Fig. 951.
Fig. 952.
Thus in [Figs. 950] and [951] the diameters of the work w and the top rake of the respective tools are equal, but the tool that is set above the centre, [Fig. 950], has more bottom rake but no more clearance, which occurs from the manner in which the cutting edge is presented to the work; the dotted lines represent the line of severance for each, and it is obvious that in [Fig. 950], being of the shortest length for the depth of the cut will require least power to drive, because it is, as presented to the work, the sharpest wedge, as will be perceived by referring to [Fig. 952], in which the tool shown in [Fig. 950] is simply placed below the work centre, all other conditions as angle, &c., being equal.
From these considerations it appears that while for roughing cuts it is advantageous to set the tool above the centre, it is better where great cylindrical truth is required to set it at the centre for finishing cut.
Fig. 953.