metrology note

UNIVERSITI MALAYSIA PAHANG FACULTY OF MECHANICAL ENGINEERING

DMM 2412

METROLOGY


Table o f Contents

CHAPTER 1 Fundamentals Of Metrology

1.1 WHAT IS METROLOGY 2.1 NEEDS AND FUNCTIONS OF INSPECTION 3.1 OBJECTIVES OF METROLOGY 4.1 PRINCIPLES OF METROLOGY

CHAPTER 2 Basic Inspection and Procedures

2.1 INTRODUCTION 2.2 TESTING AND ITS PROCEDURES 2.3 TYPES OF MEASUREMENTS 2.4 FACTORS IN SELECTING TESTING INSTRUMENT 2.5 CALIBRATION 2.6 CARE OF MEASURING INSTRUMENTS

CHAPTER 3 Measurement Errors

3.1 INTRODUCTION 3.2 FACTORS AFFECTING THE ACCURACY OF A MEASURING SYSTEM 3.3 TYPES OF ERRORS 3.4 SOURCES OF MEASUREMENT ERRORS

CHAPTER 4 Vernier Caliper

4.1 INTRODUCTION 4.2 PARTS OF A VERNIER CALIPER 4.3 MEASURING ACCURACY 4.4 READING THE SCALE 4.5 DIAL CALIPER 4.6 DIGITAL CALIPER 4.7 DEPTH VERNIER CALIPER 4.8 APPLICATIONS OF VERNIER CALIPER

CHAPTER 5 Micrometer

5.1 INTRODUCTION 5.2 EXTERNAL MICROMETER 5.3 DEPTH MICROMETER 5.4 INTERNAL MICROMETER 5.5 SPECIAL TYPES OF MICROMETERS

CHAPTER 6 Mechanical Dial Indicator

6.1 INTRODUCTION 6.2 PRINCIPLE OF A DIAL INDICATOR (PLUNGER TYPE) 6.3 PARTS OF A DIAL INDICATOR 6.4 HOW DOES A DIAL INDICATOR WORK 6.5 MEASURING ACCURACY 6.6 READING THE SCALE 6.7 GUIDELINES WHEN USING DIAL INDICATOR 6.8 SOURCES OF ERRORS 6.9 APPLICATIONS OF DIAL INDICATOR


CHAPTER 7 Gauge Block

7.1 INTRODUCTION 7.2 TYPES AND GRADES 7.3 STANDARD SET OF GAUGE BLOCKS 7.4 TO DETERMINE THE GAUGE BLOCKS COMBINATION 7.5 CHECKING SURFACE FLATNESS OF GAUGE BLOCKS 7.6 GAUGE BLOCK APPLICATIONS 7.7 MAINTENANCE AND CARE OF GAUGE BLOCKS

CHAPTER 8 Surface Plate Inspection

8.1 INTRODUCTION 8.2 WHAT IS A SURFACE PLATE 8.3 ADVANTAGES OF GRANITE SURFACE PLATE 8.4 CARE OF SURFACE PLATE 8.5 SOURCES OF ERRORS 8.6 SURFACE PLATE ACCESSORIES OR HOLDING DEVICES 8.7 PRINCIPLES OF SURFACE PLATE INSPECTION 8.8 EXAMPLES OF HOLDING DEVICES USED IN CONJUNCTION WITH A SURFACE PLATE

CHAPTER 9 Instruments for Testing Angles

9.1 INTRODUCTION 9.2 TESTING ANGLES

9.3 EXAMPLES OF APPLICATION 9.4 CALCULATION METHOD

CHAPTER 10 Gauges

10.1 INTRODUCTION 10.2 ADVANTAGES OF GAUGES 10.3 DISADVANTAGES OF GAUGES 10.4 FACTORS IN SELECTING MATERIALS FOR GAUGES 10.5 MATERIALS FOR GAUGES 10.6 TYPES OF GAUGES

CHAPTER 11 Profile Projector

11.1 INTRODUCTION 11.2 APPLICATION 11.3 TEST PROCEDURES 11.4 DIFFERENT STANDARD OVERLAY CHARTS 11.5 TYPES OF MEASUREMENT 11.6 MAINTENANCE OF OPTICAL COMPONENTS

CHAPTER 12 Surface Roughness Measurement

12.1 INTRODUCTION 12.2 SURFACE TEXTURE MEASUREMENT 12.3 DEFINITIONS OF SURFACE ROUGHNESS TERMS 12.4 WAVE LENGTH LIMIT C 12.5 BASIC TERMS OF SURFACE TEXTURE 12.6 EFFECTS OF VARIOUS CUT-OFF VALUES 12.7 DEFINITION OF SURFACE PARAMETERS 12.8 ADDITIONS TO THE SURFACE SYMBOL


12.9 CHOICE OF THE WAVELENGTH LIMIT C 12.10 INSTRUMENTS FOR TESTING ROUGHNESS


FUNDAMENTALS OF METROLOGY

CHAPTER 1


1.1 WHAT IS METROLOGY Metrology is the science of measurement. However, we have to go one step ahead and must also deal with the correctness of measurement. We have to observe whether the measuring result is given with the sufficient correctness and accuracy for the particular need or not. Thus, in industrial terms metrology is primarily concerned with methods and techniques of measurement based on agreed units and standards. The practice of metrology involves precise measurement, which requires the use of apparatus and equipment to permit the degree of accuracy required to be obtained. In a broader sense, metrology is not limited to length measurement. It is also concerned with the industrial inspection and its various techniques from the raw material to the finished product or even assembled parts.

1.2 NEEDS AND FUNCTIONS OF INSPECTION

a. To determine good or bad parts Our five senses are basically instruments, which are used to inspect certain objects based on observation, curiosity or enjoyment. We can use our nose to smell (i.e. to check) whether there is a gas leak. We can use our tongue to taste whether the food is good or bad. In industrial terms, inspection basically is defined as the function of comparing or determining the conformance of a product to specifications or requirements. In other words, the function of inspection is to inspect a product in order to determine whether it is good or bad, and whether it can be accepted or whether it has to be rejected. More specifically, inspection refers to the measurement, visual assessment or testing of a product, process or the act of making a product.

b. To achieve interchangeability Nowadays many new production techniques have been developed and products are being manufactured in large scale due to low-cost methods of mass production. It is very essential that products must be fit and mate if any product is chosen at random for interchangeability purposes. Thus, to achieve interchangeability of products, inspection has to be performed sufficiently and this can be done either by measuring or gauging. The gauging method is very economical for mass production.

c. To improve and develop precision measuring instruments Inspection also led to the development of precision measuring instruments and improvements of inspection methods due to demands of high accuracy and precision works or products. Inspection has also created a spirit of competition and led to the production of quality products on a large scale basis by eliminating variations, thus improving processing techniques.

d. To support the manufacturing department Inspection also supports the manufacturing department by designing and maintaining a system that assesses the quality levels of the work that is done, and the products that are made, according to objectified standards of measurement criteria.


1.3 OBJECTIVES OF METROLOGY a. To ensure the products designed are within the process and measuring instrument

capabilities available in the plant. b. To determine the process capabilities and ensure that these are better than the

relevant parts tolerances. c. To determine the measuring instrument capabilities and ensure that these are

adequate for their respective measurements. d. To minimize the cost of inspection by effective and efficient use of available

facilities, and to reduce the cost of rejects and rework through application of Statistical Process Control Techniques.

e. Standardization of measuring methods: This is achieved by laying down the inspection methods for any product right at the time when the production technology is prepared.

f. Maintenance of the accuracy of measurement: This is achieved by periodical calibration of all measuring instruments used in the plant.

1.4 PRINCIPLES OF METROLOGY

a. Fundamental Units and Standards To determine whether the parts meet the requirements or specifications, we need to perform measurement to collect the data or information. Of course, we need both measuring unit and measuring instrument according to standards before we can start to take any measurement. Units are defined and expressed in standards. Units are the language of measurement and must be constant. The measuring unit of length is Meter. Originally, in 1889 a meter is defined as the distance between two lines on a specific bar which is made of platinum-iridium rod to represent the length of a meter. Thirty of these bars are manufactured. One was kept at the International Bureau of Weights and Measures in Paris as the international standard. The others were sent to laboratories around the world. However, this standard bar has its limitation. It is not stable and constant due to the effect of temperature and environmental factors. Thus, in 1960 a Meter was redefined as 1,650,763.73 wavelengths of a particular orange light emitted by the gas krypton 86. Again, in 1983 the meter was redefined in terms of speed of light. The new definition says: The meter is defined as the length of path traveled by light in vacuum during a time interval of 1/299,792,458 of a second.

b. Units used in Metrology The units used are laid down in the International Units System (S.l = System International) as shown in the table in the following page.

