EGR242 Lecture02 Measurement 2012

7/29/2019 EGR242 Lecture02 Measurement 2012

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EGR 242 Manufacturing Processes January 2012

Lecture 02: Measurement

Todays Topics

-- Quiz on the reading assignment

-- Vocabulary of measurement

-- Reading and use of common measurement tools

-- Homework assignment: Chap 3: Problem Set: 3- 1 Prob. 11

Problem Set 3-3 Prob. 18

Problem Set 3-4 Prob. 8

Video Presentation:

Modern Marvels: Measure It

Workshop:

Lab 02: Measurement Workshop

Part a) Using a Vernier caliperPart b) Using a micrometer

Part c) Using a dial gage

Part d) Using a sine bar and gage blocks

Part e) Using Go/NoGo gages

Objectives:

-- To learn to use a Vernier caliper (either with or without a direct readscale) to measure external, internal, and depth dimensions.

-- To learn to use a micrometer (in inches or mm) to read an


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Measurement Vocabulary:Metrology -- The science and application of measurement.

Measurement -- The act of defining a measureable property of an object.

Instrument -- A device used to make or take a measurement.

Inspection -- Examining a part to determine whether it exceeds or fails to meet arequirement.

Testing -- A determination of how well a product will perform.

Nominal Size -- An approximate dimension or size of a part that is used for the purpose

of general identification.

Basic Size -- The theoretical size from which limits of size are derived or calculated byapplying allowances and tolerances.

Actual size -- The measured size of a finished part.

Tolerance -- The total amount by which a given dimension is allowed to vary.

Limit dimensions -- The maximum and minimum dimensions of a machined part.

Bilateral Tolerance -- Deviation of measurement (plus or minus) from the basic size.

Unilateral Tolerance -- Deviation of measurement in one direction only from the basicsize.

Fit -- The looseness or tightness that can result from the application of a specific

combination of allowance and tolerance in the design of mating part features.Hole Basis -- A system of fits based on the minimum hole size as the basic diameter.

Clearance The space between mating parts


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Tolerances:

Generally the size of a machined or manufactured part doesn't need to, nor can it be, exact.To be functional, it will need to be of a size that falls somewhere between some upper

and lower size limit. Giving the range of acceptable values for a size dimension of a part

is tolerancing.

Why Tolerances?

-- An exact measurement is impossible to actually manufacture.-- Tolerances contribute to the cost of making a part.

Tighter tolerance means "more expensive".

-- Acceptable tolerances lead to interchangeability of parts.

Types of Tolerances:

-- General Tolerance: defines theallowable error of all dimensions

on a drawing.

This note says that all dimensions written with 2 decimal places have tolerance to within0.05....dimensions written with 3 decimal places

have a tolerance within 0.010

-- Linear Tolerance: defines the allowable

error for a specific linear dimensionon a drawing.

This diagram shows a shaft with a minimum size of

0 4990 and maximum size of 0 4994 or a tolerance of


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on the shape of a feature on

a drawing.

This drawing shows a parallel feature tolerance. The feature must not be out of parallel

with Datum A by more than 0.01 inch anywhere on its surface.

There are a variety of ways to specify linear tolerances:

Limit dimensions: The minimum and maximum size of a feature are specified.Placement is either written as the maximum on a line above the minimum or else on a

single line with the minimum in front of the maximum.

Plus and Minus dimensions: The basic size of the feature is given followed with abilateral or unilateral addition to the basic size.

Bilateral Unilateral

19.1019.05

19.05-19.10

+0.10+0.05

19.00 +0.00-0.0519.10


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or

ALL FRACTIONAL DIMENSIONS TO 1/64"UNLESS OTHERWISE NOTED.

International Tolerance Grade Symbols: Different types of fits have been categorizedby application: Running, Sliding, Locational, or Force Fits. These can be specified by

use of established standardized sizes. These have symbols which define the particular

fit.

19.05 H8 19.05 f7

H11

H7

H9 H8H7

H7 H7H7H7

f7

k6

h6g6

s6p6n6

u6HoleTolerance

MinimumClearance

Clearance

Interference

MaximumInterference

Shaft Tolerance

MinimumInterference

Hole Tolerance

Hole

MaximumClearance

Transition

Basic

Size


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Clearance Fit: A fit that always allows for sliding or

rotation between mating parts. There will always be somegap or space between the largest interior part and the

smallest exterior size.

Interference Fit: A force or shrink fit that results in

surface contact and surface forces due to theoverlap and the resulting deformation of physical

material for any two mating parts.

Transition Fit: A fit between mating parts which

might be a clearance or interference fit depending

upon which two specific parts are fit together. Thistype of fit is used to obtain accurate part location.

