Excellon Format - Excellon-like Files

Excellon-like Files

The name Excellon format or Excellon file is also commonly used for files that only vaguely follow any specification. These files contain a few Excellon commands, but follow neither the Excellon nor the IPC-NC-349 specification. It would be more appropriate to call them Excellon-like or generic NC files. Commands are not used properly, or are used in a syntactically incorrect way, and binary data objects may be included. Sometimes the historic EIA or EBCDIC character encoding is used instead of ASCII as required by the standards. Usually the header is incomplete: essential information such as the scale or the tool diameters is missing. Sometimes there is no header at all, and the file only contains tool numbers, with an unspecified diameter, and X,Y coordinates, in an unspecified unit. An example:

% T01 X006272Y001092 X006354Y001093 X006653Y001092 ... T02 X008091Y001754 X-002028 M30

These files are meaningless without additional information, typically put in a free format human readable tool file. This information must be re-entered manually by the CAD/CAM operator. When critical information is missing (e.g. omitting leading or trailing zeroes without properly documenting if and which zeroes are omitted) the file is ambiguous. The user may substitute his own judgement or stop the job pending clarification.

These inadequate Excellon-like files are often used. They result in unnecessary manual labor and possibility of delays or errors. These so-called Excellon files give the format a worse reputation than it deserves.