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MECHANICAL MEASUREMENTS AND METROLOGY LABORATORY MANUAL

MECHANICAL MEASUREMENTS AND METROLOGY LABORATORY

Sub code: 15MEL37B/47B IA Marks: 25

Hrs/Week: 03 Exam Hours: 03

Total Hrs: 42 Exam Marks: 80

Part-A:MECHANICAL MEASUREMENTS

1. Calibration of Pressure gauge2. Calibration of Thermocouple3. Calibration of LVDT4. Calibration of Load cell5. Determination of modulus of elasticity of a mild steel specimen using strain gauges.

Part-B:METROLOGY

6. Measurement using Optical Projector/Tool marker’s Microscope7. Measurement of angle using Sine Center/Sine Bar/Bevel Protractor8. Measurement of alignment using Autocollimator/roller Set9. Measurement of cutting tool forces using

a. Lathe tool dynamometerb. Drill tool dynamometer

10. Measurement of screw thread parameters using two wire or three wire method11. Measurement of Surface roughness using talysurf/mechanical Comparator12. Measurement of gear tooth profile using gear tooth Vernier/gear tooth micrometer13. Calibration of a micrometer using slip gauges14. Measurement using Optical flates

Department of Mechanical Engineering, VSMIT, Nipani. 1


INSTRUCTIONS FOR STUDENTSStudents shall read the points given below for understanding the theoretical concepts & practicalapplications.

1) Listen carefully to the lecture given by teacher about importance of subject, curriculum philosophy, graphical structure, and skills to be developed, information about equipment, instruments, procedure,method of continuous assessment, tentative plan of work in laboratory and total amount of work tobe done in a year.

2) Students shall undergo study visit of the laboratory for types of equipment, instruments, material tobe used, before performing experiments.

3) Read the write up of each experiment to be performed, a day in advance.

4) Organize the work in the group and make a record of all observations.

5) Understand the purpose of experiment and its practical implications.

6) Write the answers of the questions allotted by the teacher during practical hours if possible or afterwards, but immediately.

7) Student should not hesitate to ask any difficulty faced during conduct of practical / exercise.

8) The student shall study all the questions given in the laboratory manual and practice to write the answers to these questions

9) Student shall visit the recommended industries and should study the knowhow of the shop floor practices and the operations of machines.

10) Student shall develop maintenance skills as expected by the industries.

11) Student should develop the habit of pocket discussion / group discussion related to the experiments/exercises so that exchanges of knowledge / skills could take place.

12) Student shall attempt to develop related hands-on-skills and gain confidence.

13) Student shall focus on development of skills rather than theoretical or codified knowledge.

14) Student shall visit the nearby workshops, workstation, industries, laboratories, technical exhibitions, trade fair etc. even not included in the Lab Manual. In short, students should have exposure to the area of work right in the student hood.

15) Student shall insist for the completion of recommended Laboratory Work, industrial visits, answers to the given questions, etc.

16) Student shall develop the habit of evolving more ideas, innovations, skills etc. than included in the scope of the manual.

17) Student shall refer technical magazines, proceedings of the Seminars, refer websites related to the scope of the subjects and update their knowledge and skills.

18) Student should develop the habit of not to depend totally on teachers but to develop self learning techniques.

19) Student should develop the habit to react with the teacher without hesitation with respect to the academics involved.



20) Student should develop habit to submit the practical exercise continuously and progressively onthe scheduled dates and should get the assessment done.

21) Student should be well prepared while submitting the write up of the exercise. This will develop thecontinuity of the studies and he will not be over loaded at the end of the term.

Instructions

The write-up should include the following in this order: Objectives, Procedures, Results, Conclusions, Tables, Graphs, Sample Calculations, and Data Sheet(s). (Tables, Graphs, Sample Calculations and Data Sheet(s) should all be on separate pages).

The objectivesof each experiment are described in the lab manual. Clear experimental objectives must be stated. If quoted or paraphrased from the lab manual, be sure to properly reference the information.

The proceduredescribes the conduct or “procedure” of the experiment indicating the significant equipment and/or instruments used.

Results and Conclusionsof the experiment should be discussed. Important results should be summarized and compared to published values (numerical values may be cited here). Known or likely reasons should be stated to explain significant discrepancies and conclusions drawn from these results. The conclusions should also reflect back to the stated objectives. Discuss what was learned and whether or not the objectives were met.

Tablesshould include experimental values, published values (or theoretical), and their respective percent differences. These tables need to be a clear representation of experimental data as compared to published or theoretical values.

Graph(s) must be prepared using a computer program. Select a scale to fill most of the coordinate area without crowding. Each scale should clearly state the name of the quantity, the units of measure, and a symbol (if any).

Sample calculations may or may not be necessary in a memo report depending on the policy of the particular company or facility involved. However, please include a sample calculation for each significant calculation made.

Note: NEVER erase a data entry, simply strike a line through or cross out any erroneous entry or mistake so that this information is not lost.



Calibration of LVDT

Aim: To calibrate the given linear variable differential transformer (LVDT)

Objectives:1. To standardize measuring methods by proper inspection methods.2. To maintain the accuracies of measurement through periodical calibration of measuring

instruments.3. To provide the required accuracy at minimum cost.

Apparatus: LVDT instrument set, Instrument Tutor, Screw driver, wires.

Description and figure of apparatus:Linear Variable Differential Transformer (LVDT) - A device which provides accurate

position indication throughout the range of valve or mechanical travel is a linear variable differential transformer (LVDT), illustrated in Figure F1. Unlike the potentiometer position indicator, no physical connection to the extension is required.

