IENG 248 Lecture 06 Basic Geometric Dimensioning Tolerancing

IENG 248 Lecture 06 Basic Geometric Dimensioning & Tolerancing (GD&T) 10/30/2020 Engineering Graphics & 3 -D Modeling D. H. Jensen 1

IENG 248 Assignment: HW 06 Due Today ® Reading n Skim CH 9, 11 l Review pp. 380 – 381 (pp. 314 – 318 in old text) (Dimensioning Do’s & Don’ts) ® Assignment: n Ex. 9. 2, p. 387 (Fig. 9. 67, p. 327 in old text): l Sketch dimensioned views for b and d, only l Scale drawing so that the parts are roughly double size on your paper (smallest hole diameter is 2 squares in width) l Draw orthographic, multi-view with straight edge (not CAD) l Use English units – 1 square is. 20 inches / side 10/30/2020 Engineering Graphics & 3 -D Modeling D. H. Jensen 2

IENG 248 Last HW Assignment: HW 07 ® Reading: Finish CH 11 n Read CH 10 and start CH 12 n ® Assignment: n CH 10, p. 429 (Project p. 390 in old text): l Exercise 10. 2 (Fig. 11. 49 in old text) using GD&T l Exercise 10. 3 (Fig. 11. 50 in old text) using GD&T 10/30/2020 Engineering Graphics & 3 -D Modeling D. H. Jensen 3

IENG 248 Fit Purposes ® Clearance n Used to allow motion between parts l Running l Sliding ® Interference n Used to mechanically join parts l Force l Shrink ® Locational n Used to constrain the position between parts l Locational Clearance Fits l Locational Transition Fits l Locational Interference Fits 10/30/2020 Engineering Graphics & 3 -D Modeling D. H. Jensen 4

IENG 248 Tolerancing Definitions ® Clearance Fit n the internal member always has a space between it and the external member ® Interference Fit n the internal member is always larger than the gap in the external member ® Transition Fit n may result in either a clearance or interference condition ® Line Fit n 10/30/2020 limits specified so that either a clearance or exact surface contact condition results Engineering Graphics & 3 -D Modeling D. H. Jensen 5

IENG 248 Definitions ® Tolerance n The total amount the feature is allowed to vary (upper limit - lower limit) ® Basic Size (Basic Dimension – GD&T) n theoretical exact value that deviations are applied to, and tolerances are computed from, in order to achieve the desired fit ® Deviation n The amount that a feature may vary from the basic size in one direction (limit – basic size) ® Allowance the minimum space between mating parts n the difference between the largest allowable shaft size and the smallest allowable hole size n l Clearance Fit has a positive allowance l Interference Fit has a negative allowance 10/30/2020 Engineering Graphics & 3 -D Modeling D. H. Jensen 6

IENG 248 10/30/2020 Hands-On 11. 1 Engineering Graphics & 3 -D Modeling D. H. Jensen 7

IENG 248 Tolerance Systems ® Basic Hole System Used to set tolerances when it is easier to change size of the shaft than the size of the hole n Minimum hole is taken as the basic size n Most common system n ® Basic Shaft System Used to set tolerances when it is easier to change the size of the hole than the size of the shaft n Maximum shaft is taken as the basic size n Least common system n 10/30/2020 Engineering Graphics & 3 -D Modeling D. H. Jensen 8

IENG 248 Extreme Conditions ® Maximum Material Condition (MMC) Prevailing conditions when the most material is contained in both features n Occurs when you have the smallest hole and the largest shaft, simultaneously n Think of it as when the part weighs the most, and still fits all constraints (perfect form) n ® Least Material Condition (LMC) Prevailing conditions when the minimum material is contained in both features n Occurs when you have the largest hole and the smallest shaft, simultaneously - or when the part has perfect form and weighs the least n 10/30/2020 Engineering Graphics & 3 -D Modeling D. H. Jensen 9

