Fistly, set the origin of both the designs to (0,0). Generate the drill files of both the designs from Manufacture->NC->NC Drill.Originally posted in cdnusers.org by kishore
Lets say that you now have two drill files ncdrill1.tap and ncdrill2.tap.
Then, open the drill files of both the designs that will be available in your allegro design folder(s) of your current project(s).
Copy the drill coordinates of the second design from your ncdrill2.tap file and paste it at the end of the first design file i.e ncdrill1.tap. Save the file and try importing it in any CAM tool, you should see the drill coordinates in a single panel.
Hope this helps!