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

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

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 + 0.001 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

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 + 0.001 × 98 = 2.172 microns For grade 7, as per the above table, the value of tolerance is, 16i = 16 × 2.172 = 35 microns Prof. M. M. Joke

Prof. M. M. Joke

Prof. M. M. Joke

Prof. M. M. Joke

Prof. M. M. Joke

Prof. M. M. Joke

Prof. M. M. Joke

Prof. M. M. Joke

Prof. M. M. Joke

Prof. M. M. Joke

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

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

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

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

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

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

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

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

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

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