Quantity Units SymbolsLength meter m Mass kilogram kg Time second s

Thermodynamic Temperature Kelvin K Electric Current Ampere A

Table 1.1 List of Basic SI Quantities, Units and Symbols


Prefixes Symbol Multiplier Meaning Giga G 1000000000 109 billion Mega M 1000000 106 million kilo k 1000 103 thousand

Hekta H 100 102 hundred Deka Da 10 101 ten deci d 0.1 10-1 tenth centi c 0.01 10-2 hundredth milli m 0.001 10-3 thousandth micro 0.000001 10-6 millionth

Table 1.2 List of Prefixes c. Derived Units and Conversions The units derived from the basic unit of meter are kilometer, decimeter, centimeter, millimeter, micrometer, and nanometer.

1 km = 1000 m 1 m = 10 dm = 100 cm = 1000 mm 1 dm = 10 cm = 100 mm 1 cm = 10 mm 1 mm = 1000 m

Convert the following for length into values in mm. 0.05m = 0.05 x 1000 = 50 mm 0.88 dm = 0.88 x 100 = 88 mm 300 = 300 x 0.001 = 0.3 mm


CHAPTER 2

BASIC INSPECTION AND

PROCEDURES


Measuring

VERNIER CALIPER

2.1 INTRODUCTION In the machine shop work, every piece must be made accurately to size and shape specified by the designer. Accurate workmanship also depends primarily on accurate inspection or measurement and layout work. To ensure the quality of a product has been achieved, the inspections or measurements must be taken to see if the design and manufacturing standards have been achieved.

2.2 TESTING AND ITS PROCEDURES The main purpose of testing or inspection is to determine whether the products conform to the specification. For example; length, angle, surface quality, shape, and color. Testing can be carried out by two methods:

a. Measuring b. Gauging

a. Measuring It is a method of inspection by means of comparing the length or angle with the scale of a measuring instrument. It is done with suitable measuring instruments such as venire caliper, micrometer, dial gauge, etc. The measured value is read off directly from these instruments. Measuring instruments are graduated calibrated instruments, which are used to determine the actual dimensions of the part for comparison with the desired size. These instruments provide actual size information and this can be useful in spotting the needs for adjustments. But generally, it takes more time and is more expensive than the gauge inspection.


SNAP GAUGE

Gauging

b. Gauging It is a method of inspection by means of comparing a part against a gauge such as plug gauge, to determine whether or not the part is within the specified limits. In gauging method, suitable gauges are used to determine if the work piece has a good or bad result without providing the actual dimensions. One of the widely used gauges is the plug gauge. Generally, it consists of 'Go' member and 'No Go' member. Gauges are used for quick verification, but it will not tell you how good or bad a part is.

Table 2.1

2.3 TYPES OF MEASUREMENT a. Direct Measurement:

The length of the work piece is compared directly against the line of measuring instrument such as vernier caliper of micrometer.

Measuring Characteristics Gauging

more information less

difficult ease of use easy

slow time fast

expensive cost/process cheap

high skill required worker less skill required

Depth Vernier CaliperWork piece


b. Indirect Measurement: The measuring value is obtained by using an intermediary (transfer) measuring device such as caliper, then comparing the measurement obtained against a scale of measuring instrument such as steel ruler.

c. Comparative measurement: It is comparison between the standard such as gauge blocks and the work piece. The gauge blocks are first set to nominal size of the work piece. Then the measuring value is obtained from the dial gauge which shows the difference between the gauge blocks and the work piece. This method is the best and very accurate measurement can be achieved.

Measurement is taken by means of caliper.

Then, it is transferred and compared with a scale of

measuring instrument.

Dial Gauge Dial Gauge

Gauge Blocks Workpiece


2.4 FACTORS IN SELECTING TESTING INSTRUMENT In general, several factors should be considered when selecting the measuring instrument so that variation in the product can be minimized at lower cost.

a. The rule of 10 : The measuring instrument should be 10 times or percent more

precise than the tolerance to be measured. The application of the rule greatly reduces the chances of rejecting good parts or accepting bad parts and performing additional work on them.

b. Repeat accuracy : How repeatable is the instrument in taking the same reading over and over again on a given standard.

c. Stability : How well does this instrument retain its calibration over a period of time. As the instrument become more accurate, they often lose stability and become more sensitive to small changes in temperature and humidity.

d. Magnification : The amplification of the output portion of the instrument over the actual input dimension. The accurate the instrument, the greatest must be its magnification factor, so that the required measurement can be read out clearly compare with the desire standard.

e. Resolution : This is sometimes called sensitivity and refers to the smallest unit of scale or dimensional input that the instrument can detect. The greater the resolution of the instrument, the smaller will be the things it can resolve and the greater will be the magnification required to expand these measurements up to the point where they can be observed the naked eye.

f. Inspection cost : This is included cost of instruments used, cost of maintaining and installing the instruments. Always select the measuring instruments and methods of inspection at minimum cost.

2.5 CALIBRATION A measuring instrument may lose its accuracy (or precision) during use or after a period of time. To maintain its accuracy, it requires a continuing system of calibration control, and this can only be carried out by trained staff in a calibration room. To put an instrument into a state of accuracy requires it to be tested first to see if it is within its calibration limits. If the instrument is found to be out of calibration, then a rectification or adjustment must be made. This adjustment is commonly called 'calibration', 'recalibration' or 'reconditioning'. Thus, calibration may be defined as a comparison of two testing instruments - one of which is a standard of known accuracy traceable to national standards - to detect any discrepancy in accuracy and adjust it to bring it within its tolerances for accuracy.

Inventory and Classification

A systematic approach to calibration control starts with a physical inventory of all standards, instruments, gauges, and test equipment. If instruments are used for product inspection they should be included within the list of items to be systematically controlled for accuracy. For each item which enters the inventory system, a record card is prepared. This card shows the historical origin of the item, its assigned serial number, checking schedule and related information. The card also provides space to record the results of checks and the repairs needed. The physical test equipment is also marked with the assigned serial number for identification and trace ability in the system.


Function of Calibration Room Measuring instruments are calibrated in the calibration room with a room temperature of 20 +1c and a humidity of 55% +3. The functions of the calibration room are: a. To detect deteriorations of instruments beyond the tolerable level of accuracy and

to provide services for the rectification or adjustment of instruments. b. To ensure that newly purchased instruments are within the specified limits. c. To provide a location where instruments are kept in proper condition to maintain

accuracy. d. To provide a centralized location for issuing and keeping production gauges. e. To provide a common place for the development and verification of test methods. f. First piece acceptance inspection prior to production.

2.6 CARE OF MEASURING INSTRUMENTS

a. Calibrate the instrument periodically before you use it. b. Do not use the instruments as a tool. c. Protect the instrument from dust, rust, shock and wear. d. Store the instruments in a proper place. e. Do not store the instruments with other tools. f. Avoid rough handling and dropping the instruments.


CHAPTER 3

MEASUREMENT ERRORS


3.1 INTRODUCTION When making the measurements, there should be one goal in mind to be as accurate as possible. But due to many variations, no measurement in the workshop is ever perfectly accurate. The result of the process (the measured value) will always differ from the actual size. If the same work piece is successively measured with a calliper, micrometer and a coordinate measuring machine (CMM), each successive measurement will show differences in dimension. In measuring technology, this difference between the unknown actual size of the work piece and measured value obtained is known as the inaccuracy of measurement or measurement error.

3.2 FACTORS AFFECTING THE ACCURACY OF A MEASURING SYSTEM

a. Standard

It may be affected by internal and external influences (thermal expansion), stability with time, elastic properties, trace ability and manipulation.

b. Work piece It may be affected by internal and external influences, cleanliness, surface condition, elastic properties, geometric truth, establishment of the work piece reference, etc.

c. Instrument It may be affected by hysteresis, backlash, friction, dents or wear, errors in amplification device, calibration errors, etc.

d. Personal can be many and mainly due to improper training and handling, skill, lack of concentration, attitude towards and realization of personal accuracy achievement, improper selection of instruments, etc.

e. Environment It may be affected by temperature, heat radiation, heating components, vibrations, people, surrounding and many other factors.

3.3 TYPES OF ERRORS

Generally, the errors which exist in any measurement can be considered to be of two distinct types:

a) Systematic error: It occurs constantly under the same measurement condition and can be detected. Thus, it can be largely eliminated.

For example: Thermal expansion of metal is affected by the temperature.

b) Random error: It occurs naturally and is inherent in the measuring process. It is the result of random situations and is difficult to detect and eliminate.

For example: The workpiece is located wrongly when being held in the fixture.


