The determination of an unknown dimension. This requires that known standards be used directly or indirectly for comparison. It is defined as the process of numerical evaluation of a dimension or the process of comparison with standard measuring instruments .The elements of measuring system include the instrumentation, calibration standards, environmental influence, human operator limitations & features of the work piece .The basic aim of measurement in industries is to check whether a component has been manufactured to the requirement of a specification or not.
The instruments used for linear measurements can be classified as: i) Direct measuring instruments ii) Indirect measuring instruments
Direct measuring instruments are of two types i) Graduated ii) Non-graduated
Line standard:
The measurement of distance may be made between two parallel lines or two surfaces. When, the length, being measured, is expressed as a distance between the centers of two engraved lines as in a steel rule, it is known as line measurement. Line standards are used for direct length comparison and they have no auxiliary devices. Yard or meter is the line standard.
Yard or meter is defined as the distance between scribed lines on a bar of metal under certain environmental condition. These are the legal standards .

Meter:
It is the distance between the center portions of two lines etched on a polished surface of a bar of pure platinum alloy (90%) or irridum alloy (10%). It has overall width and depth of 16 mm each and is kept at0°C and under normal atmospheric pressure.
The bar has a wing-like section, with a web whose surface lines arc on the neutral axis. The relationship between meter and yard is given by,
1 meter = 1.09361 yard
It is a bronze bar with square cross sectional & 38 inches long. A bar of 38 inches long has a round recess of 0.5 inches diameter & 0.5 inches deep. A round recess is 1 inch away from the two ends. A gold plug f 0.1 inches diameter having three lines is etched transversely & two lines engraved longitudinally arc inserted into these holes. The yard is then distance between two central transverse line on the plugs when the temperature of bar is at 62˚F.
1 Yard= 0.9144 meter

End standard:
E n d s t a n d a r d s , i n t h e f o r m o f t h e b a r s a n d s l i p g a u g e s , a r e i n general use in precision engineering as well as in standard laboratories such as the N.P.L
(National Physical Laboratory). Except for applications where microscopes can be used, scales are not generally convenient for the direct measurement of engineering products, whereas slip gauges are in everyday use in tool-rooms, workshops, and inspection departments throughout the world. A modern end standard consists fundamentally of a block or bar of steel generally hardened whose end faces are lapped flat and parallel to within a few millionth of a cm. By the process of lapping .Its size too can be controlled very accurately.
Although, from time to time, various types of end bar have been constructed, some having flat and some spherical faces, the flat, parallel faced bar is firmly established as the most practical method of end measurement.
P r i m a r y e n d s t a n d a r d s u s u a l l y c o n s i s t o f b a r s o f carbon steel about 20 mm in diameter and made in sizes varying from 10mm to 1200 mm. These are hardened at the ends only. They are used for the measurement of work of larger sizes.

Slip gauges are used as standards of measurement in practically every precision engineering works in the world.

These were i n v e n t e d , b y C . E . J o h a n s s o n o f S w e d e n e a r l y i n t h e p r e s e n t c e n t u r y . These are made of high-grade cast steel and are hardened throughout possible.


W i t h t h e s e t o f s l i p g a u g e s , c o m b i n a t i o n o f s l i p g a u g e e n a b l e s m e a s u r e m e n t s t o b e m a d e i n t h e ' r a n g e o f 0 . 0 0 2 5 t o 1 0 0 m m b u t i n combinations with end/length bars measurement range up to 1200 mm is
Slip gauges or gauges blocks are universally accepted end standard of length in industry. These were introduced by Johansson a Swedish engineer & are also called as Johnson gauges.
These are rectangular blocks of high grade steel with exceptionally close tolerance.
These gauges consists of a set of steel blocks, each of which has one pair of opposite faces lapped flat and parallel accurately to a few millionths of an inch. They are used to check the accuracy of workshop and similar gauges, which in use arc subjected to wearing action; slip gauges should never be used as ordinary measuring gauges, but as reference or master standards. They are generally employed in connection with comparator instruments when workshop gauges have to be checked.
The slip gauges are supplied in sets, the number in each set varying according to the purpose in view. The most widely employed set consists of 81 gauges of differing thickness made up as follows:
Nine pieces with range of 0.1 001 to 0.1009 in. in steps of 0.0001 in.
Forty-nine pieces with a range of 0.101 to 0.149 in. in steps of 0.001 in.
Nineteen pieces with a range of 0.05 to 0.95 in. in steps of 0.05 in.
Four pieces of parallel width, 1 in, 2 in, 3 in, and 4 in. respectively.
Metric unit sets of 103 pieces are made up as follows:
Forty-nine pieces with a range of 1.01 to 1.09 mm. in steps of 0.01 mm.
Forty-nine pieces with a range of 0.50 to 24.50 mm. In steps of 0.50 mm.
Four pieces of25, 50, 75, and 100 mm respectively.
One extra piece of 1.005 mm.
Smaller sets of 76, 56, 48, and 31 pieces are also supplied in the metric sizes, and sets of 49, 41,
35 and 28 in English sizes.

