What is GD&T? | GD&T symbols Explained with Example | for Beginners Understanding | Subscribe Us

Summary

This video script offers an in-depth exploration of GD&T (Geometric Dimensioning and Tolerancing), a critical system in engineering for defining product geometry. It explains the symbolic language used in engineering drawings to specify allowable deviations in size, shape, and location of features on a part. The script covers various tolerance types, datum systems, and geometric characteristics like straightness, flatness, and cylindricity. It also delves into concepts like MMC, LMC, and fit allowances, essential for ensuring parts function correctly together. The video aims to educate on the importance of precise measurements and specifications in manufacturing.

Takeaways

• 📏 GD&T stands for Geometric Dimensioning and Tolerancing, a system used to define the size, shape, and location of features on a part.
• 🔍 Dimensioning is the specification of the size of features like length, angle, or location, while tolerancing defines the allowable variation in these dimensions.
• 📉 There are three types of tolerances: limit, unilateral, and bilateral, each allowing different permissible variations in feature dimensions.
• 📐 A datum is a theoretical exact feature used as a reference for measurements, with primary, secondary, and tertiary datums controlling different degrees of freedom.
• 📏 Datum features are part features that contact a datum and are denoted with capital letters in boxes, connected to the datum with a triangle.
• 🔳 The 14 standard characteristics in GD&T are categorized into form, profile, location, orientation, and run-out types, each with specific control types.
• 🔍 Characteristics like straightness, flatness, and circularity are form type controls that ensure features match their perfect form within a tolerance zone.
• 📏 Profile of a line and surface characteristics are profile type controls that ensure the profile of a feature matches a specified curve or shape.
• 🔄 Orientation type characteristics like parallelism and perpendicularity ensure the correct angular relationship between features and datums.
• 🔄 Run-out type characteristics like circular run-out and total run-out control the form of a surface or the orientation of features in relation to a datum.
• 🔢 MMC (Maximum Material Condition) and LMC (Least Material Condition) are conditions that define the maximum and minimum material states within dimensional tolerances.

Q & A

What does GD&T stand for and what is its purpose?

GD&T stands for Geometric Dimensioning and Tolerancing. It is a system of symbols, rules, and definitions used to define the size, shape, form, orientation, and location of features on a part. It is used to define the allowable deviation of feature geometry to ensure an object functions correctly.

What are the three types of tolerances mentioned in the script?

The three types of tolerances mentioned are limit dimension, unilateral, and bilateral. Limit dimensions show the largest and smallest values allowed, unilateral tolerance allows variation in one direction, and bilateral tolerance allows variation in both positive and negative directions.

What is a datum in the context of GD&T?

A datum in GD&T is a theoretical exact feature from which dimensional measurement is done. It is generally chosen as an edge or feature that has the greatest influence in a specific measurement.

Can you explain the difference between primary, secondary, and tertiary datums?

Primary datum controls three degrees of freedom, restricting rotation around x and y axes and movement along the z axis. Secondary datum controls two additional degrees of freedom, restricting rotation around the z axis and movement along the y axis. Tertiary datum controls one additional degree of freedom, restricting movement along the x axis.

What is straightness in GD&T and how is it measured?

Straightness is a form type characteristic that controls the straightness of a feature in relation to its own perfect form. It is measured using a dial indicator by moving its plunger on the surface of the feature in a straight line, and the deflection of the dial gives the actual straightness value.

How is flatness different from straightness in GD&T?

Flatness, like straightness, is a form type characteristic, but it controls the flatness of a surface in relation to its own perfect form. It is measured using a straight edge and a dial indicator, with the deflection of the dial indicating the actual flatness value.

What is the purpose of the MMC condition in GD&T?

MMC, or Maximum Material Condition, describes the condition of a feature where the maximum amount of material exists within its dimensional tolerance. It is used to ensure proper fit and function of mating parts.

What does LMC stand for and what does it represent?

LMC stands for Least Material Condition. It represents the condition of a feature where the least amount of material exists within its dimensional tolerance, which is useful for ensuring maximum clearance or minimum interference.

What is the significance of bonus tolerance in GD&T?

Bonus tolerance is an additional tolerance for a geometric control applied to a feature of size with MMC or LMC. It allows for more flexibility in the manufacturing process while still meeting the specified tolerances.

How is the virtual condition different from the MMC and LMC conditions?

