8 - TOLERANCES ENGR 111A GC-7 Introduction Features without...

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ENGR 111A GC-7 TOLERANCES
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Introduction Features without any error are impossible to manufacture. If a hole has a design diameter of one inch, how close to one inch would it have to be to be considered acceptable? Tolerances contribute to the expense of a part. The greater the accuracy (smaller tolerance) the higher the cost of manufacturing.
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General Idea of Tolerance 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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Tolerances in Design The term tolerance refers to the permissible level of error that a machinist is allowed on a specific dimension. It can be understood as a range of acceptable values for a particular dimension. This class is not trying to teach the design aspect of tolerance. We will be interested in applying a given tolerance to a part, not in determining the “best” tolerance. Various industries (aerospace, electronics, automotive, etc.) set their own tolerances.
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Types of Tolerances General General General Tolerances apply to all dimensions on a drawing. Linear Linear Linear Tolerances refer to specific features that require more accuracy than general tolerances provide. Geometric Geometric Geometric Tolerances are concerned with a feature’s shape or profile, not its size or dimensions.
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General Tolerance Apply to all dimensions on a drawing. Often found in the title block of all drawings intended for manufacturing or as a general note. Normally given in bilateral form, defining a symmetric limit above and below a dimension. General General
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Linear Tolerance It is an overriding tolerance used when a specific feature requires greater accuracy than the one expressed by the general tolerance. Linear Linear Limit Form Unilateral Form Bilateral Form
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Linear Fit Relationships When developing designs with mating parts, such as a shaft mating with a hole or a block sliding along a slot, tolerances become critical. Not only are the individual tolerances of each part important, but also the relationship between the two parts (how tightly or loosely they are going to fit) needs to be considered. From a design point of view, there are four parameters of interest: Tolerance of the first mating part Tolerance of the second mating part Allowance Maximum Clearance Linear Linear
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Design Considerations The assembly shown will be used as an example to illustrate these concepts but the terms can be applied to any two mating parts.
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8 - TOLERANCES ENGR 111A GC-7 Introduction Features without...

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