Fits are commonly classified by their function:

By


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d) Diffraction Gratings

e) Calipers or Dividersf) Telescoping Gage

g) Toolmaker's MicroscopesComparative Length Instruments

a) Dial Indicator

b) Electronic Gages

c) Gage Blocksd) GO-NOT GO gages

Plug Gage

Ring GageSnap Gage

Angular Measurement Instruments

a) Bevel Protractorb) Sine Bar

c) Surface Plates

d) Angle Gage Blocks

Straightness Measurement Instrumentsa) Straight Edge

b) Dial Indicatorc) Autocollimator

d) Laser Beam

Flatness Measurement Instruments:

a) Surface Plate and Dial Indicatorb) Interferometry (Optical Flat)

c) Laser InterferometryRoundness Measurement Instruments:

a) Dial Gage

b) Circular Tracing


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-- usually accurate to 1/1000"

-- often come with dial gage or digital readout-- has relatively large range of measurement (0" to 6")


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part of the smallest true scale increment, by

locating the aligned Vernier mark), and addthis to the measurement noted in Step 2.

You try it:1: Smallest Incr. ___________

2: Zero reading. ___________

3. Vernier reading. __________

Total reading. ______________

For additional practice with a virtual

Vernier caliper on-line go to

http://members.shaw.ca/ron.blond/Vern.APPLET/

Or open the SolidWorks file

with assembled caliper at

J:\EME438\Undergraduate Design\EME105


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-- can be as accurate as 0.00004"

-- used for length, flatness, profile, roundness measures

Calipers or Dividers

-- indirect reading instruments without any graduations

-- used to copy a length by adjusting legs to contact part

-- length is read by lining up legs to a scale

-- accuracy is relatively limited


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-- most micrometers have a 1" range, but not necessarily the

same 1" range. Common ranges from 0 to 6 inches

-- each revolution of spindle = 0.025" length-- can be read to 0.0001 ( 1/10 000th) inch

-- also available in metric units

To read a micrometer scale:

1. Identify the smallest increment

on the true scale (along sleeve).


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by wringing, which is a twisting and sliding motion, due to the oil

and moisture on the blocks surfaces

- sets of blocks come in 4 different grades, depending upon accuracy- sets of blocks may be used for length or angular measurement

- flat blocks may also be used with sine bar for precision

measurement of angles

Sine Bar- used to make very accurate angular

measurements or to locate work at

a given angle.

- accuracy to 5 minutes or less.

- common center-to-center

distances: 5 or 10 inches

- should always be used on accuratesurface plate or flat.

- sine bar equation:


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Plug Gages

-- commonly used for holes-- consists of two plugs of slightly different sizes

Ring Gages

-- used for shafts and similar round parts

-- consists of two collars of slightly different size

Snap Gages

-- used to size external dimensions-- made with adjustable gaging surfaces which may be

set for slightly different sizes


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parts. Quality control is concerned with making sure that there are only a

limited number of parts which do not meet the dimensional or quality

requirements specified. It the number of parts which do not meetrequirements is larger than some acceptable amount, then action is taken to

correct whatever deficiency is causing the problem.

In many productions, its not cost effective to measure every finished part

made. In these cases, the finished product may be sampled to determine the

quality of the production. Statistical methods are then used to determine if

the product meets dimensional and performance requirements.

Statistical method use measurements to determine central tendencies and

the dispersion of the measurements to determine if the quality of control is

maintained. The most common statistical model is that ofNormal

Distribution. In normal distribution, random errors will result in measured

readings of the same property being centered around an average value. The

shape of a normal distribution is the well known bell curve.


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1

1i

i to N

Mean xN

=

=

Median: The middle value of all the measured values. There are an equal

number of measurements above and below this value. This can be found by

sorting the measurements from smallest to largest and taking the

( / 2 1)

( / 2) ( / 2 1)

2

sorted

sorted sorted

N

N N

x if N is odd

Median x xif N is even

+

+

= +

Mode: The most commonly occurring measured value. In other words,

which values occurs the most times. This is well defined for discretely

measured and can be arbitrarily defined for continuous or analog quantities.

For a large set of data with true normal distribution curve, the mean, mode,

and median will be the same value. In real data sets, these are oftendifferent.

Dispersion is defined in the following ways:

Range: The difference between the extreme maximum and minimum

values of measurements

max minRange x x=

Standard Deviation: A measure of spread given by the formula.1 N

SD


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Example Problem

Grades from a quiz given to a group of students are given on the tablebelow. For this data set determine each of the following:

a) mean.

b) median.

c) mode.

d) range.

e) standard deviation.

f) Is this data set compare well to a normal distribution?

Stude

nt

Quiz

Grade

1 5

2 6

3 34 9

5 5

6 7

7 7

8 8

9 6

10 511 8

12 10

13 4


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Solution calculated in Excel.

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EGR242 Lecture02 Measurement 2012

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