Figure F1The extension valve shaft, or control rod, is made of a metal suitable for acting as the movable core of a transformer. Moving the extension between the primary and secondary windings of a transformer causes the inductance between the two windings to vary, thereby varying the output voltage proportional to the position of the valve or control rod extension. Figure F1 illustrates a valve whose position is indicated by an LVDT. If the open and shut position is all that is desired, two small secondary coils could be utilized at each end of the extension’s travel.LVDTs are extremely reliable. As a rule, failures are limited to rare electrical faults which cause erratic or erroneous indications. An open primary winding will cause the indication to fail to some predetermined value equal to zero differential voltage. This normally corresponds to mid-stroke of the valve. A failure of either secondary winding will cause the output to indicate either full open or full closed.



Procedure: The required items are LVDT Set UP & Measurement Unit & one set of Rrd & black Patch chords, Dual Channel CRO.

1. Connect the respective terminals of LVDT Set UP & Measurement unit accordingly i.e., Primary&Secondary.(A to A,B to B,C to C,D to D)

2. Connect the respective terminals of DC Output to input of Voltmeter to read in terms of mm units.

3. Connect primary &secondary outputs of LVDT to input channels CRO CH1 & CH2 Respectively.

4. Turn the Gain adjustment pots fully clockwise & rotate Screw gauge in LVDT set UP approximately to read 10mm.

5. Power on the Measuring Unit & CRO wi9th selection of two channels.

6. Rotate the screw Gauge knob to slowly to read minimum volts in the voltmeter & note down the reading of screw gauge that value is the one at which the movable core of LVDT is centrally located & screw gauge position to 10mm graduation. You can also observe minimum voltage output on CRO at this position (Null Position).

7. Adjust Zero Adjustment pot to zero on the voltmeter.

8. Rotate the Screw gauge knob clockwise until it reads 0mm graduation & adjust Gain Pot to read 10mm by voltmeter. You can also see the increase in amplitude of secondary output.

9. Repeat Steps 6 to 8 have stable reading &now LVDT Measuring unit is calibrated to measure the displacement from -10 to +10mm.

10. By Varying the screw Gauge You can tabulate the reading of Screw Gauge & measuring unit as below.

Observations:1. Least count of micrometer = 0.05mm.2. Range of micrometer = 0-25mm.3. Slip gauge set = M38.

Tabular Column:

Sl.No

Core Positions

Displacements Meter Reading

‘Sm’ mm

Screw Gauge Reading ‘Sa’ in

mm

CorrectionSa-Sm

ErrorSa-Sm

% Error



Draw the following Graphs1. Sm Vs Sa

2. Correction Vs Sm

3. Error Vs Sm

4. % Error Vs Sm

Calculation:Error = Meter reading – Actual Reading% Error = (Error/Actual Reading) x 100

Results: The average percentage error of the given LVDT is found to be -------- %

Recommendations: The above practical LVDT is related theory part of unit-3 comparators and angular measurement and unit -5 Measurements and measurement systems. Students must refer unit-3 and 5 for theory part.



Calibration of Strain Gauge

Aim: To determine the Modulus of elasticity of a given mild steel specimen using strain gauges.

Objectives:1. To assess the measuring instrument capabilities and ensure that they are adequate for

their specific measurements.2. To maintain the accuracies of measurement through periodical calibration of measuring

instruments.3. To standardize measuring methods.

Apparatus: Strain indicator, Strain gauges, Weights, Connecting wire

Description and figure of apparatus:What Is Strain?Strain is the amount of deformation of a body due to an applied force. More specifically, strain (e) is defined as the fractional change in length, as shown in Figure 1 below.

Figure 1. Definition of Strain

Strain can be positive (tensile) or negative (compressive). Although dimensionless, strain is sometimes expressed in units such as in./in. or mm/mm. In practice, the magnitude of measured strain is very small. Therefore, strain is often expressed as micro strain (me), which is e x 10-6.

When a bar is strained with a uniaxial force, as in Figure 1, a phenomenon known as Poisson Strain causes the girth of the bar, D, to contract in the transverse, or perpendicular, direction. The magnitude of this transverse contraction is a material property indicated by its Poisson's Ratio. The Poisson's Ratio nof a material is defined as the negative ratio of the strain in the transverse direction (perpendicular to the force) to the strain in the axial direction (parallel to the force), or n = eT/e. Poisson's Ratio for steel, for example, ranges from 0.25 to 0.3.

While there are several methods of measuring strain, the most common is with a strain gauge, a device whose electrical resistance varies in proportion to the amount of strain in the device. The most widely used gauge is the bonded metallic strain gauge. The metallic strain gauge consists of a very fine wire or, more commonly, metallic foil arranged in a grid pattern. The grid pattern maximizes the amount of metallic wire or foil subject to strain in the parallel direction (Figure 2). The cross-sectional area of the grid is minimized to reduce the effect of shear strain and Poisson Strain. The grid is bonded to a thin backing, called the carrier, which is attached directly to the test specimen. Therefore, the strain experienced by the test specimen is transferred directly to the strain gauge, which responds with a linear change in electrical resistance.