IENG 248 Specifying Tolerances ® General Tolerances l Specified by notes in the title block, and apply to all feature sizes unless otherwise specified ® Dimensional (Parametric) Tolerances l Specified for a specific feature size n Limit Dimensioning l Both upper & lower limit dimensions are specified n Plus-or-Minus Dimensioning l Bilateral - a positive and a negative deviation ® Plus AND Minus - symmetric, bilateral deviation l Unilateral - only a positive or only a negative deviation n Single Limit Dimensioning l MIN or MAX is placed after the dimension if the other feature size deviation is controlled by another element n Angular Tolerancing l Bilateral Plus-or-Minus in degrees, minutes, seconds 10/30/2020 Engineering Graphics & 3 -D Modeling D. H. Jensen 10

IENG 248 General Tolerance Development ® Problem: n Develop a tolerance for a pneumatic cylinder guide (slide). The guide is a mating feature consisting of a pin and a hole. The pin will run back and forth within the hole as the cylinder extends/retracts. The hole will be produced with a drill and the shaft will be turned on a lathe. The nominal size is 13/16”, and the allowance is 0. 002”. The tolerances will be specified to the thousandths of an inch. ® Q: Is the hole or the shaft the basis for this application? n 10/30/2020 A: It is a basic hole system. The hole will be produced with a standard size drill bit, which is difficult to vary in fine increments. The shaft diameter can be easily varied on a lathe. Engineering Graphics & 3 -D Modeling D. H. Jensen 11

IENG 248 General Tolerance Development ® Q: What kind of fit is required? n A: Since the nominal allowance is positive, a clearance fit will result. Common sense also tells you that a clearance fit is required to allow the running motion. An interference or transition fit would/could cause binding. ® Q: What is the feature size? n A: The nominal hole size is 13/16”; converted to decimal inches it is 0. 81250. This value is rounded to. 812, using the dimensional rounding rules. ® Q: What is a reasonable tolerance for the hole? n 10/30/2020 A: From Table 10. 2 (Fig 11. 13 old text), for a drilling operation with a nominal feature size between. 600” and. 999” the middle of the range of tolerances is. 004”. Engineering Graphics & 3 -D Modeling D. H. Jensen 12

IENG 248 10/30/2020 General Tolerance Development Engineering Graphics & 3 -D Modeling D. H. Jensen 13

IENG 248 General Tolerance Development ® Q: What material condition should the tolerance be based upon? n A: Since the specified fit is a clearance fit, the worst case condition is when the hole is smallest and the shaft is largest. This is the Maximum Material Condition, as it will constrain the maximum material in either part. ® Q: What is the minimum hole dimension? n A: For a Basic Hole System, the basic size is the minimum acceptable hole size, or 0. 812”. ® Q: What is the maximum hole dimension? n 10/30/2020 A: The hole tolerance is the difference between the largest and smallest hole. The reasonable tolerance from Table 10. 2 (Fig. 11. 13, old text) was 0. 004”. Adding it to the minimum hole gives an upper limit of 0. 816”. Engineering Graphics & 3 -D Modeling D. H. Jensen 14

IENG 248 General Tolerance Development ® Q: How can we show the hole tolerance? n A: Using limit dimensioning, and standard English unit practices (no leading zeros) the following would work: . 816. 812 10/30/2020 Engineering Graphics & 3 -D Modeling D. H. Jensen 15

IENG 248 General Tolerance Development ® Q: What is the maximum dimension for the shaft? n A: The smallest hole size is 0. 812”. For a clearance fit, subtracting the allowance (0. 002”) gives the shaft size at MMC, or 0. 810”. ® Q: What is a reasonable tolerance for the shaft? n A: From Table 10. 2 (Fig. 11. 13), for a turning operation with a nominal feature size between. 600” and. 999” the middle of the range of tolerances is. 0025”. ® Q: What is the lower limit for the shaft dimension? n 10/30/2020 A: Subtract the tolerance from the maximum dimension to get 0. 80750”, then round the dimension to 0. 808”. Engineering Graphics & 3 -D Modeling D. H. Jensen 16

