Bore Measuring Instruments
Bore gauge
It is used to measure diameter, ovality, and taper of holes. Diameter of holes can be measured comparing with a ring gauge or micrometer. It consists of a dial indicator fixed at the end of a tube, fixed measuring tip, and movable measuring tip. Moving tip is connected to the dial indicator by a push rod through a spring actuated hinged member. Spring-loaded contacts are provided on either side of the measuring tip to keep the line of measurement across the true diameter.
5.2 Hemispherical gauge: -
For the measurement of bores that are too small hemispherical gauge is considered to be very useful. It consists of spring steel arms having hemispherical end within which a wedge shaped member can be moved. Thus hemisphere can be expanded or contracted by the movement of the wedge. This gauge is operated by the sense of feel. When the hole to be measured is gauged in the above way, the gauge is taken out and the measurement is taken with an external micrometer.
5.3 Telescopic gauge: -
It is used for the measurement of diameter of holes during machining operation. It consists of a fixed rod and a movable rod, both carrying spherical contacts at the ends. The movable rod can be moved within the fixed rod and locked in position by a locking screw. A spring is provided to keep the rods apart.
For taking measurements the movable rod is pressed and inserted into the hole and locked in position after rocking. The gauge is then taken out and the dimension across the two tips is measured using an external micrometer. The precaution to be taken in the use of telescopic gauge is that they should be inserted squarely into the bore.
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