LINEAR MEASUREMENT

METROLOGY METROLOGY is defined as a measurement of length and angles and other such quantities which are expressed in linear and angular measurement.

• ENGINEERING METROLOGY is the measurement of dimensions: length, thickness, diameter, taper, angle,flatness, profiles, and others.

• Traditionally: Post process inspection• Current Trend: In-process, on-line, real-time inspection• Inspection: Check dimensions of what have been produced or

what is being produced whether it conforms with the specified dimensional accuracy.

• Dimensional Tolerances: Permissible variation in dimensions of a part

• Instruments: tools for measurements

IMPORTANTCE OF METROLOGY

• IMPORTANTCE OF METROLOGY

• To achieve quality control in production• To achieve up to date production, knowledge of

The measurement require.• To reduce rejection with the help of quality

control.• To develop inspection procedure .• To calibrate measuring instrument time to time

TERMS USED IN METROLOGY

• SPECIFICATION: Every product and part have some certain

characteristics .It gives certain thoughts of that particular product. Its called specification. It gives easy to understand production method.

STANDARD : Standard is define as , it is a physical quantity

which is established by higher authority or organization .This standard is reliable and acceptable to measure physical quantity. Ex. METER

LENGTH STANDARD

THERE ARE TWO STNDARD SYSTEM TO MEASURE LENGTH

1.BRITISH SYSTEM: INCH,FOOT,YARD

2.METRIC SYSTEM: MM,CM,METER

LESSION NO:2

UNIT OF LINEAR MEASUREMENT: 1.British system : mile yard foot (‘) inch (“) 2.metric system: kilometer meter decimeter centimeter millimeter 3.S.I. System : meter

CONVERSION

BRITISH SYSTEM: 12 inch=1 foot 36 inch=1 yard 3 foot=1 yard 1760 yard=1mileMETRIC SYSTEM:1000micron=1mm 10mm=1cm 10cm =1decimeter 10decm=1meter 1000meter=1kilometer

S.I.SYSTEM

As per S.I.System fundamental unit of length is METER

1.METER=1000MM

1CENTIMETER=10MM

1MILIMETER=1000MICRON

1MICRON=0.001MM

Standards of Linear Measurement

• According to the instrument design the length can be measured by using following standards

• Line Standard. E.g. Yard, Meter

• End Standard. E.g. Slip Gauges, End Bars etc.

• Wavelength Standard E.g.Interferometers

Line Standard

• Distance is measured between two lines• A scale is quick and easy to employ• Scale marking are not subject to wear. However

significant wear on leading edge leads to under sizing

• A scale does not possess a built in datum • Scales are subjected to parallax effect• Not convenient for close tolerance measurement• Less accurate compared to end standard.

End Standard

• Distance is measured between two surfaces.• Highly accurate and well suited for close

tolerance(0.005) measurement.• Time consuming and prove one dimension

at a time• Subjected to wear on their measuring faces • Have built in datum.• Free from parallax.

Wavelength Standard• Orange radiation of Kr86 in hot cathode discharge lamp

maintained at 68C. According this standard meter is defined as 1650763.73 wavelength.

• It is not a material standard and hence not influenced by the effects of variation of environmental temperature, pressure, humidity and ageing.

• It need not stored under security and thus there is no fear of its being destroyed as in the case of meter and yard.

• There are problems of transferring this standard to other standards as in the case of meter and yard.

• Easily available to all standardizing houses, laboratories and industries.

• Easily reproducible and thus identical standard are available with all.

• Can be used for comparative measurements of a much higher accuracy.

ORDINARY MEASURING INSTRUMENT

THERE ARE TWO TYPE OF MEASURING INSTRUMENT 1. DIRECT MEASURING

Steel rule Ordinary depth gauge Protector gauge 2. IN DIRECT MEASURING Out side caliper Inside caliper

STEEL RULE

Caliper

Caliper

Caliper

SURFACE PLATE

• A surface plate is a solid, flat plate used as the main horizontal reference plane for precision inspection, marking out (layout), and tooling setup. The surface plate is often used as the baseline for all measurements to the workpiece, therefore one primary surface is finished extremely flat with accuracy up to .00001"/.00025 mm for a grade AA or AAA plate.

surface plate

• Surface plates are a very common tool in the manufacturing industry and are often permanently attached to robotic type inspection devices such as a coordinate-measuring machine.

