1. Mechanical Drawing (MDP 115)
FirstYear,
Mechanical Engineering Dept.,
Faculty of Engineering,
Fayoum University
Dr. Ahmed Salah Abou Taleb

2. FITS and TOLERANCES

3. Control Measurements of
Finished Parts

4. Indicating the Desired Dimension

5. Indication of the Real Dimension of Parts
Due to the inevitable inaccuracy of manufacturing methods, a part
cannot be made precisely to a given dimension.

6. Indication of the Real Dimension of Parts

7. Indication of the Real Dimension of Parts

8. Selection of Waste Parts

9. Selection of Waste Parts
Waste results when the manufacturing process cannot maintain size within prescribed limits.

10. Selection of Acceptable Parts

11. Selection of Acceptable Parts
There is no such thing as an "exact size".

12. Important Terms – Single Part
Nominal Size – general size, usually expressed in mms
Actual Size – measured size of the finished part
Limits – maximum and minimum sizes shown by tolerances (larger value is the upper limit and the smaller value is the lower limit)
Tolerance – total allowable variance in dimensions (upper limit – lower limit) – object dimension could be as big as the upper limit or as small as the lower limit or anywhere in between.

13. Tolerance How to decide tolerance?
Functional requirements of mating parts
Cost of production
Available manufacturing process
Choose as coarse tolerance as possible without compromising functional requirements
Proper balance between cost and quality of parts

14. Characteristics of Tolerances

15. Characteristics of Tolerances
Connection btw the characteristics:
US = N + UD
LS = N – LD
T = US – LS =

16. The Possible Positions of the Tolerance Zone

17. The ISO System of Limits and Fits (referred to as the ISO system) is covered in national standards throughout the world, as shown by the following list:
Global ISO 286
USA ANSI B4.2
Japan JIS B0401
Germany DIN 7160//61
France NF E
UK BSI 4500
Italy UNI 6388
Australia AS 1654

18. The tolerance zone is above the zero (base) line

19. The tolerance zone is on the zero (base) line

20. The tolerance zone is under the zero (base) line

21. Possible positions of the tolerance zone in case of shafts
ISO standard uses tolerance position letters with lowercase letters for the shafts.
Fundamental Deviation: is the deviation closest to the basic size.

23. Possible positions of the tolerance zone in the case of holes
ISO standard uses tolerance position letters with capital letters for the holes.
Fundamental Deviation: is the deviation closest to the basic size.

25. Representation of Tolerance 1) Letter Symbol
The selection of letter freezes one limit of hole / shaft
(how much away from Basic size)
Representation of Tolerance
1) Letter Symbol
Basic Size
45 E8/e7
One can have different possible combinations; eg. 45H6g7, 45H8r6, 45E5p7
E.S. – upper deviation
E.I. – lower deviation
H : lower deviation of hole is zero
h : upper deviation of shaft is zero

26. RANGE IN A GIVEN TOLERANCE GRADE

29. Representation of Tolerance
2) Number or Grade IT01, IT0, IT1,….IT16
Tolerance Grade defines range of dimensions (dimensional variation)
There are manufacturing constraints on tolerance grade chosen

30. IT: International Tolerance

31. Example: A shaft of nominal diameter 25 mm is going to be manufactured
Example: A shaft of nominal diameter 25 mm is going to be manufactured. IT grade is required to be IT7.
Determine the tolerance on the shaft.