Faculty of EngineeringIndustrial Engineering Department

METROLOGY

IE 225“Fixed and Deviation Type Gauges”

Eng. Nibal tawfiq

Jordan University of Science and Technology

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Introduction• Some times it is not necessary to know the exact dimensions of a part,

and it is enough to know if the dimensions are within the established

limits.

• There are some attribute –type instrument that are designed to check

limits satisfaction called gauges.

• Gauges are designed to gauge only one dimension and indicate whether it

is larger or smaller than a previously established standard.

• Gauges do not determine how much larger or smaller the measured

dimension is than the standard.

• They are relatively inexpensive and easy to use.

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Plug Gaugeso It is one of the most common type of gauges.o They are accurately ground cylinders, held in a handle.o It is used to gauge internal dimension such as holes.o The plug gauges that are used for cylindrical holes are two types:

I. Plain plug gauge

II. Step-type go, not go gaugeso To control the minimum and maximum limits of a given hole, two plug gauges are required:

I. The smaller, or “go” gauge: controls the minimum limit, because it must go (slide) into any hole that is large enough to meet the required dimension.

II. The larger, or “not go” gauge controls the maximum dimension, because it must not go into any hole that is not larger than the maximum permissible size.

Plain plug gauge having go member on one end and not-to go member on the other

Using the plug gauge

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How do we determine if the cylindrical hole meet the specification or not?

• From the designer:The hole diameter must lie in the range (A-B)A: minimum allowable diameterB: maximum allowable diameter

Max = B

Min = A

How do we determine if the cylindrical hole meet the specification or not?

• This can be done using the plug gauge into two different steps:

• Step 1: to check for the minimum diameter• Step 2: to check for the maximum diameter

Using plug gauge (GO)

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d*

d1 is made to the desired minimum allowable diameter for the hole in the work piece

Plug gauge (GO)

Work piece d1

Step 1: to check for the minimum allowable diameter

This is performed using the GO gauge

If d1 > d*: the plug gauge will not go inside the holeThen, the hole is smaller than what it should be. (The component is rejected)

If d1 < d*: the plug gauge will go inside the hole

Then, the hole is larger than its minimum allowable diameter. (GOOD)

Using plug gauges (NOT GO)

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Work piecePlug gauge (NOT GO)

Step 2: to check for the maximum allowable diameter

This is performed using the NOT GO gauge

d2

If d2 > d*: the plug gauge will not go inside the hole

Then, the hole is smaller than its maximum allowable diameter. (GOOD) If d2 < d*: the plug gauge will go inside the holeThen, the hole is larger than its maximum allowable diameter. (The component is rejected)

d2 is made to the desired maximum allowable diameter for the hole in the work piece

d*

Plug gauges

• In the plain type, the go and not-go plugs often are fastened into the

two ends of a single handle for convenience in use.

• In the step type, the go and not go diameter are on the a single plug,

the go portion is the outer end.

• The not-go plug usually is much shorter than the go plug, it is

subjected to little wear because it seldom slides into any holes.

• In using a plug or any other type of gauge, the gauge should never

be forced into, or onto the part being measured.

Plug gauge with stepped go and not-go member

Go Not-Go

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Plug gauges, types

• The common type of plug gauges are:I. Cylindrical shape plug gauges

I. Plain plug gaugeII. Step-type go, not go gauge

II.Taper plug gaugesIII.Flat plug gaugesIV.Thread plug gauges

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Taper plug gauges

• There is a pair of marks etched at the

proper pre-calibrated location.

• The tapered hole is too large if both marks

on the gauge sink down out of sight.

• The tapered hole is too small if both marks

are visible

Tapered plug gaugesPlug gauge to check a tapered hole

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Taper plug gauges

Method for checking a tapered hole with a plug gauge. If first

gauge mark enters hole, but second not, taper is correct.

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Flat plug gauges

This gauge with “go” and “not-go”

members designed to check the widths of

slots, grooves, and channels.

