Interchangeability basic knowlage

1. Classification of engineering design
Adaptive design
Concerned with adaption of existing design procedures.
Ex. I.C engines, machine tools etc. there is heardly
anything left for the designer to do except minor
modifications.
To begin with every designer must gothrough the adaptive
modification.

2. Development design
Starts from the existing design, but the final result
may differ quite markedly from the initial product.
 Methods of manufacture
 Selection of better materials
 Appearence etc.
The final product is much better than the original
version.

3. New Design
 This is this one which never exist before.
 This may be done by dedicated persons
who have personal qualities of sufficiently
higher order.
 Lot of research, experimental activities and
creative brain is required.

4. Machined parts
I.C engine

5. Fig. Coupling
Fig. Turbine

6. Fig. Lathe machine

7.  if a shaft is to rotate in a hole, there must be enough
clearance between the shaft and hole to allow the oil film
to be maintained for lubrication.
 If the clearance is too small, excessive force would be
required in rotation of shaft.
 If clearance is too wide, there would be vibrations and
rapid wear and ultimate failure.

8. Interchangeability
 This term is normally employed for the mass production of
identical items.
 The sizes of parts are within a close degree of accuracy.
 But even then there will be small variations.
 If the variations are within certain limits, all parts of
equivalent size will be equally fit for operating in machines
and mechanisms.

9. Limit and Fit
Generally in engineering, any component manufactured is required to fit
or match with some other component.
 The correct and prolonged functioning of the two components in match
depends upon the correct size relationships between the two, i.e., the
parts must fit with each other in a desired way
Fig. Machined parts and assembly

10. Nominal size: Size of a part specified in the drawing as a matter of
convience.
Limits of sizes: There are two extreme permissable sizes for a
dimensions of the part as shown in Fig.
The largest permissable size for a dimesnsion of the part is called
upper limit, where as smallest size of the part is known as lower
limit.
Fig.

11. Tolerance: It is the difference between the upper and lower limit of the
dimension. The tolerence can be unilateral and bilateral.
When tolerance is allowed one side of the nominal size. Then it is said to
have unilateral system of tolerence.
When the tolerence is allowed on both sides of the of the nominal size,
then it is said to have bilateral system of tolerance.

12. Basic size – It is the size of a part to which all limits of variations (i.e.
tolerances) are applied to arrive at final dimensioning of parts. The
nominal size or basic size of a part is often same.
Actual size – It is the actual measured dimension of the part.

13. Allowance – It is the difference between the basic dimensios of the
mating parts.
The allowance may be positive or nagative .
When the shaft size is less than the hole size – allowance is positive
When the shaft size is greater than the hole size – allowance is
negative

14. Tolerence Zone: It is the zone between the maximim limit and minimum
limit size as shown in Fig
Zero line: It is the straight line corresponding to the basic size. The
deviations are measured from this line.
Upper deviation: It is the difference of dimension between the maximum
possible size of the component and its nominal size.

15. Lower deviation : Similarly, it is the difference of dimension
between the minimum possible size of the component and its
nominal size.
Fundamental deviation : It defines the location of the tolerance zone
with respect to the nominal size. For that matter, either of the deviations
may be considered.

16. Fit: The degreeof tightness or looseness between two mating
parts is known as fit of the part.
Clearance Fit
In this type of fit, the shaft of largest possible diameter can
also be fitted easily even in the hole of smallest possible
diameter
Fig. Schematic view of fit system

17. Transition Fit : In this case, there will be a clearance between
the minimum dimension of the shaft and the minimum
dimension of the hole.
Fig. Schematic view of fit system
Interference Fit
In this case, no matter whatever may be the tolerance level in
shaft and the hole, there is always a overlapping of the mating
parts. This is known as interference fit. Interference fit is a form
of a tight fit.

19. Hole and Shaft Basis System
Fig. Hole basis system
HOLE BASED SYSTEM
Size of hole is kept constant, shaft size is varied to get
different fits.

20. Fig. Shaft basis system
SHAFT BASED SYSTEM
Size of shaft is kept constant, hole size is varied to get
different fits

21. Design of cans