Machinery's Handbook, 31st Edition
Gage Blocks 723 the optimal interval for recalibration of the gage block sets to maintain the appropriate level of measurement assurance. Calibration of the gage blocks should be done by an approved and, if necessary, certified calibration laboratory that provides impartial third party confirmation of the calibrated features of the gage block set. Precision Gage Blocks.— Precision gage blocks are usually purchased in sets containing a specific number of blocks of different sizes. The nominal gage lengths of individual blocks in a set are determined mathematically so that particular desired lengths can be ob- tained by combining selected blocks. They are made to several different tolerance grades that categorize them as master blocks, calibration blocks, inspection blocks, and work- shop blocks. Master blocks are employed as basic reference standards; calibration blocks are used for high precision gaging work and calibrating inspection blocks; inspection blocks are used as toolroom standards and for checking and setting limit and comparator gages, for example. The workshop blocks are working gages used as shop standards for direct precision measurements and gaging applications, including sine-bars. Federal Specification GGG-G-15C, Gage Blocks (see below), lists typical sets and gives details of materials, design, and manufacturing requirements, and tolerance grades. When there is in a set no single block of the exact size wanted, two or more blocks are com bined by “wringing” them together. Wringing is achieved by first placing one block cross wise on the other and applying some pressure. Then a swiveling motion is used to twist the blocks to a parallel position, causing them to adhere firmly to one another. When combining blocks for a given dimension, the object is to use as few blocks as pos sible to obtain the dimension. The procedure for selecting blocks is based on successively eliminating the right-hand figure of the desired dimension. Example: Referring to inch-size gage block Set Number 1 below, determine the blocks required to obtain 3.6742 inches. Step 1: Eliminate 0.0002 by selecting a 0.1002 block. Subtract 0.1002 from 3.6743 = 3.5740. Step 2: Eliminate 0.004 by selecting a 0.124 block. Subtract 0.124 from 3.5740 = 3.450. Step 3: Eliminate 0.450 with a block this size. Sub tract 0.450 from 3.450 = 3.000. Step 4: Select a 3.000 inch block. The combined blocks are 0.1002 + 0.124 + 0.450 + 3.000 = 3.6742 inches. Gage Block Sets, Inch Sizes (Federal Specification GGG-G-15C).— Set Number 1 (81 Blocks): First Series: 0.0001-Inch Increments (9 Blocks), 0.1001 to 0.1009; Second Series: 0.001-Inch Increments (49 Blocks), 0.101 to 0.149; Third Series: 0.050-Inch In - crements (19 Blocks), 0.050 to 0.950; Fourth Series: 1.000-Inch Increments (4 Blocks), 1.000- to 4.000-inch. Set Numbers 2, 3, and 4: The specification does not list a set 2 or 3. Gage block Set Num ber 4 (88 Blocks), listed in the Specification, is not given here; it is the same as Set Number 1 (81 Blocks) but contains seven additional blocks measuring 0.0625, 0.078125, 0.093750, 0.100025, 0.100050, 0.100075, and 0.109375 inch. Set Number 5 (21 Blocks): First Series: 0.0001-Inch Increments (9 Blocks), 0.0101 to 0.0109; Second Series: 0.001-Inch Increments (11 Blocks), 0.010 to 0.020; One Block 0.01005 inch. Set Number 6 (28 Blocks): First Series: 0.0001-Inch Increments (9 Blocks), 0.0201 to 0.0209; Second Series: 0.001-Inch Increments (9 Blocks). 0.021 to 0.029; Third Series: 0.010-Inch Increments (9 Blocks), 0.010 to 0.090; One Block 0.02005 Inch. Long Gage Block Set Number 7 (8 Blocks): Whole-Inch Series (8 Blocks), 5, 6, 7, 8, 10, 12, 16, 20 inches. Set Number 8 (36 Blocks): First Series: 0.0001-Inch Increments (9 Blocks), 0.1001 to 0.1009; Second Series: 0.001-Inch Increments (11 Blocks), 0.100 to 0.110; Third Series: 0.010-Inch Increments (8 Blocks), 0.120 to 0.190; Fourth Series: 0.100-Inch Increments (4 Blocks), 0.200 to 0.500; Whole-Inch Series (3 Blocks), 1, 2, 4 Inches; One Block 0.050 inch.
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