Personal Study Notes (Engineering Metrology - 22342)-with-numbers

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Transition Fit
Transition fit occurs when two toleranced mating parts will sometimes be an
interference fit and sometimes be a clearance fit when assembled.
It may result in either clearance fit or interference fit depending on the actual value of
the individual tolerances of the mating components.
Transition fits are a compromise between clearance and interference fits.
They are used for applications where accurate location is important but either a small
amount of clearance or interference is permissible.

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Q. How will you designate a Fit? / Interpretation of designated Fit.

Q. Explain the concept of Interchangeability? What are its advantages?
1. An interchangeable part is one which can be substituted for similar part manufactured
to the same drawing.
2.When one component assembles properly (and which satisfies the functionality
aspect of the assembly) with any mating component, both chosen at random, then it is
known as interchangeability.

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3. The parts manufactured under similar conditions by any company or industry at any
corner of the world can be interchangeable.
4. In earlier times production used to be confined to small number of units and the same
operator could adjust the mating components to obtain desired fit. With time the concept
of manufacturing techniques kept on changing and today the same operator is no more
responsible for manufacture and assembly too. With economic oriented approach, mass
production techniques were inevitable, that led to breaking up of a complete process
into several smaller activities and this led to specialization. As a result various mating
components will come from several shops; even a small component would undergo
production on several machines. Under such conditions it becomes absolutely essential
to have strict control over the dimensions of portions which have to match with other
parts. Any one component selected at random should assemble correctly with any other
mating component that too selected at random. When a system of this kind is ensured it
is known as interchangeable system.
5. Interchangeability ensures increased output with reduced production cost.

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The advantages of interchangeability
1. The assembly of mating parts is easier. Since any component picked up from its lot
will assemble with any other mating part from another lot without additional fitting and
machining.
2. It enhances the production rate.
3. It brings down the assembling cost drastically.
4. Repairing of existing machines or products is simplified because component parts
can be easily replaced.
5. Replacement of worn out parts is easy.
6. Without interchangeability mass production is not possible.

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Q. Write a short note on selective assembly.
1. Today the consumer not only wants quality, precision and trouble free products but
also he wants them at attractive prices. This has become possible only by adopting
automatic gauging for selective assembly whereby parts manufactured to rather wide
tolerances fit and function as though they were precisely manufactured in precision
laboratory to very close tolerances. This is a concept which does away with old idea of
inspection in which part is identified as ‘good’ or ‘bad’; good part being used for
assembly and bad used to be scraped.
2. In selective assembly the components produced by a machine are classified into
several groups according to size. This is done both for hole and shaft and then the
corresponding groups will match properly.
3. If some parts (shaft and holes) to be assembled are manufactured to normal
tolerances of 0.01 mm (and both are within the curve of normal distribution), an
automatic gauge can segregate them into ten different groups with a 0.001 mm limit for
selective assembly of the individual parts.
4. Thus parts with tolerances of 0.0001 mm are obtained (due to segregation) and both
the conditions of high quality and low cost can be served by selective assembly
technique.
5. In selective assembly, if the components are divided into different categories, then
the groups will be organized according to the sizes and dimensions. We have to make
sure that all the parts are grouped together and all are ready for mating, so that every
component will match with corresponding sized component to form an assembled part.

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Q. Difference between Hole Basis System and Shaft Basis System.
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Q. Give the classification of gauges / limit gauges / plain gauges.
Q. Write short note on plain gauges.

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1. According to the Type:
According to the type and principle of manufacturing the gauges may be classified as:
(a) Standard gauges,
(b) Limit gauges,
(c) Indicating gauges, and
(d) Combination gauges.
(a) Standard Gauges: If the Go gauge is an exact model of the mating member whose
dimensions to be checked, then such a gauge is termed as the standard gauge.
For Example: If a bushing is manufactured to mate or assemble with shaft, then shaft is
mating part. The busing is checked by a Go-gauge is a copy of the mating part, that is
the shaft. The use of standard gauge is shown in Figure 1.39.
Standard gauge is only an ideal concept. It is not possible to use standard gauge
because there is always some tolerance provided on the work component, and this
tolerance does not takes into account of standard gauge.