(a) Flat plug gauge designed to check slots and channels(b) Example of keys, slots that can be checked using flat plug gauge.

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Thickness or feeler gauge

It is used to measure the clearance

between two parts.

Feeler gauge sets contain a fan of

blades or leaves differing from one

another by one thousands or several

thousands in thickness.

Typical feeler gauge set which has blades of various thicknesses

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Thickness or feeler gauge

• To obtain the desired thickness, fold together the selection

of leaves that will build up to a thickness, width, height or

clearance between dimensions to be checked.

Typical feeler gauge set which has blades of various thicknesses

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Thickness or feeler gauge

One of the most common application of feeler gauge is to establish

the gap between the valve and its seat in the internal combustion

engine of an automobile.

Feeler gauge is used for valve clearance adjustment in the internal combustion engine

(a) (b)

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Limitation on using the plug gauge• Gauge Wiggling*: If the gauge can be wiggled around in the

hole, then there is a question about the real cause of the problem. There are a number of things that may cause gauge wiggling (**), including:– Tapered hole– Out of round– Bell-mouthed– Non correct plug: discrepancy between the plug diameter and the

hole size.– Inspector skill: ability of the inspector to discover the defect.

(*) Wiggle: to move back and forth with quick irregular motion(**) These conditions may be difficult to distinguish with plug gauge

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Limitation on using the plug gauge

If the taper is slight, and if the plug and hole size are close to each other, there can

be some doubt as to the inspector ability to discover the defects.

(a) Various hole conditions which may be difficult to distinguish with plug gauge (b) Out –of round hole

(a) (b)

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Limitation on using the plug gauge: Bell mouth defect

• A flared (expand or open outward)

mouth on a pipe opening.

• It is a defect which occurs during metal

drilling where a twist drill produces a

hole that is not a perfect circle.Bell mouth defect

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Ring gauges

• Ring gauges are used to gauge shafts or other external round members. They are also made in go and not-go types.

• Go ring gauges have plain knurled exteriors.• Not-go ring gauges have a circumferential (annular) groove in the

knurling.

(c) Close-up shot of a diamond-pattern knurling on a cylindrical work piece.

(a) (b) (c)

(a) Go and no-go ring gauge (b) Ring gauge

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Ring gauges

Ring gauges of a standard design

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Ring gauges (Go and not-go)

The ring gauges are used to check the over all outside diameter of a work-piece

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Ring gauges• The mating part principle was used traditionally to ensure the

correct fitting of the machined shaft and its corresponding hole.

• Ring gauges used the same mating part principle, but they own

advantages that make them more preferable.

• Advantages of using ring gauge:

– More accurate and reliable.

– Made to precise tested sizes.

– Have hardened surfaces, which decelerate the wear rate.

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Ring gauges - disadvantages

• They will accept out-of-round work without a qualm provided the largest

diameter of the piece is within bounds, although such work may not help

to make a satisfactory assembled product.

• The work must be taken out of the machine, and be deburred before an

effective check can be made.

(a) Ovality in the shape of the work piece cannot be detected by a ring gauge. (b) Excessive taper in a work piece can be detected by a ring gauge.

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Snap gauges

Snap gauges are the most common type of gauges for

measuring external dimension.

Various type of gauges are available in industry:

o Single purpose snap gauge

o Double end snap gauge

o Progressive snap gauge

These gauges offer two steps of measurement:

o Go

o Not-go24

Snap gauge

• Single-purpose snap gauge: offer only a single size

limit, “go” or “not-go”.

• Double end snap gauge: the “go” and “not go” may

be two separate calipers at opposite ends of the

gauge.

• Progressive or step-type snap gauge: offer

“progressive” measurement of succeeding caliper in

line with each other.

PROGRESSIVE SNAP GUAGE

Various types of snap gauges (a) single purpose snap gauge, (b) double-end snap gauge, (c) progressive snap gauge

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Snap gauges; progressive type gauge

(d) position assumed by work-pieces of various diameters. Illustration the “go” and “not-go” principle of the progressive type gauge.

