If it's not urgent, warn your boss that you need a vacation at his own expense, you should at least 2-3 weeks before going to take it. Of course, he may refuse, especially if your lack of a negative impact on the manufacturing process. But usually the leaders - not that monsters and are well aware that any person may be situations where it is necessary to leave the service at the time.
Remember that employers always go forward, if the slave happened some tragic (death or illness of a relative) or happy (birth) event that requires your presence and participation. Even if you are at this moment will be on sick leave or holiday schedule, which is about to end. In such cases, you can put this in chief of fame just by calling or sending a telegram. Or even after the fact (in the case of a tragic event).
In order to create a vacation at his own expense, you will need to submit an application to the employer. Sign it and will be the head of personnel, and the chief accountant. Point it to leave and give the date, if possible, its cause. If you have decided that the chief not need to know about your problems, be prepared for the fact that he may refuse or you still insist that you tell about the situation that made you to postpone the work.