unit 2 standard for length measurement

8/3/2019 Unit 2 Standard for Length Measurement

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` Prof. Charlton S. Inao` MAEng 613, Metrology and Tolerance Technology

` Department of Mechanical Engineering` School of Engineering and Information Technlogies` Adama Science and Technology University

Adama University


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` SPECIFICATION:

Every product and part have some certaincharacteristics .It gives certain thoughts of that particular

product. Its called specification. It gives easy to understandproduction method.

STANDARD :

Standard is define as , it is a physical quantity which isestablished by higher authority or organization .Thisstandard is reliable and acceptable to measure physicalquantity. Ex. METER


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Industrial Training Institute, Palana.

THERE ARE TWO STNDARD SYSTEM TO

MEASURE LENGTH

1.BRITISH SYSTEM: INCH,FOOT,YARD

2.METRIC SYSTEM: MM,CM,METER


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METROLOGY is define as a measurement of

length and angles and other such quantitieswhich are expressed in linear and angular

measurement.


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UNIT OF LINEAR MEASUREMENT:1.British system : mile

yardfoot ()

inch ()2.metric system: kilometer

meterdecimeter

centimetermillimeter

3.S.I. System : meter


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BRITISH SYSTEM: 12 inch=1 foot

36 inch=1 yard

3 foot=1 yard

1760 yard=1mile

METRIC SYSTEM:1000micron=1mm

10mm=1cm

10cm =1decimeter

10decm=1meter

1000meter=1kilometer


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

1.METER=1000MM

1CENTIMETER=10MM

1MILIMETER=1000MICRON1MICRON=0.001MM


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THERE ARE TWO TYPE OF MEASURING INSTRUMENT

1. DIRECT MEASURING

Steel rule

Ordinary depth gauge

Protector gauge

2. IN DIRECT MEASURING

Out side caliperInside caliper

Jenny caliper


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When dimension are given in a drawing without any

indication about the tolerance ,it has to be assumed that

measurement are to be made with steel rule.

MATERIAL: It is made from spring steel or stainless

steel


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The edges are accurately ground to form straight edge.

The surface of steel rule is satin chrome finished to

reduce glove and prevent rusting.

ACCURACY: Reading accuracy of steel rule is 0.5mm inmetric system and 1/64 in British system

SIZE OF STEEL RULE: Steel rule are available indifferent length .The common size being

150mm,300mm,600mm.The steel rule graduated in

10 mm,5mm,1mm,0.5mm


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For maintaining the accuracy of a steel rule ,it is

important to see to it that its edges and surfaces are protected

from damage and rust.

Do not place a steel rule with any cutting tools. Apply a

thin layer of oil when not in use.


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Caliper are simple measuring instruments used to transfer

measurement from a steel rule to objects, and vice versa.

Calipers are of different types depending on the type of

the joint and the shape of the leg .


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The commonly used caliper are

firm joint calipers and spring joint

caliper

FIRM JOINT CALIPER: In the case

of firm joint calipers ,both legs are

pivoted at one end. To take

measurem-ent of a workpiece,the

caliper is opened roughly to therequired size. Fine setting is done by

tapping the caliper lightly on a

wooden surface.


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For this type of calipers, the legs

are assembled by means of a pivotloaded with a spring. For opening

and closing the caliper legs, a

screw and nut are provided.

Spring joint calipers have the

advantage of quick setting. Thesetting made will not change un

less the nut is turned. The size of a

caliper is specified by its length

,which is the distance between the

pivot centre and the tip of the leg


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OUT SIDE IN SIDE

Out side and inside calipers are differentiated by the shape of the legs.

Calipers used for out side measurements are known

as out side calipers. The

calipers used for internal

meas-urements are known asin side caliper.

Caliper are used along with

steel rule ,and the accuracy is

limited to 0.5 mm; parallelismof jobs etc.can be checked

with higher accuracy by using

calipers.


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TYPES OF MEASURING

INSTRUMENT:1.VERNIER CALIPER.