Wringing is the process of sliding two blocks together so that their faces lightly bond. When combined with a very light film of oil, this action excludes any air from the gap between the two blocks. The alignment of the ultra-smooth surfaces in this manner permits molecular attraction to occur between the blocks, and forms a very strong bond between the blocks along with no discernible alteration to the stack’s overall dimension

First clean the surfaces as desired previously, and then place one gauge centrally across the other gauge at right angles to form a symmetrical cross. Finally rotate the upper gauge over the lower one to its final coincident position. This method results in appreciably less rubbing action than the upper gauge is slid lengthwise over the lower one.
Indian standard on slip gauges:
According to IS: 2984-1966 there are five grades
Grade 2 .
This is the workshop grade. Typical uses include setting up machine tools, positioning milling cutters and checking mechanical widths .
Grade 1.
Used for more precise work, such as that carried out in a good-class 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, and its use is confined to tool room or machine shop inspection. This means that it is the Inspection Department only who have access to this grade of slips. In this way it is not possible for these slip gauges to be damaged or abused by the rough usage to be expected on the shop floor .
Grade 00.
This grade would be kept in the Standard Room and would be kept for work of the highest precision only. A typical example would be the determination of any errors present in the workshop or Grade 2 slips, occasioned by rough or continual usage.

Calibration grade.
This is a special grade, with the actual sizes of the slips stated or calibrated on a special chart supplied with the set. This chart must be consulted when making up a dimension, and because these slips are not made to specific or set tolerances.
Dial Indicators are instruments used to accurately measure a small distance. The measurement results are displayed in a magnified way by means of a dial. They may be used to check the variation in tolerance during the inspection process of a machined part, measure the deflection of a beam or ring under laboratory conditions, as well as many other situations where a small measurement needs to be registered or indicated .
It operates on the principle, that a very slight upward pressure on the spindle at the contact point is multiplied through a system of gears and levers. It is indicated on the face of the dial by a dial finger. Dial indicators basically consists of a body with a round graduated dial and a contact point connected with a spiral or gear train so that hand on the dial face indicates the amount of movement of the contact point. They are designed for use on a wide range of standard measuring devices such as dial box gauges, portal dial, hand gauges, dial depth gauges, diameter gauges and dial indicator snap gauge .
Corresponds to a spindle movement of 1 mm. The movement mechanism of the instrument is housed in a metal case for it's protection. The large dial scale is graduated into
100 divisions. The indicator is set to zero by the use of slip gauges representing the basic size of part.

Requirements of Good Dial Indicator:
1. It should give trouble free and dependable readings over a long period.
2. The pressure required on measuring head to obtain zero reading must remain constant over the whole range.
3. The pointer should indicate the direction of movement of the measuring plunger.
4. The accuracy of the readings should be within close limits of the various sizes and ranges
5. The movement of the measuring plunger should be in either direction without affecting the accuracy.
6. The pointer movement should be damped, so that it will not oscillate when the readings are being taken.
1 In a quality environment to check for consistency and accuracy in the manufacturing process.
2 On the workshop floor to initially set up or calibrate a machine, prior to a production run.
3 By toolmakers (mold makers) in the process of manufacturing precision tooling.
4 In metal engineering workshops, where a typical application is the centering of a lathe's work piece in a four jaw chuck. The DTI is used to indicate the run out (the misalignment between the work piece's axis of rotational symmetry and the axis of rotation of the spindle) of the work piece, with the ultimate aim of reducing it to a suitably small range using small chuck jaw adjustments.
5 In areas other than manufacturing where accurate measurements need to be recorded, eg:physics.
6 Comparing two heights or distances between narrow limits.
7 . To determine the errors in geometrical form such as ovality, roundness and taper.
8 . For taking accurate measurement of deformation such as intension and compression.
9 To determine positional errors of surfaces such as parallelism, squareness and alignment.
10 To check the alignment of lathe centers by using suitable accurate bar between the centers.
11 To check trueness of milling machine arbours and to check the parallelism of shaper arm with table surface or vice.

