Machinery's Handbook, 31st Edition
Gage Blocks
721
Gage Blocks The primary standard for linear measurement is the gage block . Gage blocks were origi nally called Jo-Blocks after their Swedish inventor, Carl Edvard Johansson. These preci sion lapped blocks are the primary means of establishing measurement traceability to the prime standards located in the national laboratories of every country. The primary length standards are themselves defined by the distance traveled by light in a vacuum over a fixed time period. The gage block is critical in establishing true traceability and measurement assurance in the dimensional discipline. There are several materials and grades of gage blocks to select from. The most common material in use today is steel. However, there is also Croblox, made by Mitutoyo, a thermally stable material with a very low coefficient of thermal expansion, and ceramic blocks, with extremely good wear capabilities. The average life span of a gage block is approximately 3 years. With proper care and cleaning the gage block may last many years longer but will eventually wear beyond the limits of the allow able tolerances and will need to be replaced. The size tolerances applied to gage blocks, defined in the ANSI/ASME B89.1.9-2002, are shown in Table 1a and Table 1b, for inch and metric units, respectively. Nearly all gage blocks are manufactured and calibrated to this standard. B89.1.9 establishes the allowable deviations for size variance as well as flatness and parallelism. It is these controlled dimensions that give the gage block the properties necessary for use as a dimensional standard. Table 1a. Maximum Permitted Deviations of Length at Any Point a and Tolerance on Variation in Length, Inch b ANSI/ASME B89.1.9-2002 (R2012)
Calibration Grade K Grade 00
Grade 0
Grade AS-1
Grade AS-2
Nominal Length Range, l n inches ≤ 0.05 1 < l n ≤ 2 2 < l n ≤ 3 4 < l n ≤ 5 5 < l n ≤ 6 6 < l n ≤ 7 3 < l n ≤ 4
± t e μ in.
t v μ in.
± t e μ in. t v μ in. ± t e μ in. t v μ in. ± t e μ in. t v μ in. ± t e μ in. t v μ in.
12 10 12 16 20 24 32 32 40 40 48 56 72 88
4 3 3 4 5 6 8 8
6 5 6 8
12
24 18 24 32 40 48 64
0.05 < l n ≤ 0.4 0.55 < l n ≤ 1
8
2
12
12 16 20 24 32 40 48 56 72 88
2
4
6
10 12 16 16 20 20 24 28 36 44 52 60 68 76 80
14
3
3
5
8
16
10 10 12 14 18 20 25 30 34 38 40
80
7 <
l n ≤ 8
4
4
6
10
8 < l n ≤ 10 10 < l n ≤ 12 16 < l n ≤ 20 20 < l n ≤ 24 12 < l n ≤ 16 28 < l n ≤ 32 32 < l n ≤ 36 36 < l n ≤ 40 24 < l n ≤ 28
104 112 144 176 200 240 260 300 320
18 20 24 28 32 36 40
7 8
5 6 7 8
5 6 7 8
12 14 16 18 20 24
10
104 120 136 152 160
104 120 136 152 168
12 14 16
10
10
a Maximum permitted deviations of length at any point, ± t
e μinch, from nominal length, l e inches.
b Tolerance, t v μinch, for the variation in length. Care of Gage Blocks.— Through proper care and handling of gage blocks, their func- tional life span can be maximized and many years of use can be realized from your invest- ment. The basic care and cleaning of gage blocks should follow these simple guidelines.
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