On our way to a convoluted evolution...
From the simple wooden planes that made the basic joinery possible: Rabbet, Plough, Fillester, Dado, Tonguing and Grooving planes, to its perhaps foregone conclusion. What the... Am I talking about? Believe it or not, I am simply answering Matt question about that odd shaped metal piece I called a Stanley No 45 Cam rest. Yeah really!! :-) In the beginning it was simple, the basic joinery in Western woodworking had evolved into a set of easily executed joinery with a chisel and a saw. But being repetitive and mostly made up of square shoulders, they could easily be made with some sort of wooden planes. GROOVY PLANES A simple chisel stuck in a piece of 2X4 construction wood, could serve as a router plane, a plough plane etc depending how installed and used. The Dado, the Groove and the Rabbet only differ in their orientation to the wood grain and the open edge of the rabbet. Lets cut the rabbet first, it is the easiest. Only thing our plane need is a bottom sole the width of the rabbet ...