Machinery's Handbook, 31st Edition
counterbores 963 allowing use of various pilot diameters. Three-piece counterbores have separate holder, counterbore cutter, and pilot, so that a holder will take any size of counterbore cutter. Each counterbore cutter, in turn, can be fitted with any suitable size diameter of pilot. Counter- bores for brass are fluted straight. Counterbores with Interchangeable Cutters and Guides
B
F
A
D E
L
Range of Pilot Diameters, B
Range of Cutter Diameters, A
No. of Morse Taper Shank
Total Length, C
Length of Cutter Body, D
Length of Pilot, E
Dia. of Shank, F
No. of Holder
1 2 3 4
1 or 2 2 or 3 3 or 4 4 or 5
1
3 ⁄ 4 -1 1 ⁄ 16 1 1 ⁄ 8 -1 9 ⁄ 16 1 5 ⁄ 8 -2 1 ⁄ 16 2 1 ⁄ 8 -3 1 ⁄ 2
1 ⁄ 2 - 3 ⁄ 4
7 1 ⁄ 4 9 1 ⁄ 2
3 ⁄ 4
5 ⁄ 8 7 ⁄ 8
1 1 ⁄ 16 -1 1 ⁄ 8
1 3 ⁄ 8 1 3 ⁄ 4 2 1 ⁄ 4
1 1 ⁄ 8 1 5 ⁄ 8
7 ⁄ 8 -1 5 ⁄ 8 1-2 1 ⁄ 8
12 1 ⁄ 2
1 1 ⁄ 8 1 3 ⁄ 8
15
2 1 ⁄ 8 Small counterbores are often made with three flutes, but should then have the size plainly stamped on them before fluting, as they cannot afterwards be conveniently measured. The flutes should be deep enough to come below the surface of the pilot. The counterbore should be relieved on the end of the body only, and not on the cylindrical surface. To facilitate the relieving process, a small neck is turned between the guide and the body for clearance. The amount of clearance on the cutting edges is, for general work, from 4 to 5 degrees. The accompanying table gives dimensions for straight shank counterbores. Solid Counterbores with Integral Pilot
Pilot Diameters
Overall Length
Straight Shank Diameter
Nominal
+ 1 ⁄ 64 0.076 0.089 0.102 0.115 0.128 0.141 0.154 0.180 0.206 0.232
Counterbore Diameters
+ 1 ⁄ 32
Short
Long
… … … … … … … … … …
0.110 0.133 0.155 0.176 0.198 0.220 0.241 0.285 0.327 0.372
0.060 0.073 0.086 0.099 0.112 0.125 0.138 0.164 0.190 0.216
… … … … … … … … … …
2 1 ⁄ 2 2 1 ⁄ 2 2 1 ⁄ 2 2 1 ⁄ 2 2 1 ⁄ 2 2 1 ⁄ 2 2 1 ⁄ 2 2 1 ⁄ 2 2 3 ⁄ 4 2 3 ⁄ 4 3 1 ⁄ 2 3 1 ⁄ 2
7 ⁄ 64
1 ⁄ 8
5 ⁄ 32
11 ⁄ 64
3 ⁄ 16 3 ⁄ 16 7 ⁄ 32
1 ⁄ 4
9 ⁄ 32 5 ⁄ 16
5 1 ⁄ 2 5 1 ⁄ 2
1 ⁄ 4
17 ⁄ 64 21 ⁄ 64 25 ⁄ 64 29 ⁄ 64 33 ⁄ 64
9 ⁄ 32
3 ⁄ 8 3 ⁄ 8 1 ⁄ 2 1 ⁄ 2 1 ⁄ 2
13 ⁄ 32
1 ⁄ 2
5 ⁄ 16
11 ⁄ 32 13 ⁄ 32 15 ⁄ 32 17 ⁄ 32
4 4 5
6 6 7
19 ⁄ 32 11 ⁄ 16 25 ⁄ 32
3 ⁄ 8
7 ⁄ 16
1 ⁄ 2
All dimensions are in inches. Three-Piece Counterbores.— Data shown for the first two styles of counterbores are for straight-shank designs. These tools are also available with taper shanks in most sizes. Sizes of taper shanks for cutter diameters of 1 ⁄ 4 to 9 ⁄ 16 in. are No. 1; for 19 ⁄ 32 to 7 ⁄ 8 in., No. 2; for 15 ⁄ 16 to 1 3 ⁄ 8 in., No. 3; for 1 1 ⁄ 2 to 2 in., No. 4; and for 2 1 ⁄ 8 to 2 1 ⁄ 2 in., No. 5.
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