Gage Blocks

length measures in which the distance between two mutually parallel measuring planes is constant. Gage blocks first appeared in 1900, when the Johanson Company of Sweden demonstrated them at the Paris Exhibition; by fitting them together they could be combined into larger blocks. Therefore, gage blocks are sometimes called Johanson plates. The manufacture of gage blocks in the USSR was first organized at plants in Tula and Sestroretsk; series production began in the 1930’s. Production is now concentrated at the Kalibr Instrument Plant in Moscow and the Krasnyi Instrumental’shchik Plant in Kirov.

Gage blocks are used to transfer dimensional values from the state length standard to a manufactured article. The use of gage blocks ensures standardization of measuring instruments used in machine building. They are also used to check tooling in checking and measurement devices, to establish methods of measuring nominal dimensions, and in adjusting tool machines and fixtures and performing layout work.

Gage blocks have the shape of a rectangular parallelepiped or a circular cylinder. Cylindrical gage blocks are usually made with dimensions ranging from 25 to 1, 000 mm in 25-mm steps. They are most frequently used to check measuring machines.

In the Soviet Union steel is the most widely used material for gage blocks. Most gage blocks have the shape of a rectangular parallelepiped with dimensions of 0.1 to 2, 000 mm and gradations of 0.001, 0.01, 0.1, 0.5, 10, 25, 50, 100, and 1, 000 mm in nominal values. The dimensions of the measuring surfaces are 5 × 15 mm for gage blocks up to 0.29 mm, 9 × 30 mm for blocks up to 10 mm, and 9 × 35 mm for blocks larger than 10 mm. Gage blocks with dimensions in excess of 10 mm have two apertures 12 mm in diameter spaced 25 mm from the measuring planes to facilitate the joining of two blocks by means of special rods.

Gage blocks are produced in sets packed in a case; from such sets blocks can be assembled to measure any dimension, using a minimum number of blocks (not more than five). As of 1972 there were 15 sets manufactured in the USSR. The largest set has 115 gage blocks with nominal dimensions from 0.5 to 100 mm. For verification and layout work involving dimensions up to 1, 500 mm, special accessory sets are used with the gage blocks. The property of adhesion by rubbing is used in working with gage blocks. If one gage block is moved over the surface of another in the presence of an extremely thin layer of lubricant, adhesion arises between the surfaces, and the lubricant accumulated in the microscopic pores flows out. This makes it possible to build up groups of gage blocks up to 100 mm long without additional fastening. To provide adhesion through friction, the roughness of the working surfaces of gage blocks must be of the 13th or 14th class and the Rockwell C hardness of the material must be not less than 62. The size of the composit block differs from the combined dimensions of the component gage blocks by not less the 0.1-0.05 microns for each intermediate layer.

The parameters of accuracy of plane-parallel gage blocks are the length of a perpendicular line drawn from any point of a measuring surface to the opposite surface and the deviation of two planes from parallelism’that is, the difference between the mean length and the length of a gage block at a given point. In the USSR the accuracy of gage blocks is standardized according to classes of accuracy (from 0 to 4) and ranks (from 1 to 5). The class is determined by permissible deviations of length and plane-parallelism; the rank is assigned depending on the accuracy of length measurement after certification of the length and permissible deviation from plane-parallelism. A set of gage blocks of the highest rank available at an enterprise is called a primary set and is used as the original set for maintaining standardized measures at the enterprise. In foreign practice there is no accuracy classification of gage blocks according to classes or ranks.

Soviet manufacturing plants have introduced gage blocks made from hard alloys; their abrasion resistance is higher than that of steel blocks by a factor of 10 to 40. However, such gage blocks have the disadvantage of a greater measurement error, particularly for large dimensions, which is explained by the difference in linear coefficients of expansion of hard alloys (the gage block material) and the material of the manufactured articles (usually steel). A possible solution is the production of gage blocks with measuring surfaces reinforced by hard-alloy plates.