If the work piece is of such size it can enter the “go” end of the gauge as at (a) in the figure, but not enter the “not-go” part of the gauge as at (b), then it is within the tolerances if the gauge has been properly set.

When the work piece is too small, it will not enter the “not-go” caliper, position (c) in the figure, and is consequently reject.

An oversize diameter of the work piece, as in the position (o) of the figure, would not enter the “go” step of the gauge, and it will be rejected.

Work that is within specifications must go in “go” section of the gauge, but it must not go in the “not-go” section.

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Checking the setting of the snap gauges

(b) Using gauge blocks to check the “go” and “not-go” settings of a snap gauge.(c) Adjusting a snap gauge to the required “go” and “not-go” settings

Tools required:

Two sets of precision gauge blocks:

I. First set for the prescribed “not-go” limit of the gauge.

II. Second set for the “go” section.

If the gauge is properly set, the “not-go” gauge blocks should just enter between the “not-go” jaws.

If the snap gauge anvils are not properly set (the gap between them may be too wide or too narrow, loosen the locking screws (c), and unscrew the adjusting screws a turn or so. 27

Radius and template gauges

• Most parts and products are designed with rounded edges and with corners filled

in. WHY?• Some design for appearance.

• For technical reasons, i.e. in stepped shaft design it is always desirable to have

fillets wherever change in diameter is needed. Sharp edges act as a stress

concentrators and reduce the fatigue life of the rotating shaft.

• Sharp edges become readily nicked and broken.

Stepped shaft

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Radius and template gauges

• Rounded outer edges enable rough handling

of the piece without getting nicked or burred.

• Another example in connection with fillets is

the common fact that the sharp corners or

edges of cutting tools and wheels wear off

readily.

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Radius and template gauge

• The tools that are used for checking

the radii and fillets.

• Commercial radius gauges consists

of a series of thin steel sheet or

leaves, which are used to check the

radius.

Radius gauge set for checking both internal and external radii

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Radius gauges

• It is better to hold the gauge and work piece

between a light and the eye of the observer.

• Proper light must be shined down on the junction of

the radius gauge with the radius or fillet being

compared.

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Radius gauge

Using the radius gaugeThis set of six gauges can be used for reference while turning, checking the radius when you’re rounding edges, measuring moldings you want to duplicate, or any other task that requires precisely radiused curves.

Radius and template gauge

Use of radius gauge to check various radii found on the work piece

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Template gauge• A pattern or gauge, such as a thin

metal plate with a cut pattern, used as a guide in making something accurately, as in woodworking or the carving of architectural profiles.

• Template gauges are not confined to small sizes.

• Inspectors in aircraft work are familiar with the man-size sheets of metal with carefully calculated curvatures profiled in them to check the contours of wing surfaces, etc.

This profile or contour gauge can make life easier when cutting lines around difficult shapes

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Flush pin gauges

• These are practically always single-purpose gauges designed

for control of a particular dimension on a particular

component.

• They are used for gauging work produced in continuing

operations, mass production, or where patches of the same

sort of part are made every so often.

• Flush-pin gauges have one moving part and are used to gauge

the depth of shoulders .

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Flush pin gauge

• The main section is placed on the higher of the two surfaces with the movable pin resting on the lower surface.

• If the depth between the two surfaces is sufficient but not too great, the top of the pin, but not the lower step, will be slightly above the top surface of the gauge body.

• If the depth is too great, the top of the pin will be below the surface.

Step pin

Dimension to be gauged

Flush pin gauge

Work piece

A type of flush pin gauge being used to check the height of step

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Flush pin gauge

• If the depth is not great enough, the lower step on the

top of the pin will be above the surface of the gauge

body.

• By running a finger, or a fingernail, across the top of the

pin, its position with respect to the gauge body can be

determined.

