Basic Geometric Dimensioning & Tolerancing (GD&T) Lecture 06 Basic Geometric Dimensioning & Tolerancing (GD&T) 4/22/2017 Engineering Graphics & 3-D Modeling

Assignment: HW 06 Due Today Reading Skim CH 9, 11 Review pp. 380 – 381 (pp. 314 – 318 in old text) (Dimensioning Do’s & Don’ts) Assignment: Ex. 9.2, p. 387 (Fig. 9.67, p.327 in old text): Sketch dimensioned views for b and d, only Scale drawing so that the parts are roughly double size on your paper (smallest hole diameter is 2 squares in width) Draw orthographic, multi-view with straight edge (not CAD) Use English units – 1 square is .20 inches / side 4/22/2017 Engineering Graphics & 3-D Modeling

Engineering Graphics & 3-D Modeling Last HW Assignment: HW 07 Reading: Finish CH 11 Read CH 10 and start CH 12 Assignment: CH 10, p. 429 (Project p. 390 in old text): Exercise 10.2 (Fig. 11.49 in old text) using GD&T Exercise 10.3 (Fig. 11.50 in old text) using GD&T 4/22/2017 Engineering Graphics & 3-D Modeling

Engineering Graphics & 3-D Modeling Fit Purposes Clearance Used to allow motion between parts Running Sliding Interference Used to mechanically join parts Force Shrink Locational Used to constrain the position between parts Locational Clearance Fits Locational Transition Fits Locational Interference Fits 4/22/2017 Engineering Graphics & 3-D Modeling

Tolerancing Definitions Clearance Fit the internal member always has a space between it and the external member Interference Fit the internal member is always larger than the gap in the external member Transition Fit may result in either a clearance or interference condition Line Fit limits specified so that either a clearance or exact surface contact condition results 4/22/2017 Engineering Graphics & 3-D Modeling

Engineering Graphics & 3-D Modeling Definitions Tolerance The total amount the feature is allowed to vary (upper limit - lower limit) Basic Size (Basic Dimension – GD&T) the theoretical exact value that deviations are applied to, and tolerances are computed from, in order to achieve the desired fit Deviation The amount that a feature may vary from the basic size in one direction (limit – basic size) Allowance the minimum space between mating parts the difference between the largest allowable shaft size and the smallest allowable hole size Clearance Fit has a positive allowance Interference Fit has a negative allowance 4/22/2017 Engineering Graphics & 3-D Modeling

Engineering Graphics & 3-D Modeling Hands-On 11.1 4/22/2017 Engineering Graphics & 3-D Modeling

Engineering Graphics & 3-D Modeling 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 Minimum hole is taken as the basic size Most common system Basic Shaft System Used to set tolerances when it is easier to change the size of the hole than the size of the shaft Maximum shaft is taken as the basic size Least common system 4/22/2017 Engineering Graphics & 3-D Modeling

Engineering Graphics & 3-D Modeling Extreme Conditions Maximum Material Condition (MMC) Prevailing conditions when the most material is contained in both features Occurs when you have the smallest hole and the largest shaft, simultaneously Think of it as when the part weighs the most, and still fits all constraints (perfect form) Least Material Condition (LMC) Prevailing conditions when the minimum material is contained in both features Occurs when you have the largest hole and the smallest shaft, simultaneously - or when the part has perfect form and weighs the least 4/22/2017 Engineering Graphics & 3-D Modeling

Specifying Tolerances General Tolerances Specified by notes in the title block, and apply to all feature sizes unless otherwise specified Dimensional (Parametric) Tolerances Specified for a specific feature size Limit Dimensioning Both upper & lower limit dimensions are specified Plus-or-Minus Dimensioning Bilateral - a positive and a negative deviation Plus AND Minus - symmetric, bilateral deviation Unilateral - only a positive or only a negative deviation Single Limit Dimensioning MIN or MAX is placed after the dimension if the other feature size deviation is controlled by another element Angular Tolerancing Bilateral Plus-or-Minus in degrees, minutes, seconds 4/22/2017 Engineering Graphics & 3-D Modeling

General Tolerance Development Problem: 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? 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. 4/22/2017 Engineering Graphics & 3-D Modeling

General Tolerance Development Q: What kind of fit is required? 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? 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? 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”. 4/22/2017 Engineering Graphics & 3-D Modeling

