Dimensioning Standards Introduction to Engineering Design © 2012 Project Lead The Way, Inc.

Dimensioning Standards In order for the drawings to be dimensioned so that all people can understand them, we need to follow standards that every company in the world must follow. Standards are created by these organizations: ANSI ISO MIL DOD CEN DIN JIS

Standards Institutions ANSI - American National Standards Institute. This institute creates the engineering standards for North America. ISO - International Organization for Standardization. This is a worldwide organization that creates engineering standards with approximately 100 participating countries.

Standards Institutions The United States military has two organizations that develop standards. DOD - Department Of Defense MIL - Military Standard

Standards Institutions DIN - Deutsches Institut für Normung. The German Standards Institute created many standards used worldwide, including the standards for camera film. JIS - Japanese Industrial Standard. Created after WWII for Japanese standards. CEN - European Standards Organization.

Dimension Components Dimension Line Dimension Text Arrow Head Extension Lines

Dimension Text Guidelines If the dimension text will not fit between the extension lines, it may be placed outside them

Dimension Text Guidelines Dimension text is placed in the middle of the line both horizontally and vertically

Dimensioning Methods Dimensions are represented on a drawing using one of two systems, unidirectional or aligned. The unidirectional method means all dimensions are read in the same direction. The aligned method means the dimensions are read in alignment with the dimension lines or side of the part, some read horizontally and others read vertically.

Dimensioning Methods Aligned Unidirectional Dimensions are placed so that they can be read from the bottom of the drawing sheet. This method is commonly used in mechanical drafting. Aligned Dimensions are placed so the horizontal dimensions can be read from the bottom of the drawing sheet and the vertical dimensions can be read from the right side of the drawing sheet. This method is commonly used in architectural and structural drafting.

Classification of Dimensions Size. Dimensions are used to identify the specific size of a feature on an object. Location. Dimensions are used to identify the physical proximity of a feature to another feature within an object. Size dimension Location dimension Location dimension Size dimension

Linear Dimensioning Chain Dimensioning Dimensioning from feature to feature Common dimensioning technique

Chain Dimensioning Examples Presentation Name Course Name Unit # – Lesson #.# – Lesson Name Chain Dimensioning Examples METHOD 1 METHOD 2 Dimension from feature to feature across entire part Manufacturing inaccuracies can accumulate Dimension from feature to feature except omit one partial dimension in the chain Dimension overall length/width/height to limit manufacturing inaccuracies Preferable chain dimensioning method It is impossible to manufacture a part to an exact dimension. If a part is measured precisely enough, the part configuration will deviate from the specified dimensions. Typically a small amount of deviation from the specified dimension is allowed, but the error can add up in a chain of dimensions compounding the error and resulting in a part that is much smaller or larger than intended. Therefore, specifying the overall dimension (with its small allowable error in that one dimension) will reduce the deviation of the overall part size. We will talk about tolerances, the allowed deviation of a dimension on a manufactured part from the specified dimension, later in this unit. For now, when chain dimensioning, use the preferred method (Method 2) when possible.

Datum Dimensioning Datum Dimensioning Dimensioning from a single point of origin called a DATUM Reduces dimensional deviations in manufactured parts because each size/location dimension is referenced to a single point

Datum Dimensioning

Dimensioning Symbols Presentation Name Course Name Unit # – Lesson #.# – Lesson Name Dimensioning Symbols Some common dimensioning symbols.

Dimensioning Angles Angled surface may be dimensioned using coordinate method to specify the two location distances of the angle. Angled surfaces may also be dimensioned using the angular method by specifying one location for distance and the angle. Coordinate Method Angular Method

Dimensioning Chamfers Presentation Name Course Name Unit # – Lesson #.# – Lesson Name Dimensioning Chamfers Internal Chamfers Two options for 45 degree external chamfers Chamfers are used on outside edges to avoid sharp corners for safety and handling. External chamfers other than 45 degrees

Dimensioning Arcs and Circles Arcs and circles are dimensioned in views that show the arc or circle. Arcs are dimensioned with a leader to identify the radius; in some cases, a center mark is included. Circles should have a center mark and are dimensioned with a leader to identify the diameter.