Strain gauges are available commercially with nominal resistance values from 30 to 3000 W, with 120, 350, and 1000 W being the most common values. It is very important that the strain gauge be properly mounted onto the test specimen so that the strain is accurately transferred from the test specimen, though the adhesive and strain gauge



Figure 2. Bonded Metallic Strain Gauge

A fundamental parameter of the strain gauge is its sensitivity to strain, expressed quantitatively as the gauge factor (GF). Gauge factor is defined as the ratio of fractional change in electrical resistance to the fractional change in length (strain):

Principle:It is based on bending theory &bending equation is represented by,

MI

= ER

= fy

Where, M=Bending MomentI = Moment of InertiaE=Modulus of elasticity (young’s modulus)R=Radius of Curvaturef= Stress,y (or c) =Distance from the neutral axis to extreme fiber,

Procedure:1. Observe load hanger without weights & D connector firmly in the socket.2. Keep KGS/µ STRAIN to KGS position. Gain adjustment Pot to fully clockwise position.ARM

selector switch to 4ARM.3. Switch on the strain gauge set up by connecting 3 pin mains chord to 230V AC mains & leave 2 to 3

minutes to warm up so as to get stable readings.4. Measure S.G Excitation Voltage “E” by a multimeter to read 10Volts across Red & black Sockets.5. Place the multimeter probes across Blue & Yellow Sockets to measure milliVolts output of the Strain

Gauge Bridge.6. Load hanger without weights adjusts Bridge balancing Pot ZERO to read zero volts across Gauge

Bridge as well as on the Display reading weights in Kgs.7. Apply load 50×4gms slotted weights one by one to the load Hanger.8. Adjust amplifier gain by slowly turning the GAIN Pot to read 0.200Kgs on the Display.

9. Repeat Steps 6, 7&8 until we get the stable readings.10. Note down the Value of mill volts output by a multimeter against the applied load of 200gms.



11. Change the position of KGS/µ STRAIN Selector to µ STRAIN to read that Quality on the display.12. The Valve obtained in mill voltsby the multimeter is E1-E2.We Know that E1-E2=E(ΔR/R).We Know

E& E1-E2 By This ΔR/R is obtained. The Gauge factor of Strain Gauge given by Manufacturer GF=2.09. Gauge factor is the ratio of the percent change in resistance of a gauge to its percent change in length. So G.F= ΔR/R.

13. By this formula we get the value of strain ΔL/L i.e., ε. This is expressed in µstrain. If any change in the reading of µStrain is different from the value calculated then adjust µStrain preset below ZERO pot.

14. Now Instrument is calibrated to read directly the µStrain&for different values of Lad directly Strain value read on the display. Tabulate the reading as given in the Table Below.

Note: You can change the position of ARM selector Switch to 1ARM & 2ARM where value of weight & strain has to be multiplied by 4& 2 respectively by only adjusting zero for bridge balancing i.e., step No.6

TERMINOLOGY & FORMULAE USED Strains, ε=σ/E Stress, σ=Mc/I in N/m2

Moment, M=P×L in N-m Distance from the neutral axis to extreme fiber(or y)=t/2 in m Moment of Inertia, I=bt3/12 in m4

P-Applied load in Newton’s L-Length of the beam in m t-Thickness of the beam in m b-Width of the beam in m E-Young’s modulus of material in N/m2

Observations:ε=Strain (e×106micro strains)σ= Stress N/m2

P-Applied load in Newton’sL-Length of the beam (between support and load) (270×10-3m)t-Thickness of the beam (3×10-3m)b-Width of the beam (40×10-3m)E-Young’s modulus of material (20×1010N/m2)

Tabular Column:Sl.No. Load

(Kg)Load(N)

Moment(Nm)

Stress×106

(N/m2)Strain×10-6 Error % Error



Error = strain (actual) – strain (meter)% Error = {Error/ strain (actual)} x 100

Specimen Calculation:1. Distance of neutral axis from outer most layer = c = t/2 2. Moment of Inertia (I)= bt3/12 3. Bending moment (M) = applied load x L = 1 kg x 273 mm = 273 kg-mm4. Bending stress (f) = M x c/ I because {M/I =f/c}5. Bending Strain = Bending stress/E E= Young’s modulus = 2 x106 N/mm2

6. Error = strain (actual) –strain (meter) 7. % Error = (Error/strain actual) x 100

Graphs:

Stress V/s Strain

Results: Strain measured theoretically = Strain shown by digital indicator = Modulus of elasticity of given beam is found to be =

Recommendation: The above practical is related to unit-8 Temperature and Strain Measurement.Students are recommended to go through unit -8 of theory part.



Calibration of Thermocouple

Aim: To calibrate the given thermocouple.

Objectives:1. To maintain the accuracies of measurement through periodical calibration of measuring

instruments.2. To assess the measuring instrument capabilities and ensure that they are adequate for

their specific measurements.3. To determine the process capabilities,

Apparatus: Thermocouple, Thermometer, Instrument tutor, water bath, connecting wires, screw driver, cold bath.

Description and figure of apparatus:Thermocouples are a widely used type of temperature sensor and can also be used as a means to convert thermal potential difference into electric potential difference. They are cheap and interchangeable, have standard connectors, and can measure a wide range of temperatures. The main limitation is precision; system errors of less than 1 °C can be difficult to achieve.

Principle of operationIn 1821, the German-Estonian physicist Thomas Johann Seebeck discovered that when any conductor (such as a metal) is subjected to a thermal gradient, it will generate a voltage. This is now known as the thermoelectric effect or Seebeck effect. Any attempt to measure this voltage necessarily involves connecting another conductor to the "hot" end. This additional conductor will then also experience the temperature gradient, and develop a voltage of its own which will oppose the original. Fortunately, the magnitude of the effect depends on the metal in use. Using a dissimilar metal to complete the circuit will have a different voltage generated, leaving a small difference voltage available for measurement, which increases with temperature. This difference can typically be between 1 to about 70 microvolts per degree Celsius for the modern range of available metal combinations. Certain combinations have become popular as industry standards, driven by cost, availability, convenience, melting point, chemical properties, stability, and output.It is important to note that thermocouples measure the temperature difference between two points, not absolute temperature.

