TABLE OF CONTENTS External and internal machining, commonly known as turning and boring, are the most common operations on CNC lathes. Either operation involves roughing and finishing toolpaths and can range from very simple to very complex. Roughing means removal of a significant portion of the material and forming the shape that will be finalized during finishing. Multiple repetitive cycles G70, G71, G72 and a to a much smaller extent G73, are very useful for this type of work. Depending on the job setup and complexity, the CNC programmer has to deal with many issues that relate to roughing and finishing, with or without using multiple repetitive cycles. This chapter describes various techniques that can be used in many turning and boring operations on CNC lathes.
Selecting program zero (part zero) for lathe parts is always related to the Z-axis. Without an exception, the program zero for the X-axis must be the spindle centerline. When it comes to the Z-axis zero selection, there are several methods that may at least be evaluated and either rejected or accepted.
The illustration at right shows five reasonable options, identified by a reference letter. The Z-zero position can be anywhere, but there is some credibility in the five options.
Position A Front face of the stock
Although this face is easy to reach during tool setup, selecting the stock front face has several disadvantages. First one is that the stock will be removed by facing in the early stages of machining, but the amount removed...