IENG 248 General Tolerance Development ® Q: How can we show the shaft tolerance? n A: Using limit dimensioning, and standard English unit practices (no leading zeros) the following would work: . 810. 808 10/30/2020 Engineering Graphics & 3 -D Modeling D. H. Jensen 17

IENG 248 Std. Tolerance Development ® Problem: n Develop a tolerance for an enhanced pneumatic cylinder guide. The hole will still be produced with a drill and the shaft will be turned on a lathe. The nominal size is still 13/16”, but the tolerances will be specified to tenthousandths of an inch. ® Q: How can I specify a tolerance when an allowance is not given? n 10/30/2020 A: Empirical design. Look for standard tables or (previous practices) that help. Start with Table 10. 1 (11. 1) and note that an RC fit is what is needed for a running clearance. Then Appendix 7 (5) shows that a Close Running Fit (RC 4) is most appropriate. Appropriate clearances would run from 0. 8 to 2. 8 thousandths of an inch for a nominal feature size between 0. 71” and 1. 19”. Engineering Graphics & 3 -D Modeling D. H. Jensen 18

IENG 248 10/30/2020 General Tolerance Development Engineering Graphics & 3 -D Modeling D. H. Jensen 19

IENG 248 Lecture 07 B GD&T & Examples 10/30/2020 Engineering Graphics & 3 -D Modeling D. H. Jensen 24

IENG 248 Geometric Tolerances ® Geometric Dimensioning & Tolerancing n Abbreviated GD&T n Controls feature form / location variations, NOT feature size variations (width, height, depth); examples include: l how cylindrical l how flat l how straight l how symmetric l how parallel n 10/30/2020 Specified using internationally recognized graphic symbols for geometric characteristics Engineering Graphics & 3 -D Modeling D. H. Jensen 25

IENG 248 Symbols ® Straightness ® Flatness ® Circularity ® Cylindricity ® Perpendicularity ® Parallelism ® Position ® Concentricity ® Material Conditions ® etc. . 10/30/2020 M L See Table 11. 4 p. 373 Engineering Graphics & 3 -D Modeling D. H. Jensen 26

IENG 248 10/30/2020 GD &T Symbols Engineering Graphics & 3 -D Modeling D. H. Jensen 27

IENG 248 GD&T Symbol Construction ® Datums n specify their capital letter label in a frame distinguish them from section labels) and connect them to the feature by: (to l a leader, terminated with a triangle, or l an extension line, immediately adjacent to the frame (in this case, there are dashes bracketing the letter) ® Basic Dimensions n 10/30/2020 specify basic dimensions between controlled features (just as with size dimensions), but distinguish them with frames Engineering Graphics & 3 -D Modeling D. H. Jensen 28

IENG 248 GD&T Symbol Construction ® Feature Control n Construct Feature Control Frames by: l specifying the symbol for the geometric characteristic to be controlled (i. e. position) in a box l specifying the tolerance zone shape and the tolerance (i. e. diameter of the tolerance zone) in an adjacent box, modifying for material condition at tolerance specification l specifying the relevant datum(s) in adjacent boxes, modifying for the material condition at measurement ® Append notes as necessary to clarify 10/30/2020 Engineering Graphics & 3 -D Modeling D. H. Jensen 29

IENG 248 Why GD&T? ® GD&T allows us to: n n n 10/30/2020 control more of the important aspects of the feature - the geometry as well as the size avoid tolerance stacking have a cleaner, clearer drawing specify tolerance zones in a manner more similar to the way they will be verified – it identifies the datum surfaces from which a feature is to be dimensioned helps specify how the part is to be inspected and manufactured – implies how the part is to be fixtured Engineering Graphics & 3 -D Modeling D. H. Jensen 30