The dial indicator typically consist of a graduated dial and needle to record the minor increments, with a smaller embedded clock face and needle to record the number of needle rotations on the main dial. They may be graduated to record measurements of between 0.001" down to 0.00005" for more accurate usage.
The dial face can be rotated to any position, this is used to orient the face towards the user as well as set the zero point, there will also be some means of incorporating limit indicators (the two metallic tabs visible in the right image, at 90 and 10 respectively), these limit tabs may be rotated around the dial face to any required position. The dial indicators are normally set up in a fixture (possibly a magnetic base) which would secure the dial indicator and allow its adjustment to read zero at the optimal size of a sample part.
How to Read:
Dial face has dual directional graduation of 0.001.
Revolution counter is graduated in 0.1”.
One full revolution of large pointer is one increment of revolution counter.
Example:
The small pointer is between 1. and 2. or between 6 and 7=0.1. or 0.6.
The large pointer is close to line 21 of black digit=0.021.

So the reading is 0.1. +0.021.=0.121. Or 0.6.+0.021.=0.621
Micrometers are designed on the principle of 'Screw and Nut’. It is one of the most common & most popular forms of measuring instrument for precise measurement with 0.01 mm accuracy.
Micrometer with 0.001 mm accuracy are also available .These are classified as a) Outside micrometer c)) Inside micrometer b) Depth gauge micrometer d) screw thread micrometer
Parts of micrometer:
A micrometer is composed of:
Frame
The C-shaped body that holds the anvil and barrel in constant relation to each other. It is thick because it needs to minimize flexion, expansion, and contraction, which would distort the measurement. The frame is heavy and consequently has a high thermal mass, to prevent substantial heating up by the holding hand/fingers. It is often covered by insulating plastic plates which further reduce heat transference.
Anvil
The shiny part that the spindle moves toward, and that the sample rests against.
Sleeve / barrel / stock
The stationary round part with the linear scale on it. Sometimes vernier markings.
Lock nut / lock-ring / thimble lock
The knurled part (or lever) that one can tighten to hold the spindle stationary, such as when momentarily holding a measurement.
Screw
( not seen) The heart of the micrometer, as explained under "Operating principles" . It is inside the barrel. ("measuring screw".)
Spindle
The shiny cylindrical part that the thimble causes to move toward the anvil.
Thimble

The part that one's thumb turns. Graduated markings.
Ratchet stop
(not shown in illustration) Device on end of handle that limits applied pressure by slipping at a calibrated torque.
Principle of micrometer:
It consists of screw which revolves in a fixed nut. So its principle is same as that of screw advancing in a nut .when a screw is advanced or turned through the nut on revolution it means screw covers on pitch distance i.e the rotary distance by screw in one revolution is equal to linear distance equal of the screw is dived into ‘n’ number of equal parts then the minimum distance screw advances is (pitch/n).
We can say that minimum length that can be measured by this instrument is (pitch/n).
To measure the still smaller length. The number of division should be increased or pitch of the screw should be decreased thus increasing the accuracy.
Least count of micrometer:
L.C is the minimum measurement of the instrument. The thimble of a micrometer has a pitch of 0.5 mm. so the minimum distance a micrometer can measure is
Pitch/n = 0.5/50=0.01mm
Thus least count of a micrometer is 0.01mm & it can be formulated as
L.C of micrometer= pitch of spindle screw/number of divisions on the spindle.
Inside micrometer:
The inside micrometer is the most direct measuring tool used for inspection (Figure 1). The total length of the inside micrometer is itself the overall length being measured. The inside micrometer is a much more accurate measuring tool for inside measurement than the caliper.
The inside micrometer is almost always purchased as a set. The only way to use the inside micrometer over a range of sizes is by using extension rods. Only one micrometer head is needed, along with extension rods, to cover a broad range of measurements.
Tubular style extension rods are available in the intermediate to extended length, while solid extension rods are used for ranges of up to approximately 32 inches. Figure 1 Inside micrometer set