3.4 SOURCES OF MEASUREMENT ERRORS a. Effects of heat Because of expansion due to heat, the length of a body is different at different temperatures. For this reason, a standard temperature of 20C has been fixed for the measurement. b. Parallax error The parallax error is the change in the apparent relative positions of objects when viewed from different positions. It causes measurement errors when there is a height difference between two graduated faces as shown below. In this case, the apparent alignment of the graduation lines differs depending on the eye position. To avoid this error you have to observe vertically against the measuring.

c. Positioning or alignment errors It may be caused if the measuring surface of the instrument is misaligned (or tilted at an angle) with respect to surfaces of the workpiece. To avoid this error, always ensure that the instrument is positioned vertical to the workpiece.

d. Reading errors How accurately can a scale be read? This depends upon the thickness of the line scale, the spacing of the scale divisions and the thickness of the datum of pointer used to give the reading. e. Instrument errors Pitch errors in the instrument such as micrometer, errors of scale division, play, wear and friction in the movable parts; etc. give rise to instrument errors.

f. Abbes Law It states that maximum accuracy may be obtained when the standard is in line with the axis of the workpiece to be measured. For example, take a vernier calliper to measure the workpiece. In this case, the contact point or measuring surfaces may not move in parallel with or keeping squareness to the line of standard, causing error. So when measuring with a vernier calliper, care must be taken, not to apply excessive force on the workpiece for fear of error by out-of-squareness of measuring surfaces.


g. Error caused by force The measuring surfaces of the instrument must be in contact against the workpiece. If this measuring pressure is too high, then the measuring instrument will bend and the workpiece might also become dented or flattened at the point of contact area. Thus, some instruments are provided with a mechanical means (such as a ratchet like in micrometer) to prevent from excessive pressure.

h. Airy points When a long bar is resting on two points (called airy points), errors may arise from sagging. To minimize these errors, the airy points of a long bar of uniform cross-section has to be supported at suitable point from each of the end surfaces. Gauge blocks should be supported at airy points so that both ends of the long bar are kept parallel.


CHAPTER 4

VERNIER CALIPER


4.1 INTRODUCTION The Vernier Caliper is a common measuring instrument which is widely used in the workshop. It comes in various types of design and accuracy. It is made up of a graduated beam (main body) with a fixed measuring jaw and a movable jaw which carries a vernier scale. It is especially suitable for quick and relatively accurate measurements. It is capable of making both outside and inside measurements. In addition, it is also provided with a depth measuring rod which is used for depth measurement. Generally it has a measuring accuracy of 0.02 - 0.05mm and measuring range of 0 - 300mm.

4.2 PARTS OF A VERNIER CALIPER

a. Fixed measuring jaw b. Measuring surfaces c. Movable measuring jaw d. Metric vernier scale e. Main graduation scale f. Depth measuring rod g. Blade measuring surfaces h. Graduated beam

4.3 MEASURING ACCURACY Basically, there are three types of the standard vernier scale available. They are 1/10mm, 1/20mm, and 1/50mm.

a. Measuring accuracy of the Tenth Value Vernier

On the main scale, a distance of 10mm is divided into 10 equal parts, thus the distance between markings = 1 mm. On the vernier scale, 9mm is divided into 10 parts, thus the distance between markings = 0.9mm. Therefore, measuring accuracy (graduation difference) = 1mm - 0.9mm = 0.1mm


b. Measuring accuracy of the Twentieth Value Vernier

On the main scale, a distance of 20mm is divided into 20 equal parts, thus the distance between marking = 1mm. On the vernier scale, 19mm is divided into 20 parts, thus the distance between marking = 0.95. Therefore, measuring accuracy = 1mm - 0.95mm = 0.05mm

4.4 READING THE SCALE Example of read-off ; 1. tenth value vernier, One division is represented as 1mm on the main scale and for the vernier scale, one division is represented as 0.1mm. The mark 0 on the vernier scale shows that the distance measured is more than 21 mm. Reading the graduation on the vernier scale which coincides exactly with the main scale is 0.6mm. Measurement result: 21mm + 0.6mm = 21.6mm

2. Twentieth value vernier

Measurement result: 73mm + 0.6mm + 0.05mm = 73.65mm


3. 1/128 inches vernier On the main scale, 16 divisions = 1 inch

Therefore, on the main scale, 1 division = 1

16 inches

On the vernier scale, 8 divisions = 1

16 inches

Therefore, 1 division on vernier scale = 1

16 8

= 1

128 inches

Refer to the diagram below:

On the main scale : the zero line is fall between 2 1 31 6

and 2 1 41 6

inches

Hence, reading = 21 31 6

inches

On the vernier scale: The 7 divisions coincide with one of the division on the main scale.

Hence, reading = 7 x 1128

= 7

1 2 8inches

Therefore, measurement =21316 +

7128

= 21 1 11 2 8


4.5 DIAL CALIPER

The Dial Caliper is very useful for accurate, reliable, and quick measurements. It is much easier to handle than measuring instruments with vemier reading and it has a measuring accuracy of 0.02mm. The dial face itself is represented by the vemier scale, so that we do not have to find the coincidence line. The movement of the pointer is amplified by means of a rack-pinion mechanism. Zero setting can be easily reset by rotating the dial face. The application of dial caliper is the same as vernier caliper. The measured value can be obtained by simply reading the value of the main scale and add the value found in the dial face. Example of read off:

On the main scale, it shows that the distance is more than 10mm and the pointer is at 0.4mm on the dial face. Thus, the measured value = 10mm + 0.4mm = 10.40mm

4.6 DIGITAL CALIPER

The Digital Caliper is an electronic measuring instrument which is precise, accurate, reliable, sensitive, and gives quicker measurement than the dial caliper. The advantage of using this instrument is that the reading can be read off directly on the display indicator and thus misreading can be avoided. It has measuring accuracy of 0.01mm. The application of the digital vemier is the same as that of the vemier caliper. Guidelines when using vernier calipers a. The measuring surfaces should be clean and free from burrs. b. Open the measuring jaw clear of the workpiece and push the movable jaw slowly to

the workpiece. c. Always ensure that the vernier caliper is not tilted or twisted. d. Use gentle pressure when measuring.


e. When taking a reading make sure your view point is vertical to the scale. f. Before you lift the calipers off the workpiece, realize the slide, otherwise the

measuring surfaces will get worn. g. Check vernier caliper for accuracy at frequent intervals. Clean the entire measuring surfaces. When the jaws are pushed together there should be no light gap between them. The zero markings of main and vernier scales must be positioned exactly,

coinciding or opposite to each other when the jaws are closed. The movable jaw must be able to slide along the beam without any play.

Sources Of Errors a. Workpiece not inserted far enough into the measuring jaws. Errors will become more

when too much force is applied during measurement.

b. Vernier caliper tilted during use, especially when taking the depth.

c. Dirty measuring surfaces. d. Too little or too much force applied during measurement. e. Damage and worn out of the measuring surfaces.

4.7 DEPTH VERNIER CALIPER

The Depth Vernier Caliper is used to check the depth of holes, recesses, slots, counterbores, etc. It is carefully made so that the beam (main body) is perpendicular to the base in both directions. Generally, the base has a larger area for better stability


which is rested on the reference surfaces of the workpiece. To read off the measured value is the same as that of the vernier caliper.

Guidelines when using depth vernier caliper:

a. Ensure it is at vertical position when it is resting on the reference surface. b. Press the base of the instrument firmly against the reference surface. c. Apply light measuring pressure when sliding the beam until it touches the

surface. d. View at vertical when taking the reading to avoid parallax error

Sources of errors

The measuring surfaces do not rest perpendicular to the reference (tilted) as shown.


4.8 APPLICATIONS OF VERNIER CALIPER


CHAPTER 5

MICROMETER


5.1 INTRODUCTION One of the most widely used measuring instrument in the workshop is the Micrometer. It is very useful for accurate, reliable, precise, and quick measurements. It comes in different designs, shapes, ranges, and accuracies, depending on its applications. However, one thing that they have in common is the way they are read off. Generally, it consists of a "C" shape frame with an anvil which comes in different shapes (flat, point, ball, disk, etc.) and a movable spindle. The movement of the spindle is carried out by means of very accurate screw threads principle. Micrometers have a measuring accuracy of 0.001 - 0.010mm.

5.2 EXTERNAL MICROMETER It is used to check external dimensions such as the diameter of a shaft and thickness of a work piece. It consists of a fixed anvil and a movable spindle. The anvil can be made of carbide which has a very flat surface. The object to be measured is positioned between the fixed anvil and the measuring surfaces. Both measuring surfaces are very accurately ground. Parts of an external micrometer

A. Anvil B. Measuring Surfaces C. Movable spindle D. Ratchet E. Thimble F. Sleeve G. U-shaped frame with insulator plate

(to prevent heat transfer from hands)

Measuring range The length of the threads on the measuring spindle is usually 25mm. This means that the measuring ranges of the external micrometer are stepped at every 25mm. The measuring ranges of the micrometer are divided into:

Measuring accuracy There are 50 graduations on the thimble for the micrometer with 0.5mm pitch on the spindle. If the thimble is rotated one complete revolution, the spindle will move 0.5mm. Thus, one graduation on the thimble scale represents 0.01 mm.