In traditional applications, one of the junctions — the cold junction — was maintained at a known (reference) temperature, while the other end was attached to a probe. For example, in the image above, the cold junction will be at copper traces on the circuit board. Another temperature sensor will measure the temperature at this point, so that the temperature at the probe tip can be calculated.


http://en.wikipedia.org/wiki/Thermoelectric_effect

http://en.wikipedia.org/wiki/Thomas_Johann_Seebeck

http://en.wikipedia.org/wiki/Estonia

http://en.wikipedia.org/wiki/Germany

http://en.wikipedia.org/wiki/1821

http://en.wikipedia.org/wiki/Celsius

http://en.wikipedia.org/wiki/Potential_difference

http://en.wikipedia.org/wiki/List_of_temperature_sensors

http://en.wikipedia.org/wiki/Image:Tc-dia.jpg


Thermocouples can be connected in series with each other to form a thermopile, where all the hot junctions are exposed to the higher temperature and all the cold junctions to a lower temperature. Thus, the voltages of the individual thermocouple add up, which allows for a larger voltage.Having available a known temperature cold junction, while useful for laboratory calibrations, is simply not convenient for most directly connected indicating and control instruments. They incorporate into their circuits an artificial cold junction using some other thermally sensitive device (such as a thermistor or diode) to measure the temperature of the input connections at the instrument, with special care being taken to minimize any temperature gradient between terminals. Hence, the voltage from a known cold junction can be simulated, and the appropriate correction applied. This is known as cold junction compensation.Additionally, cold junction compensation can be performed by software. Device voltages can be translated into temperatures by two methods. Values can either be found in look-up tables or approximated using polynomial coefficients.Usually the thermocouple is attached to the indicating device by a special wire known as the compensating or extension cable. The terms are specific. Extension cable uses wires of nominally the same conductors as used at the thermocouple itself. These cables are less costly than thermocouple wire, although not cheap, and are usually produced in a convenient form for carrying over long distances - typically as flexible insulated wiring or multicore cables. They are usually specified for accuracy over a more restricted temperature range than the thermocouple wires. They are recommended for best accuracy.Compensating cables on the other hand, are less precise, but cheaper. They use quite different, relatively low cost alloy conductor materials whose net thermoelectric coefficients are similar to those of the thermocouple in question (over a limited range of temperatures), but which do not match them quite as faithfully as extension cables. The combination develops similar outputs to those of the thermocouple, but the operating temperature range of the compensating cable is restricted to keep the mis-match errors acceptably small.The extension cable or compensating cable must be selected to match the thermocouple. It generates a voltage proportional to the difference between the hot junction and cold junction, and is connected in the correct polarity so that the additional voltage is added to the thermocouple voltage, compensating for the temperature difference between the hot and cold junctions.

Voltage-Temperature RelationshipThe relationship between the temperature difference and the output voltage of a thermocouple is nonlinear and is given by a polynomial interpolation.

The coefficients and are given for n from 0 to between 5 and 9.


http://en.wikipedia.org/wiki/Polynomial_interpolation

http://en.wikipedia.org/wiki/Nonlinearity

http://en.wikipedia.org/wiki/Image:Tc-db.jpg


ApplicationsThermocouples are most suitable for measuring over a large temperature range, up to 1800 K. They are less suitable for applications where smaller temperature differences need to be measured with high accuracy, for example the range 0–100 °C with 0.1 °C accuracy. For such applications, thermistors and RTDs are more suitable.

Procedure: a. Calibration of thermocouple Unit1. Connect RTD Sensor probe to read ambient Temperature.2. Keep “cal/means.”Switch to cal Position & “S.C/mV” switch to S.C Position3. Position the thermocouple selector switch to “J type” and keep “set Temp.High” Fully

Clockwise.4. Adjust “set Temp.Amb.”Pot to read ambient temp. On”meas. /Cal. Temp”.5. Keep “S.C/mV” to mV Position & adjust 0-50mV to 21.85mV.6. Adjust “Set Temp.High” to 400-0C+Amb.Temp.on “Means. /Cal Temp”.Indicator.7. Keep Back Switch to”S.C/mV” to S.C Position &check for ambient temp. If not adjust “Set

Temp.Amb.”8. Repeatedly check the temperature reading performing steps 6 & 7.b. Measurement of Temperature of a oven9. Connect J type thermo couple to the terminals marked J-Type change the position of

“cal/meas.” To Meas Position.10. Insert the Thermocouple into the oven & vary the supply Voltage by turning the Oven Pot to

Maximum.11. Note Down the mv & Temp. In degree centigrade as the ovenwn temperature raises. Turn

oven pot anticlockwise to some position so the temperature raises slowly.12. When temperature increased to 400-0C turn oven pot to fully anticlockwise position to cool.

Switch on your Table fan &Direct it to cool the oven &again you can take the reading of mV V/S temp as the temperature decreases.

13. Repeat the above procedure to calibrate K-Type & J-Type Thermocouples.

Observations:1. Least count of Thermometer = 1 C2. Wattage of heater = 1000W.3. J-type thermocouple range =-200 C – 800 C4. K-type thermocouple range = -250 C – 1100 C5. T-type thermocouple range = -250 – 400 C

Tabular Column:

Sl. No.

Thermometer(actual) reading (oC)

Thermocouple reading (meter) (oC)

Error while temp. increasing

% Error Error while temp. decreasing

% Error


http://en.wikipedia.org/wiki/Resistance_temperature_detector

http://en.wikipedia.org/wiki/Thermistor


12

Error = thermometer reading – thermocouple reading% Error = {Error/ thermometer reading} x 100

Results:The graph of -0C against mV has to be draw to get the characteristic of a particular thermocouple

The above said tabulation &graph can done K-Type & J-Type thermocouples as well.

Recommendations: The above practical is related to unit-8 of theory part. The students are recommended to refer unit-8 in theory part.