IENG 248 Example: Flatness (No Datum) ® Flatness is a characteristic of a single surface: n If a surface is sufficiently flat, then all points on the surface will lay in-between two parallel planes separated by the tolerance distance ® Tolerance Zone Depiction: . 002 ® Feature Control Frame & Leader: . 002 10/30/2020 Engineering Graphics & 3 -D Modeling D. H. Jensen 31

IENG 248 Example: Identifying Datums ® Datums are theoretically perfect: The datum is assumed to be exact for the purposes of manufacture and inspection. n For practical purposes, they need to be 10 X more accurately produced than any measurement that will be derived from them. n For manufacturing purposes, these are the first features to produce, since they control the remaining characteristics of the part. n ® Identification: A 1. 02 B 10/30/2020 Engineering Graphics & 3 -D Modeling D. H. Jensen 32

IENG 248 Example: Parallelism (One Datum) ® Parallelism is a characteristic of two surfaces: n If a surface is parallel, then it will lay inbetween two planes parallel to the datum and to each other, offset by the tolerance distance ® Tolerance Zone Depiction: . 003 ® Feature Control Frame: . 003 A 2. 62 A 10/30/2020 Engineering Graphics & 3 -D Modeling D. H. Jensen 33

IENG 248 Example: True Position (Multi-Datum) ® True Position is a relationship between at least three surfaces: n If the centerline of the feature is positioned accurately, then it will lay within a tolerance zone envelope sized by the tolerance value ® True Position is a tolerance of location: Location is specified by BASIC DIMENSIONS n The basic dimensions originate at DATUM surfaces n It may be affected by the size of the produced feature, so design intent should be indicated by the MATERIAL CONDITION modifier n 10/30/2020 Engineering Graphics & 3 -D Modeling D. H. Jensen 34

IENG 248 Two-Dimensional Tolerance View ® To place a hole in the part, we need to locate the center of the hole in the coordinate plane relative to the axis of the hole, and then size the hole (allowing a hole size tolerance) 11. 200 ±. 002 10. 000 15. 500 10/30/2020 Engineering Graphics & 3 -D Modeling D. H. Jensen 35

IENG 248 Three-Dimensional Tolerance View ® Then we add the GD&T information to control the location of the hole center C 11. 200 ±. 002 . 001 M A B C 10. 000 B 15. 500 Note: Datum A forms the bottom surface of the hole, and so the tolerance zone is a perfect, right cylinder – resting on Datum A and located from Datum B and Datum C. A 10/30/2020 Engineering Graphics & 3 -D Modeling D. H. Jensen 36

IENG 248 Three-Dimensional Tolerance View ® This tells us the DATUMS that we will measure from to locate or inspect the hole C 11. 200 ±. 002 . 001 M A B C 10. 000 B 15. 500 A 10/30/2020 Engineering Graphics & 3 -D Modeling D. H. Jensen 37

IENG 248 Three-Dimensional Tolerance View ® It tells us the BASIC DIMENSIONS that control where the hole is located C 11. 200 ±. 002 . 001 M A B C 10. 000 B 15. 500 A 10/30/2020 Engineering Graphics & 3 -D Modeling D. H. Jensen 38

IENG 248 Three-Dimensional Tolerance View ® It tells us the size and shape of the tolerance zone for the hole center C 11. 200 ±. 002 . 001 M A B C 10. 000 B 15. 500 A 10/30/2020 Engineering Graphics & 3 -D Modeling D. H. Jensen 39

IENG 248 Three-Dimensional Tolerance View ® And it tells us the worst case material condition used to inspect the hole center C 11. 200 ±. 002 . 001 M A B C 10. 000 B 15. 500 In this case, when the hole is at its’ smallest permissible size, the feature location is in its’ most critical state. A 10/30/2020 Engineering Graphics & 3 -D Modeling D. H. Jensen 40