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Tolerancing Engr 135. Tolerance Theory. Tolerances are used to control the variation that exists on all manufactured parts. The amount that each part is allowed to vary in size and shape depends on the end use of the part.

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Tolerancing engr 135

TolerancingEngr 135

Tolerance theory
Tolerance Theory

  • Tolerances are used to control the variation that exists on all manufactured parts.

  • The amount that each part is allowed to vary in size and shape depends on the end use of the part.

    • How would the tolerances of parts for a children’s bicycle compare to the tolerances of parts for a supersonic jet aircraft?

Tolerance values
Tolerance Values

  • The dimension for a part is given as:

    4.250 ±0.002

    What is the upper limit (largest value) allowable for the part?

    What is the lower limit (smallest value) allowable for the part?

    The upper and lower allowable sizes are called limit dimensions.



Tolerancing and design
Tolerancing and Design

  • Tolerancing enables an engineer to design parts that are interchangeable, or parts that may be replaced.

  • For example, you expect to be able to purchase new brushed aluminum wheels for your car and have them be an identical replacement of your factory rims.


  • Tolerances are assigned to the dimensions of parts that are mated together. This allows for the interchangeability of parts with like parts.

  • We are not only concerned with the size of a part but also the variation in the size of a part.

Manufacturing parts
Manufacturing Parts

  • Tolerances are necessary because it is impossible to manufacture parts without some degree of variation.

  • We want to be able to manufacture parts in different locations and different time and still be able to put them together in a functional assembly. (For example, Boeing 787)

Tolerancing standards
Tolerancing Standards


    • American National Standards Institute

    • American Society of Mechanical Engineers

  • ISO

    • International Standards Organization

Manufacturing tolerances
Manufacturing Tolerances

  • Why are manufacturing tolerances important for LEGOs?

  • LEGO reports their tolerance in some cases to be 0.002 mm

Wikipedia on legos
Wikipedia on LEGOs

  • Bricks, beams, axles, mini figures, and all other elements in the Lego system are manufactured to an exacting degree of tolerance. When snapped together, pieces must have just the right amount of "clutch power"; they must stay together until pulled apart. They cannot be too easy to pull apart, or the resulting constructions would be unstable; they also cannot be too difficult to pull apart, since the disassembly of one creation in order to build another is part of the Lego appeal. In order for pieces to have just the right "clutch power", Lego elements are manufactured within a tolerance…

Tolerance types
Tolerance Types

  • Limit Dimensions

  • Plus-Minus Dimensions

  • Page or Block Tolerances

Limit dimensions
Limit Dimensions

  • Limit Dimensions are the maximum and minimum size a part can be and still be a functional part.

  • The largest number is always place first or on top.

Plus or minus dimensions
Plus or Minus Dimensions

  • Plus or minus dimensions give a basic size and the variation that can occur around that basic size.

Page or block dimensions
Page or Block Dimensions

  • A page tolerance is actually a general note that applies to all dimensions not covered by some other tolerancing type.

  • These are usually found in the general notes or in the title block of a drawing.