General Tolerance Development Q: What material condition should the tolerance be based upon? 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? 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? 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”. 4/22/2017 Engineering Graphics & 3-D Modeling

General Tolerance Development Q: How can we show the hole tolerance? A: Using limit dimensioning, and standard English unit practices (no leading zeros) the following would work: .816.812 4/22/2017 Engineering Graphics & 3-D Modeling

General Tolerance Development Q: What is the maximum dimension for the shaft? 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? 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? A: Subtract the tolerance from the maximum dimension to get 0.80750”, then round the dimension to 0.808”. 4/22/2017 Engineering Graphics & 3-D Modeling

General Tolerance Development Q: How can we show the shaft tolerance? A: Using limit dimensioning, and standard English unit practices (no leading zeros) the following would work: .810.808 4/22/2017 Engineering Graphics & 3-D Modeling

Std. Tolerance Development Problem: 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 ten-thousandths of an inch. Q: How can I specify a tolerance when an allowance is not given? 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”. 4/22/2017 Engineering Graphics & 3-D Modeling

Std. Tolerance Development Q: What are the standard limits to be applied to the basic hole size? A: The nominal size was 0.8125”, falling between 0.71 and 1.19 in the left-most column of Appendix 7(5). The standard hole limits for an RC 4 Class fit are + 1.2 and - 0 thousandths of an inch, or + 0.0012” and - 0.0000”. Q: What are the standard limits to be applied to the basic shaft size? A: The nominal size is also 0.8125”, falling between 0.71 and 1.19 in the left-most column of Appendix 7(5). The standard shaft limits for an RC 4 Class fit are - 0.8 and - 1.6 thousandths of an inch, or - 0.0008” and - 0.0016”. This gives an allowance of + 0.0008” between the shaft and hole at MMC, and a clearance of + 0.0028 at LMC. 4/22/2017 Engineering Graphics & 3-D Modeling

Std. Tolerance Development Q: How can we show the mating tolerances? A: Using dimensions with a unilateral tolerance and English unit practices (no leading zeros) the following would work (use computations similar to those for the hole example): + .0012 - .0000 + .0000 - .0008 .8125 .8117 4/22/2017 Engineering Graphics & 3-D Modeling

Std. Tolerance Development Q: How can we show the mating tolerances? A: Using dimensions with a symmetric bilateral tolerance, the following would work (center the dimensional value and adjust the unilateral deviations): + .0006 - .0006 + .0004 - .0004 .8131 .8113 4/22/2017 Engineering Graphics & 3-D Modeling

Std. Tolerance Development Q: How can we show the mating tolerances? A: Using the basic size, ISO notation standards for fits, and English unit practices (no leading zeros) the following would work. H8 and f7 are the fit designations from the column headings in Appendix 7(5): .8125 H8 .8125 f7 4/22/2017 Engineering Graphics & 3-D Modeling

Engineering Graphics & 3-D Modeling Lecture 07B GD&T & Examples 4/22/2017 Engineering Graphics & 3-D Modeling

Engineering Graphics & 3-D Modeling Geometric Tolerances Geometric Dimensioning & Tolerancing Abbreviated GD&T Controls feature form / location variations, NOT feature size variations (width, height, depth); examples include: how cylindrical how flat how straight how symmetric how parallel Specified using internationally recognized graphic symbols for geometric characteristics 4/22/2017 Engineering Graphics & 3-D Modeling

Engineering Graphics & 3-D Modeling Symbols Straightness Flatness Circularity Cylindricity Perpendicularity Parallelism Position Concentricity Material Conditions etc. ... M L See Table 11.4 p. 373 4/22/2017 Engineering Graphics & 3-D Modeling

GD&T Symbol Construction Datums specify their capital letter label in a frame (to distinguish them from section labels) and connect them to the feature by: a leader, terminated with a triangle, or an extension line, immediately adjacent to the frame (in this case, there are dashes bracketing the letter) Basic Dimensions specify basic dimensions between controlled features (just as with size dimensions), but distinguish them with frames 4/22/2017 Engineering Graphics & 3-D Modeling

GD&T Symbol Construction Feature Control Construct Feature Control Frames by: specifying the symbol for the geometric characteristic to be controlled (i.e. position) in a box 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 specifying the relevant datum(s) in adjacent boxes, modifying for the material condition at measurement Append notes as necessary to clarify 4/22/2017 Engineering Graphics & 3-D Modeling