(b) Limit Gauges:
Limit gauges are widely used in industries. As there are two limits of a component (high
and low), two gauges are required to check each dimension of the component.
One gauge is called a “Go-Gauge” should pass through or over the part, while the other
gauge called a “Not-Go-Gauge” should not pass through or over the part.
Two limit Gauges are shown in figure 1.40. A little consideration will show that (i)
Gauges and component to be checked should be at same temperature and (ii) Gauges
should pass through or over the component under their own weight with no noticeable
pressure.

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(c) Indicating Gauges:
Indicating gauges are complex in design and construction as compared to the other
types of gauges. They are used to indicate the value of dimensions on a visual display
system.
Dial gauge is a popular example of indicating gauges. Like dial gauge, all the indicating
gauges incorporate some magnification system. For dimension control of a component,
the pointer must lies between two prefixed points.
(d) Combination Gauges:
These are special designed gauges to measure or check more than one dimensions of
a component in a given setup.

2. According to the Purpose:
According to the purpose, the gauges may be classified as:
(a) Workshop Gauges,
(b) Inspection Gauges, and
(c) Master Gauges (Reference Gauges).

(a) Workshop Gauges:
Workshop gauges are used by the machine operator to check the dimensions of the
components as they are being produced. These gauges are designed to keep the size
of the component near the centre line of the tolerance.
(b) Inspection Gauges:
Inspection gauges are used by the inspectors for the final acceptance of manufactured
components when finished. These gauges have slightly larger tolerance than the
workshop gauges so as to accept component slightly nearer the tolerance limit than the
workshop gauges.

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(c) Master Gauges:
Master gauges are also referred as reference gauges. These are used only for checking
of other gauges. Due to expenditure involved, master gauges are seldom used and
gauges are checked by conventional measuring instruments like, comparators, slip
gauges, optimizers etc.

3. According to the Function:
According to the function, the gauges may be classified as:
(i) Dimension Measuring Gauges.
(ii) Geometry Measuring Gauges.
Dimension Measuring Gauges again may be classified as:
(a) Inside Dimension Measuring Gauges.
(b) Outside Dimension Measuring Gauges,
(c) Both side Dimension Measuring Gauges.
Geometry Measuring Gauges again may be classified as:
(a) Concentricity measurement.
(b) Taper measurement.
(c) Profile measurement
Inside dimension measuring gauges are:
i. Plug Gauges.
ii. Pin Gauges, etc.
Outside dimension measuring gauges are:
i. Snap Gauges,
ii. Ring Gauges,
Both side dimensions measuring gauge are:
i. Calliper Gauges

4. According to the Design:
According to the design, the gauges maybe classified as:
(i) Single limit, double limit.
(ii) Single ended, double ended.
(iii) Fixed, Fastened
(iv) Integral end, Renewable end.
(v) Solid end, Hollow end.

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Q. Explain Maximum Material (Metal) Conditions (MMC) and Minimum / Least
Material (Metal) Conditions (LMC).

Q. Explain Taylors principle applied to gauges.
Taylor’s Principle of Gauge Design:
The Taylor’s Principle of gauge design gives two statements which are discussed here:
Statement 1:
The “Go” gauge should always be so designed that it will cover the maximum metal
condition (MMC), whereas a “NOT-GO” gauge will cover the minimum (least) metal
condition (LMC) of a feature, whether external or internal.

