Don , that was very interesting......The 1767 add in the Philadelphia's
Penn. Chronicle was placed by S. Caruthers, one of Phila. earlist plane
makers, it in part read"Double iron planes of late construction far exceding
any tooth planes or uprights whatsoever for cross grained or curled
stuff"[taken from American planes].......sort of leaves no doubt who and
what for thease new planes were intended, cabnet makers using difficult
wood......I was interested also in seeing in your research that even the
high grade single planes were still cheaper then equal grade double iron
ones, which sort of shoots down the theory that it was cheaper to make
double iron planes because of the precsion fitting required of the single
iron ones ..........I  think many plane makers were forced by a competive
market to evolve with the times, if they didn't produce what the craftsmen
wanted somone else would, and that it was thease craftsmen that decided the
fate of the single iron, just as they would later with them chosing the
metal plane over the wooden ones ..........As always just my opinion, Todd