CALIBRATION OF LOAD CELL

Aim: To calibrate the given load cell.

Objectives:1.

Apparatus: Load Cell, Digital Display for load read outs, standard

Description and figure of apparatus:If a metal conductor is stretched or compressed, its resistance changes on account of the fact that both length and diameter of conductor changes, also there is a change in the value of receptivity of the conductor when it is strained and this property is called piezo resistive erect, Therefore resistance strain gauges are also known as piezo resistive gauges. The strain gauges are used for measurement of strain and associated stress in experimental stress analysis, secondly, many other detectors and transducers and notably load cells, torque cells, diapharagm type pressure gauges, temperature sensors, accelerometers and flow meters employ strain gauges as secondary transducer. When strain gauges are subjected to tension or in other words positively strained. Its longitudinal dimension will increase while there will be reduction in lateral dimensions. So when a gauge is subjected to a positive strain, its length increases while its area of cross section decreases. Since t6he resistance of the conductor is proportional to its length and inversely proportional to its area of cross section, the resistance of the gauge increases with positive strain. This change in resistance is an electrical parameter. This property is used in instruments to get calibration to various parameters like load, pressure, torque etc.

Specifications:Load cell

Sensor : Strain gauges bonded on plain surface of rectangular aluminum bar Range : IKg-10kg Excitation :10V Accuracy :1% Linearity :1%

IndicatorDisplay: 31/2 digits, 7thsegments LED display is used for indicator with full scale of 200mV to read up to +/- 1999.Accuracy:Power supply:230V +/- 10%, 50HzTransducer: The transducer here is a suitable force of strain gauge for a particular parameter will convert mechanical changes to electrical parameters.Signal condition:It is electronic circuits that well convert compensate or manipulate to a more useful electrical quantity strain gauges are connected in whetstone bgidge.The change in resistance converted to changes in voltage.Amplifier: Amplifier here increased the output from transducer since output from the transducer is small.

Load cell



Load cell utilizes an elastic member as the primary transducer and strain gauge as secondary transducer strain gauges may be attached to any elastic member and there exists a suitable plain area to accommodate them, this arrangement may be used to measure load supplied to deform or deflect the member provide that the resultant is large enough to produce detectable outputs. Hence, Strain gauge elastic member combination used for weighing is called load cell.

Procedure: Switch on the equipment and wait for a minute for it to stabilize. Adjust the load indicator to show zero for no load condition. Place a standard weight of 0.1 Kg and note down the load indicated from the corresponding indicated

load. Calculate error by the formula: Error=Wactual-Windicated

Calculate % Error by the formula: % error= (Wactual-Windicated) x100/ Wactual

Tabulate the results and plot the graphs.

Observations:L.C. of load indicator=

Calibration Range=

Tabular Column:Sl.No. Applied Load

Wa (Kg)Indicated Load Wi (Kg)

Error Wa- Wi

% Error

Specimen Calculation:

Graphs:

Results:



Measurement GearTooth Profile Using Gear Tooth Vernier

Aim: To measure spur gear tooth element.

Objectives:1. To reduce the cost of inspection by effective and efficient utilization of available facilities.2. To reduce cost of rejections and rework .3. To provide the required accuracy at minimum cost.4. To standardize measuring methods.

Apparatus: Flange micrometer, Gear tooth Vernier caliper.

Description and figure of apparatus:

Gears are mainly used for transmission of power and motion. It is a round wheel that has teeth, which meshes with another gear allowing force to be fully transferred without slippage. Depending on their construction and arrangement, geared devices can transmit forces at different speeds, torques, or in a different direction, from the power source. A gear can also mesh with any device having compatible teeth, such as linear moving racks. For closer control over the accuracy of manufacture of the gear, precision measurement of gear plays a vital role. A brief overview of different types of gear has been documented herewith. Spur Gear - The edge of each tooth is straight and aligned parallel to the axis of rotation. Terminology for Spur Gears

Backlash: Play between mating teeth. Gear: The larger of two meshed gears. If both gears are the same size, they are both called "gears".

Pinion: The smaller of two meshed gears.



Face: The working surface of a gear tooth, located between the pitch diameter and the top of the tooth.

Flank: The working surface of a gear tooth, located between the pitch diameter and the bottom of the teeth

Addendum: The radial distance between the Pitch Circle and the top of the teeth.

Dedendum: The radial distance between the bottoms of the tooth and the pitch circle.

Module: Millimeter of Pitch circle Diameter to Teeth.

Base Circle: The circle from which is generated the involute curve upon which the tooth profile is based.

Center Distance: The distance between centers of two meshing gears.

Circular Pitch: Distance measured on the circumference of the pitch circle from a point of one tooth to the corresponding point on the next tooth.

Tooth Thickness: The thickness of the tooth measured along an arc following the Pitch Circle

Clearance: The distance between the clearance circle and Dedendum circle..

Face Width: The width of the tooth measured parallel to the gear axis.

Top land: The top surface of the tooth.

Line of Action: That line along which the point of contact between gear teeth travels, between the first point of contact and the last.

Pitch Circle: The circle, the radius of which is equal to the distance from the center of the gear to the pitch point.

Pitch Point: The point of tangency of the pitch circles of two meshing gears, where the Line of Centers crosses the pitch circles.

Pressure Angle: Angle between the Line of Action and a line perpendicular to the Line of Centers.

Root Circle: The circle that passes through the bottom of the tooth spaces.

Root Diameter: The diameter of the Root Circle.

Working Depth: The depth to which a tooth extends into the space between teeth on the mating gear.



Diametral Pitch: It is the ratio of number of teeth to the pitch circle diameter in millimeter.

