As long as you know CAD, a CNC Machined Component to draw three figure on a piece of paper: main view, from the top part of the figure, the left view. Generally simple parts painting these three paintings can be expressed clearly, like the gear axis and so on. The complex structure needs to draw the sectional view, partial enlargement map. Open the part and express it internal structure and size clearly, such as screw hole, gear box and so on. If you want to know more about how to draw, you should see more about the CNC machined parts drawings. 

Precision Machined Parts also have their own standardized production, such as screw length, diameter and so on. So that once the machine fails, it is easy to repair.