2.VERNIER

DEPTHGAUGE

3.VERNIER HEIGHT

GAUGE

4.MICRO METER OUT

SIDE

5.MICRO METER INSIDE

6.MICRO METER

DEPTH GAUGE7.DIAL CALIPER

8.DIAL INDICATOR


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A vernier caliper is a precision measuring instrument. It is

used to measure up to an accuracy of 0.02 mm .

MATERIAL: It is made from nickel chromium steel

USE: Vernier caliper is use to measure out side ,inside, depth

of the size.


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PARTS OF A VERNIER CALIPER

FIXED JAWS(1 AND 2) :Fixed jaws are part of the

beam scale one jaw is used for taking externalmeasurement ,and the other for internal measurement.


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MOVABLE JAWS: Movable jaws are part of the vernier slide. One jaw isused for external measure-ments,


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VERNIER SLIDE: A vernier slide moves overthe beam and can be set in any position by

means of a spring loaded thumb leven.


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BEAM: The vernier slide , and the depth bar

attached to it, slide over the beam. The

graduation on the beam are called the main

scale division.


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DEPTH BAR: The depth bar is attached to the

vernier slide and is used for depthmeasurement.


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THUMB LEVER: The thumb lever is a spring

loaded lever which helps to set the vernier slabin any position on the beam scale.


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VERNIER SCALE: The vernier scale is the

graduation marked on the vernier slide. Thedivisions of this scale are called vernier divisions.


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MAIN SCALE: Main scale graduations or divisions are

marked on the beam.


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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.


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Never use a vernier caliper for any purpose other than

measuring. Vernier calipers should be used only to

measure machined or filed surfaces. They should never be

mixed with any other tools. Clean the instrument after use,

and store it in a box.


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Vernier calipers are available with different accura-cies.

The selection of the vernier caliper depend on the

accuracy needed and the size of the job to be mea-sured.

This accuracy/least count is determined by the gra-

duation of the main scale and the vernier scale division.


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In the verner 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 =1mm(MSD)

one vernier scale division =9/10mm(VSD)Least count is 1 mm-9/10 =1/10mm

The difference between one MSD and one VSD=0.1mm

m1


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Slide 30

m1 megha, 8/29/2012


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

In this vernier caliper main scale division (49mm) are divided in to 50equal 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


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Main scale reading =35mm

The vernier division coinciding

with the main scale is the 20th

division. Value=20multiplied by 0.02=0.20mm.

Total reading is

35mm+0.20= 35.20mm

35.20 mm


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A vernier depth is very commonly used precision

instrument for measuring depth of holes recesses, slot and

step.

Its construction and method of reading are similar

to those of a vernier caliper.


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Base (1), Graduated

beam (2), Clamping

screw (3), Fine

adjustment mechan-

ism (4) and Vernier

scale (5).


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The base (anvil) is the fixed unit and serves as a

datum for measurement. It also carries the vernier scale

and the fine adjustment mechanism.

The beam with the main scale graduations is thesliding member or part

Fine adjustments for measurement are made after

tightening the clamping screw and the fine adjustment

mechanism.


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While taking

measurements the baseshould be firmly held against

the reference surface. The

relief given at the end of the

beam of some vernier height

gauges is to avoid theseating in the corners of slots

and to ensure correct

reading.


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REMOVE BURRS, IF ANY, BEFORE TAKING

MEASUREMENTS. EXCESSIVE PRESSURE ON THE

BEAM, WHILE TAKING MEASUREMENTS WILL

LIFT THE BASE FROM THE REFERENCE SURFACE

AND WILL SHOW WRONG MEASUREMENTS.


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Accurate measurements are important in layout (marking

off) and inspection work.Vernier height gauges are particularly suitable for marking

off accurate distances, and centre location.

The graduations and readings are the same as

those of avernier caliper.


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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


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The offset scriber permits zero setting instrument from the

datum surface. While using a straight scriber, the zero setting of the

instrument is at a level above the datum surface. In this case the zero

setting is to be checked using the precision round block, supplied

along with the instrument. Vernier height gauges with which we can

measure from the datum surface without the special offset scribers

are also available.

SIZE: The size of the vernier height gauge is stated by the

height of the beam. The most commonly used size has a beam of 300

mm height.

Vernier height gauges are used with surface plates or other accurate

flat surface.