Virtual condition is a theoretical extreme boundary condition of a feature generated by the collective effects of MMC size limit, LMC, and any applicable geometric tolerances. It represents the boundary within which any portion of a feature may possibly fall.

What is the purpose of the projected tolerance zone in GD&T?

The projected tolerance zone is a modifier used for threaded or blind holes to ensure proper fitment of mating parts. It extends the tolerance zone beyond the surface of the part to the functional length of the mating part, controlling the perpendicularity of the hole to the extent of the projection.

Outlines

00:00

🔍 Introduction to GD&T

The paragraph introduces the concept of Geometric Dimensioning and Tolerancing (GD&T), a system used in engineering to define the allowable variations in size, shape, and position of features on a part. It explains that GD&T uses a symbolic language on drawings and models to ensure parts function correctly within specified tolerances. The paragraph distinguishes between different types of tolerances: limit dimension, unilateral, and bilateral. It also introduces the concept of datums, which are theoretical exact features used as references for measurement, and explains the role of primary, secondary, and tertiary datums in controlling the degrees of freedom of a part.

05:02

📏 GD&T Control Types and Characteristics

This section delves into the various control types and characteristics in GD&T, such as form, profile, orientation, location, and run-out. It explains specific characteristics like straightness, flatness, circularity, cylindricity, and how they relate to the form of a feature. The paragraph also describes how these characteristics are measured using tools like dial gauges and CMM (Coordinate Measuring Machine), emphasizing the importance of ensuring that the measured values fall within the designated tolerance zones.

10:02

🔩 Advanced GD&T Concepts

The paragraph discusses advanced GD&T concepts like profile of a line and surface, parallelism, perpendicularity, angularity, concentricity, symmetry, position, circular run-out, and total run-out. It explains how each characteristic is measured and the significance of maintaining tolerances for these measurements. The paragraph also introduces the concepts of Maximum Material Condition (MMC), Least Material Condition (LMC), and bonus tolerance, which are crucial for understanding the extreme material limits of a feature.

15:05

🔧 GD&T Tolerances and Fit

This section explores the practical applications of GD&T in ensuring proper fits between mating parts. It explains terms like allowance, clearance, and interference fit, and how they relate to the maximum and minimum material limits of parts. The paragraph also discusses the concept of projected tolerance, which is used for threaded or blind holes to ensure proper fitment with mating parts. Additionally, it touches on the use of the tangent plane and Regardless of Feature Size (RFS) modifier in GD&T.

20:06

🛠 GD&T Symbols and Surface Finish

The final paragraph covers various GD&T symbols and their meanings, such as basic dimensions, reference dimensions, all-around symbols, and countersinks. It also explains the concept of surface finish, which includes surface roughness, waviness, and form. The paragraph discusses how surface finish is measured and the different components that contribute to it, such as roughness, waviness, and form. It concludes with a brief overview of how surface roughness is symbolically represented and measured in micrometers.

Keywords

💡GD&T

GD&T stands for Geometric Dimensioning and Tolerancing, which is a system of symbols, rules, and definitions used to define the size, shape, form, orientation, and location of features on a part. It is crucial for ensuring that parts meet the necessary specifications for fit, function, and assembly. In the video, GD&T is the central theme, as it is the language used to communicate design intent and manufacturing tolerances.

💡Datum

A datum in GD&T is a theoretical, exact feature from which dimensional measurement is made. It is typically chosen as an edge or feature that has the greatest influence in a specific measurement. The video explains that datum features are denoted with capital letters in boxes and are tied to the datum feature with a black color field triangle. Datums are essential for establishing a reference frame for measuring other features on a part.

💡Tolerance

Tolerance in the context of the video refers to the total permissible variation in the size of a dimension. It is what allows an object to function correctly by accounting for manufacturing variations. The script mentions different types of tolerances, such as unilateral and bilateral, which define the allowable deviation from a nominal dimension in one or both directions, respectively.

💡Form

Form in GD&T controls the shape of a feature in relation to its own perfect form. The video provides examples such as straightness, flatness, and circularity, which are all form characteristics. For instance, straightness controls the straightness of a feature, ensuring it is within a specified tolerance zone, which is measured using a dial indicator and is crucial for the feature's functionality.

💡Profile

Profile in GD&T controls the shape of a line, curve, or surface at any point. The video distinguishes between profile of a line and profile of a surface, explaining that these characteristics ensure that the actual profile of a feature matches a specified nominal profile within a tolerance zone. This is critical for maintaining the intended function and fit of parts.