The smallest sizes of inside micrometers have a travel range of ¼ inch. The largest sizes of inside micrometers have a range of 1 inch. The most popular inside micrometer sets have a ½ inch range.
The inside micrometer is very similar to the outside micrometer, except that it has no frame
(Figure 3). In some cases a micrometer handle (shown in figure 1) is used to reach into inaccessible places or in small areas where the inspector's fingers would get in the way.
Figures 2 and 3 An inside micrometer is the same as a plain micrometer without the frame.
When using the inside micrometer it is necessary to rotate the head end of the micrometer in an axially direction as well as up and down (Figure 4), all the while adjusting the head to the proper feel.
Rotating the head in this manner assures that the micrometer is accurately centralized in the part. The inside micrometer, in most cases, is removed from the part while the actual reading is being done. For this reason the barrel lock is relatively snug to retain the reading.
Figure 4 When possible, hold the reference end of the inside micrometer in one hand while rotating and adjusting the micrometer head

.
Outside micrometer:
It is used to measure the outside diameter & length of small parts to accuracy of 0.01 mm. Its accuracy can be increased up to 0.001 mm. The working principle of outside micrometer is
The main parts of an outside micrometer are U-shaped steel frame, anvil, spindle, lock nut, sleeve or barrel , thimble & ratchet. At first, check zero reading & place the part to be measured in between the measuring faces. Advance the spindle by rotating the ratchet until it begins to slip & clicks are heard. This indicates that there is no further movement of the spindle. Note the reading both on barrel scale & on the circular scale f the thimble. The barrel scale indicates whole millimeter while the thimble scale indicates tenths & hundredth of a millimeter
Reading on micrometer= reading uncovered on the barrel+ 0.001* number of division on thimble scale which coincides with horizontal line on the barrel .
It is used for measuring the depth of holes, slots & recessed areas. It has one shoulder which acts as reference surface & it is held firmly & perpendicular to the centre line of hole. The length of micrometer depth varies from 0 to 225 mm. The rod is inserted through the top of the micrometer. It is marked after every 10 mm so that it can be clamped at any position while using it must be ensured that the edge of hole is free from burns. The scale here is calibrated in reverse direction. The accuracy depends upon the sense of touch. The depth gauge micrometer is a precision measuring instrument, used by engineers to measure depths. Each revolution of the ratchet moves the spindle face 0.5mm towards the bottom of the blind hole. The diagram below shows how the depth gauge is used. The ratchet is turned clockwise until the spindle face touches the bottom of the blind hole. The scales are read in exactly the same way as the scales of a normal micrometer

It is the simplest instrument for measuring angles between two faces. It consists of two arms and an engraved circular scale. The two arms can be set along the faces between which the angle is to be measured. The body of the instrument is extended to form one of the arms, and this is known as the stock. It is the fixed part of the protractor and should be perfectly straight.
The other arm is in the form of a blade that rotates in a turret mounted on the body. One of the bodies of the turret carries the divided scale and the other member carries a vernier or index.
The ordinary protractor measures angles only in degrees and used for non-precision works. By using angular vernier scale along with it, precision up to 5’ can be achieved. Figure 6.1 shows the diagram of a protractor.
It is used to measure angles accurately to 5 minutes. it is finely made tool with dial, graduated in degrees, a base and a sliding blade. The blade can be locked against dial by tightening the blade clamp nut. The blade and dial can be rotated as one unit to any position