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Flush pin gaugeStep pin

Flush pin gauge

Work piece

Dimension to be gauged

a

b

a

b

Top surface of the gauge body

Top (upper step) of the gauge pin

d

Case (1): if d is within specification, sufficient but not too great, b > a & a ≈ cCase (2): if d is too large, b < aCase (3): if d is not great enough, c >a

c

c Lower step of the gauge pin

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Fixed and deviation type gauges

• The basic two type of gauges are:– Fixed gauges

• All gauges studied in the first part of the chapter

– Deviation type gauges• High amplification mechanical comparators• Electrical comparator• Pneumatic comparator

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Deviation type gauge• Those type of gauges determine the amount by

which a measured part deviate, plus or minus, from a standard dimension to which instrument has been set.

• The comparators are often calibrated against standards such as gauge blocks.

• In most cases, the deviation is indicated directly in units of measurement.

• In some cases, the deviation is within a permissible (allowable) range.

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Deviation type gauges• These gauges employ mechanical, electrical, or fluid

amplification techniques so that very small linear

deviations can be detected.

• These instruments try to reduce the friction that is such

a problem for the dial indicators.

• Deviation type gauges are available in a variety of

amplifications and sizes.

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High amplification mechanical comparator

• Mechanical comparators• It works on the same principle as dial indicator.• It is used for taking accurate linear measurements by

comparison with a standard.• Components:

– Base– Column– Adjusting devices– Gauging head

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Mechanical comparator

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As the plunger is depressed, it causes the strip to stretch. As the twisted strip is stretched, it changes the angle of the pointer, and thus the indicated deflection.

High amplification mechanical comparators

High amplification dial indicator (HADI):

• The most commonly used dial indicator

are graduated, for reading in 0.02 mm

(0.001”) and 0.002 mm (0.0001”).

• HADI is graduated so that each divisions

equals 0.0005mm (0.00002”).

High amplification dial indicators (HADL) 44

Mechanical comparator – cont’d

• Any dimensional variations between the part being

measured and the standard against which the

instrument is set is shown on a magnified scale.

• The scale is graduated with a plus or minus inch or

metric units of measurement.

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Electric comparator

Electrical comparator is a device in which movement results in a change in some electrical quantity, then amplified by electrical means.

Electrical Comparator operates on the Principal of the Change of Inductance of a coil by movement of a steel armature, which is moved by a plunger arrangement in contact with the surface to be checked.

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Electric comparator

Undersize work

Oversize work

Continue shining as long as the work being measured is within specifications

Advantages of electric comparator:I. FastII. Accurate to 0.003 mm (0.0001”)III. Used in automatic inspection and

control, example micro-switches comparator for die casting inspection.

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Pneumatic comparators• It is a technique of measuring lengths and diameters have

been developed using controlled air pressure as an amplifying medium.

Schematic diagram for comparator in gauging an internal diameter of a hole

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Pneumatic comparators

• Correlate the flow of air between the faces of the jets in the gauging head and the work piece.

• The clearance between the gauging and the work piece controls both the velocity and the pressure of air.

• The larger the clearance (work piece is much larger than the gauging head), the greater the velocity and the lower the back pressure.

• The smaller the clearance, the slower the velocity and the greater the back pressure.

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Pneumatic comparators, types

• Flow pneumatic gauges: indicate the velocity of the air.

• Pressure pneumatic gauges: indicate the air pressure.

Both types are operated from either a portable or a plant supply of compressed air.

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Pneumatic comparators, How does it work?• Stage 1 (calibration):

– Place a setting master gauge (1) over the gauging head.

– Employ compressed air.– Adjust the pneumatic comparator pointer (needle)

to read zero.

• Stage 2 (measurement):– Any variation between the size of the master gauge

and the part causes a change in the zero reading.

51(1) A measuring device of a standard size that is used to calibrate other measuring instruments.

Pneumatic comparators advantages

Simple operation Relatively low cost Non-scratching, even of the finest or softest

finish. Low gauge wear. Minimum skill required.

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