This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
Clearly the adze must be sharpened from the inside; and when the action of it is considered, it is also clear that the curvature of the adze iron must be circular, or nearly so. The true curvature of the metal may be approximately deduced from considering the radius of the circle described by the workman's arms and the handle of the adze. The edge of the adze is convex (Fig. 425), the projection in the middle being so formed for the same reasons as influenced the curvature of the edge of the axe already alluded to. The curvature in the blade also serves (though partially) as a fulcrum, for, by slightly thrusting the handle from him, the workman may release such flakes of timber as are over the adze, and yet so slightly adherent as not to require another blow. Thus the adze when applied lever-fashion discharges its duty as the curvature in the claw of a hammer does. Fig. 428 is a gouge formed adze; a modification of this is used in making wooden spouts and similar hollow work.
The principal forms of adze are illustrated below. Fig. 421 is an ordinary carpenters' adze; Fig. 425, ship carpenters' adze; Fig. 426, coopers' adze; Fig. 427, improved wheelers' adze; Fig. 428, spout adze; Fig. 429, coopers' adze with sexagon eye; Fig. 430, coopers' nail adze.