The ®rst problem we meet using NC machines is that
when the programmer makes a mistake in writing the part
program, the piece will not be realized the way we want, but
it will have a different shape or different features. But it
could be more dangerous (and also expensive) if the programming
mistake gives the tool a motion command that can
generate a collision between the tool and the ®xed parts of
the machine, because of the speed of the NC machine tool is
higher than that of the traditional machine tool.