Metrology # 3

METEROLOGY

UNIT#3

GAUGES

Gauge Design: Every gauge is copy of the part which mates with the part for which the gauge is designed. For example, a bushing is made which is to mate with a shaft, in this case, the shaft is the opposed (mating part)part. The bushing is checked by a plug gauge. If a gauge is designed as an exact copy of the opposed part in so far as the dimension to be checked is concerned, it is called a 'Standard Gauge'.

‘’No Go’’ Gauges: According to Taylor, ‘Go’ and ‘No Go’ gauges should be designed to check maximum and minimum material limits which are checked as below.

'Go' Limit: The designation is applied to that limit of the two limits of size which corresponds to the maximum material limit considerations, i.e. upper limit of a shaft and lower limit of a hole. The form of the 'Go' gauge should be such that it can check one feature of the component in one pass.

'No Go' Limit: This designation is applied to that limit of the two limits of size which corresponds to the minimum material condition, i.e. the lower limit of a shaft and the upper limit of a hole.’No Go' gauge should check only one part or feature of the component at a time. Thus a separate 'No Go gauge is required for each different individual dimension.

By Taylor's Principle for Hole and Shaft: This principle is based on the use of a correct system on limit gauges to inspect shafts and holes. According to Taylor's Principle. It is not adequate to use simple 'Go' g on outer diameter only but the shape is an important actor, that is the 'Go' gauge hold be full formed g and it should be constructed with reference to the geometrical form of the part being check in edition to its size .In other words 'go' gauge should check all the dimension of a work piece in the maximum metal condition.

Allowance: The difference between the maximum shaft size and minimum hole size is known as allowance. Maximum allowance is obtained by subtracting the minimum shaft size from the largest hole size and the minimum allowance is the difference between the largest shaft and the smallest hole size. Thus allowance is positive for clearance fit and negative for interference fit.