Objectives for today. Exercise DrE-5 - Week 7. Representation of features Geometric tolerances. Prof Ahmed Kovacevic. ME 1110 Engineering Practice 1

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1 ME 1110 Engineering Practice 1 Engineering Drawing Design - Lecture 6 Representation features Geometric tolerances Pr Ahmed Kovacevic School Engineering Mathematical Sciences Room C130, Phone: 8780, a.kovacevic@city.ac.uk 1 Objectives for today How to represent stard engineering features Gears; Bearings; Seals; Springs Shafts, tubes; Fasteners What are tolerances how are they specified Geometric tolerances Surface finish & machining 2 Exercise DrE-5 - Week 7 Parts to be measured drawn 3

2 Representing stard features 4 Gears 5 stard 6

3 stard 7 stard 8 stard 9

4 stard 10 stard 11 stard 12

5 stard 13 stard 14 stard 15

6 stard 16 stard 17 stard 18

7 BS 8888 for features Representation features BS EN ISO 6411 Technical drawings Simplified centre holes BS EN ISO 6413 Technical drawings Representation splines serrations BS EN ISO Technical drawings Symbolic presentation indication adhesive, fold pressed joints BS EN Welded, brazed soldered joints Symbolic on drawings NOTE The BS ISO 128 series stards covers the general subject feature. Representation BS EN ISO Technical product documentation Springs Part 1: Simplified BS EN ISO Technical product documentation Springs Part 2: Data for cylindrical helical compression springs BS EN ISO Technical product documentation Springs BS EN ISO 2203 Technical drawings Conventional gears BS EN ISO Technical drawings Simplified the assembly parts with fasteners Part 1: General principles BS EN ISO Technical drawings Screw threads threaded parts Part 1: General conventions BS EN ISO Technical drawings Screw threads threaded parts Part 2: Screw thread inserts BS EN ISO Technical drawings Screw threads threaded parts Part 3: Simplified BS EN ISO Technical drawings Roller bearings Part 1: General simplified BS EN ISO Technical drawings Roller bearings Part 2: Detailed simplified BS EN ISO Technical drawings Seals for dynamic application Part 1: General simplified BS EN ISO Technical drawings Seals for dynamic application Part 2: Detailed simplified 19 Tolerances Definition:» A tolerance is the total permissible variation a size, or the difference between the maximum minimum limits size. 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 variation must be specified» Large variation may affect the functionality the part» Small variation will effect the cost the part requires precise manufacturing requires inspection the rejection parts 20 Example detailed drawing 21

8 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 Geometrical tolerancing» Allows for specification tolerance for the geometry a part separate from its size» GDT (Geometric Dimensioning Tolerancing) uses special symbols to control different geometric features a part 22 Datums Plane surface or axis Designated in order that some other feature(s) may relate to it Datums are drawn as shown in the picture 23 Geometrical Tolerances Geometric tolerance a feature (point, line, axis, surface) specifies the tolerance zone in which the feature is required to contain. 24

9 Supplementary symbols Notation Tolerance frame variations 25 Straightness Flatness 26 Form Roundness 27

10 Symmetry Angularity 28 Squareness 29 Parallelism Position 30

11 Position 31 Concentricity 32 Cilindricity Maximum material condition Prile tolerance 33

12 Surface Roughness +Y Average deviation about the mean line measured A A 3 An 1 a O Mean Line -Y A 2 L Surface Roughness Measured by value R a n A o = L 34 Surface texture quality (µm) (µinch) N-Grade N1 N2 N3 N4 N5 N6 N7 N8 N9 N10 N11 N12 Finish Ground Finishes Smooth Turned Medium Turned Rough Machined 35 Manufacture methods roughness values 36

13 Conclusions Today we reviewed: Representation features parts Importance tolerance Geometric tolerances Surface finish machining To be continued (next week) 37