Motion and coordinate system for CNC machine
Z-axis: Always aligned with the spindle that imparts cutting power. This spindle might rotate the work-piece as in a lathe, it might rotate a tool as in a milling machine. It is perpendicular to work-holding surface if there is no such spindle. Positive motion in z axis tends to increase the separation between the work-piece and the tool
X axis: Positioning the moving element, parallel to the work-holding surface, horizontal (if possible).
On machines with rotating work-pieces, it is radial and parallel to the cross-slide
On machines with rotating tools,
1. If the Z-axis is horizontal, the positive x motion is to the right when looking from the spindle to the work-piece.
2. If the z axis in vertical, the positive x axis is to the right when looking from the spindle to the column
On machines with non-rotating work-pieces and non-rotating tools, the xaxis is parallel to and directed toward the principal cutting direction
Y-axis: be in such a direction as to complete a right-handed Cartesian coordinate system

Motion control system
 - Point to point
 - Straight cut system
 - Continuous path
    · Linear path interpolation
    ·Incremental path approximation
    ·Interpolation using circular or other equations