I need to have two parts which are the opposite mirrors of either other, or in other words mirrored along two axis or work planes. I know there is a mirror option when deriving a part and I have accomplished what I want (2 parts) by essentially using 3 files.

File 1 : Original part,
File 2 : Original part derived with the first mirror
File 3 : File 2 derived with the second mirror

All the work gets done in File 1 and File 3.
File 2 is just a dummy mirror file.

While this works it seems like there could be a better way. Can some please offer a suggestion, or is this just how its done.
Thanks.