Statement 2:
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The “Go” gauge should always be so designed that it will cover as many dimensions as
possible in a single operation, whereas the “NOT-GO” gauge will cover only one
dimension.
Means a Go plug gauge should have a full circular section and be of full length of the
hole being checked as in shown figure 1.62:

According to the first statements let us take examples of a bearing (hole) and a shaft
whose dimensions are to be controlled.
Example 1: For Bearing (Hole):
High limit of hole = 38.70 mm tow limit of hole = 38.00 mm
Maximum Metal Limit of hole (Low limit of hole) = 38.00 mm “Go” gauge dimension
become = 38.00 mm Minimum Metal Limit of hole (high limit of hole) = 38.70 mm “Not -
Go” gauge dimension become = 38.70 mm
For the bearing (hole) to be within 38.00Sqq mm the Go-gauge should enter and NOT-
GO gauge should refuse to enter. If the GO-gauge does not enter, the hole is smaller in
dimension and if the NOT-GO gauge also goes in the hole, then the hole is bigger in
dimension.
Example 2: For a shaft:

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Maximum Metal and Limit of shaft (high limit of shaft) = 37.98 mm “GO” gauge
dimension become = 37.98mm Minimum Metal Limit of shaft (low limit of shaft) = 37.96
mm “NOT-GO” gauge dimension become = 37.96mm.

For the shaft to be within mm the Go-gauge should slide over and NOT-GO

gauge should not slide over the shaft. Is the GO-gauge does not go (slide) then the

shaft is bigger in dimension and if NOT-GO gauge slide over the shaft, then the shaft

size is smaller in dimension.

According to the second statement, Let us take an example of checking of a bush

(hole), as shown in Fig. 1.63:

Example 3:
If a short length Go-plug gauge is employed to check the curved bush, it will pass
through all the curves of the bend busing. This will lead to wrong selection of curved
bush.
On the other hand, a GO-plug gauge of adequate length will not pass through a bent or
curved bush. This eliminates the wrong selection. The length of NOT-GO gauge is kept
smaller than GO-gauge.

Q. Explain Taylors principle.
TAYLOR’S PRINCIPLE
A GO Gauge will check all the dimensions of the work piece in what is called the
maximum metal condition (indicating the presence of the greatest amount of material
permitted at a prescribed surface)

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That NOT GO Gauges shall
check only one dimension of
the work piece at a time, for the
minimum metal conditions
(indicating the presence of the
least amount of material
permitted at a prescribed
surface) size. In case of hole,

the maximum metal condition
obtains when the hole is machined
to the low limit of size, & minimum
metal condition results when the
hole is made to the high limit of
size. In case of shaft the limits
taken would be inverse of hole.

Q. Give advantages and disadvantages gauges.

Advantages of Limit Gauges:
1. Quicker Inspection Method:

It is quicker than direct measurement. The time to inspect on shop-floor is
minimized.
2. Used In-Mass Production:

Limit gauges are conveniently used in mass production for checking and
controlling various dimensions.
3. Ensure Interchangeability:

A Limit gauge ensures interchangeability and hence components can be
assembled without difficulty.
4. Need Semiskilled Operator:

Limit gauges can easily be used by semi-skilled operators.
5. Check both Linear and Geometric Features:

A proper designed limits gauge can check both linear and geometric features
simultaneously.
6. Economical:

Limit gauges are economical in their own cost as well as in inspection cost.

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Limitations or Disadvantages of Limit Gauges:
1. Do not Indicate Exact Size:

Limit gauges do not indicate exact size of the component. They only indicated
whether the component is within the tolerance zone or not.
2. Errors due to Wear:

Limit gauges are subjected to errors due to wear of gauges during use.
3. Difficulty in Checking of Finer Tolerance:

It is generally uneconomical to manufacture a limit gauge with 0-0.0013 mm
tolerance, to check the work tolerance of about 0.013mm. Such fine limit gauges are
also difficult to use in shop-floor, due to wear.

Q. Write short note on Need of Limit Gauges.
Need of Limit Gauges:
There are two methods to ensure whether the components being produced on the shop
floor are as per the pre-decided specifications or not.