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A micro meter is a precision instrument used to

measure a job, generally within an accuracy of0.01mm.Micrometer used to take the outside

measurements are know as outside micrometer.


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FRAME: The frame is made of drop forge steel or malleable cast iron.

All other part of the micrometer are attached to this.

BARREL/SLEEVE: The barrel or sleeve is fix to the frame. The datum

line and graduation are marked on this.


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SPINDLE: One end of the spindle is the measuring face. The other end is

threaded and passes through a nut. The threaded mechanism allows for

the forward and backward movement of the spindle.

SPINDLE LOCK NUT: The spindle lock nut is used to lock the spindle at

a desired position.


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THIMBLE: On the beveled surface of the thimble also,

graduation is marked. The spindle is attached to this.

ANVIL: The anvil is one of the measuring faces which is

fitted on the micrometer frame. It is made of alloy steel and

finished to a perfectly flat surface.

RATCHETSTOP: The ratchet

stop ensures a uniform

pressure betw-een themeasuring surface.


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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.


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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).


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The graduations are numbered as 0,5,10,15,20&25 mm

The circumference of the bevel edge of the thimble is graduated in to 50

division and marked 0-5-10-1540-50 in a clockwise direction. The

distance moved by the spindle during one rotation of the thimble is 0.5 mm.

Movement of

One division of the thimble =0.5

1/50

=0.01 mm

ACCURACY= 0.01mm


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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 allrange of micrometer, the graduations marked on

the barrel is only 0-25 mm.


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First note the minimum rang of the outside micro

Meter . While measuring with a 50to75mm micrometer, note it as

50mm.Then read the barrel graduation. Read the value of the

visible line on the left of the thimble edge. See below fig. i.e. main

div.= 13.00 sub div.=0.5 mm so, total =13.50mm. Next read the

thimble graduations in line with the barrel datum line, 13th

div.Multiply this value with 0.01mm, 13 0.01mm=0.13mm

so, barrel reading=13.50

thimble reading=00.13

total =13.63 mm


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CONSTRUCTIONAL FEATURES : The depth

micrometer consists of a stock on which agraduated sleeve is fitted.

The other end of the sleeve is threaded witha 0.5 mm pitch v thread.

A thimble which is internally threaded to

the same pitch and from, mates with thethreaded sleeve and slides over it.

The other end of the thimble has

an external step machined and

threaded to accommodate

a thimble cap.


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A set of extension road isgenerally supplied. On each

of them the range of sizes that

can be measured with that

road, is engraved as 0-25,25-

50,50-75,75-100, 100-125,125-150. This extension

road can be inserted in side

the spindle and the sleeve.

The extension rods have a

collar-head which helps

the road to be held firmly.


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The measuring faces of

the stock and the rods are

hardened, tempered and

ground. The measuring face

of the stock is perfectly

machined flat. The extension

roads may be removed and

replaced according to the

size of depth to be measured.


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On the sleeve a datum line is

marked for a length of 25 mm.this

is divided into 25 equal part andgraduated ,each line representing

one millimeter. each

Fifth line is drawn a little longer andnumbered. Each line representing

1mm is further subdivided into two

equal part.Hence each sub-division

represents 0.5 mm. The graduation arenumbered in the reverse direction to

that marked on an outside

micrometer


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The zero graduation of the sleeve is on

the top and the 25mm graduation near

the stock. The bevel edge of-

the thimble is also graduated. Thecircumference is equally divided into 50

equal parts and every 5th division line is

drawn a little longer and numbered. The

numbering is in the reverse direction

and increases from 0, 5, 10, 15, 25, 30,35, 40, 45 and 50 (0).


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The advancement of the extension rod for one full turn ofthe thimble is one pitch which is 0.5 mm Therefore the

advancement of the extension rod for one division

movement of the thimble will be equal to 0.5/50

=0.01mm. This will be the smallest measurement that can

be taken with this instrument, and so, this is the least

count of this instrument.


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Depth micrometers are special micrometers used to

measure

The depth of holes.

The depth of grooves and recessesThe heights of shoulders or projections.


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unit 2 standard for length measurement

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