Dimensioning Arcs Use a capital R to indicate radius Arrows can be inside or outside for small arcs. Small arcs do not need center marks. Large arcs need a center mark

Presentation Name Course Name Unit # – Lesson #.# – Lesson Name Fillets and Rounds Fillet. An inside radius between two intersecting planes Round. An outside radius applied to corners Fillet Round A round is used to avoid sharp edges for safety and handling. A fillet is used to provide strength at inside corners to avoid fracture. In addition fillets and rounds (as opposed to sharp corners) can make it easier to remove molded parts from molds. Identify which arcs are fillets and which are rounds.

Dimensioning Circles Holes should use hole notes Full circles should be dimensioned using the diameter This hole note specifies a hole with a 0.50 diameter and 1.00 deep

Cylindrical parts may be dimensioned in this manner Dimensioning Circles Cylindrical parts may be dimensioned in this manner Note that the diameter symbol is used so that the dimension is not assumed to be linear

Dimensioning Splines and Curves Points are placed along the contour of splines and dimensioned from a datum. DATUM

Dimensioning Splines and Curves Presentation Name Course Name Unit # – Lesson #.# – Lesson Name Dimensioning Splines and Curves This section view provides coordinate dimensions for the curvature of the windshield of the Automoblox T9 truck. We refer to these dimensions as coordinate dimensions because the horizontal and vertical distances from a given point, the datum (or origin), are given for each identified point along the curve. DATUM

Reference Dimensions “X” indicates the number of places (or occurrences) 2 X indicates that there are two identical holes

Dimensioning Radial Patterns Angles and radius values are used to locate the center of radially patterned features

Alternate Views Introduction to Engineering Design © 2012 Project Lead The Way, Inc.

Presentation Name Course Name Unit # – Lesson #.# – Lesson Name Alternate Views In some cases, orthogonal projections and pictorials are not sufficient to specify all the details of a part. Section View. Used to show “inside” details not apparent on the exterior of the part Auxiliary View. Used to show features that are located on an inclined surface in true size and shape Detail View. Used to show a “close-up” view of features that are too small to adequately specify in another view

Section View Provides a view of an object as if it were cut by a saw Location is indicated by a cutting plane line on another view Cutting plane line

Section View Cutting plane line Indicates location of the cut Thick and broken line Arrows indicate direction of view Labeled with a letter for identification on drawing Cutting plane line

Section View Section lines Hatch lines that indicate material that was “cut” at the cutting plane line Thin lines Section lines Cutting plane line

Section View Types Full Section Half Section Offset Section

Full Section Cutting plane line passes fully through the part The part of the object behind the cutting plane line (away from the direction of the arrows) is removed

Full Section Example Section lines indicate material that is cut by the cutting plane line Imagine the part is cut at cutting plane line Direction of View This half of the part is removed

Full Section Example Section lines indicate material that is cut by the cutting plane line Imagine the part is cut at cutting plane line Direction of View This half of the part is removed

Half Section Used on symmetrical parts to show inside as well as outside details in one view One quarter of the part is cut away Cutting plane line goes halfway through the part

Half Section Example Half Section Only one arrowhead in the direction of view Note that the cutting plane line cuts away a quarter of the part Half Section

Offset Section Interior features not in line with each other can be shown in an offset section view Note how the cutting plane line changes direction and follows the center of each feature

Presentation Name Course Name Unit # – Lesson #.# – Lesson Name Auxiliary Views Orthographic projection of an inclined plane (angled surface) which appears foreshortened in a principle orthographic projection Used to show the true size and shape of an inclined plane and the features on it

Auxiliary Views Foreshortened surfaces do not give a clear or accurate representation of the size or shape of the surface or features and should not be dimensioned foreshortened face TOP FRONT RIGHT SIDE

Presentation Name Course Name Unit # – Lesson #.# – Lesson Name Auxiliary Views An auxiliary view allows the viewer to look perpendicular to an angled surface to witness the true size and shape of that surface and its features (a hole in this example). True Height Auxiliary Distance TOP We will not use auxiliary views in this unit, but they will be presented in more detail in Unit 8. FRONT RIGHT SIDE

Detail Views An enlargement of a portion of another view to illustrate small features on a part Not to be confused with a Detail Drawing which is any drawing that contains all the information needed to manufacture a part

Detail View Example A feature is broken out and enlarged for clarity

Holes and Hole Notes Introduction to Engineering Design © 2012 Project Lead The Way, Inc.

