interchangeability

IMS Engineering College, Ghaziabad - Delhi NCR

LIMITS,FITS,AND TOLERANCES AND SURFACE

ROUGHNESS

SUBMITTED TOProf. DEEPAK SHARMA

SUBMITTED TODIVYANSHU VERMAME-1 1214340058

Objective

• To inform about standardization

,interchangeability , Terms limits

,fits and tolerances ,surface

roughness and preferred number

1- Standardization2- Interchangeability

(a)definition(b) advantages

3- Limits and Fits(a) Terminology(b) Types of Fits(c) Basis of Limit system(d) Limit gauge

4- Surface roughness5- Preferred numbers

TOPICS COVERED

Standardization

The main purpose of standardization is to establish mandatory or obligatory norms for the design and production of machines so as to reduce variations in their types and grades and to achieve quality characteristics in raw materials, semi-finished and finished products.

In standardization, the concept of preferred numbers helps to reduce unnecessary variations in sizes.ISO- International Organization of Standard IS - Indian Standard

Benefits of Standardization

• Better product quality

• Mass production of components at low cost.

• Easy availability of parts for replacement and maintenance

• Less time and effort required to manufacture.

• reduction in variations in size and grades of an article.

Interchangeability

Definition-Situation where two or more items are so similar in functional and physical characteristics that they are considered equivalent in performance and durability. Each is capable of replacing the other without causing a need for alteration or adjustment to fulfill the same requirement.

Examples

Nuts and bolts Rims Tires

Advantages For Interchangeable

Manufacture• Replacement: One such part can freely replace another,

without any custom fitting (such as filling).

• Easy to Assembly: This interchangeability allows easy assembly of new devices

• Repairing: Easier repair of existing devices.

• Minimizing time and cost :Minimizing both the time and skill required of the person doing the assembly or repair.

• Rapid Manufacturing :Machine tool enables the components to be manufactured more rapidly

Limits and Fits

LIMITS:‐ These are two extreme permissible

sizes of dimension between which actual dimension is

contained .

FITS:‐It is the relationship existing between mating

parts with respect to amount of play or interference

which is present when they assembled together.

It is the degree of tightness or looseness between two

mating parts to perform definite function

Terminology for LIMITS & FITS1. Basic Size:- It is the size based on which the

dimensional deviations are given.

2. Actual Size:- It is the size of the component by actual

measurement after it is manufactured. It should lie

between the two limits of size.

3. Limits of size:- These are the maximum and minimum

permissible sizes of the part.

4. Maximum limit:- Is the maximum size permitted for the

part.

5. Minimum limit:- it is the minimum size permitted for the

part limit of size.

Tolerance- the difference between the upper limit and lower limit of a dimension is called Tolerance.

When both tolerances on one side ,system is said to be Unilateral.

when tolerances is allowed on both of nominal size, said to be Bilateral

• Deviation:- It is the algebraic difference between a

size, to its corresponding basic size. It may be positive,

negative or zero.

• Upper Deviation:- It is the algebraic difference

between maximum limit of size and its corresponding

basic size.

• Lower Deviation:- It is the algebraic difference

between minimum limit of size and its corresponding

basic size.

• Actual Deviation:- It is the algebraic difference

between actual size and its corresponding basic size

• Fit- is the relationship that exists between two mating parts, a hole and shaft with respect to their dimensional difference before assembly.

• Three types of fit .

Types of fits

• Clearance Fit : In clearance Fit shaft is always smaller than the hole

• Interference Fit: It is also called Press or force fit, In this fit shaft is always larger than the hole

Continued..

• Transition Fit: it is called sliding Fit . It occurs when the resulting fit due to the variations in size of the male and female components due to their tolerance, varies between clearance and interference fits.

• Hole basis -Hole is keep constant and the shaft diameter is varied . The actual size of the hole is within the tolerance limit

• Shaft basis -Shaft is kept constant and the hole diameter is varied .

Basis of limit system

Limit gauge• It inspection tool used to

check a workpiece against its allowed tolerances.

• A Go-No gauge refers to an

inspection tool used to

check a workpiece against

its allowed tolerances . Its

name derives from its use:

the gauge has two tests;

the check involves the

workpiece having

to pass one test (Go) and fail the other (No Go).

Surface roughness and its measurement

• Each type of cutting tool leaves its own individual pattern which therefore can be identified. This pattern is known as surface finish or surface roughness.

Continued..• Types of expressing surface roughness

1- Centre line average method (CLA method)

It is defined as the average value of the ordinates between the surface and mean line , measured on both side of it .

CLA value or Ra (in microns)=𝑦1+𝑦2+𝑦3+...𝑦𝑛

𝑛

2- Root mean square method (RMS method)

It is defined as the square root of the arithmetic mean of the squares of the ordinates.

R.M.S. value(in micron)=(𝑦12 + 𝑦22+. . 𝑦𝑛2)/𝑛

Continued…

Symbols Surface roughness (Ra) in microns

V 8 to 25

VV 1.6 to 8

VVV .025 to 1.6

VVVV Less than .025

According to the Indian Standard following symbols are used to denote the various degree of surface roughness.

Preferred numbers• In industrial design, preferred numbers (also called

preferred values) are standard guidelines for choosing exact product dimensions within a given set of constraints. Product developers must choose numerous lengths, distances, diameters, volumes, and other characteristic quantities.

the series of preferred numbers are designated as R5 ,R20 and R40 respectively.

• R5: 1.00 1.60 2.50 4.00 6.30

• Example - If our design constraints tell us that the two screws in our gadget should be placed between 32 mm and 55 mm apart, we make it 40 mm, because 4 is in the R5 series of preferred numbers.

Preferred numbers of the basis series according to ISO3

References• Google.com

• K.M. Moeed

• V. B. Bhandari

Thank you