These are:
(i) Measurement by measuring instruments.
(ii) Limit Gauging by fixed design limit gauges.
Obviously, measurement is the best method, but is not practical to check every
dimension on each manufactured part. On the other hand, Limit gauging is faster,
easier, and does not required skill inspector.
Also, accuracy of component greatly reflects itself in the cost of the product. To achieve
a greater accuracy than necessary, it makes the project uneconomical. Thus, in
repetition work it is not possible to check dimensions with the precision instruments like
vernier, micrometer etc. This conventional measurement requires skilled or semiskilled
workers.
Hence, in mass production where inter changeability is to be maintained at relatively low
cost, the dimensional tolerance (high and low limits) are controlled by the limit gauges.

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Q. Write short note on Plug Gauges.

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The various plug gauges are shown in figure 1.41:
Q. Write short note on Ring Gauges and Snap Gauges.

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The various snap gauges are shown in figure 1.41:

Pin Gauge:
When the holes to be checked are large than 75mm, such as automobile cylinder, it is
convenient to use a pin gauge as shown in Fig. 1.42. During measurement, the gauge is
placed lengthwise across the cylinder bore and measurement is made. These gauges
are especially useful in measurement of width of grooves or slots.

Calliper Gauge:
A calliper gauge is similar to a snap gauge, but it is used to check both the inside and
outside dimensions. It’s one end check the inside dimensions (hole diameter) while it’s
another end checks outside dimensions (shaft diameter).

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Q. Write short note on Design of Limit Gauges.

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Q. Explain Indian standard (IS 919 – 1963).
1. The Indian standard system of limits and fits comprises suitable combination of 18
grades of fundamental tolerances or grades of accuracy of manufacturer (IT0 to IT16),
and 25 types of fundamental deviations represented by letter symbols for both holes
and shafts (capital letters A to ZC for holes and lower case letters a to zc for shafts).
2. In diameter steps up to 500mm.
3. The 25 fundamental deviations of hole are represented BY
A,B,C,D,E,F,G,H,JS,J,K,M,N,P,R,S,T,U,V,X,Y,Z,ZA,ZB,ZC.
For more details,
http://www.questin.org/sites/default/files/standards/is.919.1.1993.pdf

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Engineering Metrology (22342) Class – ME3I
Screw Thread Measurements

Q. Write short note on Screw Thread Measurement.

Screw Thread Measurement

Screw threads are used to transmit t e power and motion, and also used to fasten two
components with the help of nuts, bolts and studs. There is a large variety of screw
threads varying in their form, by include angle, head angle, helix angle etc. The screw
threads are mainly classified into 1) External thread 2) Internal thread.

Fig 3.1 External Thread Fig 3.2 Internal Thread
Q. Explain terminology of Screw Thread.

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Q. Suggest the measuring instruments to measure the following features of
external thread and internal threads.

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Q. Define screw thread errors? Explain in brief.
Error in Thread
The errors in screw thread may arise during the manufacturing or storage of threads.
The errors either may occur in following six main elements in the thread.
1) Major diameter error

It may cause reduction in the flank contact and interference with the
matching threads.
2) Minor diameter error

It may cause interference, reduction of flank contact.
3) Effective diameter error

If the effective diameter is small the threads will be thin on the external
screw a d thick on an internal screw.
4) Pitch error

If error in pitch, the total length of thread engaged will be either too high or
too small.
The various pitch errors may classified into
1. Progressive error

The pitch of the thread is uniform but is lo ger or shorter its nominal value
and this is called progressive.

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Causes of progressive error:
1. Incorrect linear and angular velocity ratio.
2. In correct gear train and lead screw.
3. Saddle fault.
4. Variation in length due to hardening.

2. Periodic error
These are repeats itself at regular intervals along the thread
Causes of periodic error:
1. Uniform tool work velocity ratio.
2. Teeth error in gears.
3. Lead screw error.
4. Eccentric mounting of the gears.

