OVERVIEW

From all available machining operations, contouring or profiling is the single most common CNC application, perhaps along with hole making. During contouring, the tool motion is programmed in at least three different ways:

• Tool motion along a single axis only

• Tool motion along two axes simultaneously

• Tool motion along three axes simultaneously

There are additional axis motions that can also be applied (the fourth and fifth axis, for example), but on a CNC machining center, we always work with at least three axes, although not always simultaneously. This reflects the three dimensional reality of our world.

This chapter applies only to CNC milling systems, since turning systems normally use only two axes, and planes are therefore not required or used. Live tooling on CNC lathes does not enter this subject.

Any absolute point in the program is defined by three coordinates, specified along the X, Y and Z axes. A programmed rapid motion G00 or a linear motion G01 can use any number of axes simultaneously, as long as the resulting tool motion is safe within the work area. No special considerations are required, no special programming is needed.

That is not the case for the following three programming procedures, where the various considerations change quite significantly:

• Circular motion using the G02 or G03 command

• Cutter radius offset using the G41 or G42 command

• Fixed cycles using the G81 to G89 commands, or G73, G74 and G76 commands

In all three...