Study of slip, block, plug and snap gauges (Lab Report) PDF

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Abstract: In this experiment different gauges were used to find thickness, outer diameter and internal diameters of several objects. Slip gauges/ block gauges were measured through accurate instruments for thickness. Their thickness is so accurate that can be used to calibrate measuring instruments. But we obtained some error due to environmental factors: dust particles, improper surface cleaning, thermal expansion, weather conditions etc. Similarly, we used Snap gauge applying go and no-go condition to ensure tolerance does not exceed. We studied Plug gauge also which checks for hole dimension using go and no-go condition.

Introduction: Measurements and Instrumentation lab is aimed for measurements of the physical and supplementary quantities and define calibration for the instruments used for the measurement. There are basically two kinds of measurement.

Absolute measurement: The measurements which are taken directly through a measuring instrument like Vernier calipers or any other measuring instrument is called absolute measurement.

Relative measurement: The measurement which are taken indirectly by comparing it to the object which is already measured by the measuring instrument is called relative measurement. For example, measuring by a string which is already marked by meter rule is relative measurement.

Theory: In this experiment, 4 kind of gauges were used. First, gauges need to be explained.

Gauge: A gauge or gage, in science and engineering, is a device used to make measurements or in order to display certain dimensional information. A wide variety of tools exist which serve such functions, ranging from simple pieces of material against which sizes can be measured to complex pieces of machinery. Following gauges were used in the experiment:

1. Slip or block gauge: Slip Gauges are known as Gauge Blocks. They are precise measuring instruments. These Slip Gauges are universally accepted end Standard of length. Johnson first introduced the slip gauges, so they can be called as Johnson gauges as well. And he is a Swedish Engineer. Construction of Slip Gauge / Gauge Blocks / Johnson gauges: Slip gauges are rectangular in shape made up of high-grade steels with very close tolerances. The Working faces of any slip gauge are made truly flat and parallel. The slip

gauges undergo Hardening to resist wear and tear. They are further heated and cooled down successively to remove the hardening stresses induced during the hardening Process. The Slip Gauges can be made up of Tungsten Carbide because of it is extremely capable of hard and wear resistance. The size of the slip gauges is permanently marked on any of the measuring faces of individual slip gauge. Making up a dimension With Slip Gauges The Slip gauges come in several sizes. The sizes will be marked on the measuring faces. See the Slip gauges Box.

Figure 1: Slip/Block Gauges

Wringing of Slip Gauges: a. Before using slip gauges, the faces should be cleaned b. Slide the one slip gauge over the other (With 90° as shown in the Fig: Pos2) with little pressure. This way we can expel the air between the slip gauges faces. c. Once placed the one gauge 90° to another gauge by using little pressure, then rotate it by clockwise to make them in line as shown in below figure. (fourth position)

Figure 2: Wringing Process

d. Wringing helps to achieve a dimension by summation of the individual size of slip gauge. The need of clamping is also avoided. e. To make any dimension with slip gauges, we will Wring set of slip gauges to achieve the true dimension. See the following Example. Uses of Slip Gauge

    

Setting up a comparator to a specific dimension Direct Precise measuring purpose. To inspect the Vernier Caliper, Micrometers and some other linear measuring instruments. Conjunction with sine bar to measure the angle of the workpiece. Used to Check the distance between the parallel faces.

2. Limit (Go or no-go) Gauge: They are the gauges that work on the principle of go or not-go. That is maximum material limit and minimum material limit checking. This defines the tolerance. Using limit gauge in the industry tolerance of the manufacturing products can be checked. There are following limit gauges that were used in this experiment. 2.1.

Snap gauges:

A Snap Gauge is a go/no go gauge for outside diameters. They look like a Micrometer. Micrometers can used to measure outside diameters. The Snap Gage will have anvils like a micrometer. It is a limit gauge with permanently or temporarily fixed measurement aperture(s) (gaps) which is used to quickly verify whether an outside dimension of a part matches a preset dimension or falls within predefined tolerances. Here are some pictures of Snap Gages we have seen.

Figure 3: Adjustable Snap Gauge

Figure 4: Fixed Snap Gauge

Snap Gages have different shapes and sizes. They can be "C" type, "A" type, "U" type as well as include a digital or dial indicator. They are used for attribute measurement of outside diameters, groove diameters and width. There are also double ended snap gages, progressive snap gages and adjustable snap gages. 2.2.

Plug gauge:

Plug gauge is used for the checking of holes and internal threads validity. A fixed mechanical plug gage provides fast, accurate and easy to use measurement to the point of manufacture. (Source: Mahr Federal Inc.) Plug gages are commonly used in the inspection of several product lines as a result of their ease of use. A plug gage assesses the conformity of objects to the prescribed

specifications. A typical plug gage resembles a rod whose ends are carefully fashioned so that one end is the upper limit while the other end is the lower limit. Plug gages can determine if a part should be accepted or rejected in a fast and relatively accurate manner. They are primarily preferred for their simple working principle, as the operator does not require a strong scientific or metrology background to use the instrument and apply the data gathered-the major advantage of plug gages over other types of measuring equipment.

