1. LIMITS FITS AND TOLERANCES

2. NEED OF LIMITS, FITS & TOLERANCES
MASS PRODUCTION
INTER CHANGEABILITY
STANDARDISATION
NEED OF LIMITS, FITS & TOLERANCES
Human inaccuracy, errors ,lack of sophistication ,nature of job material .

3. TERNOLOGY Maximum and minimum limit size Nominal Size: It is the size
represented on the drawing.
Basic Size : It is the theoretical
size to which limits of size are
applied.
Actual Size: is the measured
size of the finished part.
Limits of size: is the extreme permissible size of mating parts.
Maximum and minimum limit size

4. Tolerance: the permissible variation in size.
Tolerance zone: B/W max. &min. limit size .
Deviation: is the diff. b/w the basic size and the given size.
Upper Deviation: is the diff. b/w the basic size and the permitted maximum size of the part.
Lower Deviation: is the diff. b/w the basic size and the minimum permitted size of the part.

5. Fundamental Deviation: is the deviation closest to the basic size.
Zero line: is the diff. b/w the permitted minimum and maximum sizes of a part.

6. Tolerances
The Tolerance is 0.001” for the Hole as well as for the Shaft

7. Allowance is diff. b/w two mating parts
Allowance & Clearance
Allowance is diff. b/w two mating parts

8. Fits Between Mating Parts
Fit : Degree of tightness or looseness b/w two mating parts.
Three types
Clearance Fit: clearance is left between the parts.
Minimum air space is 0.002”. This is the allowance and is always positive in a clearance fit

9. Interference Fit: The internal member is larger than the external member l. The smallest shaft is ” and the largest hole is ”,. This interference is the allowance, and in an interference fit it is always negative.

10. Transition Fit: may result in either a clearance or interference condition. eg the smallest shaft ” will fit in the largest hole ”, with ve allowance. But the largest shaft, ” will have to be forced into the smallest hole, ” with –ve allowance of 0.009”.

11. Push fit
Driving fit
Other.
Forced fit
Running fit

12. Hole basis system Shaft basis system
Minimum hole is taken as the basic size, an allowance is assigned, and tolerances are applied on shaft.
Maximum shaft is taken as the basic size, an allowance is assigned, and tolerances are applied on hole.
Shaft basis system

14. Specifications of Tolerances
Limit Dimensioning
The high limit is placed above the low limit.
In single-line note form, the low limit precedes the high limit separated by a dash

15. Specifications of Tolerances
Plus-or-minus Dimensioning
Unilateral Tolerance
Bilateral Tolerance

16. Tolerances representation
LEAST & MAXIMUM MATERIAL CONDITION
When a work piece contains max. or least amount of material
In max. and min. limit size of that work piece respectively.
Max. material condition :- min. hole size & max. shaft size.
Min. material condition :- max. hole size & min shaft size

17. International Tolerance Grade (IT):
They are a set of tolerances that varies according to the basic size and provides a uniform level of accuracy within the grade.

18. DIFFERENT LIMIT SYSTEMS
The Newall system
British standard system
ISO system
ISI system

19. Usage of standards for deciding tolerance
Helps in improvement of communication
Standard tables are common
Standards lead to efficient production
Position tolerance
selection
Different opportunities for its selection