Measuring Instruments

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have an important role in a mechanical works hop. The quality of work is based on the accuracy and precision of the instruments used for inspection.

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Measuring Instruments

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is a measuring instrument having a long, thin stainless steel strip with a marked scale of unit division such as in centimetres or inches, used for drawing lines, measuring distances between two points, etc. These are available in different sizes, such as in 15cm, 30cm, 60cm, 1m, 1.5m, 2m, 3m, 4m, 5m & 6m. Generally, least count of a steel rule is 0.5mm

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Steel Rule

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is a device used to measure the distance between two opposite sides of an object.

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Calipers

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Used to measure outside diameter of a round shaped objects or to measure distance between two points.

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Outside caliper

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Used for measuring inside diameter of a pipe or to measure inside dimensions of hollow sections.

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Inside caliper

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It is also known as odd leg caliper or hermaphrodite caliper. It used for scribe a line at a distance from the edge of a work piece.

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Jenny caliper

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is a precision instrument used for measuring internal and external distances between two points extremely accurately. It has two versions, manual and digital. The manual version has both an imperial and metric s cale. The digital version requires a small battery whereas the manual version does not need any power source.

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Vernier Caliper

Vernier callipers are available in the range of 0 -100mm, 0- 150mm, 0-200mm, 0-300mm, 0-600mm and 0-1000mm. Accuracy of metric scale vernier caliper is 0.02mm and imperial scale vernier caliper is 0.00 2”.

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Used to measure external diameter or width of an object

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Outside jaws

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Used to measure internal diameter of an object

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Inside jaws

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Scale marked every mm (metric scale)

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Main Scale

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gives interpolated measurements to 0.1 mm or better

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Vernier Scale

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gives interpolated measurements in fractions of an inch

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Vernier Scale

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used to block movable part to allow the easy transferring of a measurement

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Retainer

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Used to lock movable jaw with main scale.

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Locking screw

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is the smallest value that can be read directly in that scale.

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Least Count

Least Count (L.C) = 1 Main Scale Division (MSD) – 1 Vernier Scale Division (VSD) 1 MSD = 1mm 1 VSD = 49/50mm = 0.98mm Therefore, LC = MSD – VSD = 1-0.98mm = 0.02mm

Each division on the main scale is 1mm. The metric Vernie r scale is 49mm long and divided into 50 equal parts. Each division is 49/50, which is equal to 0.98mm. The difference between one division on the main scale and one division on the metric vernier scale is 1/50 or 0.02mm which is the Least Count.

Procedure:  Note the main scale reading, immediately preceding the zero line on vernier scale.  Here, zero of the vernier scale immediately preceding 28mm.  This (28mm) must be added with decimal reading on the vernier scale.  Note the line on the vernier scale, which is coinciding, with a line on the main scale.  31t h line coincides with a line on the main scale. So, the reading is 28mm plus 31 divisions of 0.02mm TOTAL: 28mm + 31 * 0.02 = 28.62mm

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(also known as screw gauge) is used for measuring dimensions smaller than those measured by the Vernier caliper. A micrometer screw gauge is a small measuring device, which works on the “screw” principle. The accuracy of micrometers are varies between 0.01mm and 0.001 mm depending on the type of micrometer. Figure and detailed specifications of micrometers are given below.

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Micrometer

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is a measuring device used either for determining the height of something, or for repetitive marking of items to be worked on. The pointer is sharpened to allow it to act as a scriber and assist in marking on work pieces.

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Vernier Height Gauge

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have been used in the machine shop to test alignment and rotation measurement of machine parts.

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Dial Test Indicator

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is used to check or find the pitch of a thread. It is a series of thin marked blades which have different pitched teeth.

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Screw thread pitch guage

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Is an important tool used in a machine shop, made from hardened and polished stainless steel. It is also known as Center gauge or Fish tail gauge. It is used for checking tool angles while machining threads in metal turning lathes. Metric, BSW, BSF, BA, American National and Acme thread angles are clearly etched on the plate for easy understanding. The angle on the thread cutting tool is checked on the V slots in the gauge as shown in figure.

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Screw cutting guage