Do you have plenty of free disk space, Bob?
Select a drive with enough free space to hold a merged library plus plenty of working space. Aperture will blow up the library considerably while merging libraries. Back up all your libraries before proceeding, so you can revert to the original versions.
- Then repair all libraries that you want to merge into one library by running the Aperture Library First Aid Tools on each of the libraries; see: Repairing and Rebuilding Your Aperture Library: Aperture 3 User Manual
- Then select one of your libraries - preferably the largest library - and open it in Aperture. To merge another library into this libraryuse the command "File > Import > Library" and select one of your other libraries to be imported. If your libraries contain duplicate images, Aperture will ask you, if you want to merge the libraries and only keep one of the images, or if the duplicates should be added.
Proceed to import your other libraries in the same way.
Check the merged library carefully, before deleting the original libraries. It has been reported, that occasionally images have been missing in the merged libraries, e.g.images imported from Photo Stream, so check the numbers of the images in the separate libraries and the combined library.
P.S. You may want to have a look at this section of the Aperture User manual for additional information: Working with Library Files