworking and you are making rabbet joints
I believe this is discussed in: http://carbide3d.com/docs/tutorials/tool-change/ or it’s in one of the videos: Getting Started with Carbide Create or it’s in the tutorial: http://carbide3d.com/docs/tutorials/makey/