Finish Reaming

Reaming is traditionally a finishing process for a rough hole produced by a twist drill. With the modified drills discussed earlier, high-grade reamers corresponding to ISO Grade 4 or 5, instead of the traditional 6, give fine finished holes. Recent developments by a Japanese firm include the broach reamer, which rotates, and the carbide mill reamer, which can be used in a machining center or preferably a jig borer (Fig. 10). Broach reamers are available in sizes from 3 to 100 mm and carbide mill reamers are available in sizes from 5 to 100 mm. Both reamers give Ra of 1 ^m and cylindricity and roundness of <2 ^m.

Fig. 10 Broach and carbide mill reamers. (a) Broach reamer, made of high-speed steel with a left-handed helix of 60° or more, that can cut at 20 m/min (65 ft/min) at a feed of 0.25 mm/rev (0.1 in./rev). (b) Carbide mill reamer that can cut at 30 m/min at a feed of 0.3 mm/rev (0.1 in./rev)
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