💡Orientation

Orientation in GD&T controls the angular relationship of a feature to a datum reference frame. The video script mentions characteristics like parallelism and perpendicularity, which ensure that features are oriented correctly relative to datums. This is essential for assembly and for ensuring that parts align correctly in their intended positions.

💡Location

Location in GD&T controls the exact position of a feature in relation to a datum reference frame. The video explains concepts like concentricity and symmetry, which are used to ensure that features are located correctly. For example, concentricity ensures that the center of a cylindrical feature aligns with a datum axis, which is critical for rotational components.

💡Run-out

Run-out in GD&T is a characteristic that controls the circularity and coaxiality of each circular segment of a surface independently about the datum axis. The video provides an example of circular run-out, which ensures that a feature's circular segments are within a specified tolerance zone when measured about a datum axis. This is important for maintaining the integrity of rotating parts.

💡MMC and LMC

MMC (Maximum Material Condition) and LMC (Least Material Condition) are terms used in GD&T to describe the conditions of a feature where the maximum or minimum amount of material exists within its dimensional tolerance. The video explains that these conditions are used to ensure proper fit and function of parts, such as in the case of a pin fitting into a hole, where the MMC and LMC conditions define the tightest and loosest possible fits.

💡Surface Finish

Surface finish refers to the allowable deviation from a perfectly flat surface, which is a result of the manufacturing process. The video script distinguishes between roughness, waviness, and form as components of surface finish. Understanding surface finish is important for ensuring that parts not only meet dimensional requirements but also have the appropriate texture for their intended function, such as reducing wear or improving sealing.

Highlights

GD&T stands for Geometric Dimensioning and Tolerancing, a system used to define the size, shape, and location of features on a part.

Dimension is a geometric characteristic whose size is specified, such as length, angle, or center distance.

Tolerance is the total permissible variation in size, allowing an object to function correctly.

There are three types of tolerances: limit, unilateral, and bilateral.

Datum is a theoretical exact feature from which dimensional measurement is done.

Primary, secondary, and tertiary datum features control different degrees of freedom of a part.

Geometric characteristics are categorized into form, profile, location, orientation, and run-out types.

Straightness controls the straightness of a feature in relation to its own perfect form.

Flatness controls the flatness of a surface in relation to its own perfect form.

Circularity controls the form of a surface in relation to its own perfect form by independent cross-sections.

Cylindricity controls the form of a variable surface like circularity but applies to the entire surface.

Profile of a line controls the profile at any point of a feature, usually of the current shape.

Profile of a surface controls the profile by describing a three-dimensional tolerance zone around a surface.

Parallelism controls the orientation of a feature nominally parallel to the primary datum of its datum reference frame.

Perpendicularity controls the orientation of a feature normally perpendicular to the primary datum.

Angularity controls the orientation of a feature at a specific angle in relation to its primary datum.

Concentricity controls the central axis of a feature with respect to a datum axis.

Symmetry controls the uniformity of two features on a part across a datum plane.

Position controls the variation of a feature from a specified exit to location.

Circular run-out controls circularity and co-axiality of each circular segment of a surface independently.

Total run-out controls circularity, straightness, co-axiality, and taper of a cylindrical surface about a coaxial datum.

Maximum Material Condition (MMC) and Least Material Condition (LMC) describe the conditions of a feature where the most or least amount of material exists.

Bonus tolerance is an additional tolerance for a geometric control attached to a feature of size with MMC and LMC.

Virtual condition is the theoretical extreme boundary condition of a feature generated by the collective effects of MMC size limits and geometric tolerances.

Allowance is the difference between the maximum material limits of mating parts, indicating the minimum clearance or maximum interference.

Projected tolerance zone is a modifier used for threaded or blind holes to ensure proper fitment of mating parts.

Tangent plane is a simulated plane that contacts the high points of a surface for orientation of the datum.

Regardless of Feature Size (RFS) is a modifier used when the size feature does not affect the specified tolerance.

Basic dimensions are used to describe the exact size, profile, orientation, or location of a feature without involving any tolerance limits.

Surface finish refers to the allowable deviation from a perfectly flat surface made by some manufacturing process.

