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Lecture #6 EGR 110 – Engineering Graphics

Lecture #6 EGR 110 – Engineering Graphics. Reading Assignment: Ch. L in Engineering Graphics Workbook, Series 1.2 or Series 2 Sketching Assignment: Sketching Assignment #5.

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Lecture #6 EGR 110 – Engineering Graphics

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  1. Lecture #6 EGR 110 – Engineering Graphics Reading Assignment:Ch. L in Engineering Graphics Workbook, Series 1.2 or Series 2 Sketching Assignment:Sketching Assignment #5 Dimensioning Example - Work problem DIM-6 in class (Engineering Graphics Workbook, Series 1.2, by Craig & Craig). Grids are 0.25”.

  2. Lecture #6 EGR 110 – Engineering Graphics • Tolerance • Tolerance - the total amount of variation permitted for a specific dimension • - the difference between the maximum and minimum limits • Limit Dimensions - the minimum and maximum dimensions • Example: If a dimension is 0.875  0.003, determine the: • Maximum dimension • Minimum dimension • Limit dimensions • Tolerance

  3. Cost Tolerance 0.0001 0.001 0.01 0.1 Lecture #6 EGR 110 – Engineering Graphics Why is tolerance important? The use of interchangeable parts would be limited unless the accuracy of each part was controlled. No parts can be made to exact size. Even finely machined parts will vary by some small amount (for example: one thousandth of an inch). Keep in mind that increased accuracy (smaller tolerance) results in increased costs. An engineer must carefully weigh the cost of each tolerance that he specifies.

  4. 7.00 3.50 2.75 5.50 GEN. TOL. ±0.02 UON Lecture #6 EGR 110 – Engineering Graphics Tolerance examples Tolerance can be expressed in various ways. Some examples are shown below. Symmetrical tolerance Non-symmetrical tolerance (deviation) Limit Dimensions Tolerance is often expressed using notes as shown below (add hole dimension).

  5. Shaft Cylinder Lecture #6 EGR 110 – Engineering Graphics Mating Shafts and Cylinders Tolerance is particularly important in mating parts, such as a shaft and a cylinder. In some cases the shaft may fit loosely into a cylinder (clearance fit) or in other cases it may fit very tightly (interference fit). With a clearance fit, the shaft is slightly small than the cylinder and with an interference fit, the shaft is slightly larger than the cylinder. A couple of terms are important with mating shafts and cylinders: Maximum clearance = Maximum cylinder dimension - Minimum shaft dimension Allowance (= minimum clearance) = Minimum cylinder dimension - Maximum shaft dimension Note that allowance will be negative for an interference fit.

  6. Lecture #6 EGR 110 – Engineering Graphics • Example: For the mating shaft and cylinder below, determine: • Shaft tolerance • Cylinder tolerance • Maximum clearance • Allowance • Is it a clearance fit or an interference fit? Shaft 1.749 1.747 1.753 1.750 Cylinder

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