Unfortunately, many CAD systems generate drill files that cannot be unambiguously interpreted. Since the coordinates in drill files have no decimal points, some guessing may be required.
By default, a drill file is assumed to be in inches, with leading zero suppression and 4 digits after the decimal point. However, the file might actually be in mm, it might have trailing zero suppression, and there might be 3 or 5 digits after the decimal. If the file does not contain a command to specifically indicate that its coordinates are different from the default, then the Macaos Import Module will have trouble interpreting the file correctly.
One of the tricks we use is to look at the tool diameters. If there are tool diameters larger than 0.5, then the file is assumed to be in mm, even though there is no specific mm command (M71 or METRIC) in the file. This can lead to problems if you have more than one mm drill file, where none of them have mm commands and some of them do not have diameters larger than 0.5. In such a case, some files will be interpreted in mm and others in inch.
The workaround in such a case is to add to the file a line containing the command
M71
at the beginning of the data section of the file. If the file has a header section (ends with a % line and might begin with an M48 line) then the M71 line should be added just after the header section.
