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engr 111c_13_2_08c_otey

# engr 111c_13_2_08c_otey - Tolerances A dimensioning...

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Tolerances A dimensioning technique that ensures the interchangeability of parts ENGR 111C Class 13.2 November 20, 2008

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Learning Objectives Apply linear tolerances in both the English and Metric systems by hand and with AutoCAD Calculate the following parameters, given a dimensioned set of mating parts: Allowance, Clearance, Hole Tolerance, Shaft Tolerance Match Geometric Tolerancing symbols with their meaning Apply geometric tolerances with AutoCAD
Tolerance ??? What does the word “Tolerance” mean to you? The dictionary defines tolerance as: tol·er·ance: n. 2.a. Leeway for variation from a standard. b. The permissible deviation from a specified value of a structural dimension, often expressed as a percent. Paraphrased to “Tolerance is how accepting of errors you are”.

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General Concepts A measurement with a zero tolerance is impossible to manufacture in the real world Tolerances on parts contribute to the expense of a part, the smaller the tolerance the more expensive the part
Types of Tolerances General Tolerances - limit the error a machinist is allowed on all dimensions, unless otherwise specified Linear Tolerance - specific error limits for a particular linear measurement Geometric Tolerances - Error limits, not on the size, but on the shape of a feature

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General Tolerance Are specified in the title block of a drawing Must always be included on “real” parts
Linear Tolerance Is an overriding tolerance which specifies a tolerance for one specific dimension Can be listed in limit or deviation form, but normally should be specified on an engineering drawing in limit form Should only be used in the case of real necessity, not just because

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Example of Linear Tolerance The parts shown to the right illustrate the proper form of linear tolerance shown in limit form.
Design Considerations From a design point of view, there are four parameters of interest: Hole Tolerance Shaft Tolerance Allowance Maximum Clearance

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Hole Tolerance The difference between the diameters of the largest and smallest possible holes Determines the cost of manufacturing the hole Does not consider the Shaft at all
Shaft Tolerance

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