Hole Definitions Through/Thru Clearance Blind Hole cuts through entire thickness Clearance Hole large enough to allow screw head (and driver) to pass through Blind Hole does not cut through entire thickness

Hole Definitions Countersink Counterbore Tapped Conical-shaped recess around hole at surface Often used to accept tapered screw Counterbore Cylindrical recess around hole at surface Often used to receive a bolt head or nut Tapped Hole has internal threads

Hole Note Symbols

Hole Notes A 0.25” diameter blind hole is drilled 0.75” deep. Then a 0.38” diameter counter bore is drilled 0.25” deep. Counterbore or Spotface symbol Depth symbol

Hole Notes A 0.38” diameter blind hole is drilled 0.50” deep.

Hole Notes A 0.38” diameter hole is drilled completely through the object.

Hole Notes Countersink or symbol A 0.50” diameter hole is drilled completely through the object. Then a countersink is created with a 1.00” diameter at the surface and tapering at 82º.

Thread Notes Thread are dimensioned with the use of local notes. Two methods Unified National Thread method ISO

Unified National Thread Notes Thread per Inch Major Diameter Coarse or Fine threads. In this case C for course, F is for fine.

ISO Thread Notes 1.5, Pitch of the threads 12, Nominal Diameter in mm Prior to THRU may appear an LH for Left Hand thread M for Metric H, allowance. H means no allowance, G means tight allowance. 6, Grade of tolerance in the threads. Can be whole number from 3 to 9.

Tolerances Introduction to Engineering Design © 2012 Project Lead The Way, Inc.

Tolerances Variation is unavoidable Presentation Name Course Name Unit # – Lesson #.# – Lesson Name Tolerances Variation is unavoidable No two manufactured parts are identical – some degree of variation will exist Tolerances are used in production drawings to control the manufacturing process and control the variation between copies of the same part In particular, tolerances are applied to mating parts in an assembly One advantage in using tolerances is that interchangeable parts can be used Without tolerances, copies of individual parts could vary significantly, disallowing the use of a copy of the part because is does not fit or does not operate properly within an assembly.

Do not specify a tolerance that is smaller than necessary! Presentation Name Course Name Unit # – Lesson #.# – Lesson Name Tolerances Large tolerance may affect functionality of part Specify tolerances to ensure proper function Small tolerance will affect the cost of the part Cost generally increases with smaller tolerances Will require precise manufacturing Will require quality control with inspection and rejection of parts Do not specify a tolerance that is smaller than necessary! Without tolerances, copies of individual parts could vary significantly, disallowing the use of a copy of the part because is does not fit or does not operate properly within an assembly.

Tolerances ANSI/ASME Standard Y14.5 Each dimension shall have a tolerance, except those dimensions specifically identified as reference, maximum, minimum, or stock. The tolerance may be applied directly to the dimension or indicated by a general note located in the title block of the drawing.

Tolerances A tolerance is an acceptable amount of dimensional variation that will still allow an object to function correctly.

Tolerances Three basic tolerances that occur most often on working drawings are: limit dimensions bilateral tolerance unilateral tolerance

Presentation Name Course Name Unit # – Lesson #.# – Lesson Name Limit Dimensions Provide an upper limit and lower limit for the dimension. Any size between or equal to the upper limit and/or lower limit is allowed The upper limit dimension is 0.126 The lower limit dimension is 0.125

Bilateral Tolerance Provides an equal allowable variation, larger and smaller Uses a plus/minus (±) symbol to specify the allowable variation Counter bore depth can be .003 larger or smaller than .25 Hole location can be .05 larger or smaller than 1.50

Unilateral Tolerance Provides an allowable variation in only one direction (either larger or smaller) Uses separate plus (+) and minus (–) signs The hole diameter may vary .004 larger but may not be smaller than .500

Tolerances Identify the type of tolerance displayed in red Presentation Name Course Name Unit # – Lesson #.# – Lesson Name Tolerances Identify the type of tolerance displayed in red Limit dimensions Bilateral Unilateral Have students identify each type of tolerance displayed in red. Start with the upper left. Have students offer their answers, then click to reveal the correct tolerance type. Proceed to middle red dimension, then lower right dimension.