Engineering Graphics & 3-D Modeling Why GD&T? GD&T allows us to: 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 4/22/2017 Engineering Graphics & 3-D Modeling

Example: Flatness (No Datum) Flatness is a characteristic of a single surface: 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: Feature Control Frame & Leader: .002 .002 4/22/2017 Engineering Graphics & 3-D Modeling

Example: Identifying Datums Datums are theoretically perfect: The datum is assumed to be exact for the purposes of manufacture and inspection. For practical purposes, they need to be 10X more accurately produced than any measurement that will be derived from them. For manufacturing purposes, these are the first features to produce, since they control the remaining characteristics of the part. Identification: A 1.02 B 4/22/2017 Engineering Graphics & 3-D Modeling

Example: Parallelism (One Datum) Parallelism is a characteristic of two surfaces: If a surface is parallel, then it will lay in-between two planes parallel to the datum and to each other, offset by the tolerance distance Tolerance Zone Depiction: Feature Control Frame: .003 .003 A 2.62 A 4/22/2017 Engineering Graphics & 3-D Modeling

Example: True Position (Multi-Datum) True Position is a relationship between at least three surfaces: 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 The basic dimensions originate at DATUM surfaces It may be affected by the size of the produced feature, so design intent should be indicated by the MATERIAL CONDITION modifier 4/22/2017 Engineering Graphics & 3-D Modeling

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 4/22/2017 Engineering Graphics & 3-D Modeling

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 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. B 15.500 A 4/22/2017 Engineering Graphics & 3-D Modeling

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 4/22/2017 Engineering Graphics & 3-D Modeling

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 4/22/2017 Engineering Graphics & 3-D Modeling

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 4/22/2017 Engineering Graphics & 3-D Modeling

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 In this case, when the hole is at its’ smallest permissible size, the feature location is in its’ most critical state. B 15.500 A 4/22/2017 Engineering Graphics & 3-D Modeling

Inspection of the Tolerance Example inspection gage for the hole C  11.200 ± .002  .001 M A B C In this case, when the hole is at its’ smallest permissible size and perfectly located, the feature is in its’ most critical state, and just fits about the red gage pin. B A 4/22/2017 Engineering Graphics & 3-D Modeling

Total Effective Tolerance Engineering Graphics & 3-D Modeling Effect of Material Condition Modifiers with Feature Size and Geometric Tolerances Effect of Feature Size with M Tolerance Modifier: C 10.000  11.200 ± .002  .001 M A B C B 15.500 Produced Hole Size Geometric Tolerance Feature Size ‘Bonus’ Total Effective Tolerance 11.197 out of size tolerance 11.198 .001 11.199 .002 11.200 .003 11.201 .004 11.202 .005 11.203 M 4/22/2017 Engineering Graphics & 3-D Modeling

GD&T Tolerance Development Problem: Develop a geometric tolerance to control the location of the hole for the enhanced pneumatic cylinder guide. The hole is still drilled, the nominal size is still 13/16”, and the limits for an RC 4 class fit will still be used; but the positional tolerance will be specified to be within a .0001” circular diameter of the true position of the hole, located 2.250” and 5.500” from the bottom left corner. Q: How do I specify a tolerance like that? A: Use GD&T. The locational parameters become basic dimensions (so put a frame around them). These dimensions should originate with a datum, so label the each datum on the drawing. The feature size is called out with a leader, and a symmetric size tolerance can be developed, just as before. A feature control frame is needed for the positional tolerance. Fill it out with the symbol for true position, specify the shape and size of the tolerance zone at MMC, and call out each datum needed to locate the hole. 4/22/2017 Engineering Graphics & 3-D Modeling

Total Effective Tolerance Engineering Graphics & 3-D Modeling Effect of Material Condition Modifiers with Feature Size and Geometric Tolerances Effect of Feature Size with M Tolerance Modifier: C 2.250 .8131 ± .0006  .0001 M A B C B 5.500 Produced Hole Size Geometric Tolerance Feature Size ‘Bonus’ Total Effective Tolerance .8122 out of size tolerance .8125 .0001 .8128 .0003 .0004 .8131 .0006 .0007 .8134 .0009 .0010 .8137 .0012 .0013 .8140 M 4/22/2017 Engineering Graphics & 3-D Modeling