and locked by tightening the dial clamp nut for accurate measurement, a vernier or a fine adjustment device, is fitted on the dial. The dial is graduated into, I treads, , The vernier scale is divided into twelve equal parts on each side of zero, every third division is numbered 0, 15,
30, 45, 60 representing minutes
The name universal refers to the capacity of the instrument to be adaptable to a great variety of work configurations and angular interrelations. It consists of a base to which a vernier scale is attached. A protractor dial is mounted on the circular section of the base. The protractor dial is graduated in degrees with every tenth degree numbered. The sliding blade is fitted into this dial; it may be extended to either direction and set at any angle to the base. The blade and the dial are rotated as a unit. Fine adjustment are obtained with a small knurled headed pinion that, when turned, engages with a gear attached to the blade mount. The protractor dial may be locked in any position by means of the dial clamp nut.
Measurement in a universal bevel protractor is made either by embracing the two bounding elements of the angle or by extraneous referencing, for example, the part and the instrument resting on a surface plate.
The vernier protractor is used to measure an obtuse angle, or an angle greater than 90 o but less than 180 o . An acute angle attachment is fastened to the vernier protractor to measure angles of less than 90 o . The main scale is divided into two arcs of 180 o . Each arc is divided into two quadrants of 90 o and has graduation from 0 o to 90 o to the left and right of the zero line, with every tenth degree numbered.
The vernier scale is divided into 12 spaces on each side of its zero (total 24). The spacing in the vernier scale is made in such a way that least count of it corresponds to 1/12th of a degree, which is equal to 5 o .
If the zero on the vernier scale coincides with a line on the main scale, the number of vernier graduations beyond the zero should be multiplied by 5 and added to the number of full degrees indicated on the protractor dial.

:
It is a recent development of vernier bevel protractor. By using this instrument it is possible to take reading up to app. 2 minutes of an arc. The interval circular scale graduated in division of
10 minutes of arc.
Reading are taken against a fixed index line or vernier by means of optical magnifying system which is integral the instrument.
The scale is graduated as a full circle marked 0-90-0-90. The zero position corresponds to the condition when the blade is parallel to the stock. Provision is also made for adjusting the focus of the system to accommodate normal variation in eye sight. The scale & vernier are so arranged that they are always in focus in the optical system.

In this method, the auto collimator used in conjunction with the angle gauges. It compares the angle to be measured of the given component with the angle gauges. Angles gauges are wedge shaped block and can be used as standard for angle measurement. They reduce the set uptime and minimize the error. These are 13 pieces, divided into three types such as degrees, minutes and seconds. The first series angle are 1°, 3°, 9°, 27° and 41 ° And the second series angle are 1', 3', 9' and27' And the third series angle are 3", 6", 18" and 30".
These gauges can be used for large number of combinations by adding or subtracting these gauges, from each other.
Nominal angles of combination angle gauges
Degrees
Minutes
Fraction of minute
(or seconds)
1
1
0.05
3
3
3
0.1
6
9
9
0.3
18
27
27
0.5
30
41
-
-
-
Spirit level is one of the most commonly used instruments for inspecting the horizontal position of surfaces and for evaluating the direction and magnitude of minor deviation from that nominal condition. It essentially consists of a close glass tube of accurate form. It is called as the vial. It is filled almost entirely with a liquid, leaving a small space for the formation of an air or gas bubble. Generally, low viscosity fluids, such as ether, alcohol or benzyl, are preferred for filling the vial. The liquid due to its greater specific weight tends to fill the lower portion of the closed space. Upper side of the vial is graduated in linear units. Inclination of a surface can be known from the deviation of the bubble from its position when the spirit level is kept in a horizontal plane. Temperature variations in the ambient condition cause both liquid and vial to expand or contract. Therefore, selection of proper liquid and material for the spirit level is very important for accurate result. To reduce the effect of heat transfer in handling spirit levels are made of a relatively stable casting and are equipped with thermally insulated handles.

Principle:
The bubble always tries to remain at the highest point of the tube.If the base of the spirit level is horizontal, the center point is the highest point of the tube .So that, when the level is placed on a horizontal surface, the bubble rests at the center of the scale. If the base of the level is titled through a small angle, the bubble will move relative to the tube a distance along its radius corresponding to the angle. Below fig shows two positions of the base of the level(OA1 and
OA2) and corresponding positions of the bubble(B1,B2).When the base (OA1) is horizontal, the bubble occupies position B1.Let ‘ɵ’ be the small angle through which the base is tilled. The bubble now occupies the position B2 . Let ‘l’ be the distance travelled by bubble along the tube
& ‘h’ the difference in height between the ends of base then, l= R ɵ & h= L ɵ
Therefore , =l/R= h/L (or) l= h* R/L
Where R= radius of curvature of the tube
L= length of base.
It is a precision instrument used along with slip gauges for the measurements of angles sine bar is used: i) To measure the angles very accurately ii) To locate of a steel bar to a given angle with in very close tolerance.
It is used for measurement of an angle of a given job or for setting an angle. They are hardened and precision ground tools for accurate angle setting. It can be used in conjunction with slip gauge set and dial gauge for measurement of angles and tapers from horizontal surface. As shown in Figure, two accurately lapped rollers are located at the extreme position.
The center to center distance between the rollers or plugs is available for fixed distance i.e.