Measuring accuracy = 0.5 spindle pitch 50 graduations = 0.01 mm


Reading the scale

One graduation on the thimble represents 0.01mm. The upper scale on the sleeve represents whole numbers such as 1, 2 3, 4mm and so on. One graduation on the lower scale of the sleeve represents 0.5mm. Measurement result:-

Guidelines when using external micrometer

a. Check the micrometer for accuracy at frequent intervals. b. Measuring surface should be clean and free from burrs. c. Hold in the right hand with one of the smaller fingers hooked through the frame

eaving the thumb and forefinger free to turn the spindle.

d. Advance the spindle gradually towards the workpiece.

e. Use a ratchet to avoid excessive pressure when rotating the spindle. When hecking the outside diameter, ensure that the measuring surfaces touch the highest point of the workpiece.


f. When it is not used, wipe it clean and ensure that it is free from dirt. Do not close the measuring surfaces together, otherwise it will be damaged due to expansion of the spindle during the changing of temperature.

g. Apply oil to protect it from rust and keep it in the proper place.

Sources of errors a. Misreading - most common misreading is by 0.5mm, incorrectly counting sleeve

graduations. b. Dirt, nicks, durrs, oil, etc., on the anvil and spindle will prevent proper contact

and cause inaccurate reading. c. Wear and damage on the anvil and spindle. d. Pitch errors - the screw of the spindle is worn out. e. Miscalibrate - the zero setting is set wrongly. f. Applied too much force when measuring.

5.3 DEPTH MICROMETER

It is used to check the depth of holes, recesses, slots, counterbores, etc. It consists of a large flat base and an interchangeable measuring rod with measuring range 0 -300mm. The large base provides stability and stands vertically when it rests on the reference surfaces. To read off the measured value is the same as the external micrometer, but watch it because the thimble hides the scale on the sleeve. Basically, it has a measuring accuracy of 0.01mm.


Guidelines when using depth Micrometer

a. Clean the instrument free from dust, dirt, oil, etc. b. Insert the measuring rod to check within the desired depth range an securely

tighten the locking cap. c. Always calibrate when changing the rod by using gauge blocks. d. Hold the base firmly when it rests on the reference surface and carefully turn the

thimble until the measuring rod makes contact with the surface to be measured. e. Clean entirely when it is not used and keep it in the proper place. Sources of errors a. Bend and worn out of measuring rod. b. Damaged and worn out of screw thread on the spindle. c. Dent, burr, dirt and rust on measuring surfaces. d. Instrument does not stand vertically to the reference surface.

5.4 INTERNAL MICROMETER It is used to check internal dimensions such as diameter of a hole and width of a slot. It comes with different designs, ranges, and shapes depending on its applications. Internal Micrometer with central locking device

It consists of a single micrometer head and series of extension measuring rods to provide a large measurement range (35 - 1 25mm). It has round measuring surfaces to provide better contact point on the round wall. Generally it has a measuring accuracy of 0.01mm. To read off the measured value is the same as the external micrometer. Guidelines when using Internal. Micrometer Calibrate the instrument by means of a ring gauge. Hold the instrument against the hole wall and move the measuring surfaces about while locking the instrument to


locate the center of the hole. Ensure the instrument is located perpendicular to the hole center line. Apply only light pressure to ensure good contact. Sources of errors

Bend and worn out measuring rod. Improperly assembled extension measuring rod. Instrument is not located perpendicular to the hole center line (common error).

Internal Micrometer with measuring jaws

Generally, it consists of two different pairs of jaws. One has a smaller measuring range (5 - 30mm) located on the upper jaw side and the larger measuring range (30 - 55mm) is located on the lower jaw side. It is commonly used to check the width of the slots. It has a measuring accuracy of 0.01mm. Calibration of this instrument can be carried out by using a ring gauge.

Sources of errors a. Bending and worn out measuring jaws. b. Measuring jaws are not positioned perpendicular to reference surfaces.

Internal Micrometer with self centering pin


It consists of three movable measuring pins. It is suitable to check large hole diameters. It has a measuring accuracy of 0.005mm and measuring range of 6 - 300mm. It has better advantages since the three measuring pins serve to locate it exactly perpendicular to the hole center line.

Guidelines when using internal micrometer

a. The measuring pins are contracted enough to allow the instrument to enter the part.

b. The thimble is rotated to tighten the contacts against the hole wall. c. Give slightly jiggling action while tightening it will help to ensure proper

alignment. d. Apply light pressure to ensure good contact. e. To read off the measured value is the same as the external micrometer. f. Clean the instrument from burrs, dirt, oil etc if it is not in use. g. Calibrate the instrument for accuracy at frequent intervals by using a ring

gauge.

5.5 SPECIAL TYPES OF MICROMETERS

a. Micrometer with spheres measuring surfaces

Application : To check thickness of pipe wall. Accuracy : .01mm Range : 0 -25mm


b. Micrometer with dish measuring surfaces

Application : To check gear tooth thickness, steps, grooves, recesses. Accuracy : 0.01mm Range : 0 - 25mm

c. Micrometer with cone points

Application : To check steps, key shafts, grooves, recesses, core dias. Accuracy : 0.01mm, 0.001mm Range : 0 - 25mm, 25 - 50mm

d. Micrometer with blade measuring surfaces

Application : To check small steps, grooves recesses Accuracy : 0.01mm, 0.001mm Range : 0 - 25mm, 25 - 50mm


CHAPTER 6

MECHANICAL DIAL INDICATOR


6.1 INTRODUCTION The mechanical dial indicator is a precision measuring instrument which is designed to provide more flexibility and increased accuracy in the measurement processes. Such instruments are often used in conjunction with surface plates, height gauges, gauge blocks and measuring holding devices to check length measurement by using the so-called comparative method and to inspect geometric features such as roundness. The dial indicator has a measuring accuracy of 0.001 - 0.01mm and a measuring range of 0 - 10mm.

6.2 PRINCIPLE OF A DIAL INDICATOR (PLUNGER TYPE) The principle of the dial indicator is to amplify the movement of the plunger with a small displacement to give a large deflection of the pointer by means of toothed rack and gears. The transmission ratio is usually 100 : 1. Thus, a small value of displacement by the plunger can be read directly or detected very accurately as it is amplified on the measuring scale.

Amplification = movement of the pointer on scale

movement of plunger = 80mm 0.8mm = 100 : 1

6.3 PARTS OF A DIAL INDICATOR

A. Measuring insert B. Plunger C. Clamping shank D. Small dial face (1 div = 1mm) E. Rotating scale (1 div = 0.01mm) F. Setting ring


6.4 HOW DOES A DIAL INDICATOR WORK? It operates based on gears and the rack principle. A rack with a pitch of 0.625mm is cut on the plunger which is than meshed with a pinion (small gear) with 16 teeth. On a pinion, a small pointer and a large gear with 100 teeth is connected to it in which they share a common shaft. Another small gear with 10 teeth - which carries a long pointer - is meshed with a large gear which has 100 teeth at the center of the dial indicator. Thus, any movement of the plunger is amplified to the pointer in which it will show the measurement value on a graduated scale.

6.5 MEASURING ACCURACY

One completed turn on pinion = One completed turn on large gear Thus, one completed turn on pinion , the plunger will move = 16 teeth x 0.625

= 10mm One completed turn on large gear = 10 turns on the small gear (10 teeth) 10 turns on the small gear = 10mm Thus, one complete turn on the small gear = 10mm divided by 10 teeth = 1mm However, there are 100 divisions on the rotating scale; Therefore, 1 division on rotating scale = 1mm divided by 100 divisions = 0.01mm


6.6 READING THE SCALE

On a small dial face, 1 division represents 1mm On a rotating scale, 1 division represents 0.01mm Refer to the diagram: Small pointer is just before 2; Reading = 1mm Large pointer is at 0.89mm Thus, measurement result = 1.89mm

6.7 GUIDELINES WHEN USING DIAL INDICATOR a. Calibrate it at frequent intervals for accuracy by using gauge blocks. b. Clamp the dial indicator securely on holder of measuring stand. c. Keep the measuring insert clean and free from dirt. d. Ensure that it stands vertically to surface of workpiece. e. Avoid excessive pressure when applying the measuring insert to the surface of

workpiece. f. Avoid dropping it and store it at a proper place when it is not used.


6.8 SOURCES OF ERRORS

a. Damage on the measuring insert and worn out of the gear teeth. b. Dial indicator is not positioned perpendicular to the surface of the workpiece -

cosine error. c. Misreading - a person using a dial gauge that makes more than one revolution

must be aware of how many revolutions the pointer has made when taking the measurement.

d. The dial indicator is not clamped and secured properly. This will cause vibrations.

6.9 APPLICATIONS OF DIAL INDICATOR a. To measure the thickness of a workpiece by using comparative method.

b. To measure flatness of workpiece surface.

c. To measure roundness of a shaft.


d. To measure straightness of a shaft.

e. To measure parallelism of a work piece.


