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Lecture Engineering drawing and design - Lecture 7: Fits and tolerances

Lecture Engineering drawing and design - Lecture 7: Fits and tolerances. After reading the material in this chapter, you should be able to: To learn what are geometric fits and how to define these, to learn how to define tolerance in order for parts to function correctly. | Design web ME 1110 – Engineering Practice 1 Engineering Drawing and Design - Lecture 7 Fits and Tolerances Prof Ahmed Kovacevic School of Engineering and Mathematical Sciences Room C130, Phone: 8780, E-Mail: a.kovacevic@city.ac.uk www.staff.city.ac.uk/~ra600/intro.htm 1 Ahmed Kovacevic, City University London Design web Objectives for today • To learn what are geometric fits and how to define these • To learn how to define tolerance in order for parts to function correctly 2 Ahmed Kovacevic, City University London Design web Example detailed drawing 3 Ahmed Kovacevic, City University London Design web Tolerancing Definition: • » Allowance for specific variation in the size and geometry of a part Why is tolerancing necessary? • » It is impossible to manufacture a part to an exact size or geometry » Since variation from the drawing is inevitable the acceptable degree of variation must be specified » Large variation may affect the functionality of the part » Small variation will effect the cost of the part requires precise manufacturing requires inspection and the rejection of parts 4 Ahmed Kovacevic, City University London Design web Tolerance Declaration Tolerance can be expressed in different ways: 1. Direct tolerancing method (size) » Limits specifying the allowed variation in each dimension (length, width, height, diameter, etc.) are given on the drawing 2. General tolerance note » Notes like “ALL DIMENSIONS HELD TO 0.05” 3. Geometric tolerancing » Allows for specification of tolerance for the geometry of a part separate from its size » GDT (Geometric Dimensioning and Tolerancing) uses special symbols to control different geometric features of a part 5 Ahmed Kovacevic, City University London Design web Direct Tolerancing method (1) (2) unilater al Limit Dimensioning Deviation tolerancing bilateral equal unequal 6 Ahmed Kovacevic, City University London Design web Tolerancing - Terminology 1 Basic Size:Deviation:- 2 Max