l = 100, 200, 250, 300 mm. The diameter of the plugs or roller must be of the same size and the center distance between them is accurate. The important condition for the sine bar is that the surface of sine bar must be parallel to the center lines of the plug
A sine bar is made up of a hardened steel beam having a flat upper surface. The bar is mounted on two cylindrical rollers. These rollers are located in cylindrical grooves specially provided for the purpose. The axes of the two rollers are parallel to each other. They are also parallel to the upper flat surface at an equal distance from it. Unlike bevel protractors sine bars make indirect measurements. The operation of a sine bar is based on known trigonometric relationship between the sides and the angle of a right angle triangle. Here, dimension of two sides determine the size of the third side and of the two acute angles. The accuracy attainable with this instrument is quite high and the errors in angular measurement are less than 2 seconds for angle up to 45 o . Generally, right-angled triangle is obtained by using a horizontal and precise flat plate on which gage blocks are stacked in the direction normal to the plane of the plate. Sine block itself is not a measuring instrument. It acts as an important link in the angle measuring process. The actual measurement consists in comparing the plane of the part’s top element to the plane of supporting surface plate. Mechanical or electronic height gauges are essentially used in the process.
Principle of Working :
As shown in Figure the taper angle θ of the job WX YZ is to bemeasured by the sine bar. The job is placed over the surface plate. Thesine bar is placed over the job with plug or roller of one end of the bar touching the surface plate. One end of the sine bar is rested on the surface plate and the other end is rested on the slip gauges

The angle of the job is then first measured by some non-precision instrument, such as bevel protector. That angle gives the idea of the approximate slip gauges required, at the other end of sine bar. And finally the exact number of slip gauges are added equal to height h, such that, the top most slip gauges touches the lower end of the roller. The height of the slip gauges required is then measured. Then the taper angle can be measured by making sine bar as a hypotenuse of right angle triangle and slide gauge as the opposite side of the triangle as shown in Figure
h = Height in mm
L = Center distance in mm
Sinθ = Opp / Hyp = (h/ L)
When the size of the job is large having taper then we use slip gauges for the both the side to find the taper angle of the job

For a small component, the component or work piece can be placed over a sine bar asshown in Figure. The job is held on the sine bar with some suitable accessories. The dial indicators are provided at the top position and the reading is taken at A position. The dial indicator is then moved to the right hand side and the reading is taken at position B. If there is a difference between reading at position A and B, then the height of the slip gauges is adjusted until the dial indicator shows the same reading at A and B. Then the angle is calculated similar to previous method as
Sinθ = Opp / Hyp = (h/ L)
Use of Sine Bar.
.
(1) Measuring known angles or locating any work to a given angle

For this purpose the surface plate is assumed to be having a perfectly flat surface, so that its surface could be treated as horizontal. One of the cylinders or rollers of sine bar is placed on the surface plate and other roller is placed on the slip gauges of height h. Let the sine bar be set at an angle θ. Then sin θ = h/l, where l is the distance between the centres of the rollers. Thus knowing θ, h can be found out and any work could be set at this angle as the top face of sine bar is inclined at angle θ to the surface plate. The use of angle plates and clamps could also be made in case of heavy components. For better results, both the rollers could also be placed on slip gauges, of height h1 and h2 respectively.
Then sin θ= (h2-h1)/l
(2) Checking of unknown angles .
Many a times, angle of a component to be checked is unknown. In such a case, it is necessary to first find the angle approximately with the help of a bevel protractor. Let the angle be θ. Then the sine bar is set at an angle θ and clamped to an angle plate. Next, the work is placed on the sine bar and clamped to the angle plate as shown in Fig. and a dial indicator is set at one end of the work and moved to the other, and deviation is noted. Again slip gauges are so adjusted (according to this deviation) that dial indicator reads zero across the work surface. If deviation noted down by the dial indicator is δh over a length l‘ of work, then height of slip gauges by which it should be adjusted is equal to δh * (l/ l‘)

