How does one go about zeroing the machine coordinates?
This is usually done in conjunction with a homing routine upon starting the machine. Otherwise, wherever the machine happens to be on startup, will be machine zero.
However, you do not need to work in the machine coordinate system when it is time to machine parts, as work shifts are commonly used for that purpose, which is a G54, or G55, etc zero offset from the machine coordinate system. All you need ask from the machine coordinate system is an exact repetitive procedure to home it to exactly the same point upon every startup.
First you get good, then you get fast. Then grouchiness sets in.
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)