Fig. 1081.
An excellent form of boring bar and cutter is shown in [Figs. 1080] and [1081].
Fig. 1082.
[Fig. 1082] shows a side view of the cutter removed from the bar; [Fig. 1081] an end, and [Fig. 1080] a side view of the bar and cutter. The cutter is turned at a and b to fit the bore of the bar. The cutting edge c extends to the centre of the bar, while that at d does not quite reach the centre. These edges are in a line as shown in the end view. On account of the thickness of the cutter not equaling the diameter of the bore through the bar there is room for a stream of water to be forced through the bar, thus keeping it cool and forcing out the cuttings which pass through the passages g and h in the bar. The cutter drives lightly into the bar. By reason of one cutting edge not extending clear to the centre of the cutter there is formed a slight projection at the centre of the hole bored which serves as a guide to keep the cutter true, causing it to bore the hole very true.
Fig. 1083.
For finishing the walls of holes more true, smooth, and straight, and of more uniform diameter than it is found possible to produce them with a drill, the reamer, or rymer, is employed. It consists of a hardened piece of steel having flutes, at the top of which are the cutting edges, the general form of solid reamer for lathe work being shown in [Fig. 1083]. The reamer is fed end-ways into the work at a cutting speed of about 15 to 18 feet per minute.