Machinery's Handbook, 31st Edition
908
Reamers REAMERS
Hand Reamers.— Hand reamers are made with both straight and helical flutes. Helical flutes provide a shearing cut and are especially useful in reaming holes having keyways or grooves, as these are bridged over by the helical flutes, thus preventing binding or chatter ing. Hand reamers are made in both solid and expansion forms. The American standard dimensions for solid forms are given in the accompanying table. The expansion type is useful whenever, in connection with repair or other work, it is necessary to enlarge a reamed hole by a few thousandths of an inch. The expansion form is split through the fluted section and a slight amount of expansion is obtained by screwing in a tapering plug. The diameter increase may vary from 0.005 to 0.008 inch (0.127–0.2 mm) for reamers up to about 1 inch (25.4 mm) diameter and from 0.010 to 0.012 inch (0.25–0.3 mm) for diam- eters between 1 and 2 inches (25.4 and 50.8 mm). Hand reamers are tapered slightly on the end to facilitate starting them properly. The actual diameter of the shanks of commercial reamers may be from 0.002 to 0.005 inch (0.05–0.13 mm) under the reamer size. That part of the shank that is squared should be turned smaller in diameter than the shank itself, so that, when applying a wrench, no burr may be raised that may mar the reamed hole if the reamer is passed clear through it. When fluting reamers, the cutter is so set with relation to the center of the reamer blank that the tooth gets a slight negative rake; that is, the cutter should be set ahead of the center, as shown in the illustration accompanying the table giving the amount to set the cutter ahead of the radial line. The amount is so selected that a tangent to the circumference of the reamer at the cutting point makes an angle of approximately 95 degrees with the front face of the cutting edge. Amount to Set Cutter Ahead of Radial Line to Obtain Negative Front Rake
Size of Reamer
a , Inches 0.011
Size of Reamer
a , Inches 0.038
Size of Reamer
a , Inches 0.087
Fluting Cutter
a
2
B
1 ⁄ 4
7 ⁄ 8
C
95
0.016
1
0.044
0.098
2 1 ⁄ 4
3 ⁄ 8
A
0.022
0.055
0.109
1 1 ⁄ 4
2 1 ⁄ 2
1 ⁄ 2
Reamer Blank
0.027
0.066
0.120
1 1 ⁄ 2
2 3 ⁄ 4
5 ⁄ 8
3 ⁄ 4 0.131 When fluting reamers, it is necessary to “break up the flutes,” that is, to space the cutting edges unevenly around the reamer. The difference in spacing should be very slight and need not exceed two degrees one way or the other. The manner in which the breaking up of the flutes is usually done is to move the index head to which the reamer is fixed a certain amount more or less than it would be moved if the spacing were regular. A table is given showing the amount of this additional movement of the index crank for reamers with dif ferent numbers of flutes. When a reamer is provided with helical flutes, the angle of spiral should be such that the cutting edges make an angle of about 10 or at most 15 degrees with the axis of the reamer. 0.033 1 3 ⁄ 4 0.076 3 The relief of the cutting edges should be comparatively slight. An eccentric relief, that is, one where the land back of the cutting edge is convex, rather than flat, is used by one or two manufacturers and is preferable for finishing reamers, as the reamer will hold its size longer. When hand reamers are used merely for removing stock, or simply for enlarging holes, the flat relief is better because the reamer has a keener cutting edge. The width of the land of the cutting edges should be about 1 ⁄ 32 inch (0.79 mm) for a 1 ⁄ 4 -inch (6.35 mm), 1 ⁄ 16 inch (1.59 mm) for a 1-inch (25.4 mm), and 3 ⁄ 32 inch (2.38 mm) for a 3-inch (76.2 mm) reamer.
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