Florida Virtual High School - ENGINEERING 101Activity 7

Activity 7.3 Tolerances Introduction The term variation describes the degree to which an object or idea differs from others of the same type or from a standard. Examples of variation are everywhere you look. When you ...

Activity 7.3 Tolerances Introduction The term variation describes the degree to which an object or idea differs from others of the same type or from a standard. Examples of variation are everywhere you look. When you see yourself in the mirror, you notice the left side of your face is not exactly the same as the right side. There is a variation. Or, if you see identical twins, they are not exactly the same. Likewise, no two manufactured objects are the same. A degree of variation will exist. The use of tolerancing in engineering design provides a means by which variance can be controlled within acceptable limits so that parts of a product fit together in a way that allows the product to function properly. In the field of mathematics and science, tolerances are used regularly. You will see reference to an allowance or tolerance given in many settings. After completing this activity, take note when you see tolerances given in the media or on product labels. In this activity you will analyze engineering drawings, identify tolerances, explain the meaning and purpose of those tolerances, and calculate allowances between mating parts of a product. You will also assess the need for tolerances in the manufacture of a consumer product and create part drawings to specify your recommended tolerances. Equipment  Engineering notebook  Pencil  Highlighter Procedure 1. Study the drawings below to identify specified tolerances. a. Highlight each dimension that has a tolerance associated with it using something like a highlight marker. b. Identify the type of tolerance in each highlighted example by labeling each tolerance dimension with one of the following: limit dimensions, unilateral tolerance, or bilateral tolerance. c. Label each identified tolerance with a separate letter, A through Z. d. Beginning on a new page in your engineering notebook for each part, record the letter of each tolerance identified on that part drawing, the type of tolerance, a short written phase that describes the dimensional variation allowed for that dimension, the tolerance (a number representing the total allowed dimensional variation), and an explanation as to why that © 2012 Project Lead The Way, Inc. Introduction to Engineering Design Activity 7.3 Tolerances – Page 1particular dimension requires a tolerance. You may wish to duplicate the following table in your notebook to organize your notes. Part Name: ____Adjustable_rocker_arm______ Lette r Tolerance Type Written Explanation Tolerance Why? A Bilateral Can vary in size whether bigger or smaller + .003 The size can vary; the variation is small bc the hole needs to fit something well B unilateral The tolerance only goes one direction. Either bigger or smaller than the ideal dimension. But not both + .004 The tolerance only gets bigger bc another piece needs to be able to move around in the hole C limited Gives the ranges of what the dimension can be . 005 The hole needs to be extremely fit w/ the insert piece D Bilateral Can vary in size either bigger or smaller . 1 The screws need to be collinear when placed E Limiting Gives the ranges of what the dimension can be . 005 The diameter of the circle need to fit w/ another circle so it needs to be fit; it needs to move around F Limiting Gives the range of what the dimension can be . 004 The diameter of the circle need to fit w/ another circle, so it needs to be fit; it needs to move around G Limiting Gives the ranges of what the dimension can be . 01 There is an interlocking piece; the shape of the piece makes it so the dimensions can be more free & still lock