Transcripts

[Music]

you

let us learn about GD&T basics

what is meant by GD&T GD&T stands for

geometric dimensioning and tolerancing

it is a system of symbols rules and

definitions use it to define the size

shape form orientation and location of

pictures on a part it is a symbolic

language used on engineering drawings

and models to define the allowable

deviation of feature geometry dimension

is a geometric characteristic the size

of which is specified such as length

angle location or center distance etc

tolerance on a dimension is the total

permissible variation in its size which

is equal to the difference between the

limits of size to allow an object to

function correctly now there are three

types of tolerances limit dimension type

unilateral type bilateral time limit

dimensions are two dimensional values

stacked on top of each other these show

the largest and smallest values allowed

anything in between these values is

acceptable

Yury lateral type exists when the target

dimension is given along with the

tolerance that allows variation to occur

in only one direction a bilateral

tolerance exists if variation from a

target dimension is shown occurring in

both the directions positive and

negative if no tolerances are specified

then general tolerances are applied at

the dimension level unless otherwise

specified now let us learn some basic

concepts data a datum is a theoretical

exact feature from which dimensional

measurement is done which is generally

chosen as an edge or feature which has

the greatest influence in a specific

measurement a datum feature is a part

feature that contacts a data it is

denoted with the capital alphabetic

letters these letters are in boxes and

tied to the datum feature with the black

color field triangle as shown below

there are three types of datum and all

are perpendicular to each other primary

datum secondary datum and tertiary data

its presence shown in the below example

of feature of control plane

primary data the primary datum feature

has at least three points of contact

with its datum plane it controls three

degrees of freedom of the feature means

three degrees of freedom are restricted

that is rotation around x axis rotation

around y axis movement along the z axis

secondary data the secondary datum

feature has at least two points of

contact with its datum plane it controls

two additional degrees of freedom of the

feature means two additional degrees of

freedom are respected rotation around z

axis moment along the y axis tertiary

datum the tertiary datum feature has at

least one point of contact with this

datum plane it controls one additional

degree of freedom of the picture means

one additional degree of freedom are

restricted that is movement along the x

axis these are the putting standard

characteristics and their symbols of

GD&T these fourteen characteristics fall

into five different control types they

are form profile location orientation as

a note let us learn about straightness

characteristic it's control category

form type and it controls straightness

of a feature in relation to its own

perfect form in the given example

tolerance zone of point one of

cylindrical future will be measured

using Dale gates by moving its plunger

on the surface of the pitcher in a

straight line and deflection of the dial

gives actual straightness value that

value should be within the tolerance

zone

let us discuss about flatness

characteristic its control category form

type and it controls the flatness of the

surface in relation to its own perfect

form in the given example total zone of

point 1 of the rectangular feature will

be measured using tail gauge by moving

its leaver plunger on the surface of the

pitcher which is located on the two

identical B blocks as shown in the

picture and deflection of the dial gives

actual flatness value that value should

be within the tourist zone let us learn

about circularity characteristic its

control category form type and contours

the form of varivolt surface in relation

to its own perfect form by independent

cross-sections in a given example

tolerance on 0.1 of the cylindrical

feature will be measured using dial

gauge by moving its plunger on the

surface of the pier in a circular

direction which is located on the two

identical B blocks as shown in the

picture and deflection of the dial gives

actual circularity value that value

should be within the tolerance zone let

us go through cylindricity

characteristic its control category from

type and controls in the form of

variable surface like circularity but

apply simultaneously to entire surface

in the given example tolerance zone of

0.005 of the cylindrical feature will be

measured using dial gauge by moving its

