Fig. 1137.
The tools employed for the roughing cuts of boring bars should, for wrought iron, cast iron, steel, or copper, have a little front rake, the cutting corner being at a in [Fig. 1137].
Fig. 1138.
If the cutters are to be used for one diameter of bore only, they will work more steadily if but little or no clearance is given them on the end b, [Fig. 1138], but it is obvious that if they are to be used on different diameters of bores they must have clearance on these ends. The same tool may be used both for roughing and finishing cuts.
Fig. 1139.