Definitions Specified Dimension is the target dimension from which the limits are calculated Specified dimension 1.50

Definitions Limits are the maximum and minimum sizes shown by the toleranced dimension Upper limit is the maximum allowable dimension Lower limit is the minimum allowable dimension Upper Limit = Specified Dimension + positive variance 1.55 = 1.50 + 0.05 Lower Limit = Specified Dimension + negative variance 1.45 = 1.50 + (– 0.05)

Presentation Name Course Name Unit # – Lesson #.# – Lesson Name Definitions Tolerance is the total variance in a dimension and is equal to the difference between the upper and lower limits. Tolerance = Upper Limit – Lower Limit 0.10 = 1.55 – 1.45 If a part is manufactured outside of the limits established by the tolerance, the part is said to be “out of tolerance”.

Calculating Tolerance .010 - .05 + .05 1.45 1.50 1.55 Lower Limit Upper Limit Tolerance = Upper Limit – Lower Limit 0.10 = 1.55 – 1.45

Presentation Name Course Name Unit # – Lesson #.# – Lesson Name General Tolerances General tolerances are tolerances that are assumed if no specific tolerance is given for a dimension Typically tolerances are specified based on the number of digits to the right of the decimal point in a dimension Shown on drawing Linear Dimensions X.X = ± .020 X.XX = ± .010 X.XXX = ± .005 So, for example, using these general tolerances, a linear dimension specified with a precision of one digit to the right of the decimal point is specified to be manufactured within a variation of 0.02 larger or smaller than the specified dimension. A part showing a specified length dimension of 3.64 must be manufactured to a length of between 3.63 and 3.65 (or equal to either of those values). Angles = ± .5°

General Tolerances Tolerance = Upper Limit – Lower Limit Presentation Name Course Name Unit # – Lesson #.# – Lesson Name General Tolerances Upper Limit = 3.00 + 0.010 = 3.010 Lower Limit = 3.00 + - 0.010 = 2. 990 For example, the depth of a part is specified to be 3.00 with no indication of tolerance associated with the dimension. Therefore, the general tolerances apply. Because the dimension has two digits places to the right of the decimal point, the bilateral tolerance of +/- 0.010 applies. Therefore the upper limit is 3.010 and the lower limit is 2.990. This gives a tolerance of 0.020, the total allowed variation in the depth of the part. Tolerance = Upper Limit – Lower Limit 0.10 = 3.010 – 2.990 = 0.020

Presentation Name Course Name Unit # – Lesson #.# – Lesson Name Out of Tolerance A manufactured part is said to be out of tolerance if the part is not within specified limits Manufacturing facilities often institute quality control measures to help ensure that parts are within tolerance

Types of Fit Clearance Fit limits the size of mating parts so that a clearance always results when mating parts are assembled Interference Fit limits the size of mating parts so that an interference always results when mating parts are assembled Transition fit occurs when two mating parts can sometimes have a clearance fit and sometimes have an interference fit

Presentation Name Course Name Unit # – Lesson #.# – Lesson Name Types of Fit Clearance Fit – Always a clearance between the axle and the opening Here, the maximum size of the axle is 10 and the minimum size of the hole is 10.15. If these parts are manufactured correctly, there will always be a clearance between these two parts when the axle is inserted through the hole.

Presentation Name Course Name Unit # – Lesson #.# – Lesson Name Types of Fit Interference Fit - Always an interference between the axle and the opening In this case, the minimum size of the axle is 9.92, but the maximum size of the opening is 9.90. Therefore, if the parts are manufactured correctly, the axle will always be larger than the opening. This type of fit may be called a press fit or force fit such that the two parts must be pressed together in order to assemble them.