The number of teeth of a gear per inch of its pitch diameter. A toothed gear must have an integral number of teeth. The circular pitch, therefore, equals the pitch circumference divided by the number of teeth. The diametral pitch is by definition, the number of teeth divided by the pitch diameter. That is,

p= πDN and p=

ND pp=π

Where,P=diametric pitchp=circular pitchN=number of teeth

D=pitch diameter

It should be noted that M is a chord AC, but the tooth thickness is specified as an arc distance ADC. Also h is the distance EB and this is slightly greater than the addendum ED.



Procedure: 1) Count the number of teeth (N). 2) Calculate the Pitch Diameter (D) = Outer dia. of gear(mm) - depth of tooth(mm)3) Calculate diametral pitch (P) = N/D4) Calculate module (m) = 1/P5) Calculate h (see fig.2) = mN/2{1+(2/N)- cos(90/N)}6) Measure M using gear Vernier set at h 7) From equation M(see fig.2) =mN sin(90/N)Also the actual thickness i.e., arc length (M’) can be determined as follows.

M’= {M sin-1(90/N)}/sin (90/N)

Observations:1. Least count of vertical scale = 0.05mm2. Least count of vertical scale = 0.05mm3. Range of vertical scale = 0 – 70mm4. Range of vertical scale = 0 – 80mm

Tabular column: Sl.no. Theoretical values Values measured by

instrumentDifference

Result:1. Width of a given gear tooth =---------mm.2. Depth of a given gear tooth = ---------mm.

Recommendation: The above practical is related to unit-4 of theory part. Students are recommended to refer unit -4 of theory part.



Measurement of Taper Angle (Sine bar)

Aim: To determine the of the given specimen using Sine bar.


Apparatus: Sine bar, Dial gauge, Slip gauges, Surface plate, CCl4(Carbon tetrachloride), Magnetic clamp, Taper/Angular specimen




The sine principal uses the ratio of length of the two sides of a right angled triangle in deriving a given angle. It may be noted that devices operating on sine principle are of capable of self-generations. Here measurement is usually limited to 450.

10" and 100mm Sine barsSine bar are used to measure angles accurately for locating any work to a given angle within very close limits. The sine bar in itself is not a complete instrument. Another datum such as surface plate is needed. In addition slip gauges are used. The taper angle is calculated by the formula:

θ=sin-1(h/L)Where, h=Height of slip gauge blockL=Centre distance between two rollers

The hypotenuse is a constant dimension — (100 mm or 10 inches in the examples shown). The height is obtained from the dimension between the bottom of one roller and the table's

surface.

The sine bar is set up on a surface plate to the nominal angle of the taper plug, which is then placed in position on the bar, being prevented from sliding down by the stop plate at the end. Care must be taken to ensure that the axis of the plug gauge is aligned with the sine bar. Pieces of “plasticizes” will be found to be useful for preventing sideways movement. The dial gauge, supported in a stand on the surface plate, is then passed over the plug gauge near each end and also at one or two positions between the ends. If there is any variation in the readings, two alternatives are available for finding the true angle of the cone. Either the variation over a measured distance along the surface of the plug gauge can be used to obtain the difference between the true angles or the angle set up, as the height of the slip gauge pile can be adjusted until no variation occurs in the reading of the dial gauge.


http://en.wikipedia.org/wiki/Image:SineBarStyles.jpg


Sine bars are made from high carbon; high chromium corrosion resistant steel, hardened, ground and stabilized two cylinder of equal diameter are attached at ends. The axes of these two rollers are mutually parallel to each other and also parallel to and at equal distance from the upper surface of the sine bar. The distance between axes of the twocylinders is 10’ 100, 200, or 300 mm. All working surface of the sine bar are finished to a surface finish of 0.2µm Ra value or better, dependingupon accuracy of centre distance. Sine bar also provided with holes to reduce the weight of the sine bar and facilitate handling.

Procedure:1. The sine bar is placed on the surface plate and the specimen is placed on the sine bar.2. The dial gauge is moved such that it touches the larger diameter end of the specimen and

reading is noted.3. A stock of slip gauge is kept underneath the rollers at the smaller diameters end.4. Dial gauge is moved from larger to smaller end and the reading is noted at extreme points.5. The above process is repeated till the extreme reading obtained is same.6. The results are tabulated and angle of taper calculated using the formula.

Precautions:A compound angle should not be formed by misalignment of the work piece with a sine bar. As far as possible, large sine bars should not be used for the purpose of reduction in measurement error.

Calculations:

θ=sin-1(h/L)

Results: Angle calculated theoretically =----------- Angle valulated by sine bar = -------------

Recommendation:



The above practical is related to unit-3 comparators and angular measurements.the students are recommended to refer unit-3 of the theory part.

MEASUREMENT OF ANGLE USING BEVEL PROTRACTOR

Aim: To measure the angle subtended at different corners of the given specimen using Bevel Protractor. Objectives:

1. To reduce the cost of inspection by effective and efficient utilization of available facilities.2. To reduce cost of rejections and rework .3. To provide the required accuracy at minimum cost.4. To standardize measuring methods.

Apparatus:Bevel protractor, Specimen


Bevel protractors are used for measuring and lying out of angles accurately and precisely. Measurement of any angle is precisely one of the most important tasks. It is due to precise angular measurement that ships and airplanes can navigate confidently without sight of sand. The relations of stars and these approximate distances are computed by means of angular measuring devices. In workshops we come across problems involving angular measurements.

The Bevel protractor is simplest instrument for measuring the angles between two faces of a component. It is consists of important parts such as Stock, Blade, Body, Vernier Scale etc.