CHAPTER 7

GAUGE BLOCK


7.1 INTRODUCTION The need for standardization of measurement is vital in order to meet interchangeability and functionbility. Today's widespread manufacturing can function only if machinist everywhere are able to check and adjust their measuring instruments to the same standards. Gauge blocks are the most accurate form of representing size by means of its two parallel surfaces which are very flat. They permit a comparison between the working measuring instruments of manufacturing and recognized international standards of measurement. They are one of the most important measuring tools which served as a standard for comparison in achieving the standardization of measurements. They are the most accurate form of representing size. Gauge blocks are commonly used in metrology laboratories for calibration of measuring instruments in tool rooms and machine shops for measurement of components and the establishment of precise angles such as sine-bar.

7.2 TYPES AND GRADES Gauge blocks are commonly available individually or in a set. They usually come in three standard shapes: round, square, and rectangular. They are made of hardened tool or ceramic in which the measuring surfaces are well finished by lapping. The measuring surfaces of the gauge blocks are so smooth, flat, and even, that they can be attached together by wringing method to obtain the length required for measurement.

7.3 STANDARD SET OF GAUGE BLOCKS Gauge blocks are made with 3 different grades of accuracy, depending on the purpose

Table 7.1

for which they are used. - a. Grade 00 : used in laboratories as a master set for calibration : accuracy = O.OOOO5mm b. Grade 0 : used for setting or calibrating measuring instruments or gauges : accuracy= O.OOO15mm c. Grade 1 :used in the workshop to test the components :accuracy = 0.00025 m


7.4 TO DETERMINE THE GAUGE BLOCKS COMBINATION When composing gauge block combinations, start with the last figure of the dimension required and eliminate the last place of decimal first. Then continue to build up the dimension working from the right hand side:. The gauge blocks combination should comprise as few as possible so that the total error (size deviation) is kept to a minimum.

Example: Required length = 50.255mm Subtraction

1st gauge block = 1.005mm 49.250 2ndgaugeblock = 1.050mm 48.200 3rd gauge block = 1.200 mm 47.000 4th gauge block = 7.000 mm 40.000 5th gauge blocks = 40.000mm 00.000

50.255mm

Wringing gauge blocks Gauge blocks should be wrung immediately after cleaning. To wring gauge blocks, the following procedures should be used: a. Clean gauge blocks entirely by means of solvent and chamois cloth or clean tissue

after cleaning, do not touch the measuring surfaces. b. Slide the blocks together while lightly pressing together. During the sliding process,

you should feel an increasing resistance. This resistance should then level off. c. Then position the blocks so that they are in line d. Make sure that the blocks are wrung by- holding one block and releasing the other.

Hold your hand under the stack in case the blocks should fall. e. If, during the wring process, the blocks tend to slide freely, slip them apart

immediately and recheck clean and try again.

7.5 CHECKING SURFACE FLATNESS OF GAUGE BLOCKS The flatness of gauge blocks can be checked by using an optical flat. An optical flat is an extremely flat piece of quartz. It uses the principles of light interferometer to make measurements. When it is placed onto the surface of blocks, a series of interference bands are produced. These bands will detem1ine whether the surfaces are flat or not. If the bands show straight and parallel lines, its indicated the surfaces are flat. If the bands are curved, its indicated the surfaces are not flat.

7.6 GAUGE BLOCK APPLICATIONS

a. Used to set up length dimension in comparative measurements b. To set or calibrate the measuring instruments and gauges. c. Used in setting sine for angle measurements e. Used to set-up tool height or spacing at required length in the staddle milling cutters

7.7 MAINTENANCE AND CARE OF GAUGE BLOCKS a. Clean the gauge with solvent and chamois before or after use b. A combination of gauge blocks should not be wrung together for a long time, otherwise the cold-welding on the measuring surfaces will be formed. c. After used, gauge blocks should be greased with non-acidic parafin jelly d. Gauge blocks should be handled with clean tissue and must protected from

heat.


e. Any- burns on a gauge blocks can prevent a proper wring and possibly damage the surfaces. Deburring is carried out with a special deburring stone.

f. Partly flat -falling off to or sloping to hump


CHAPTER 8

SURFACE PLATE INSPECTION


8.1 INTRODUCTION Part dimensions can be checked very precisely and accurately by means of the surface plate method in conjunction with many types of height gauges, measuring instruments and holding devices. However, accurate measurements can only be maintained when the reference surfaces of the parts are established with respect to the surface plate which acts as a simulated datum or reference. Thus, surface plates provide a true, flat reference surface for any types of dimensional measurements.

8.2 WHAT IS A SURFACE PLATE? Surface plates are truly flat surfaces which are available in many sizes and difference accuracy. Their surfaces are very accurately machined and well-polished. They are supported by means of a steel table which rests on a 3-point stopper. It is used as a means to establish a reference plane or datum surface from which measuring and marking-out activities of all kinds may be performed. Generally they are made of 2 types of materials:

a. cast iron b. granite stone

8.3 ADVANTAGES OF GRANITE SURFACE PLATE Granite surface plates have many advantages over cast iron: a. They are twice as hard as cast iron. b. There are minimal changes in dimension due to temperature changes. c. They are free from burrs because of the fine grain structure which ensures a high

degree of flatness over a long service life. d. They are free from wringing, so there is no interruption of work. e. Damaged wares do not produce raised material or build-up edges. f. They have a long life and are rust-free,

8.4 CARE OF SURFACE PLATE a. Do not abuse surface plates; they are precision tools. b. Clean entirely the surface plate before and after use with soap and water

or alcohol. c. Part should be deburred and clean before they are placed onto the

surface plate. d. Do not allow unnecessary objects or tools to be placed on the surface

plate. e. Do not drop any objects onto the surface plate. f. Keep the surface plate covered when it is not used.


8.5 SOURCES OF ERRORS a. Eventually wear may cause loss of accuracy, but this takes quite some time. b. A workpiece which has burrs and dirt will cause poor readings as well as

increasing unnecessary wear.

8.6 SURFACE PLATE ACCESSORIES OR HOLDING DEVICES A Surface Plate must always be used in conjunction with numerous measuring instruments, accessories and holding devices. The commonly and widely used accessories or holding devices to the surface plate are vernier height gauge, dial gauge, gauge blocks, parallel bars, V-block, angle plate, sine-bar, precision vice, precision try-square, cylindrical pin, and etc. These holding devices come in many shapes or designs to enable holding parts in horizontal, vertical, and angular planes. They must be kept clean and free from burrs and nicks. When necessary a fine stone can be used to clean and remove burrs. The prime concern is their flatness, squareness and parallelism.

Types of Height Gauges

Generally, height gauges may be classified into three types: a. vernier height gauge b. dial height gauge c. digital height gauge

a) Vernier Height Gauge

The vernier height gauge is a self-supporting measuring instrument which consists of a heavy base with a vertical vernier scale similar to that on a vernier caliper. It is easily adjustable over a large range. To read-off the measured value is the same as a vernier caliper. It is mainly used in conjunction with a surface plate for marking or lay-out the workpiece when the scriber is attached. It can also be used to measure the height of the workpiece. A dial gauge may be attached to the height gauge to provide greater accuracy in measurement by means of comparative method with the help of a Master Height Gauge.


Sources of errors a. The slide arm is not parallel with the base. b. An unclean and damaged base causes inaccuracy. c. The scriber is worn-out. d. The height gauge is not calibrated properly. When you check for accuracy

always ensure that the zero mark of the vernier and main scale coincide when the base of the scriber makes contact flat with the surface plate. Alternatively we can use a gauge block and compare it with the scale of the height gauge.

e. Avoid parallax errors. When you read the measured value, always look vertical to the scale.

Guidelines for using a Vernier Height Gauge a. Always ensure that the height gauge had been calibrated. b. Clean the height gauge and surface plate entirely before use. c. Hold the base firmly to the surface plate to avoid tipping. Always lock the

main scale when in use. d. Move the height gauge slowly and gently. Do not slam it around. e. Clamp the scriber as near as possible to the column. This will increase

accuracy and less vibration. f. A dial gauge may be attached to provide greater accuracy.

Application of the Vernier Height Gauge It is always used in conjunction with a surface plate and it can be used for marking the workpiece with a scriber attached to it.

Normally, a dial gauge is attached to it to provide better accuracy.


8.7 PRINCIPLES OF SURFACE PLATE INSPECTION The basic intention of surface plate inspection is to secure the workpiece in the propoer position to enable measurement in a plane vertical or horizontal to the surface plate. It is desirable to hold the workpiece in such manner that it can be turned and remained held in the position 90 from the original plane. The accuracy of this inspection is dependant upon our ability to secure the part in the proper position. Always locate the surface which are parallel to or perpendicular to the features being checked. If possible, position the workpiece so that you are able to look at it the same way it appears on the drawing.