plunger on the entire surface of the

future in a circular direction which is

located on the two identical B blocks as

shown in the picture and the deflection

of seed oil gives actual cylindricity

value that value should be within the

tolerance zone selection of points on

the cylindrical surface based on

tightness of the tolerance

let us go through profile of the line

characteristic its control category

profile type and controls the profile of

the line at any point of the future

usually of the current shape in the

given example torrent zone 0.25 of the

curvature will be measured using del

gauge by moving its plunger on the

surface of the creature by keeping

master profile as reference for the

moment as sure in the picture and

deflection of the del gives actual

profile of the line value that value

should be within the tolerance zone

let us study profile of a surface

characteristic its control category

profile type and controls the profile of

the surface by describing a

three-dimensional tolerance zone around

a surface usually it is an advanced

curve or shape in the given example

total zone 0.25 of the carbon future

will be measured using CMM by moving its

probe on the surface of the future by

taking necessary reference points as

shown in the picture and automatically

calculates actual profile of the surface

value that value should be within the

tolerance zone here CMM is a coordinate

measuring machine used for measuring the

physical geometrical characteristics of

an object its probe will measure the

different characteristics by taking

necessary preference points rows may be

mechanical optical laser or white light

etc this machine takes readings in 6

degrees of freedom and displays those on

the computer monitor

let us study about parallelism

characteristic its control category

orientation type and controls

orientation of a feature it is nominally

parallel to the primary datum of its

datum reference frame in the given

example the order in zone of point one

of the rectangular feature will be

measured with respect to datum a using

del gauge by moving its liver plunger on

the surface of the creature which is

placed on the another respective surface

as shown in the picture and deflection

of the del gives actual parallelism

value with respect to datum a that value

should be within the tolerance zone let

us learn about perpendicularity

characteristic its control category

orientation type and controls

orientation of a picture which is

normally perpendicular to primary datum

of its datum reference frame in the

given example tolerance zone of point

one of the pitcher will be measured with

respect to datum a which is clamped on

the you clamp B block using L cage by

moving its plunger in perpendicular

direction of the surface of the picture

as shown in the picture and deflection

of the Dell gives actual

perpendicularity value with respect to

datum a that value should be within the

tolerance zone

[Music]

let us discuss about angularity

characteristic its control category

orientation type and controls

orientation of the creature at a

specific angle in relation to its

primary datum of its datum reference

frame in the given example tolerance

zone of point 2 pi of the feature will

be measured with respect to datum a by

using dial gauge by moving its plunger

in a straight line which is located on

this sign bar and click page setup as

shown in the picture and deflection of

the del gives actual angular ative value

with respect to datum a that value

should be within the tolerance zone let

us study about concentricity

characteristic its control category

location type and controls the central

axis of reference in future P a datum

axis it is also called as Co actually in

the given example tolerance zone of

point one of the cylindrical feature

will be measured with respect to datum a

using dial gauge by moving its plunger

on the surface of the creature in a

circular direction by rotating reference

or respective portion of the pitcher

which is located on the B block as shown

in the picture and deflection of the

dial gives actual concentricity value

with respect to a that value should be

within the tolerance zone let us go

through symmetrical check its control

category location type and controls

uniformity of two features on a part

across a datum plane in the given

example Jordan zone of 0.05 of the

pitcher will be measured with respect to

datum a using Bell gauge by moving it

sliver plunger on the surface of the

pitcher BC first place it on one surface

then another as shown in the picture a

deflection of the dial gives actual

Symetra value with respect to a that

value should be within the tolerance

zone

[Music]

