Gauge blocks

In the simple case of a gauge block, three major parameters define the accuracy class of a gauge block maximum permissible flamess error, maximum deviation from nominal length, and maximum permissible length error. 

End standards of length used in the workshop are of two types gauge blocks and length bars. These are calibrated and intended for use at 20 "C. 

Gauge blocks are made from a wear-resisting material - hardened and stabilised high-grade steel, timgsten carbide and ceramic and their dimensions and accuracy are covered by BS EN ISO 3650 1999. 

Each gauge block is of a rectangular section with the measuring faces finished by precision lapping to the required distance apart - known as... 

To build up a size combination, the smallest possible number of gauge blocks should be used. This can be done by taking care of the micrometres (0.001 mm) first, followed by hundredths (0.01 mm), tenths (0.1mm) and whole millimetres e.g. to determine the gauge blocks required for a size of78.748 mm using the M88/2 set previously listed ... 

The 2,24 mm second gauge block is used as it conveniently leaves a 0.5 increment for the third gauge block. 

In some instances protector gauge blocks, usually of 2 mm gauge length, are supplied with a set, while in other instances they have to be ordered separately. These are available in pairs, are marked with the... 

Having estabUshed the sizes of gauge blocks required, the size combination can be buUt up. Select the required gauge blocks from the case and close the Ud. It is important that the lid is kept closed at all times when not in actual use, to protect the gauge blocks from dust, dirt and moisture. 

When two gauge blocks are pressed and sUd together on their measuring surfaces, they wUl adhere and are said to wring together. They wUl only do this if the measuring surfaces are clean, flat and free from damage. 

Immediately after use, slide the gauge blocks apart, clean each one carefully, replace in the case and close the lid. Do not break the wringing joint but slide the blocks apart, and never leave the gauge blocks wrung together for any length of time. 

Gauge blocks are also widely used in conjunction with sine bars and with calibrated steel balls and rollers, as well as for checking straightness and squareness. They are also used in conjunction with a range of accessories. 

The use of gauge blocks for measuring can be extended by the use of a range of accessories. These are covered by BS 4311-2 2009. A typical set of gauge-block accessories is shown in Fig. 5.5 and consists of (1) two pairs of jaws, type A and type B, which when combined with gauge blocks form an external or internal caliper, Figs 5.6(a) and (b) a centre point and a scriber, used in combination with gauge blocks to scribe arcs of precise radius. Fig. 5.6(c) ... 

The accessories other than the holders are made from high-quality steel, hardened and stabilised, with their wringing faces precision-lapped to give flamess, parallelism and surface finish to the same degree as gauge blocks, to which they are wrung to assemble any combination. Accessories can be purchased in sets as shown or as individual items. 

The measurement of angles can be simply carried out by using a protractor, but the degree of accuracy obtainable is, at best, 5 minutes using a vernier instrument. Greater accuracy can be obtained by using a sine bar in conjunction with gauge blocks. 

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