3. Drunken error
Drunken errors are repeated once per turn of the thread in a drunken

thread. In Drunken thread the pitch measured parallel to the thread axis. If the
thread is not cut to the true helix the drunken thread error will form

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4. Irregular error
It is vary irregular manner along the length of the thread.
Irregular error causes:

1. Machine fault.
2. Non-uniformity in the material.
3. Cutting action is not correct.
4. Machining disturbances.

5) Flank angles error
6) Crest and root error

Effect of pitch errors
1. Increase the effective diameter of the bolt and decreases the diameter of nut.
2. The functional diameter of the nut will be less.
3. Reduce the clearance.
4. Increase the interference between mating threads.

Q. Explain Measurement of various elements of Thread?
To find out the accuracy of a screw thread it will be necessary to measure the
following:

1. Major diameter.
2. Minor diameter.
3. Effective or Pitch diameter.
4. Pitch
5. Thread angle and form

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1. Measurement of major diameter:
The instruments which are used to find the major diameter are by
Ordinary micrometer
Bench micrometer.
Ordinary micrometer
The ordinary micrometer is quite suitable for measuring the external major

diameter. It is first adjusted for appropriate cylindrical size (S) having the same
diameter (approximately).This process is known as ‘gauge setting’. After taking
this reading ‘R the micrometer is set on the major diameter of the thread, and the
new reading is ‘R2.

Bench micrometer
For getting the greater accuracy the bench micrometer is used for

measuring the major diameter. In this process the variation in measuring
Pressure, pitch errors are being neglected. The fiducial indicator is used to
ensure all the measurements are made at same pressure. The instrument has a
micrometer head with a vernier scale to read the accuracy of 0.002mm
Calibrated setting cylinder having the same diameter as the major diameter of
the thread to be measured is used as setting standard. After setting the standard,
the setting cylinder is held between the anvils and the reading is taken. Then the
cylinder is replaced by the threaded work piece and the new reading is taken.

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Measurement of the major diameter of an Internal thread
The Inter thread major diameter is usually measured by thread comparator
fitted with ball-ended styli. First the Instrument is set for a cylindrical reference
having the same diameter of major diameter of internal thread and the reading is
taken. Then the floating head is retracted to engage the tips of the styli at the root
of spring under pressure. For that new reading is taken,

2. Measurement of Minor diameter
The minor diameter is measured by a comparative method by using

floating carriage diameter ensuring machine and small V pieces which make
contact with the root of the thread. These V pieces are made in several sizes,
having suitable radii at the edges. V pieces are made of hardened steel. The
floating carriage diameter-measuring machine is a bench micrometer mounted
on a carriage.

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Measurement process
The threaded work piece is mounted between the centers of the instrument and the V
pieces are placed on each side of the work piece a d then the reading is noted. After
taking this reading the work piece is then replaced by a standard reference cylindrical
setting gauge.

Measurement of Minor diameter of internal threads
The Minor diameter of internal threads are measured by
1. Using taper parallels
2. Using Rollers
Using taper parallels
For diameters less than 200mm the use of Taper parallels and micrometer is very
common. The taper parallels are pairs of edges having reduced and parallel
outer edges. The diameter across their outer edges can be changed by sliding them
over each other.

Using rollers
For more than 20mm diameter this method is used. Precision rollers are inserted inside
the thread and proper slip gauge is inserted between the rollers. The minor diameter is
then the length of slip gauges plus twice the diameter of roller.

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3. Measurement of effective diameter
Effective diameter measurement is carried out by following methods.
1. One wire,
2. Two wires, or
3. Three wires method.
4. Micrometer method.
a) One wire method
The only one wire is used in t is method. The wire is placed between two t reads at
one side and on the other side the anvil of the measuring micrometer contacts the
crests. First the micrometer reading dl is noted on a standard gauge whose dimension
is approximately same to be obtain d by this method.