let us learn the board position

characteristic its control category

location type and controls variation of

the feature from a specified exit to

location the given example tolerance

zone of 0.1 at maximum it'll condition

of the feature will be measured with

respect to datums a b and c using c mm

probe by taking reference points of the

feature as shown in the picture and

automatically calculates actual position

value with respect to datum a b and c

that value should be within the

tolerance zone let us study circular

run-out characteristic it's control

category run-out type and control

circularity and co actuality of each

circular segment of the surface

independently about the coaxial data in

the given example tolerance zone of

point one of the picture will be

measured using dial gauge by moving its

plunger on any ponta feature with

respect to datum a which will be rotated

by placing it on the b block as shown in

the picture and deflection of the dial

qs and actual circular are not value

that value should be within the

tolerance zone

let us learn about total run-out

characteristic it's control category

run-out type and control circularity

straightness Co actuality and taper of

the cylindrical surface about a coaxial

data the given example torrid zone of

0.05 of the future will be measured

using bail gauge by moving its plunger

on the entire surface of the pitcher

with respect to datum a which will be

rotated by placing it on the B block as

shown in the picture and deflection of

the Dell gives an actual total run Note

value that value should be within the

tolerance zone maximum material

condition MMC MMC describes the

condition of a feature where maximum

amount of material exists within its

dimensional tolerance this condition

exists at minimum clearance or maximum

interference example largest pin

diameter smallest hole size in the

picture you can see that shaft with the

diameter 10 mm width Dalton's pass or

minus 0.1 mm C is equal to ten point one

and for the hole diameter 10 mm plus or

minus point one tolerance mm C is equal

to nine point nine mm least material

condition LM c LM C describes the

condition of a feature where the least

amount of material exists within its

dimensional tolerance this condition

exists at maximum clearance or minimum

interference examples smallest pin

diameter largest hole diameter in the

following example we can see that shaft

with the diameter 10 mm plus or minus

point 1 tolerance LM C is equal to nine

point nine mm and for the hole diameter

10 mm plus or minus point one tolerance

LM C is equal to ten point one mm

bonus codons bonus tolerance is an

additional tolerance for a geometric

control it is the additional tolerance

available for a geometric control attach

it to a feature of size with MMC maximum

mental condition and LMC least material

condition modifier so bonus tolerance is

equal to shaft size MMC

- shaft says at LMC example chopped-up

diameter 25 plus or minus 3 here at MMC

shaft size is equal to diameter 28 so

bonus tolerance is 0 for shaft size

diameter 27 bonus tolerance is 1/4 shop

size diameter 26 bonus tolerance is 2

and so on so total bonus tolerance is

equal to MMC - LM C that is diameter 28

- diameter 22 that is equal to 6

let us discuss about virtual condition

virtual condition is the theoretical

extreme boundary condition of a feature

of size generated by the collective

effects of MMC size limit of the teacher

and any applicable geometric tolerances

in the below figure of hole of diameter

10 plus or minus 0.2 the MMC is equal to

9 point 8 the worst case would be the

smallest hole that is also out of

position that is 9 point 8 - point 3

that is equal to nine point five this

case is called virtual condition

condition this is similar to virtual

condition but considers least material

condition of the feature that is least

metal condition plus stated geometrical

tolerance plus bonus that is equal to

ten point two plus point three plus

point four that is equal to ten point

nine this represents barrier where any

portion of the holes age may possibly

fall allowance allowance is defined as

the difference between the maximum

material limits of the mating parts xi

is the minimum clearance or maximum

interference between mating parts that

is equal to MMC hole - mm C sharp

clearance clearance is the loosest width

or maximum intended difference between

hitting parts that is equal to l MC hole

- l MC shop let us discuss about

different types of its clearance width

the tolerance of the parts is such that

the largest shaft is smaller than the

smallest hole in this one part fits

easily into another with the resulting

clearance gap in this picture we can see

the powders on the shop is equal to zero

point zero zero two and tolerance on the

hole is equal to zero point zero zero

two minimum clearance 0.66 zero minus

point 6 5 5 that is equal to zero point

zero zero five and maximum clearance

zero point six six two minus zero point

six by 3 that is equal to zero point

zero zero nine interference fit in this

type one part must be forcefully fitted

into another that is maximum clearance

is always negative in this example we

can see that orders on shop is equal to

zero point zero zero one and tolerance

on the whole is equal to zero point zero

zero one minimum clearance is equal to

0.51 zero minus point five one three

that is equal to minus zero point zero

zero three inch that is the tightest fit

0.003 in interference maximum clearance

that is equal to point five one one

minus point 5 1 2 that is equal to minus

0.001 in the loosest bit 0.001 in

interference

transition fit the tolerance of the

parts is such that the allowance is

negative and the maximum clearance is

positive a transition pit exists when

the maximum clearance is positive and

minimum clearance is negative in this

example tolerance on the shaft is 0.005

and tolerance on the hole is 0.005

minimum clearance that is equal to 0.51

zero by the zero point five one seven

that is equal to minus zero point zero

zero seven inch it is stupid is zero

point zero zero seven in interference

maximum clearance that is equal to zero

point five one five minus zero point 5 1

2 that is equal to zero point zero zero

three in the loser stupid is zero point

zero zero three in clearance let us

learn about project a tolerance zone the

projected tolerance is a modifier used

for threaded or brisket holes in order

to ensure the proper fitment of the

mating parts by means of studs pins

screws bolts etc the projected tolerance

zone extends above the surface of the

part to the functional length of the pin

stud or screw related to its assembly

with the mating part it controls the

perpendicularity of the hole to the

extent of the projection from the hole

as it relates to the mating part

clearance in the following example let

us take plate with the hole in which a

stud will be inserted with the

positional tolerance with respect to

datum a here you can see that positional

totals of die appoint to apply to the

datum a of lower plate that can be

buried at the worst case within the

mentioned zone as shown in the figure

now it is clear that if the stud axis

follows the worst case then the start

may interfere with the mating plate for

avoiding that interference

specifying the projected tolerance zone

in the drawing is required so here you

can see that projected tolerance of Y

has been mentioned in the drawing after

the value of positional tolerance the

meaning of the projected tolerance of

Phi is in positional tolerance zone of

point 2 will extend by PI units beyond

the surface of the bottom plate

and by doing so interference problem

will avoid

[Music]

