Merging iCal calendars

Anyone know how I merge two iCal calendars? They are in the same account, just two different calendars, e.g. "home" and "work"? I want to move everything from, for example, "work" to "home".

I have tried to export one of the calendars and then re-import it into the other. The export seems to work fine, but every single time I try to re-import the ics file iCal crashes at the end of the import process, and the import is not completed.

I'm on 10.8 Mountain Lion.

Help appreciated!