Procedure:

1. The blade is clamped to the body of the bevel protractor.2. The given plate various angles is placed on over faceplate and the specified angle is chosen.3. The angle intended to measure on the specimen is suspended by two surfaces, which are

brought in contact with the blade surface and working edge.4. The adjustable blade is slide to the specimen surfaces and locked using locknut.5. The working edge and the blade are adjusted to the specified angle.6. The angle is noted down from the scale.7. The procedure is repeated for different angles.

Observations:1. Least count of bevel protractor = 5”

Tabular column:

Sl No. Type of Component Angle

Specimen Calculation:

Angle = Main scale reading+ (Least count* vernier scale division)

Results: Angle measured by bevel protractor = ------------ Recommendation: The above practical is related to unit-3 comparators and angular measurements. The students are recommended to refer unit-3 of the theory part.



MEASUREMENT OF SCREW THREAD PARAMETERS USING TOOLMAKER’S MICROSCOPE

Aim:To measure the following parameters of a given screw thread using a Toolmaker’s microscope: Effective diameter Major Diameter Minor Diameter Depth of Thread Pitch Tool Thickness Angle


Apparatus: Toolmaker’s microscope Vernier Calipers Specimens




The Tool Maker’s Microscope (TMM) essentially consists of the cast base, the main lighting Unit, the upright with carrying arm and the sighting microscope. The rigid cast base is resting onthree foot screws by means of which the equipment can be leveled with reference to the built-in spirit level. The base carries the co-ordinate measuring table, consists of two measuring slides: one each for directions X and Y, and a rotary circular table provided with the glass plate. The Slides run on precision balls in hardened guide ways warranting reliable travel. Two micrometer screws each of them having measuring range of 0 to 25 mm permit the measuring table to be displaced in the directions X and Y. The range of movements of the carriage can be widened up to 75 mm in the X direction and up to 50mm in the Y direction with the use of gauge blocks. The rotary table has been provided with 360 degrees graduation and with a 60 minute Vernier. The rotary motion is initiated by activation of knurled knob. Slots in the rotary table serve for fastening different accessories and completing elements. The sighting microscope has been fastened to column with a carrier arm. The carrier arm can be adjusted in height by means of a rack. The main lighting unit has been arranged in the rear of the cast base and equipped with projection lamp where rays are directed via stationary mounted mirror through table glass plate into the sighting microscope.

Tool Maker’s Microscope is a precision Optical Microscope that consists of single or multiple objective lenses, which magnifies the object under observation and by the help of eyepiece



lens the object is focused and viewed. A high precision micrometric X-Y stage and the Z axis travel are used to measure the three dimensions [Length (X), Width (Y), and Depth (Z)]. The angle is measured with the help of a rotating stage and eyepiece graduation.

Procedure:

Switch on the projection lamp. Get familiar with the least count, linear and angular readings of the tool maker’s microscope and nomenclature of the thread shown in Fig.2. Place the given specimen (thread gauge shown in Fig.3) on the glass table plate. Viewing through the eyepiece, rotate the knob for moving carrier arm on column to get the sharp image of the specimen kept on the glass plate. Position the specimen such that the table movement in the X direction is parallel to the direction of the pitch measurement. This is checked by ensuring the crosswire touching the tips (crests) of all the teeth during table movement in the X direction.To measure the pitch:Rotate micrometer head for X direction to touch the intersection point of the crosswire to the crest of the thread as seen from the eye piece. Note down the reading of the micrometer. Again rotate the micrometer head to move the specimen so that the next successive crest will come in contact with the crosswire intersection point. Note down the reading. The difference in reading will give the pitch.

To measure the depth of the thread:Similarly rotate micrometer head for Y direction to touch the intersection point of the crosswire (along with the horizontal dotted line) to the root of the thread, as seen from the eye piece. Note down the reading of the micrometer. Again rotate the micrometer head to move the specimen so that the horizontal dotted line touches all the crests. Note down the reading. The difference in reading will give the depth of the thread.To measure the thread angle:

The screen is rotated until a line on the screen coincides with one flank of the thread profile and the angle of the screen rotation is noted (a1’).

The screen is further rotated till the same line coincides with the other flank of the thread. The angle is again noted down (a1”).

Two similar angular reading are taken on the other side of the thread profile image (a2’ and a2”) The angle is found by:

Thread angle, a= (a1+a2),Where, a1= (a1’+a1”)/2 ; a2=(a2’+a2”)/2

Observations:1. Least count of x-axis movement micrometer = 0.05mm.2. Least count of y-axis movement micrometer = 0.05mm



3. Range of micrometers = 0- 25mm

Tabular Column:

Sl.No. Parameter Initial Reading 1(mm)

Final Reading 2(mm)

Actual Reading=2-1 mm

Major Diameter

Minor Diameter

Depth of thread

Effective Diameter

Pitch

Angle of screw thread a1’=a1”=

a2’=a2”=

Calculation:Actual reading = Final reading – initial reading

Results: Major diameter of given screw thread = Minor diameter of given screw thread = Depth of given screw thread = Pitch of given screw thread =

Flank angle of given screw thread =

Recommendation: The above practical is related to unit-3 comparators and angular measurements. The students are recommended to refer unit-3 of the theory part.



The dial test indicator (DTI)

It is also known as dial gauge indicator or ‘clock’ gauge (because of its similarity with a clock).The DTI is a mechanical device for sensing linear variations. It measures the displacement of its plunger or a stylus on a circular dial by means of a rotating pointer.There are two types of DTI. a) Plunger type b) Lever type

Plunger type DTI

Figure shows the Plunger type DTI. It generally consists of a rack and pinion mechanism together with a gear train to give a scale movement larger than the plunger movement. The main scale is graduated into equal divisions corresponding to a 0.01 mm movement of the plunger. As there are 100 equal divisions, one complete revolution of the pointer corresponds to0.01 x 100 i.e., 1 mm of the plunger movement. Hence it is obvious that pointer movement from mark 10 to mark 20 or mark 20 to mark 30 and so on indicates a plunger movement of 0.1 mm.

