Originally Posted by Mr IGH

The frame shop I worked at faced the shell referenced to the threads, then aligned the frame on a surface plate with the shell bolted to the table using the face as the reference. It works.

If the frame is already built up and in the hands of a consumer then it might be an issue, esp if the frame wasn't built with the bb threads as the original reference for all subsequent alignment steps.

OTOH, the need for the faces to be perfectly parallel for a bottom bracket to work correctly has mostly past. If a cartridge bb is used then there's no need at all. In the case of Hollowtech II bb, there's some slop available in the nylon bushing that line the bearing and if the shell isn't too far off it'll work.