Part Overview

PART I - LOOKING BACK

Any look forward has to be matched by the look back. The historical viewpoint is a necessary step to think about the present, and it is equally important to look into the future. Since its beginning in the 1950's, numerical control (NC) technology has gone through several important periods. These periods had a major effect on the metalworking industry and machining, and can be divided into three major areas:

1. Period of columns

2. Period of zeros

3. Period of decimals

In the early period, the era of columns covers hard-wired machine tools of the NC type (no computer numerical control-CNC in those days), and the programming format that required an input of data in a columnar form, Fig. 9-1. The position of data in a column specified which axis or function was to be performed. Letters were not allowed in the program.

Figure 9-1: The EIA standard NC tape consisted of eight vertical channels where holes were punched to provide coded machining information.

In the middle period, Computerized Numerical Control became popular, and CNC machines started finding their way into medium-sized manufacturing companies. Using a letter oriented programming format ( word address programming) with trailing zeros input was a major break-through in part programming. In machining, the CNC technology introduced unique program editing options, right at the operator's fingertips.

The latest improvement was not far behind. CNC technology has matured and preprogrammed cycles and special routines that are very easy to use...