Definitions Maximum material condition (MMC) is the condition of a part when it contains the largest amount of material. The MMC of an external feature, e.g., the length of a plate, is the upper limit of the dimension The MMC of an internal feature, e.g., the diameter of a hole, is the lower limit of the dimension

Definitions Least material condition (LMC) is the condition of a part when it contains the smallest amount of material. The LMC of an external feature, e.g., the length of a plate, is the lower limit of the dimension The LMC of an internal feature, e.g., the diameter of a hole, is the upper limit of the diameter dimension

Definitions Allowance is the minimum clearance or maximum interference between parts For a clearance fit, the allowance is the tightest possible fit between mating parts Allowance = MMC internal feature – MMC external feature

Calculate Allowance Allowance = MMC internal feature Presentation Name Course Name Unit # – Lesson #.# – Lesson Name Calculate Allowance Allowance = MMC internal feature – MMC external feature Allowance = 10.15 – 10.00 = 0.15 MMC MMC In the case of a clearance fit, the allowance is the smallest space between mating parts. The maximum material condition (MMC) of the hole is 10.15 since the smaller hole will result in the most material in the part The maximum material condition (MMC) of the axle is 10.00 since the larger axle will result in the most material in the part

Calculate Allowance Allowance = MMC internal feature Presentation Name Course Name Unit # – Lesson #.# – Lesson Name Calculate Allowance Allowance = MMC internal feature – MMC external feature MMC internal feature External feature MMC Allowance = 9.85 – 10.00 = – 0.15 Have students calculate the allowance for this interference fit, then click to show the answer. In the case of an interference fit, the allowance is negative and represents the maximum interference. In this case, the axle can be as much as 0.15 larger than the hole into which it fits. The larger the interference, the more difficult it is to force the axle into the hole. The allowance, or maximum interference, is 0.15

A Note About Dimension Tolerance Presentation Name Course Name Unit # – Lesson #.# – Lesson Name A Note About Dimension Tolerance In general, the more significant figures in the dimension, the tighter the tolerance Overly precise dimensions and overly tight tolerances increase manufacturing costs Specify dimensions only to the precision and tolerance necessary for the part to function properly For example, specifying a tight tolerance , say +/- .005 would be excessive and increase the cost of the coaster needlessly. However, specifying a tight tolerance on connections on an astronaut’s suit is necessary to ensure no leakage of gas.

Documentation Introduction to Engineering Design © 2012 Project Lead The Way, Inc.

Documentation Once a design has been approved and fully researched, the part needs to be prototyped or manufactured. To do so, we need to have the appropriate documentation to communicate the idea to everyone in the company. Documentation is the most difficult, time consuming, yet most important part of engineering communication. This documentation is done with working drawings.

Working Drawings Working drawings are a complete set of drawings that document how an object will be manufactured and assembled. Each set should include: Part Drawings Assembly Drawings Parts List Specifications or Instructions

Part Drawing A part drawing is the drawing that contains all the information for making one part of the design. This drawing consists of dimensioned orthographic views. If necessary, section, auxiliary, detail, and an isometric view can help document the part. All features of the part will be dimensioned so that it can be manufactured.

Part Drawing Example

Title Blocks Title blocks are necessary to identify the drawing and the general details that go along with that part. An example showing the parts of a title block are shown on the next slide.

© Project Lead The Way, Inc. Title Blocks Size of sheet. Important when reading a drawing to ensure that the drawing is printed to display the proper scale accurately. Also valuable when printing. General notes and information. Located here you will see information on fillet and rounds, tolerances, and other general information that would take up too much space on the drawing if repeated on every feature. Zoning is used to find specific locations on the drawing. Usually shown in numbers and letters. Example: ANSI Large style title block. Title blocks can be customized by a company but may contain the following information Remember working drawings are made of many different types of drawings. More than one sheet usually goes with a design. The drawing may be checked by Quality Assurance to be sure that it meets all company standards and requirements. Title of the project, as opposed to a specific part. Name of person who checked the drawing. Just like first drafts of papers written in English class, drawings go through many revisions. Another person will check the drawing and approve the part for manufacture. Documentation of how many times the drawing has been changed. Name of person who created the drawing. Drawing number or specific part name in relationship to the total design. Scale of the part is important so that the reader understands the relative size of the part. © Project Lead The Way, Inc.