OVERVIEW

The majority of CNC programs will be programs for a single job - a job that is relative to a specific machine available in the shop. Such a particular job will have its unique characteristics, its special requirements as well as its own toolpath. Toolpath is the most important of all features of a typical CNC program.

It is the CNC programmer's main responsibility to develop a functional toolpath for any given job, without errors and in the most efficient way. Toolpath development is very important, because it represents a machining pattern unique to the job at hand. In most programming jobs, this machining pattern is executed for the given job only and is irrelevant to any other CNC program. Often, programmers encounter opportunities, where an existing machining pattern can be used for many new jobs. This discovery will encourage development of all programs more efficiently and produce CNC programs for many additional applications and without errors.

Programming method that addresses this issue is known as Translation of a Machining Pattern or, more commonly, a Datum Shift. The most typical example of this method is a temporary change of program reference point (program zero) from the original position to a new position, so called work shift. Other programming methods include Mirror Image, described in the next chapter, Coordinate Rotation and Scaling Function, described in the chapters that follow.

This chapter describes in detail the advanced subject of Datum Shift, also known as Machining...