To inspect the height or length of the workpiece

Case I

a. Position and hold the part at perpendicular to the surface plate by help of

angle plate. b. Determine how you will find feature dimension wanted. In this case, a = c

- b

Case II

a. Position and hold the part at parallel to the surface plate by help of parallel bar.

b. Determine how you will find feature dimension wanted. In this case, a = c - b.


To inspect hole location of the part Case I

a. Position the part vertically in such a way that the reference surface is placed

directly on the surface plate. b. Determine how to find dimension a (i.e. center line of the hole to the

reference surface.) c. In this case, a = (b + c) divided by 2.

To inspect a workpiece using vernier height gauge and dial gauge Case I

a. Attach a dial gauge to the height gauge by means of locking screw. b. Slide down the dial gauge until the tip touches the surface plate and set to

zero the dial gauge. c. Record down the reading of height gauge (for example:5.6) d. Raise the dial gauge and make the tip of the dial gauge touch the surface of

the workpiece to be measured at zero mark of the dial gauge. e. Record down the reading of the height gauge, (For example; 9.8) f. Now, the actual dimension of the part is simply the difference between the

highest and lowest readings you have taken. g. Reading = 9.8 - 5.6 = 4.2

To inspect the part using transfer method (comparative)

Case 1

a. Set up the gauge blocks to the nominal size of the part (20.00) b. Set zero to the dial gauge when It touches the gauge block


c. Then, transfer the dial gauge to the surface of workpiece to be measured. d. Watch the movement of the pointer and record the reading (e.g. + 0.05) e. Then, the actual measurement is; 20 + 0.05 = 20.05 f. Compare the reading with the tolerance of the part. In this case the part is

accepted because it is within the tolerance zone.

8.8 EXAMPLES OF HOLDING DEVICES USED IN CONJUNCTION WITH A SURFACE PLATE

1. Parallel bar

It is made of harden tool steel and rectangular in shape which come in diffrent sizes. They are machined very accurately in such a way that the surfaces are parallel, straight and squared to each other. Generally, they are used in conjunction with a surface plate for stack-up or supporting the workpiece to establish the reference the reference surfaces.

2. Angle block

They are used to hold and locate the workpiece vertical to the surface plate. They are made of cast iron and machined very accurately to maintain the squareness and flatness. They can also be used to check the squareness of the workpiece by means of light gap.


3. Vee block

They are made of harden tool steel and precisely ground. They have to Vee-grooves. They are used hold and locate the round workpieces to establish the centerline or axis of a round workpiece with respect to the surface plate. Commonly, they can be used to check the roundness of the workpiece.


CHAPTER 9

INSTRUMENTS FOR TESTING ANGLE


9.1 INTRODUCTION a) Units for angles The unit used for measuring angle is the degree or radian. In SI unit, the magnitude of a plane angle is defined in terms of a circle with the apex of the angle as its center. The magnitude of the angle is the ratio of the arc enclosed (subtended) by its side to the radius of the circle is known as the radian.

b) Relationship Between Radians and Degrees There are 360 in a circle. One degree is subdivided into 60 minutes and each minute is divided into 60 seconds.

rad23600 rad0180 000 180360

21 radrad

00

2.571801 rad 1 degree = 60 minutes = 3600 seconds.

Radian and Degree

9.2 TESTING ANGLES

Angle may be tested with : a. Fixed angle gauges

i. steel square ii. knife-edge square

iii. back square iv. angular end blocks

b. Angle measuring instruments

i. universal protractor ii. profile projector

iii. dividing head c. Calculation method

i. using gauge blocks and sine bar ii. using gauge blocks and cylindrical pins


a. Fixed Angle Gauges (Solid steel square, back square and knife-edge square)

Steel squares with angles of 90, 60, 45 and 120 are used in industry as fixed angle gauges. Steel squares are differentiated into :

a. solid steel square b. back square c. knife-edge square

The positions of the work piece edges and surfaces, with respect to each other, are tested with these instruments in conjunction with the light-gap method. It can detect angle errors of as little as 1 minute and detect evenness errors of up to 5 micron. The back square is used to check lines marked-out as bending edges for correctness of measurements and angles. The distance on the scribed line from the reference edge of the work piece is checked with a measuring ruler. The knife-edge square is used to check angularity and surface finish by light-gap method. If the surface of the work piece and the testing edge of the angle gauge are pressed together and held against the light, a light slit will appear. The more uniform this light slit along both the testing edges of the angle gauge, the more exact the angularity.

9.3 EXAMPLES OF APPLICATION

Angle too small Angle correct Reference surface

Solid steel square Back square


. Knife-edge square

a. Angular End Blocks Angular end blocks are made of steel and can be combined together like parallel gauge blocks to set the required angles. They are used to check :

a. gauges b. tools and work pieces c. to set machine and attachments d. in marking and dividing

A complete set of angular end blocks consists of :

a. 6 end blocks of 1, 3, 5, 15, 30, 45 degrees. b. 5 end blocks of 1, 3, 5, 20, 30 minutes. c. 5 end blocks of 1, 3, 5, 20, 30 seconds

Examples of application

To set 20 30 35 = 15+ 5+ 30 + 30+ 5 To set 25 17 = 30- 5 + 20 - 3

Addition Subtraction

Note : The combination of angular end blocks should comprise as few as possible so that the total error is kept to a minimum.

b. Angle Measuring Instruments Angles can also be checked by using measuring instruments; such as, a simple protractor and a universal bevel protractor. These are display instruments for direct measuring of any angle within a given measuring range.


c. Simple Protractor

In a simple protractor, the pointer-like arm can be set against a circular degrees scale from 0 to 180 (measuring range). Only whole degrees can be measured using this protractor. Intermediate values can only be estimated. The measuring accuracy is one degree.

d. Universal Bevel Protractor This protractor makes it possible to measure any angle with a reading accuracy of 5 minutes. It consists of a fixed and a movable measuring edge. The circular main scale is divided into 4 sections of 90 and serves to read the complete angular degrees. The angle nonius (vernier) consists of an arc of 23, divided into 12 equal intervals.

e. Angle Vernier The graduation of the vernier from 0 to 60 represents 23 exactly and is divided into 12 equal parts. This means the distance between graduated marks is 23/12 = 155 the difference at 2 produces a reading accuracy of 5.


Read-off Procedure The whole degrees are shown on the main scale with the zero marker on the vernier scale. To get the minute values, read off which graduated marking on the vernier scale is positioned next to obtain the complete reading. Depending upon the setting, one counts the full degrees from 0 to 90 up to the zero mark of the nonius (angle vernier). Then one proceeds along the same direction on the nonius scale to the point where a mark on the main scale coincides with a mark on the nonius scale. This tells us how many units of 5 have to be added to the number of full degrees.

a. Read-off result from 0o = 52o 15

b. Read-off result from 90o = 37o 45

Advantages of Universal Bevel Protractor a. More positioning possibilities b. More accurate reading c. Angles with more than 1800 can be measured.

Examples of Application


9.4 CALCULATION METHOD

a) Sine Bar A sine bar may be used to check accurate angle measurement. It consists of an accurately ground bar on which two accurately ground pins (or rollers) of the same diameter are mounted in an exact distance. The fixed distance between two pins are usually 100 mm or 200 mm. Measurements are made by using the principle base of trigonometry, i.e. sine rule

hypotenuseoppositesin

The workpiece being measured is placed on the sine bar and the inclination of the sine bar is raised by stacking-up gauge blocks until the top surface is exactly parallel with the surface plate. The sine-bar itself forms the hypotenuse and gauge blocks form the opposite side to the angle being measured. The dial gauge is used to measure the angle required by moving it along the surface of the workpiece. Example of application

Given : Angle = 9 30

L = 100 mm a.To find H Sine rule : H = Sine x L

= 0.1651 X 100 = 16.51 mm

b. Combination of gauge blocks H = 16.51 1.01

1.5 4.00 10.00 16.51


Testing Angles With Cylindrical Pin (Roller) And Gauge Block Angles also may be checked by calculation method with the help of cylindrical pins and gauge blocks. By using this application many problems in measurements can be solved. Example 1

Calculate the outer taper , as shown in the diagram. Given : d1 = 47.25, d2 = 35.70, L = 30, of rollers = 10 mm. Solution Half of taper angle =

2

Refer to ABC : AB = d1 - d2

2 = 47.25 - 35.70 2

= 5.78 ABC = 90 BC = L = 30 Then, tan = AB 2 BC

= 5.78 30 = 0.193 = 10.9 2

Hence, outer taper, = 10.90 x 2 = 21.8


Example 2

Using two balls of 25.00 and 20.00 mm diameter respectively inspect the tapered hole as shown. The measurements indicated in the diagram below were obtained. Find :

a. the included tapered angle b. the top diameter d of the hole

Solution a. A and B are the centres of the balls and D and E are points where the balls just

touch the sides of the hole.

