Hi,
So far the conversation would appear to revolve around using either square or rectangular section timbers. When round, polygonal, moulded, profiled or tapered timbers are employed then the ability to establish offset lines from references faces will become more problematic and so this might well demonstrate the ultimate value of using centre lines as a method to establish reference planes.
Regards
Ken Hume
Ken, the examples you mention (all quite rare in traditional American timber work) may well call for center lines, but in most historic square rule applications a center line was not used.
This is what I have seen on old timbers where the lines were still as well as visible. My experience backs up this as I have found that lines which correspond to the tenon/mortise offset (usually 1.5" or 2") saves work by delineating one edge of the joinery.
