When not carefully sharpened, all forms of reamers have a tendency to produce a rough hole. Too much clearance reduces the support of the reamer in the hole and tends to make it work unsteadily.
Reamers are made from tool steel and then hardened and tempered to a straw color; they may be straight or tapered, and may have a square end or tapered shanks. The square-end reamer is generally operated by hand. Reamers may be solid or may be made with inserted, adjustable blades. The solid reamer has the disadvantage of becoming undersized as soon as worn, but the adjustable reamers are considerably more expensive.
Figure 138a shows a straight-fluted reamer with a square end, the type most commonly used. Figure 138b shows a spiral straight reamer, which is used when a slow feed is required. The spiral is made left-handed, while the reamer, in cutting, turns right-handed; this construction tends to prevent the reamer from drawing into the hole and sticking. Figure 138c is a straight-fluted shell reamer, so called because it is made hollow in the center in order that it may be used with a mandrel. Figure 138d shows a rose reamer. There are a great many other kinds of special reamers made for different classes of work, but space will not permit their being described here.
Reamers are rarely given less than 6 flutes, and usually have from 6 to 20, the number depending upon the size of the reamer. The number of flutes is generally made odd in order that there will always be two teeth opposite one tooth. These two teeth stay or hold the tool better so that it does not tend to wobble or chatter as much as it would with but one tooth opposite one tooth. It is easier, however, to caliper (measure) a reamer with an even number of flutes, having one tooth exactly opposite another on the diameter. With reamers having a large number of teeth, the odd or even feature is not of so much consequence. Shell and rose reamers may be given the same number of flutes and have their cutting edge formed in the same manner as solid reamers.
(a) Straight-Fluted Reamer (b) Spiral Straight Reamer.
(c) Straight-Fluted Shell Reamer.
(d) Rose Reamer.
Fig. 138. - Reamers.