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b) Two wire method
Two-wire method of measuring the effective diameter of a screw thread is given below.
In this method wires of suitable size are placed between the standard and the
micrometer anvils. First the micrometer reading is taken and let it be R. Then the
standard is replaced by the screw thread to be measured and the new reading is
taken.

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c) Three-Wire method
The three-wire method is the accurate method. In this method three wires of equal and
precise diameter are placed in the groves at opposite sides of t e screw. In this one wire
on one side and two on t e other sides are used. The wires either may hold in hand or
hung from a stand. This method ensures the alignment of micrometer anvil faces
parallel to the thread axis.

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BEST WIRE SIZE-DEVIATION
Best wire diameter is that may contact with the flanks of the thread on the pitch line. The
figure shows the wire makes contact with the flanks of the thread on the pitch.
Hence best wire diameter,

4. Pitch measurement
The most commonly used methods for me suring the pitch are
1. Pitch measuring machine
2. Tool maker’s microscope
3. Screw pitch gauge

Pitch measuring machine
The principle of the method of measurement is to move the stylus along the screen
parallel to the axis from one space to the next. The pitch- measuring machine provides
a relatively simple and accurate method of measuring the pitch.
Initially the micrometer reading is near the zero on the scale, the indicator is moved
along to bring the stylus, next the indicator adjusted radially until the stylus engages
between the thread flank and the pointer ‘K’ is opposite in the line L. To bring T in
opposite in its index mark a small movement is necessary in the micrometer and then

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the reading is taken next. The stylus is moved along into the next space by rotation of
the micrometer and the second reading is taken. The difference between these two-
measured readings is known as the pitch of the thread.

Tool maker’s microscope
Worktable is placed on the base of the base of the instrument. The optical head is
mounted on a vertical column it can be moved up and down.
Work piece is mounted on a glass plate. A light source provides horizontal beam of light
which is reflected from a mirror by 900 upwards towards the table. Image of the outline
contour of the work piece passes through the objective of the optical head. The image is
projected by a system of three prisms to a ground glass screen.
The measurements are made by means of cross lines engraved on the ground glass
screen. The screen can be rotated through 360°. Dif ferent types of graduated screens
and y pi c s are used.

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Applications
1. Linear measurements.
2. Measurement of pitch of the screw.
3. Measurement of pitch diameter.
4. Measurement of thread angle.
5. Comparing thread forms.
6. Centre to center distance measurement.
7. Thread form and flank angle measurement
Screw pitch gauge

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Q. Enlist types of Screw Threads.
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Q. Explain profile projector with fig.

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Engineering Metrology (22342)
Gear Measurement

Q. Write short note on Gear Terminology.

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Q. What are the errors in Gears?

Q. Explain Analytical and functional inspection Gear.
Inspection of gear is mainly of two types: (i) Analytical, and (ii) Functional.
Analytical Inspection:
- It is necessary to differentiate between the measurements of the individual parameters
of gear, i.e. their individual errors.
- To measure all the individual gear parameters and their errors, it is necessary to know
the errors of gear cutting machine, so that, the gear production can be controlled and
the machine eon be reset.
- The analytical inspection of gear involves in determination of following teeth elements,
in which, the errors are caused due to manufacturing errors.
(a) Tooth profile, (b) Spacing, (c) Pitch, (a) Run out (e) Thickness or tooth. (f) Lead, (g)
Backlash.
- But, this inspection method is not preferred in Industries, because it Is very slow,
Complex and tedious method.
- Also, the discrete error values of pitch, tooth profile etc. cannot give overall
assessment regarding the accuracy of gear. It is not easy to assess accurately, how
these elements, values combine in practice to give a prescribed performance under
operational conditions,
Functional Inspection:
- The overall accuracy of gear may be determined by checking the combined effect of
errors in the individual parameters. Therefore, it is preferred and widely used In
industries,
- It consists of carrying out the running test of a manufactured gear with master gear, to

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