ME 300 CH35 Metrology

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Engineering Metrology and

Instrumentation

Measurement Standards

Line-graduated Instruments

Measuring Straightness, Flatness, Roundness andProfile

Coordinate Measuring and layout Machines

Gages

Optical Instruments

Automated Measurement

Geometric Dimensioning and Tolerancing

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Engineering Metrology

Measurement of dimensions

Length

Thickness

Diameter

Taper

Angle

Flatness

profiles

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Engineering Metrology

Postprocess Inspection

In-process, on-line, real-time inspection

Dimensional Tolerances The smaller tolerancehigh cost, but more

accurate

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Measurement Standard

Inch, foot; based on human body 4000 B.C. Egypt; Kings Elbow=0.4633 m, 1.5 ft, 2

handspans, 6 hand-widths, 24 finger-thickness

AD 1101 King Henry I yard(0.9144 m) from his nose tothe tip of his thumb

1528 French physician J. Ferneldistance between Parisand Amiens

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1872,Meter (in Greek, metron to measure)- 1/10 of amillionth of the distance between the North Pole and theequator

Platinum (90%)-iridium (10%) X-shaped bar kept incontrolled condition in Paris39.37 in

In 1960, 1,650,763.73wave length in vacuum of the orangelight given off by electrically excited krypton 86.

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Sensitivity (Resolution);the smallest difference indimensions that the instrument can detect or distinguish

Precision;the degree to which the instrument givesrepeated measurements of the same standard(sometimes called accuracy)

Standard measuring temperature 20 0C

Instrument, gage

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Line-graduated Instruments Graduatedmarked to indicate a certain quantity

Rules; Steel rule (machinists rule), bar or tape, [1 mm or1/64 in]

Vernier calipers; after P. Vernier 1600s, caliper gages, [25mm or 0.001 in],With digital readout

Micrometers; sensitivity[2.5mm or 0.0001 in],

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Line-graduated Instruments

Diffraction gratings; with two flat optical glasses,interference fringes with 40 lines/mm (1000 lines/in)gratings. [2.5mm or 0.0001 in]

Indirect-reading; dividers, calipers, telescoping gage forholes and cavities.

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Comparative Length-Measuring Instruments

Also called deviation-type instruments Dial Indicator; using rack-and-pinion and

gear-train mechanism, accuracy [1mm or40 min]

Electronic gage; using sensors (straingage, inductance or capacitance),

LVDT (Linear variable differential transformer)for small displacement

Laser Scan micrometer; non-contactmeasurement; high temperature, tooelastic or brittle material, on-linemeasuring, [0.125mm or 5 min]

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Other Measurements

Straightness; Knife edge, dial indicator,autocollimator (like a telescope with alight beam that bounces), Optical(transits and laser)

Flatness; dial indicator, precision steelsquare, interferometry (if not flat, lightfringes are curved)

Roundness;

V-block with dial gage, read TIR(totalindicator reading)

Circular tracing; platform rotates

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Other Measurements

Profile Template, profile gage to check shape conformity

Measuring screws and gear teeth

Threaded plug gages, screw-pitch gages (similar to radiusgages), micrometer with cone shaped points, snap gages

Optical contour projector

Coordinate measuring machines

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Gages

Heat treated, stress-relieved alloy steels orfrom carbide

C.E. Johansson 1900s Gage blocks[0.05mmor 2 min]

Grade 0.5 (AAA)-reference gage, very high

precision work Grade 1 (AA)-laboratory grade, for calibration of

instruments

Grade 2 (A+)-precision grade, tool room andinspection

Grade 3 (A)-working grade, use in production

Plug gage, GO gage, NOT-GO (NO-GO)

Pneumatic (air) gage

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Selection of Measuring

Instruments Accuracy The degree of agreement of the measureddimension with its true magnitude

Magnification (amplification)

Precision

Resolution

the smallest dimension that can be read on aninstruments

Rules of 10(gage makers rule)

At least 10 times accurate than the tolerance Sensitivity

Stability (drift);capability to maintain calibratedstatus

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Precision vs. Accuracy16


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Tolerance

Tolerare; put up with, endure Impossible to make perfect parts

Too small tolerance, cost is high

Boeing 747-400 has 6 million parts,measurement of 28 features, 150 millionmeasurements

NIST (U.S. National Institute of Standard

and technology); tolerance shrink by afactor of 3 every 10 yearsultraprecisionion-beam machining 0.001mm

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Definitions

Allowance; the specific difference indimensions between mating parts

Basic size; dimension from which limits of sizeare derived

Bilateral tolerance; deviation from the basicsize (+ or -)

Clearance; the space between mating parts

Clearance fit; fit that allows for rotation orsliding between mating parts

Datum; theoretically exact axis, point, line orplane

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Definitions Feature;Physically identifiable portion of a

part, e.g. hole, slot, pin, chamfer Fit; the range of looseness or tightness

Geometric tolerancing; tolerances thatinvolve shape features of the part

Hole-basis system; tolerances based on azero line on the hole

Interference; negative clearance

Interference fit

International Tolerance grade (IT);a group oftolerances that the same relative level ofaccuracy within a grade (varies dependingon basic size)

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Definition 23 Limit dimension;Maximum and minimum

dimension of a part, MMC(maximum material condition); condition

where a feature of size contains the maximumamount of material within the stated limits of size

Nominal size;

Positional tolerancing; A system of specifying thetrue position, size, and form of the feature of apart, including allowable variation

Shaft-based system;

Standard size Transition fit; Fit with small clearance or

interference that allows for accurate location ofmating parts


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Tolerances

Unilateral tolerancing

Zero line; reference line along the basic size from which arange of tolerances and deviations are specified.

Limits and Fits

See the separate lecture note

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Micrometer

The micrometer is a basic precision

measuring tool. To a machinist, this

tool is indispensable. The engineer should also realize the

importance of being able to use

this tool properly. This discussion

should help in mastering the use of

the common "Mike," whether it is an

outside, inside or depth type.

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End of Metrology 35

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ME 300 CH35 Metrology