1. Limits, Fits and Tolerances
Chapter 3
Limits, Fits and Tolerances
Prof. M. M. Joke

2. Graphical Illustration of Tolerance Zones
Prof. M. M. Joke

3. The fundamental tolerance is a function of the nominal size and its unit is given by the emperical relation, standard tolerance unit,
i = 0.45 × 3 √D D
where i is in microns and D is the geometrical mean of the limiting values of the basic steps mentioned above, in millimetres. This relation is valid for grades 5 to 16 and nominal sizes
from 3 to 500 mm.
IT5
IT6
IT7
IT8
IT9
IT10
IT11
IT12
IT13
IT14
IT15
IT16 7i
10i
16i
25i
40i
64i
100i
160i
250i
400i
640i
1000i
Relative magnitude of IT tolerances for grades 5 to 16 in terms of tolerance unit i for sizes upto 500 mm
Prof. M. M. Joke

4. The tolerance unit, i = 0.45 * 3 √98 + 0.001 × 98 = 2.172 microns
Example 1 Calculate the fundamental tolerance for a shaft of 100 mm and grade 7.
The shaft size, 100 lies in the basic step, 80 to 120 mm and the geometrical mean is
D = √80 × 120 = 98 mm
The tolerance unit, i = 0.45 * 3 √ × 98 = microns
For grade 7, as per the above table, the value of tolerance is,
16i = 16 × = 35 microns
Prof. M. M. Joke

5. Prof. M. M. Joke

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9. Prof. M. M. Joke

10. Prof. M. M. Joke

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14. Gauges and Gauge Design
1. Plug Gauge
Prof. M. M. Joke

15. Gauges and Gauge Design
1. Plug Gauge
Prof. M. M. Joke

16. Gauges and Gauge Design
2. Snap Gauge
Prof. M. M. Joke

17. Gauges and Gauge Design
2. Snap Gauge
Prof. M. M. Joke

18. Gauges and Gauge Design
2. Snap Gauge
Prof. M. M. Joke

19. Gauges and Gauge Design
3. Ring Gauge
Prof. M. M. Joke

20. Multi Gauging and Inspection
Eg: 1. Connecting rod Multi gauging
2. Cam shaft Multi gauging
Prof. M. M. Joke

21. Taylor’s Principle
Statement 1:- The “Go” gauge should always be so designed that it will cover the maximum metal condition (MMC), whereas a “NOT-GO” gauge will cover the minimum (least) metal condition (LMC) of a feature, whether external or internal.
Prof. M. M. Joke

22. Taylor’s Principle
Statement 2:- The “Go” gauge should always be so designed that it will cover as many dimensions as possible in a single operation, whereas the “NOT-GO” gauge will cover only one dimension.
Means a Go plug gauge should have a full circular section and be of full length of the hole being checked as in shown figure
Prof. M. M. Joke

23. Taylor’s Principle
According to the second statement, Let us take an example of checking of a bush (hole), as shown in Fig. If a short length Go-plug gauge is employed to check the curved bush, it will pass through all the curves of the bend busing. This will lead to wrong selection of curved bush.
On the other hand, a GO-plug gauge of adequate length will not pass through a bent or curved bush. This eliminates the wrong selection. The length of NOT-GO gauge is kept smaller than GO-gauge.
Prof. M. M. Joke