Figure 5: Plug gauge

Measuring instrument used in this experiment – Vernier micrometer detail and functions are described below:

Vernier micrometer:

Figure 6: Vernier Micrometer

The description of main parts of an outside micrometer is given below: a) U shaped steel frame: The outside micrometer has “U” shaped or “C” shaped frame. It holds all the micrometer parts together. The gap of the frame permits the maximum diameter or length of the job to be measured. b) Anvil and spindle: The micrometer has a fixed anvil protruding from the left-hand side of the frame. Another movable anvil is provided on the front side of the spindle. The anvils are accurately ground and lapped with its measuring faces flat and parallel

c) d) e) f)

to the spindle. The spindle is the movable measuring face with the anvil on the front side. The spindle engages with the nut. It should run freely and smoothly throughout the length of its travel. Locknut: A lock nut is provided on the micrometer spindle to lock it when the micrometer is at its correct reading. Sleeve or Barrel: The sleeve is accurately divided and clearly marked in 0.5 mm division along its length, which serves as a main scale. Thimble: The thimble can be moved over the barrel. It has 50 equal circular divisions around its circumference. Each division having a value of 0.01mm. Ratchet: The ratchet is provided at the end of the thimble. It is used to assure accurate measurement and to prevent too much pressure being applied to the micrometer. When the spindle reaches near the work surface to be measured the operator uses the ratchet screw to tighten the thimble. The ratchet automatically slips when the correct uniform pressure is applied and prevents the application of too much pressure. The micrometer usually has a maximum opening of 25mm.

Principle of Micrometer: Micrometers work on the principle of screw and nut. We know that when a screw is turned through one revolution, it advances by one pitch distance i.e. one rotation of screw corresponds to a linear movement of a distance equal to pitch of the thread. Least count of Micrometer: Micrometer works on the principle of screw and nut. We know that when a screw is turned through nut by one revolution, it advances by one pitch distance i.e. one rotation of screw corresponds to a linear movement of a distance equal to pitch of the thread. If the circumference of the screw is divided into number of equal parts say “n”, its rotation through one division will cause the screw to advance through (Pitch/n) length. L.C. = Pitch minimum length that can be measured. Thus, by reducing the pitch of the screw thread or by increasing the number of divisions on the circumference of screw, the length value of one circumferential division (L.C.) can be reduced and accuracy of measurement can be increased considerably. e.g. micrometer has a screw of 0.50 mm pitch; with a thimble graduated in 50 divisions to provide a direct reading of L.C. of = Pitch of spindle screw Micrometer No of divisions on thimble Accuracy of the measurement increases as the value of least count decreases. This means that different Vernier Calipers having different value of least count will have different result and different accuracy of the same measurement. Precautions in use of Vernier caliper:    

Clean the micrometer by wiping of oil dirt, dust etc. before using it. Clean the measuring faces of anvil and spindle with a clean piece of paper or cloth. Set the zero reading of instrument before measuring. Hold the work piece whose dimensions to be measured and micrometer properly. Then turn the thimble with forefinger and thumb, till the measuring tip just touches work piece. Fine adjustment should be made by ratchet so that uniform pressure is applied.  Handle and grip the instrument near the C- frame of micrometer.

Procedure: 1.

2. 3. 4. 5. 6. 7.

First snap gauges were studied. There were two types of snap gauges: fixed and adjustable. Each of these have two parts go part and no-go part. Tolerance or correctness of piece is ensured such that piece should pass from go part and should not pass from no-go part. Then plug gauges were studied. They were checked on holes and inner diameters. They work on same go and no-go principle. Then, slip gauges box was opened. Slip gauges were cleaned for dust particles, oil and moisture. The slip gauges’ thickness readings were noted and those thickness were also measured through micrometer. Reading was noted. Then slip gauges were wringed to check for sum of the thickness of slip gauges through micrometer. Readings were noted Experiment was repeated to get 7 readings.

Observations and Calculations: The measurements taken from the experiment were tabulated and some basic calculations were performed to fill up the following table. Percentage error was also found. Table 1: Observation and Calculation

The error shows the experiment was performed carefully but some errors are unavoidable.

Results and Discussion: This experiment enabled to analyze and use different gauges – slip/block gauge, snap gauge and plug gauge. Snap gauges are the gauges which are used to check the cross sectional/outer dimensions measurement of the products on the industrial level. Two types of snap gauges were studied. Fixed snap gauges’ dimension cannot be changed and hence can be used to check only same products in an industry. While, adjustable snap gauges can change dimensions and can check multiple kind of products in an industry. Plug gauges are the gauges which check the dimension of hole and internal threads of an industrial product. If go side of gauge passes through the hole and no-go side of gauge does not passes through the hole, then hole dimension is perfect.

Slip gauges are the accurate thickness gauges that can be used to calibrate the measuring instruments. The measurements of slip gauges were taken through Vernier micrometer and were found to be very precise and accurate depending upon its least count. There were small errors in the measurements. Possible errors in the measurements could arise due to several reasons:      

Parallax Error Environmental factors Weather conditions Temperature variations Thermal expansion Dust particles and oil between the surfaces.

However, the experiment gave results very close to the expected values and micrometer was marked as correctly calibrated.

Conclusion: The purpose of the experiment was achieved. Slip/Block, Snap and Plug gauges were studied, analyzed and were used in this experiment. Slip gauges were used to check the calibration of micrometer which was a success.

References: [1] https://extrudesign.com/slip-gauges-gauge-blocks/ [2] https://www.alliancecalibration.com/blog/what-is-a-snap-gage [3] https://en.wikipedia.org/wiki/Snap_gage [4] https://www.qualitymag.com/articles/88983-plug-gages-indispensable-inspection-tools...