• Material Granite, CI, Glass

surface plate

ANGLE PLATE

An angle plate is a work holding device used as a fixture in metalworking.The angle plate is made from high quality material (generally spheroidal cast iron) that has been stabilized to prevent further movement or distortion. Slotted holes or T bolt slots are machined into the surfaces to enable the secure attachment or clamping of workpieces to the plate, and also of the plate to the worktable.Angle plates also may be used to hold the workpiece square to the table during marking out operations.Adjustable angle plates are also available for workpieces that need to be inclined, usually towards a milling cutter.

Use of “V” blocks

Align V-Block with Straight-edge on Surface Plate

Use clamps to secure rod to V-block surface

Indicate along top surface while moving along straight edge - straightness

Indicate along side surface while rotating cylinder - circularity

BENCH CENTRES

Straight Edges• These are used for checking the straightness and flatness of

parts in conjunction with the surface plates and spirit level. These may be made of steel or cast iron. Steel straight edges are available up to 2 m length and widely used for testing machine tool slide ways. They are heavily ribbed and bow shaped to prevent distortion. These are provided with feet for rest when they are idle to prevent distortion. Feets are placed at points of minimum deflection.

• Types• Tool Makers Straight edge• Wide edge• Angle • box

Straight Edges

Spirit Level

Surface Gauge

Radius Gauges

Feeler Gauges

PRECISION MEASURING INSTRUMENT

TYPES OF MEASURING INSTRUMENT:

VERNIER CALIPER.

VERNIER DEPTHGAUGE

VERNIER HEIGHT GAUGE

MICRO METER OUTSIDE

MICRO METER INSIDE

MICRO METER DEPTH GAUGE

SLIP GAUGES

END BARS

VERNIER CALIPER.

VERNIER CALIPER.

Vernier calipers are available in size of 150 mm, 225 mm, 900 mm and 1200 mm. The selection of the size depends on the measurements to be taken. Vernier calipers are precision instruments, and extreme care should be taken while handing them.

VERNIER CALIPER.

In the Vernier caliper shown in fig the main scale division (9mm) are divided in to 10 equal parts in the Vernier scale.

i.e. one main scale division (MSD) =1mm

one Vernier scale division (VSD) =9/10mm

Least count is 1 mm- 9/10 =1/10mm

The difference between one MSD and one VSD=0.1mm

VERNIER CALIPER.

VERIER CALIPER WITH 0.02MM LEAST COUNT IS GENERLY USED IM WORK SHOP.

In this Vernier caliper main scale division (49mm) are divided in to 50 equal part in the Vernier scale.

i.e. 1 main scale division =1 mm

(MSD)

1. Vernier scale division =49\50 mm

(VSD)

Least count is 1mm – 49\50 =1\50 mm

THE DIFFERENCE BETWEEN 1.MSD and 1. VSD=0.02MM

USES OF VERNIER DEPTH GAUGE

Base (1), Graduated beam (2), Clamping screw (3), Fine adjustment mechanism (4) and Vernier scale (5).

The main parts of a Vernier height gauge and their function are given.

1.base

2. beam

3.Vernier slide

4. fine setting device

5. Vernier plate

6. locking screws

7. scriber

MICRO METER OUTSIDE

A micro meter is a precision instrument used to measure a job, generally within an accuracy of 0.01mm.Micrometer used to take the outside measurements are know as outside micrometer

WOKING PRINCIPLE: The micrometer works on the principle of screw and nut .The longitudinal movement of the spindle during one rotation is equal to the pitch of the screw. The movement of the spindle to the distance of the pitch or its fractions can be accurately measured on the barrel and thimble.

In metric micrometer the pitch of the spindle thread is 0.5mm. Thereby ,in one rotation of the thimble, the spindle advances by 0.5 mm.

On the barrel a 25 mm long datum line is mar-ked. This line is further graduated to millimeters and half millimeters (i.e. 1 mm& 0.5 mm).

• RANGES OF O.S. MICROMETER: Outside micrometer are available in ranges of 0 to 25mm, 25 to 50mm, 50 to75mm, 75 to 100mm,100to125mm, 125 to 150mm. For all range of micrometer, the graduations marked on the barrel is only 0-25 mm

DEPTH MICROMETERS

Depth micrometers are special micrometers used to measure

The depth of holes.

The depth of grooves and recesses

The heights of shoulders or projections.

•Used for measuring cylinder bores, housing bores •Screw pitches same as outside micrometer•One inch of travel•Used more often with ‘transfer’ measurements

COMBINATION SET

Gauge or Jo Blocks – ISO 3650Come in sets to 150 mm with 88

blocks

Minimum step 1 μm

Make up any dimension by wringing blocks together

Sets come in several grades, typical for shop use is grade AS-1 with thinner blocks good to sub-microns

Sets include two wear blocks to be mounted to either end of stack to protect the measurement blocks from wear