NC machines offered a reliable way of producing machine parts using pre-programmed commands. These commands consisted of alphanumeric characters defined by the RS233 IEEE code. These characters were coded on punch paper tape in formats specifically planned for a certain machine tool. These programs (punched tape) would then be read into the NC control using a paper tape reader. If during testing a program error was detected, the paper tape would have to be edited. This process meant duplicating a tape up to the incorrect character(s), retyping the correct characters, and then continuing with the duplication process. This is time-consuming process. During the running of NC programs, if a tool would begin to wear causing part dimensions to approach tolerance limits, the operator would have to stop and adjust the tool(s) to compensate for this wear.
In CNC machines, data for the control are still coded using either RS233 or the newer, more acceptable RSxyz ASCII code (American Standard Code for Information Interchange). Entire CNC programs may be loaded into the memory of the CNC control enabling the programmer or machine operator to edit the programs at the machine. If program changes are required, many CNC machines have built-in paper tape punch machines that allow for the generation of a new tape at the control. Tool wear is handled by adjusting program data in memory or calling in from a tool register one of several pre-programmed tool offsets.
As the implementation of microprocessors expanded, OEM’s of NC/CNC machines began using them in the construction of controls. By the late 1970s, nearly all NC/CNC manufacturers were using microprocessors (computers) in their controls. Today the phrase NC is commonly used when referring to CNC machines because the need to differentiate the two no longer exists. Today, ALL modern NC machines are in fact CNC machines.
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