Fig. 1104.
Reamers for roughing out taper holes may be made with steps, as in [Fig. 1104], which is taken from The American Machinist, there being a cutting edge where each step meets a flute. Such a reamer may be used to enlarge parallel holes, or to rough out taper ones, and the flutes (if not to be used for brass work) may be spiral, as in the figure. The end step being guided by the hole serves as a guide to the first cutting edge; the second step serves as a guide for the cutting edge that follows it, and so on.
Fig. 1105.
The steps are best turned a trifle larger, say 1⁄1000 inch larger, at the cutting end. Half-round taper reamers, such as shown in [Fig. 1105], are used for finishing holes. The flat face is cut down, leaving rather more than a half circle; the clearance being filed or ground on the cutting side so as to enable the reamer to cut, and extending from the cutting edge to nearly half-way to the bottom of the reamer.
For holes, however, that are large enough to admit a tool of sufficient strength, the single-pointed boring tool produces the most true work.
Brass finishers use square taper reamers, which produce upon brass more true work than the half-round reamer.