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Engineering Engineering Metrology & Metrology & InstrumentsInstruments

Eng/ Mohammed Abd Elghany. 2nd I.E.D 2

“Content”► Introduction. - Important concepts.► Measuring Instruments.4) Length measuring Instruments.

1.Rules and tapes.2.Vernier caliper.3.The Micrometer.4.Calipers.

5) Angle measuring Instruments.6) Gages.7) Comparative length-measuring instruments.

4.1) Dial indicator.► References.


► Introduction:

► Engineering Metrology:Measurement of dimensions such as length, hickness, diameter, taper, angle, flatness, profile and others.

► Post-Process Inspection:Measurements taken after the part is produced

► In-process, On-line or Real-Time Inspection:Checking part characteristics while part is being produced.


► Sensitivity:Is the smallest difference in dimensions that the instrument can detect.► Accuracy:The ability of a measurement to match the actual value of the quantity being measured.► Precision:The degree to which the instrument gives repeated measurements of the same standard.


The difference between precision and accuracy can be shown by the spread of shooting of a tar-get (as shown in Diagram below):


► Range of measurement:The physical variables that are measured between two values. One is the higher calibration value H, and the other is Lower value L.► Error:The deviation between the results of measured value to the actual value.► Correction:The numerical value which should be added to the measured value to get the correct result.


üMeasurements Standards:

→ English Speaking Countries (English System): Pound, Foot, Second

→ Metric System (SI – System International): Kilogram, Meter, Second


►Measuring Instruments:

1) Length measuring Instruments. 1.1) Direct measuring. 1.2) Indirect measuring.2) Angle measuring Instruments.3) Instruments for surface finish.4) Instruments for deviations.


1) Length measuring Instruments: (Direct measuring)

1.1) Rules and tapes:Rules and tapes are the simplest way of

measuring larger dimensions. Steel rules are generally only available to measure dimensions up to 1 meter. Beyond this, steel tapes (measuring to 30 m)



1.1) Rules and tapes:►Rules and tapes used for/

1. measuring lengths. 2. Measuring the outside diameter of pipe.3. Measuring the inside diameter of pipe.4. Measuring the circumference of pipe.5. Measuring inside dimensions.6. Measuring the thickness of stock through a hole.7. Measuring outside dimension with a tape



1.2) Vernier caliper:The vernier calipers found in the laboratory

incorporates a main scale and a sliding vernier scale which allows readings to the nearest 0.02 mm



1.2) Vernier caliper:

► This instrument may be used to measure/

-outer dimensions of objects (using the main jaws).

-inside dimensions (using the smaller jaws at the top).



1.2) Vernier caliper:► How to read vernier calipers?



1.3) The Micrometer :The micrometer screw gauge is used to measure even smaller dimensions than the vernier calipers.

The micrometer screw gauge also uses an auxiliary scale (measuring hundredths of a millimeter) which is marked on a rotary thimble



1.3) The Micrometer :► How to read a micrometer?

- the object is placed between the jaws and the thimble is rotated using the ratchet until the object is secured.- Note that the ratchet knob must be used to secure the object firmly between the jaws, otherwise the instrument could be damaged or give an inconsistent reading.- The manufacturer recommends 3 clicks of the ratchet before taking the reading.- The lock may be used to ensure that the thimble does not rotate while you take the



1.3) The Micrometer :► How to read a micrometer?

Example:

In figure shown the last graduation visible to the left of the thimble is 7 mm and the thimble lines up with the main scale at 38 hundredths of a millimeter (0.38 mm); therefore the reading is 7.38 mm.


1) Length measuring Instruments: (Indirect measuring)

1.3) Calipers:

These are used to transfer the measured dimension from the workpiece to a steel rule.

In the basic caliper, careless use can allow the setting of the caliper to be changed during transfer from the workpiece to the rule. Hence, the spring-loaded type, which prevents this happening, is preferable.


1) Length measuring Instruments: (Indirect measuring)

1.3) Calipers:► Types of calipers:

Inside caliper: are used to measure the internal size of an object.Outside caliper: are used to measure the external size of an object.Divider caliper: are used in the process of marking out suitable workpieces

Inside caliper Outside caliper Divider caliper


2) Angle measuring Instruments:

► Universal bevel protractor

- It is used to lay out, measure, or check angles.- The bevel protractor can measure angles to five minutes of a degree.


3) Gages:

- Gauge blocks, also known as slip gauges, consist of rectangular blocks of hardened steel that have flat and parallel end faces.

- For measuring; a number of gauge blocks are joined together to make up the required dimension to be checked.


3) Gages:► Grades:

- Reference (AAA): small tolerance (± 0.00005 mm or 0.000002 in) used to establish standards

- Calibration (AA): (tolerance +0.00010 mm to -0.00005 mm) used to calibrate inspection blocks and very high precision gauging

- Inspection (A): (tolerance +0.00015 mm to -0.00005 mm) used as tool room standards for setting other gauging tools

- Workshop (B): large tolerance (tolerance


3) Gages:

► Plug gages:(a) Plug gage for checking size or diameter of

internally threaded part.(b) Plug gage for checking taper of internally threaded part.(c) Ring gage for checking size or diameter of externally threaded part.


3) Gages:

► Ring gages:

(a) The Metric Trapezoidal Ring Gage.

(b) American Standard Adjustable Ring Gage.


3) Gages:

► Snap gage:


3) Gages:

► Snap gage:- Snap gage gages diameters, lengths, and thickness.- The adjustable limit snap gage is used to check outside diameter.

- There are a various types of snap gages: → adjustable snap gage. → adjustable roll snap gage. → dial indicator snap gage.


3) Comparative length-measuring instruments:

► Dial indicator:

A dial indicator is used to measure/

shaft runout, shaft thrust, gear backlash, flywheel face runout, flywheel housing concentricity, and valve seat concentricity


3) Comparative length-measuring instruments:

► Dial indicator:The main components of a dial indicator/Most dial indicators have components such as a bezel, indicator pointer, tool post and clamp, magnetic toolholder, and sensor button that are used in taking


3) References:

http://www.tpub.com/content/construction/14256/css/14256_43.htm

http://www.phy.uct.ac.za/courses/c1lab/vernier1.html

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

http://itdc.lbcc.edu/oer/machineTool/precisionTools/precisionToolsALT/precisionTools.htm

Thanks For Thanks For YouYou

THE THE ENDEND

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