Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. PowerPoint to accompany Krar Gill Smid Technology of Machine Tools 6 th Edition Measurement Section 5

History Egyptians used length called cubit –Equal to length of forearm (middle finger to elbow) James Watt measured tolerances of steam engine with thickness of thin shilling International System of Units (SI) developed in 1960 Two major systems of measurement –Inch system in US and Canada –Metric system for 90% of world

Metric (Decimal) Systems Jan 16, 1970, Canada adopted SI for implementation throughout Canada by 1980 Dec 8, 1975, US Senate passed Metric Bill Will take long time to convert –All machine tools and measuring devices will have to be redesigned –Long life expectancy of costly machine tools –People resistant to change

Inch/Metric Dimensioning 1994 ANSI Standards Inch Dimensions –Zero not used before decimal point for values less than 1 inch –Dimension expressed to same number of decimal places as its tolerance Metric Dimensions –Zero used before decimal point if < 1 millimeter –Whole number uses no decimal point nor zero –Decimal fraction of a millimeter – last digit to right of decimal point not followed by zero

Fractional/Inch System Increased use of CNC and digital data make fractional sizes impractical –ANSI recommends decimal dimensions Fractional dimensions still used to identify sizes of holes produced by drills, standard taps, and screw thread sizes

QuantityName Symbol lengthmeterm volumeliter and l massgramg timeminutemin seconds Following is list of some common SI quantities, names, and symbols you are likely to encounter when working in the machine shop. Symbols for Use with SI

QuantityName Symbol forcenewtonN pressure, stresspascalPa temperaturedegree Celsius°C areasquare meterm 2 velocity (speed)meters per minute m/min meters per second m/s anglesdegrees° minutes' seconds'' electric potentialvoltV electric currentampereA frequencyhertzHz electric capacitancefaradF

Symbols for Use with SI PrefixMeaningMultiplierSymbol microone-millionth µ millione-thousandth.001 m centione-hundredth.01 c decione-tenth.1 d dekaten10 da hectoone hundred100 h kiloone thousand1 000 k megaone million M These prefixes often used with quantities: length, volume, mass, pressure, stress, area

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. PowerPoint to accompany Krar Gill Smid Technology of Machine Tools 6 th Edition Basic Measurement UNIT 7

Objectives Identify several types of steel rules Measure round and flat work to 1/64-in. accuracy with a rule Measure with spring calipers and a rule

Inch System Unit of length is the inch –May be divided into fractional or decimal fractions –Fractional system based on binary system Common fractions: 1/2, 1/4, 1/8, 1/16, 1/32, 1/64 –Decimal-fraction system uses base 10 Number written as product of 10 or fraction of 10

Inch System ValueFraction Decimal one-tenth1⁄10.1 one-hundredth1⁄ one-thousandth1⁄ one ten-thousandth1⁄10, one hundred-thousandth1⁄100, one millionth1⁄1,000,

Metric System Linear dimensions expressed in multiples and submultiples of meter Millimeter most common Fractions of millimeter expressed in decimals Brief comparison of common inch and metric 1 yd 36 in. 1 m in m 1 km 1 km mi 1 mi km

Inch/Metric Conversion Metric Size mm cm dm m 1 in ft yd

Fractional Measurement Measured with rulers or calipers Steel rules graduated –Binary-fractional divisions 1, ½, ¼, 1/8, 1/16, 1/32, 1/64 –Decimal fractional divisions decimeters, centimeters, millimeters, half-millimeters –1/64 in. or 0.50 mm. smallest used Precision instruments –Micrometers and verniers used for dimensions of less than 0.50 mm

Steel Rules Metric steel rules graduated in millimeters and half-millimeters –Linear measurement without great accuracy –Lengths from 15 c. to 1 m. Factional steel rules graduated in common binary fractions (1/8 – 1/64 in.) –Several varieties (spring-tempered, flexible, narrow, and hook) –Lengths range from 1 to 72 in.

Fractional Steel Rules Spring-tempered quick reading 6 in. rules –Most frequently used in shop work Hook rules –Used to make accurate measurements from edge of workpiece and also flanges and circular pieces –Use for setting inside calipers to a dimension Decimal rules –Used for linear measurements smaller than 1/64 in.

Fractional Steel Rules Short-length rules –Used to measure small openings and hard-to-reach locations –Five small rules in set: range between ¼ and 1 in. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Measuring Lengths Fairly accurate measure with steel rules –Butt end of rule against shoulder or step Steel rules become worn with constant use –Can make measurements taken from end inaccurate –Compensate by measuring from 1-in or 1-cm mark and subtracting 1 from measurement Keep edge of rule parallel to edge of work Rule used as straightedge to test flatness of workpieces –Edges ground flat: place, hold to light and view

Outside Calipers Not precision tools Used to approximately measure outside surface of either round or flat work Several styles –spring joint –firm joint Do not use when accuracy <.015 in.needed Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Using Outside Calipers Hold both legs of caliper parallel to edge of rule. Turn adjusting nut until end of lower leg just splits desired graduation line on rule Place caliper on work with both legs of caliper at right angles to centerline of the work Diameter correct when caliper just slides over work by own weight

Inside Calipers Used to measure diameter of holes or width of keyways and slots Several styles –Spring joint –Firm Joint Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Measuring An Inside Diameter Place 1 leg of caliper near hole's bottom edge Hold caliper leg in position with finger Keep caliper legs vertical or parallel to hole Move top leg in direction of arrows and turn adjusting nut until slight drag felt on leg Find size of setting by placing end of rule and one leg against flat surface Hold legs of caliper parallel to edge of rule and note reading

Transferring Measurements Check caliper setting with outside micrometer for accurate measurement –Hold micrometer in right hand –Place one leg of caliper on micrometer anvil and hold position –Rock top leg of caliper in direction of arrows –Adjust thimble until slight drag felt as caliper leg passed over measuring face Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.