ADE = BED = 90 Draw BC parallel to DE, then in ABC AC = 12.5 - 10 = 2.50 mm AB = 35.36 + 4.65 -12.5 +10 = 37.51mm Now ACB = 90 and ABC = /2 Sin = AC = 2.5

2 AB 37.51 = 3 49 2 Included tapered angle = 2 x 3 49 = 7 38

b. To find d, draw AF horizontal and FG vertical. In AFD : AD = 12,5 FAD = , ADF = 90 2

AF = 12.5 cos 3 49 = 12.53 mm In GFH : GF = 12.5 - 4.65 = 7.86 mm, FGH = 90, GFH = 2 GH = Tan x GF = Tan 3 49 x 7.86 = 0.52 mm 2 Thus d = 2 (AF + GH) = 2 x (12.53 + 0.52) = 26.10 mm


Example 3

Find the checking dimension M for the symmetrical dovetail slide shown in diagram below. Solution Draw AC from the centre of the roller. In ABC : ABC = 90 ACB = 60 (bisect by AC) 2 = 30 BC = AB tan 30 = 7.5 tan 30 = 12.99 Thus, M = 64 + 2 (12.99 + 7.5) = 104.98 mm

Example 4

In the diagram shown below, a vee block is being checked by means of cylindrical pin of 25.00. What is the dimension x ? Solution Draw AB from the centre of the pin. Then in ABC : BAC = 90 (angle bet. radius and tangent) BCA = 45 (bisect by BC) AB = 12.5 = 17.68 mm sin 45 0.7071


Draw a line XY, then in XYZ CY = 25 XY = 25 = 25 mm

tan 45 X = (17.68 + 12.5) - 25 = 5.18m


CHAPTER 10

GAUGES


10.1 INTRODUCTION Gauges are commonly used as testing instruments in mass production. They come in different shapes / sizes and are rigid in design. However, they do not have a measuring scale. Therefore, they do not indicate or record the actual value (dimensions) of the work pieces form or shape. They can only be used for determining whether the inspected parts are made within he specified limits, shapes or forms or whether they meet functional requirements.

10.2 ADVANTAGES OF GAUGES a. Tests can be done quickly which helps to save time of checking. b. They can be used by less skilled workers. c. The process of inspection is very cheap. d. They help to decide whether the part is inside the tolerance or not. e. They are portable and independent from power supply.

10.3 DISADVANTAGES OF GAUGES a. They provide no actual reading of measurements. b. They give less information regarding the condition of the inspected parts. c. They cannot be manufactured entirely without errors. d. They are subjected to loss of accuracy from wear. e. The manufacturing cost of gauges may not be recovered from a small

quantity of parts.

10.4 FACTORS IN SELECTING MATERIALS FOR GAUGES Materials for gauges should fulfill most of the following requirements:

a. Hardness to resist wear is the most important aspect (min 65RC). b. Stability to preserve size and form. c. Corrosion resistance. d. Machinability for obtaining the required degree of accuracy. e. Low coefficient of linear expansion to avoid temperature effect.

10.5 MATERIALS FOR GAUGES a. High Carbon Steel:

It is relatively inexpensive and a suitable material for gauges. There is a risk of cracking during hardening. b. Chromium Plating:

It increases wear resistance and reduces friction. It is used for restoring worn gauges to the original sizes. c. Tungsten Carbide:

It increases stability and wear resistance. It is very expensive but sensitivity to chipping is limited.


d. Ceramic: It provides stability and has the greatest degree of wear resistance. It also has a low coefficient of linear expansion

10.6 TYPES OF GAUGES Some gauges like testing gauges are used to test whether the work piece conforms to the specified size of the shape, form or profile. Some gauges like limit gauges is used to test whether the work piece dimensions lie between the specified limits or tolerance ranges. It represents the minimum and maximum dimensions of the work piece. Generally, it consists of Go and No Go members. The No Go member is marked in red for easy identification. Generally, the Go member becomes worn-out faster than the No Go member because it used very often.

a) Hole gauges

A hole gauge is a metal plate which consist of various sizes of holes diameter and has a measuring range of 0.1 to 10 mm, with an increase of 0.1 mm per hole. It is use for quick determination of twist drill diameter, wire, or steel rod. When it is use, never force the test piece into the hole gauge, otherwise there will be deformation or it will wear out the gauge.

b) Feeler gauges

A feeler gauge mainly consists of steel blades of different thickness and has a measuring range of 0.05 to 0.5 mm. They are used for determining the clearance or gap between two mating parts such as guideways, bearings, or slideways. Sometimes, they can be used to set-up the machine tool onto the surface of the workpiece for the zero-setting.


c) Knife edged or straight edge gauge

It is a straight hardened steel blade and has a wedge shaped cross-section with an angle of 30 degrees. The measuring edge is hardened and lapped. It is used to check the straightness and flatness of the work surfaces. The light-gap method is used for this test.

When the knife edge is placed onto the work surface and held against the light, a series of light beams will penetrate through tiny uneven surfaces and appear to the eyes as a wide beam of light. If there is no light gap or the light beam appearance is uniform, it tells you that the work surfaces are flat or straight. d) Radius gauge

It consists of a series of hardened steel blades with a measuring range of 1-7, 7.5-15 and 15.5-25 mm. They can be used to check the internal and external radius by means of light-gap method.


Comment on the sketches a, b and c: a. radius of testpiece is too small (undersize). b. radius of testpiece coincides with the gauge (acceptable). c. radius of testpiece is too big (oversize).

e) Thread cutting gauge

It is a template which consists of V-grooves with angles of 60 for the metric thread. It is used to check the profile and flank angle of a thread cutting tool by means of light gap method. The angle is corrected if there is no light gaps.

It can be also used for setting-up and alignment of thread cutting tools with respect to the work piece f) Thread pitch gauge

It is a template which consists of numerous V-grooves at 600 for the metric thread. Generally, it comes in a set of different pitches with a measuring range of 0.25- 6.00 mm pitch. It is used to check the flank angles and pitches of the threads by means of light gap method. If the angle and pitch are correct, no light gaps should be seen between the gauge and the surface of the workpiece.


h) Twist drill gauge

It is a template with a point angle of 118 and used to check the wedge angle of twist drill. The graduated scale serves to check the length of cutting edges of the drill.

i) Limit Plug Gauge It is used to check the diameter of a straight hole and the width of a slot. It generally consists of Go and No Go members. The selection of limit plug gauge is dependent on the diameter and tolerances of the hole. a. Go end: It represents the minimum dimension and checks the lower limit of the hole. b. No Go end: It represents the maximum dimension and checks the upper limit of the hole. It is marked in red and is shorter than Go member for easy identification.

Test Procedure

It is very important to use proper procedures when checking the hole with the plug gauge if we want to get precise measurement. Hold the plug gauge very gently and let it slide into the hole under its own weight. The Go member should easily enter the hole without forcing it. The No Go member should not enter the hole. However, if the Go member does not enter the hole, it indicates that the hole is undersized And if the No Go member enters the hole, it indicates that the hole is oversized.


Limitation of Plug Gauges Remember, a plug gauge is not able to detect out-of-round, tapered, and bell-mouthed holes.

j) Limit Ring Gauge

It is used to check the diameter of a cylindrical part or a shaft. Generally it comes in a set of two ring gauges. The selection of ring gauge is dependent on the diameter and tolerances of the shaft. a. 'Go' ring: It represents the maximum dimension and serves to check the upper limit of the shaft. b. 'No Go' ring: It represents the minimum dimension and serves to check the lower limit of the shaft. It has a groove which is marked in red for easy identification. Test Procedure Hold the ring gauge very gently and let it slide into the shaft under its own weight. The Go ring gauge should be able to enter the shaft without force it while the 'No Go' ring gauge must not enter into the shaft. If the 'Go' ring gauge cannot enter the shaft, it indicates that the shaft is oversized. If the 'No Go' ring gauge enters the shaft, it indicates that the shaft is undersized. Limitations of ring gauges a. They are not able to detect out-of-roundness. b. Workpiece needs to be deburred before an effective check can be made. c. Workpiece must be taken out of the machine when it needs to be checked.


k) Snap Gauges Snap Gauges are used to check the outside diameter of a shaft and thickness of a flat workpiece or the external width of a step. Generally, it comes with Go and No Go members. a. Go member: It represents maximum dimensions and serves to check the upper limit of the workpiece. b. No Go member: It represents minimum dimension and serves to check the lower limit of the workpiece.

Basically, they consist of three types: i. Single snap gauge

It has a C-shape frame and Go and No Go members are behind each other.

ii. Double snap gauge

Go and No Go members are opposite to each other.

iii. Adjustable snap gauge


It can be adjusted and preset by using gauge blocks.

Test Procedures

Apply the snap gauge onto the shaft. The Go member must slide or go over the shaft on its own weight without forcing it.The No Go member must not go over onto the shaft. If the Go member cannot slide over onto the shaft, it indicates that the shaft is oversized. If the No Go member can be inserted onto the shaft, it indicates that the shaft is undersized.

Advantages of Snap Gauges compared with Ring Gauges

a. Part is not necessary to be deburred. b. Part can be checked directly onto the machine. c. Time is saved.

l) Thread Gauges Basically, they are used to check the flank diameter of threads. There are three types of thread gauges. i. Thread plug gauges


They are used to check the flank diameter of internal threads of a workpiece. Basically, a thread plug gauge consists of Go and No Go members. The No Go member is marked in red and has less thread for easy identification. a) Go member: Used to check the lower limit of flank diameter of internal threads. b) No Go member: Used to check the upper limit of flank diameter of internal threads. ii. Thread ring gauges

The thread ring gauge used to check flank diameter of external threads of a workpiece. Basically, they come together with a Go thread ring gauge and No Go thread ring gauge. a) Go thread ring gauge: Used to check the upper limit of flank diameter of threads. b) No Go thread ring gauge: Used to check the lower limit of flank diameter of threads.

iii. Thread roller gauges

There are two types of thread roller gauges: 1. Fixed thread roller gauges 2. Adjustable thread roller gauges


They consist of two pairs of free-turning rollers: Go roller: To check upper limit of flank diameter. No Go roller: To check lower limit of flank diameter.

Both are used to check the flank diameter of external threads. Adjustable thread roller gauges can be adjusted or preset to required thread sizes by means of thread adjusting limit gauges.

Advantages of Adjustable Thread Gauges compared with Ring Gauges a. Time is saved by not having to screw the gauge along the workpiece. b. Minimal of wear through rolling friction, therefore longer life. c. All tolerance classes can be set by means of thread adjusting limit gauge. d. They can check the part without taking out from the machine. e. Using the same thread gauge, both right and left hand threads can be checked. f. It can be checked at any parts or areas of the workpiece.

m) Taper Gauges Generally they are used to check standard internal and external tapers and to test the diameter and slope of the taper. When testing with a taper plug gauge, the workpiece edge should lie within the tolerance marks. If both marks are exceeded, the workpiece is rejected. a. Taper plug gauges

b. Taper sleeve gauges

Testing for wear in a tapered hole

a. Thoroughly clean the hole to be tested and the taper plug gauge. b. Mark the taper gauge on the surface with a fine chalk or pencil. c. Insert the taper plug gauge into the hole with light pressure (without turning). d. Turn the taper plug gauge slightly, then remove it without turning. e. Observe whether the mark is rubbed off or not.

i. If the mark is rubbed off, it tell that the two surfaces are touched. ii. If the mark is still visible, it tell that the two surfaces are not touched (worn out).


Taylors Theory of Gauging This theory is very useful for the inspection of the workpiece by using the gauging method, so that the good parts are not rejected and the bad parts are not accepted. Taylors theory states that: a. The Go member checks the minimum size of the holes and should check as

many dimensions as possible. b. The No Go member checks the maximum size of the holes and should only

check one dimension at a time.

Thus a separate No Go gauge is required for each individual dimension. To explain this theory very clearly, let us consider checking the rectangular hole as shown in the diagram beside:

If the breadth of the hole is within the specific limits but the length is oversized, and the No Go gauge is used to check both the maximum sizes of the rectangular hole, it is observed that the gauge will not enter the hole and therefore the work is accepted although the length of the rectangular hole is outside the specified limits. To overcome this situation, two separate No Go are always used. One is to check the breadth and the other to check the length of the rectangular hole.

Gauge Tolerances and Wear Allowances

Gauges cannot be manufactured entirely without error. They are subjected to loss of accuracy from wear. Thus the tolerances and wear allowances are needed for the manufactured of gauges. The gauge tolerances and permissible wear allowances depend upon the nominal size of the workpiece and the quality class.

Work piece Tolerance

Tolerance for Go and No Go gauge

Wear allowance for Go gauge only

Plug gauge Ring gauge Go No

Go Go No Go

0.009-0.018 0.001 0.001 +0.002 +0.001

+0 -

0.001

-0.001

-0.002

+0.001 -0

0.018-0.032 0.002 0.001 +0.003 +0.001

-0 -

0.002

-0.001

-0.003

+0.002 -0


0.032-0.058 0.003 0.002 +0.005 +0.002

+0 -

0.003

-0.002

-0.050

+0.003 -0

0.058-0.100 0.004 0.004 +0.008 +0.004

+0 +0.004

-0.004

-0.008

+0.004 -0

0.100-0.180 0.006 0.007 +0.0.13

+0.007

+0 -

0.006

-0.007

-0.013

+0.006 -0

0.180-0.320 0.009 0.012 +0.021 +0.012

+0 -

0.009

-0.012

-0.021

+0.009 -0

0.320-0.580 0.014 0.025 +0.039 +0.025

+0 -

0.014

-0.025

-0.039

+0.014 -0

0.580-1.00 0.025 0.048 +0.073 +0.048

+0 -

0.025

-0.048

-0.073

+0.025 -0

1.00-1.800 0.040 0.080 +0.120 +0.048

+0 -

0.040

-0.080

-0.120

+0.040 -0

1.800-3.200 0.050 0.155 +0.205 +0.155

+0 -

0.050

-0.155

-0.205

+0.050 -0

Table 10.1: Gauge Size Limits AT 20C for Ranges of Workpiece Tolerance Example; A plug gauge is to be manufactured to inspect a hole size of 25050

. Determine the total

tolerance of the gauge.

Solution: Minimum value = 50.00 and maximum value = 50.025 mm Tolerance of hole = 0.025 mm From the table: At 0.018 - 0.032 mm; gauge tolerance = 0.002 and wear allowance = 0.001. Hence, total tolerance of gauge is: For Go gauge 003.0 001.050

For No Go gauge 025.0 023.050


CHAPTER 11

PROFILE PROJECTOR


11.1 INTRODUCTION Profile projector is a large optical instrument which projects a workpiece surface or contour on a screen for dimensional measurements (linear and angular measurements) and observation. The part to be measured is mounted on a table that can be moves in X and Y directions by accurate micrometer screws. The profile projector projects the image of the part on a screen, magnifying it from 5 to more than 100 times. Measurements can be made directly, either by means of the micrometer dials, digital readouts or on the magnified image on the screen by means of a n accurate scale or template (chart)

1. Control panel 2. Focusing knob 3. Table fine feed knob 4. Table core feed knob 5. Projection lens 6. Screen rotation knob 7. Projection screen 8. Table elevation wheel 9. Contour illuminator 10. Table 11. Surface illuminator 12. Angle counter

11.2 APPLICATION Profile projector is a multi-purpose measuring instrument used for checking length, angle, radius, diameter, thread pitch and gear profiles.

11.3 TEST PROCEDURES There are three methods of testing : a. Projection by contour illumination b. Projection by surface illumination c. Projection by both the contour and surface illumination


a. Projection by contour illumination The surface image of the workpiece is projected onto the screen. Be sure to use the condenser lens, which corresponds to the magnification of the projection lens to be used

OPERATION DESCRIPTION PROJECTION

SCREEN Position the work piece so it intersects the optical axis of the projection lens (which is collinear with the axis of the contour illuminator)

b. Projection by surface illumination With the use of a half-reflecting mirror, it is possible to project the workpiece surface image on the screen. (The surface illuminator is optional for PH350) When the 5X or 10X projection is used :


SCREEN

Position the work piece so it intersects the optical axis of the projection lens. (The optical axis is collinear with the axis of a beam that comes from the surface illuminator and reflects on the half mirror). When the 5X or 10X projection lens is mounted, this half-reflection mirror is attached to the front of the projection lens.

c. Projection by both the contour and surface illumination Both contour and surface images of a workpiece are projected onto the screen


SCREEN

Position the work piece so it intersects the optical axis of the projection lens. (The optical axis is collinear with the axis of a beam that comes from the surface illuminator and reflects on the half mirror)


11.4 DIFFERENT STANDARD OVERLAY CHARTS In addition to the ordinary measuring functions where the workpiece dimensions are measured by fitting scale on the projection screen, the workpieces can be compared with a reference overlay chart to inspect the dimension of form deviation.

a. Overlay chart radial index and concentric circles

b. Overlay chart Metric and Whit worth threads

11.5 TYPES OF MEASUREMENT Basically there are two types of measurement that can be operated on a profile projector.

a. Length measurement b. Angle measurement


a. Length measurement

PROCEDURE OPERATION SCREEN COUNTER OPERATION/DISPLAY

Step 1 Position the work piece

Step 2

Press the X-axis zero set button of the A

counter to zero-set the X axis counter

Step 3

Move the microstage (or micrometer head)

by using the microstage feed knobs so that the other edge

of the workpiece image aligns with the

same cross-hair line on the screen. Dimension L1 can be counte

metrology note

Documents

surface plate chapter

types of gauges chapter

care of surface plate

metrology metrology

surface roughness measurement

surface texture measurement

surface plate accessories

mechanical dial indicator