This type has a longer plunger movement and is fitted with a secondary scale and pointer (or a smaller dial) to indicate the number of complete revolutions turned through, one revolution being equivalent to 1 mm of the plunger movement. This secondary scale is also known as revolution counter. To enable the instrument to be zero for any convenient position, the main scale can be rotated and locked into place, using the scale locking screw (bezel clamp) indicated in figure.



Gauge blocks (also known as gage blocks, Johansson gauges, or slip gauges) are precision ground and lapped measuring standards. They are used as references for the setting of measuring equipment such as micrometers, sine bars, dial indicators (when used in an inspection role).

Metric gauge blocksShown at right is an image of a metric gauge block set; close examination of the set will show that the set consists of a range of varying size blocks, along with two wear blocks.In use, the blocks are removed from the set, cleaned of their protective coating (petroleum jelly or oil) and wrung together to form a stack of the required dimension, with the minimum number of blocks. The wear pieces are included at each end of the stack whenever possible as they provide protection against damage to the lapped faces of the main pieces. After use the blocks are re-oiled or greased to protect their faces from corrosion.

Wringing is the process of sliding the 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 dimensions.

Gauge block accessory setThe pictured accessories provide a set of holders and tools to extend the usefulness of the gauge block set. They provide a means of securely clamping large stacks together along with reference points and scribers.Slip gauges are made from a select grade of carbide with hardness of 1500 Vickers hardness. Long series slip gauges are made from high quality steel having cross section (35 x 9 mm) with holes for clamping two slips together.


http://en.wikipedia.org/wiki/Vickers_hardness_test

http://en.wikipedia.org/wiki/Carbide

http://en.wikipedia.org/wiki/Molecular_attraction

http://en.wikipedia.org/wiki/Quality_control

http://en.wikipedia.org/wiki/Dial_gauge

http://en.wikipedia.org/wiki/Sine_bar

http://en.wikipedia.org/wiki/Micrometer

http://en.wikipedia.org/wiki/Image:GaugeBlockMetricSet.jpg

http://en.wikipedia.org/wiki/Image:GaugeBlockAccessorySet.jpg


Calibration of Micrometer

Aim:To calibrate the micrometer screw gauge by the slip gauges


Apparatus: Micrometer, slip gauge set.


The accuracy of any gage may be checked with the following steps for calibration. Calibration is another way of saying, "checking for accuracy." Calibration is the process for insuring the accuracy of gages. The process involves a gage block and the micrometer. A gage block is a block made from steel that is cut to size with in a millionth of an inch. Gage blocks come in various sizes and are used to check the accuracy of measuring devices such as a micrometer.

Note: Each gage is labeled with its range on the frame. (For example, 4"-5", 1"-2") see fig. 2.

1. Use a gage block that falls within the limits of the gages range.(see fig. 2)



2. Snug the gage block between the spindle and anvil of the micrometer using appropriate feel.(see fig 3)

3. Use the ratchet stop as explained in step 2 under zero checking until you have a comfortable

feel between the gage and the gage block. 4. Confirm calibration by checking that the display shows the dimension of the gage block. 5. Again, you may want to insure calibration by repeating these steps more than once.

If the reading on the micrometer display shows the gage block’s dimension, you may begin using the micrometer for measuring. The micrometer may also be checked for calibration using other gage blocks within its range. Using other blocks that fall within the range of the gage will test the gage?s accuracy from one end of the spindle to the other. This may also uncover problems and explain why the gage is loosing accuracy.Errors in screw threads may be of three types, namely progressive, periodic and erratic. The method of manufacture of micrometer screws eliminates the last of these, but there may be a progressive error and also a periodic error in the readings, which is usually caused by eccentricity of the thimble.The method of finding the errors in an external micrometer is by taking the readings over slip gauges, the sizes of which must be chosen to disclose the both types of error. A sufficient number of readings for the progressive error is obtained by using slips in steps of 2.5 mm, and for periodic error by taking five readings during one revolution of the thimble. It is advisable to check the periodic error at two positions of the spindle, one near at each end of its travel. Suitable slip gauges for testing a 0.25 mm micrometer are thereforeFor the progressive error – 2.5 to 25 in steps of 2.5 mmFor the periodic error -2.1 to 2.5 in steps of 0.1 mmThe slips in the latter series are wrung on to the 20 mm slip to obtain readings for the periodic error near to the fully open position of the micrometer.To avoid errors caused by expansion in handling, the micrometer should be clamped to the suitable stand and the slip gauges laid out in readiness some ten minutes before required, being held in tongs or with the piece of chamois leather during use. It is very important to apply the same pressure on each slip gauge. To ensure this, the spindle must be rotated very slowly during the last part of a revolution until a ratchet slips by one click.Readings of the micrometer are taken, first with the measuring faces in contact and then over each slip gauge in turn, the results being recorded as plus or minus errors in units of 0.001 mm. From the readings, two graphs of errors should be drawn; one for the progressive error and the second, to a larger scale, for the periodic error. From these, the error in the micrometer at any nominal reading, and consequently the true size of the object measured, can be obtained.



Observations:

1. Least count of micrometer = 0.05mm.2. Slip gauge set = M38

Tabular column: Sl.No. Slip gauge size in mm Micrometer read in mm Error

Calculations:

Micrometer reading = Main scale reading+ (Least count* timble scale reading)

Error = Micrometer reading – slip gauge size.

Recommendation: The above practical is related to unit-1 standards of measurements. The students are recommended to refer unit-1 of the theory part.


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