tangent plane tangent plane is a

simulated plat plane that contacts the

high points of the surface for

orientation of the data this modifier

indicates that only the tangent plane of

the dormant surface needs to be within

this tolerance zone in the example you

can see the tangent plane selected

within the zone of point three with

respect to datum B for calculation

purposes of parallelism regardless of

feature size our FS RFS is a deport

modifier if no modifier symbol shown in

the picture control which is used when

the size feature does not affect the

specified tolerance it is used and

implied when the geometrical tolerance

is to remain the same no matter what

size hole or shaft is produced within

its tolerance limit in this given

example bonus tolerance point four not

applicable therefore the position of the

shaft must lie in between tolerance zone

of point three regardless of feature

size three state variations restate

variation is a term used to describe

deformation of the part after removal of

forces applied during manufacture

basic dimension it is used to describe

the exact size profile orientation or

location of the future it does not

involve any tolerance limits reference

dimension it is a dimension usually

without tolerance user for reference

purposes only it does not control

production or inspection operations

all-around symbol this indicates the

tolerance applies to surfaces all around

the part dimension origin a circle used

in place of one of the arrowhead when a

dimension line indicates the origin for

measurement conical paper it is used to

indicate paper for conical tapers

this symbol is always shown with

vertical link to the left

slope it is used to indicate slope or

plat tapers datum target it is a

specified point line or area on the part

that is used to establish the datum

reference plane for manufacturing and

inspection operations comfortable this

symbol is used to indicate a counter

bore or a spot phase the symbol precedes

the dimension of the counterbore with no

space countersink this symbol is used to

indicate a countersink the symbol

precedes the dimension of the

countersink with the no space square

this symbol is used to indicate that a

single dimension applies to square shape

this symbol precedes the dimension with

the no space between dipped or deep it

is used to indicate that dimension

applies to the depth of the feature is

simple precedes the depth value with the

no space in between number of places the

X symbol is used along with the value to

indicate the number of times a dimension

or feature is repeated on the drawing

statistical tolerance it is the

assigning of tolerances to the related

components of an assembly on the basis

of statistics by applying statistical

tolerance tolerances of individual

components may be increased or

clearances between mating pearls may be

reduced between this is used to indicate

that a profile tolerance applies to

several contagious features or let

resume designate where the profile

tolerance begins and ends

these letters are reference in using the

between symbol target point this

indicates where datum target point is

dimensionally located on the direct view

of the surface arc length this indicates

that a dimension is an arc length

measured on orbit outline the symbol is

placed above the dimensional tetanus

feature it is used to identify a group

of two or more features of size where

there is a requirement that they may be

treated geometrically as a single

feature of size now let us discuss about

surface finish surface finish is the

allowable deviation from a perfectly

flat surface made by some manufacturing

process surface roughness is a property

of the material surface texture which is

recognized by an uneven topography as

compared to the perfectly applied

surface all machining processes will

generate some rough on the surface since

all the surfaces may not have functional

requirements so no need to have equal

finish everywhere roughness can be

measured by manual comparison against

surface roughness comparator or

profilometer

or optical method surface finish is

broken up into three components such as

roughness waviness and form here

roughness is the machine marks made on

surface by the cutting tool waviness is

the result of vibration of the tool and

form surface irregularities cause is by

one of machine bed or table etcetera

so roughness is the measure of finest

irregularities of the surface venus is

the measure of surface irregularities

with the spacing greater than that of

surface roughness layer refers to the

predominant direction of the surface

texture from this figure you can see

that for a given sample length Aria is

the average variation from mean length R

T is the distance from the highest peak

to the deepest Valley RP is the highest

peak above the mean line RV is the

deepest Valley below the beam line R

that the average RT over given length

example R that is equal to R T 1 plus RT

2 plus RT 3 divided by 3 these are the

symbolic representations of surface

roughness here in the first symbol a

obtained by any production process in

the second symbol a obtained by removal

of material by machining in the third

symbol roughness a obtained without

rimmel of any material in the fourth

symbol a 1 represents upper and a 2

represents lower limit of surface

roughness value in the tip symbol G

represents production method and in

sixth symbol B represents other than our

a value this is the general RA value in

micrometer and it's great number

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