3)Checking of unknown angles of heavy component .
In such cases where components are heavy and can’t be mounted on the sine bar, then sine bar is mounted on the component as shown in Fig. The height over the rollers can then be measured by a vernier height gauge ; using a dial test gauge mounted on the anvil of height gauge as the fiducial indicator to ensure constant measuring pressure. The anvil on height gauge is adjusted with probe of dial test gauge showing same reading for the topmost position of rollers of sine bar. Fig. 8.18 shows the use of height gauge for obtaining two readings for either of the roller of sine bar. The difference of the two readings of height gauge divided by the centre distance of sine bar gives the sine of the angle of the component to be measured. Where greater accuracy is required, the position of dial test gauge probe can be sensed by adjusting a pile of slip gauges till dial indicator indicates same- reading over roller of sine bar and the slip gauges .
Advantages of sine bar:
1. It is used for accurate and precise angular measurement.
2. It is available easily.
3. It is cheap .
Disadvantages:
1.
The application is limited for a fixed center distance between two plugs or rollers.
2. It is difficult to handle and position the slip gauges.
3. If the angle exceeds 45°, sine bars are impracticable and inaccurate.
4. Large angular error may results due to slight error in sine bar.
Sine Centers:
It is the extension of sine bars where two ends are provided on which centers can be clamped, as shown in Figure. These are useful for testing of conical work centered at each end, up to 60°. The centers ensure correct alignment of the work piece. The procedure of setting is the same as for sine bar. The dial indicator is moved on to the job till the reading is same at the extreme position. The necessary arrangement is made in the slip gauge height and the angle is calculated as θ = Sin-1 (h/L)

Taylor’s principle of gauge design:
1 Go gauges should be designed to check the maximum material condition & should check as many dimensions as possible.
2 No go gauges should be designed to check the minimum material limit & should only check one dimension at a time.Thus a separate NO GO gauge is required for each individual dimension.
“GO” gague is used to ensure that MMC is not exceede & that metal does nt encroach in to the minimum allowable hole space. It should therefore be madeto the maximum allowable condition.
“ NO Go”if this was made to gauge both the dimensions of minimum metal conditions would arise where the breadth of hole is with in the specify limit but the lengthis oversize.

“ Go” gauges should be made equal in length to about three or four time to diameter.
While “NO GO “ gauges is alwys relatively short & approximately equal in length to the hole diameter in case of circular hole.
1.
Plug gauges
2.
Ring gauges (or) Snap gauges
3.
Gap gauges
4.
Taper gauges
1.
PLUG GAUGE:
It is used to check the holes. These gauges are desgined in two ways i.e ‘GO ‘ & “ NO GO’ plug gauges. The ‘GO’ plug gauges is the size of low limit of hole while the ‘NO GAUGE’ plug gauge corresponds to high limit of hole. Generally made up of wear resisting steels.The gauging of limit plug is hardened to not less then 750 H.V. the gauging surface is then suitably stabilized ground & lapped. These gauges are referred to as plug gauges; they are used in the manner of a plug . They are generally assembled from standard parts where the gauge portion is interchangeable with other gauge pieces (obtained from a set of pin type gauge blocks ) and a body that uses the collet principle to hold the gauges firmly. To use this style of gauge, one end is inserted into the part first and depending on the result of that test, the other end is tried

2.
RING GAUGES :
It is used for gauging the shafts & male components. There gauges are also designed as
‘GO’ & ‘NO GO’ ring gauges. Snap gauges (or snap gage ) are often used when a large quantity of work pieces must be inspected.
[2] The snap gauge has four anvils or jaws, the first one or pair (outermost) are set using the upper limit (tolerance) of the part and the inner set adjusted to the lower limit of the part. A correctly machined part will pass the first set of jaws and stop at the second — end of test. In this manner a part may be checked in one action, unlike the plug gauge that needs to be used twice and flipped to access the second gauge
3.
GAP GAUGES:

4.
TAPER GAUGES: