2. UNIT NO: 02
LINEAR AND ANGULAR MEASUREMENTS
Linear Measurement Instruments,
Vernier calliper,
Micrometer,
Interval measurements: Slip gauges, Checking of
slip gauges for surface quality,
Optical flat,
Limit gauges,
Problems on measurements with gauge.
3. DEFINITION:- IT IS THE MEASUREMENT OF
PERPENDICULAR DISTANCE BETWEEN TWO POINT OR
SURFACES.
Instrument Use for Linear Measurement:-
1. Vernier calliper
2. Vernier height gauge
3. Vernier depth gauge
4. Micrometer
5. Engineer’s steel rule or scale
6. Callipers
7. Bore gauge
8. Telescopic gauge
9. Slip gauge
10. Dial indicator
4. VERNIER CALLIPER:-
Construction:-
-It consist of two scale one is fixed called main scale & other is
moveable called vernier scale.
- For precise setting of the moveable jaw an adjustment screw is
provided with movable jaw.
- The vernier is also facilitated to lock the sliding scale with the fixed
main scale.
5. WORKING:-
- The work piece to be measured is kept between the jaws for
measuring the outside dimension.
- The fine adjustment can be done by adjustment screw.
- Movable jaw is made fixed on main scale frame by clamping
screw.
- The vernier calliper is taken from work piece for taking the
reading from the main scale as well as the vernier scale.
- first the main scale reading is taken then, the vernier scale is
examined to determine which of its division coincides with a
division on the main scale.
Least count=1/10=0.1 mm
Diameter of work piece = Main scale reading
+(No. of vernier division coinciding with main
scale*least count)
6. ERRORS IN VERNIER CALLIPER:-
1. Errors due to play between the sliding jaw & fixed scale
bar.
2. Zero error due to wear & wrapping of jaws.
3. Errors due to incorrect observation of scale reading.
4. Errors due to excessive force on moving jaw.
5. Errors is also introduced if the line of measurement
does no coincide with the line of the scale.
7. VERNIER HEIGHT GAUGE:-
Construction:-
- It is similar to the vernier
calliper except that the fixed jaw
in this case is replaced by fixed
base which rests on the surface
plate or table
- The upper & lower surfaces of
the measuring jaw parallel to
base so it can be used for
measurement over or under a
surface.
- The scriber when attached
vernier is used for inspection of
parts & for layout work.
- In some cases scriber is
replaced by dial indicator.
8. Construction:-
- It is used for measuring
depths of holes, slots,
recesses and distance from a
plane surface to projection.
- Before using the gauge
make sure that the gauge
base is satisfactorily true flat &
square.
- Then lower the blade into
the hole until it contacts the
bottom surface of hole.
- The final adjustment is
depends upon a sense of
contact & is made by the final
adjustment screw.
- The instrument is then
removed from the hole &
reading is taken same as
vernier calliper.
VERNIER DEPTH GAUGE:-
9. MICROMETER:-
Principle:-
-Micrometer works on the principle of screw & nut.
-The screw is attached to a concentric cylinder which is divided into
number of equal parts.
-When the screw is turned through nut by one revolution, its axial
movement is same as pitch of the thread of screw.
10. LEAST COUNT:-
-IN A MILLIMETER MICROMETER INSTRUMENT THE SCREW HAS A
PITCH OF 0.5MM AND THIMBLE HAS 50 DIVISION SO,
THE LEAST COUNT(L.C)
= VALUE OF SMALLEST DIVISION ON MAIN SCALE OR PITCH
NO. OF DIVISION ON THIMBLE
=0.5/50
=0.01MM
Types of micrometers:-
1. Outside micrometer
2. Inside micrometer
3. Vernier micrometer
4. Depth micrometer
5. Bench micrometer
6. Digital micrometer
7. Differential screw micrometer
8. Micrometer with dial gauge
9. Screw thread micrometer
11. CONSTRUCTION:-
-IT CONSISTS OF
1. U-SHAPED FRAME 2. ANVIL
3. SPINDLE 4. THIMBLE
5. BARREL OR SLEEVE 6. RACHET 7. LOCKNUT.
-IT IS MADE OF STEEL, CAST IRON OR LIGHT ALLOY.
-THE GAP BETWEEN TWO ENDS OF U-SHAPE FRAME PERMITS
MAXIMUM DIAMETER OR LENGTH OF JOB TO BE MEASURED.
-The one end of spindle is attached to the thimble and other is to
movable anvil.
-The screw thread is made on the spindle with specific pitch.
-The barrel is accurately divided & clearly marked in 0.5mm along its
length on main scale.
-The thimble has 50equal division around its circumference & each
division has value of 0.01mm.
12. - WHEN ANVIL & SPINDLE IS BOUGHT TOGETHER THE INSTRUMENT READS
ZERO.
- THE RATCHET IS PROVIDED AT END OF THIMBLE. IT IS USED TO ASSURE
ACCURATE MEASUREMENT & TO PREVENT TOO MUCH PRESSURE APPLIED ON
MICROMETER.
- WHEN THE SPINDLE REACHES NEAR THE WORK SURFACE THE OPERATOR
USE THE RATCHET SCREW TO TIGHTEN THE THIMBLE.
- THE RATCHET IS AUTOMATICALLY SLIPS WHEN CORRECT PRESSURE IS
APPLIED & PREVENT TOO MUCH PRESSURE.
- THE LOCKNUT IS PROVIDED ON SPINDLE TO LOCK & WHEN THE
MICROMETER IS AT CORRECT READING.
Errors in micrometers:-
1. The face of anvil & spindle may not be truly flat.
2. Lack of parallelism and squareness of anvil or spindle at some or all
part of scale.
3. Setting of zero reading may be inaccurate.
4. Inaccurate reading shown by fractional division on the thimble.
5. Wear on the face of anvil, spindle the threads of spindle.
6. Error due to too much on the thimble.
13. ENGINEER’S STEEL RULE OR SCALE:-
-It is the simplest line measuring instrument.
- It is made from hardened steel or stainless steel.
- Its accuracy graduated in mm or inch division.
- It works on basic measuring technique of comparing unknown length to the
one previously calibrated.
- It manufactured in different size & style of 150mm,300mm,600mm,1000mm
length.
14. CALLIPERS:- -In some cases the dimensions of component
can not be measured directly by scale.
- In this case callipers uses with scale for
transferring length to the scale.
- It consist of two legs which hinged at top and
end of legs made from carbon & alloy steel.
- Where high accuracy is necessary callipers
not used.
Classification:-
1.Based on design aspect
(a)Firm joint callipers
(b)Spring type callipers
2. Base on their use
(a)Outside callipers
(b)Inside callipers
(c)Transfer callipers
(d)Odd leg callipers
15. BORE GAUGE:-
-It is used for measure the small bores.
-There are different types of bore gauge but the mostly
used are 1.Dial bore gauge & 2.Hemispherical bore gauge
Dial bore gauge:-
-It measure the bore directly.
-It work on proven principle of two diametrically opposed
measuring points, one fixed & one moving.
-The measuring body is connected with the dial indicator by
tube.
-The push rod is provided inside the tube to transmit the
movement of measuring head to dial indicator.
-So, the horizontal movement is convert into vertical
movement & dial indicator gives indication of variation of
size.
-The accuracy of bore gauge is 0.001mm
-It is used in injection molding or in barrel.
-It is rapid & accurate checking of bore for size, ovality,
tapper & wear within a deep bore.
16. HEMISPHERICAL BORE GAUGE:-
-This gauge consist of spring steel arms having Hemispherical ends.
- Inside the arm wedge shaped member attached to spring which moved
endwise by rotating screw head.
- Due to up & down of wedge member with spindle, the hemispherical
ends expand or contracts as per size.
- Then the bore is taken out & the reading is noted down by measuring
over the hemispheres with an micrometer.
- This bore gauge is available in 4sizes to measure 3mm to 12mm
diameter of bore.
17. TELESCOPIC GAUGE:-
- It is an indirect measuring device & used
for measuring internal diameter of holes,
slots & grooves.
- It consists of handle, two telescopic rods
& locking screw.
- One end of handle is connected with
tube in which telescopic rods slides
which has spherical contacts & it is
forced by internal spring.
- For taking measurement, telescopic
rods are compressed against spring &
inserted into the hole whose diameter to
be measured.
- Then extended up to the walls of hole.
Then they locked by locking screw &
rods can be measured by micrometer or
vernier caliper.
- This is use in measure the diameter of
IC Engines.
18. SLIP GAUGE:-
-It is also known as gauge blocks.
-They are universally accepted as end
standard of length in industry.
-It is a rectangular block made up with
high grade hardened steel.
-It is able to resist wear.
-They are independent of any variation
of size & shape. They are stabilized by
heating & cooling successively in stages
so it removed its hardening stress.
-After being hardened they are carefully
finished by high grade lapping to the
high degree of finish, flatness, and
accuracy.
-They are generally available in sets.
-The slip gauge is inspected time to time
by standard gauge blocks.
-Tool steel, chrome plated steel,
stainless steel, tungsten carbide and
chrome carbide are used for making
gauge.
19. WRINGING OF SLIP GAUGE:-
-If two slip gauge are wrung together to each other and considerable
pull is required to break the wring.
-This phenomenon of wringing occurs due to molecular adhesion
between a liquid film and mating surface.
-This wringing process is used to build up desired dimension over a
size of specific increment.
-It depends on the surface finish and flatness of the blocks used and
absence of dirt, grease, burrs and scratches.
-When it correctly wrung together, the error in total length is negligible.
20. APPLICATION:-
1. They are used to check the accuracy of vernier, micrometer, and
other devices.
2. They are used to set the comparator to a specific dimension.
3. They are used for direct measurement where the accuracy of work
piece is important.
4. They are frequently used with sine bar to measure angle of work
piece.
5. They can be used for check gap between parallel location.
21. SLIP GAUGE
Slip gauges are rectangular blocks of steel having a cross-
section of about 30 by 10 mm
Normal Set
Special Set
Range Step Pieces
1.001 to 1.009 0.001 9
1.01 to 1.09 0.01 9
1.1 to 1.9 0.1 9
1 to 9 1 9
10 to 90 10 9
Total 45
Range Step Pieces
1.001 to 1.009 0.001 9
1.01 to 1.49 0.01 49
1.5 to 9.5 0.5 19
10 to 90 10 9
Total 86
22. CLASSIFICATION
AA slip gauges
Master slip gauges
Accurate to plus or minus two microns per meter
A slip gauges
Reference purpose
Type A is guaranteed accurate up to plus or minus four
microns per meter
B slip gauges
Working slip gauges
Type 'B' for plus or minus eight microns per meter
23. CLASSES
Grade 2 : This is the workshop grade
Typical uses include setting up machine tools, positioning milling cutters and
checking mechanical width.
Grade 1 : Used for more precise work, -tool room.
Typical uses include setting up
Sine bars and sine tables
Checking gap gauges and
Setting dial test indicators to zero
Grade 0 : This is more commonly known as the Inspection grade
Inspection Department only who have access to this grade of slips
Grade 00 : This grade would be kept in the Standard Room and would be
kept for work of the highest precision only.
Determination of any errors present in the workshop or Grade 2 slips.
Calibration grade : Calibration grade are used for calibration of slip gauges,
other measuring instruments
24. DIAL INDICATORS:-
- It is used for measuring and checking linear
dimension.
- It is simpler to use than other instrument such as
vernier and micrometer.
- It consist of one round dial which has two pointer one
is main & other is smaller.
- It acts with the help of rack & pinion.
- The movement of spindle is transferred by rack to
small pinion from where it transferred to the pointer
through a gear train.
- The main dial is divided into the 100 equal division,
each division shows the 0.01mm means for 1mm
spindle moves 1 revolution.
- The small pointer records the number full turns of
main pointer.
- It is very easy to use & less expensive than other
instrument.
- Once the indicator is installed unskilled person easily
operate it.
25. OPTICAL FLAT :-
The essential equipment for measurement by light wave interference
is a monochromic light source and a set of optical flats.
An optical flat is a disk of high-quality glass or quartz. The surface of
the disk is ground and lapped to a high degree of flatness.
Sizes of optical flats vary from 25 to 300 mm in diameter, with a
thickness ranging from 25 to 50 mm.
Sometimes the optical flats are coated with a thin film of titanium
oxide. This reduces the loss of light due to reflection which makes the
band more clear.
26. Optical flats are of two types :
Type A :- It has only one surface flat. Type A are used
testing the flatness of precision measuring surfaces of flats,
slip gauges, measuring tables, etc.
The dimensions of an flat of grades can be 25*10,
30*10 , 50*15, 100*25 (diameter* thickness in mm).
Type B :- It has both surface flat and parallel to each
other. Type B are used for testing measuring surfaces of
micrometers , measuring anvils and similar length
devices for testing flatness and parallelism.
27. When an optical flat is placed on work piece surface it will not
form an intimate contact, but will be at slight inclination to the
surface, forming air wedge between the surface as shown in
fig.
When beam AB of monochromatic light falls on the optical
flat, it travels further along BC. At C, part of this light is
reflected by the bottom of the optical flat and goes along CDE.
the remaining part goes along CF , reflected at F by the
surface under test and goes further along FGHJ.
28. Thus ,θ is very small, then h=CF=FG= ,where = wave
length of source and beam HJ will lag behind DE by 2h.
In other words ,all points with air gap h will form a dark band.
As we move along the wedge to the right side, to point K,L as
shown fig.
At this point as the air gap increases, for every increases,
the bright bands will be seen as shown in fig.
