Notes on mechanical drawing
A 1922 mechanical drawing manual by Rolland S. Wallis, issued by the engineering extension department of Iowa State College at Ames for students and tradesmen learning drafting conventions. The plates are line diagrams: dimension lines with arrowheads and fractional-inch callouts, hexagonal and square bolt heads in section, radii and chamfer details, and sequences of set squares shown in every working position with direction arrows and angle rosettes.
