Dimensioning. Dimensions: Are required on detail drawings. Provide the shape, size and location description: ASME Dimensioning Standards

Transcription

1 Dimensioning Dimensions: Are required on detail drawings. Provide the shape, size and location description: - Size dimensions - Location dimensions - Notes Local notes (specific notes) General notes ASME Dimensioning Standards ASME Y14.5, Dimensioning and Tolerancing. - GENERAL NOTE: DIMENSIONING AND TOLERANCING PER ASME Y DOD-D-1000 Section 5. Several other ASME documents with standards related to dimensioning and tolerancing.

2 Dimensioning Rules; Fundamental ASME Y Each dimension has a tolerance except reference, maximum, minimum, or stock. Dimensioning and tolerancing must be complete. Show each necessary dimension of an end product. Select and arrange dimensions to suit the function and mating relationship of a part. Dimensions must not be subject to more than one interpretation. Do not specify the manufacturing processes unless necessary. Identify non-mandatory dimensions with an appropriate note. Arrange dimensions to provide required information and optimum readability. Show dimensions in true profile views and visible outlines. Dimension diameter or thickness of materials manufactured to gage or code numbers. 90 angle is implied for centerlines and lines. 90 basic angle is implied for centerlines located by basic dimensions. A zero basic dimension applies where axes, center planes, or surfaces are shown one over the other with established geometric controls. Unless otherwise specified, all: - Dimensions and tolerances are measured at 20 C (68 F). - Dimensions and tolerances apply in a free state condition except for nonrigid parts. - Tolerances apply for the full depth, length, and width of the feature. - Dimensions and tolerances apply on the drawing where specified. Coordinate systems: - Right-handed (arranged clockwise) - Labeled axes and positive direction shown 3-D model complies with ASME Y14.41, Digital Product Definition Data Practices.

3 Preferred Dimensioning Practices Avoid crossing extension lines. Do not break extension lines when they cross. Never cross extension lines over dimension lines. Break the extension line where it crosses over a dimension line when necessary. Never break a dimension line. Break extension lines when they cross over or near an arrowhead. Avoid dimensioning over or through the object. Avoid dimensioning to hidden features. Avoid long extension lines. Avoid using any line of the object as an extension line. Dimension between views when possible. Group adjacent dimensions. Dimension to views that provide the best shape description. Do not use a centerline, extension line, phantom line, visible object line, or a continuation of any of these lines as a dimension line. Stagger adjacent dimension numerals so they do not line up. Dimensioning Guidelines to Follow Dimensioning Lines: Dimension lines are placed outside the object. Never dimension to hidden lines (very few exceptions allowed). Dimension line terminators arrowheads, slashes, and dots. Arrowheads are.125 in length (plotted size). Dimension lines have terminators on both ends of the dimension line. Dimension text is placed in the break in the dimension line for engineering drawings and above the line for Architectural dimensioning. Shortest dimensions are placed closest to the part. Dimension lines terminate at extension lines. Dimension lines may cross dimension lines. Extension Lines: Leader Lines: Extension lines indicate the point or line to which the dimension applies. The extension line offset is.062. The extension line extension is.125. Extension lines are drawn perpendicular to dimension lines. Extension lines may cross extension lines. Center lines may be used for extension lines. Leader lines terminate with arrows, lighting strike,.125 diameter. Leader lines are never drawn vertical or horizontal in engineering drawings. Leader lines should be kept as short as possible. Text or dimensions used with leaders are always horizontal.

4 Dimension Text: Local Notes: General Notes: Dimensions are read from the bottom of the sheet for engineering drawings (known as unidirectional). Dimensions are read from the bottom and right side of the sheet for architectural drawings (known as aligned). Dimension text is placed between the dimension lines for engineering drawings. Call out individual features. Are connected to the feature by a leader line. Located in the upper left side of the sheet.500 inch down and.500 inch from the top and left borderlines OR the lower-left hand corner. Units of Measure: Decimal Inch (three place decimals) Feet and Inches 2-7 (architectural) Millimeters 32.3 Dual Dimensioning: To be avoided (BOTH Metric and English measurements). Angular Units : Are in Degrees, Minutes, and Seconds Reading Direction: Dimensions and Notes are read from the bottom of the sheet (Unidirectional). Reference Dimensions: Shown for reference only. Are called out some place else on the drawing and shown in parentheses. Example: (23.127) Manufacturing Methods: Not called out on the drawing. Examples: Drill, Bore, Ream, Turn, Tap, Thread. Designer must know how these processes take place. Diameters: Radii: Actual size Basic Size: Design Size: Limit of Size: Nominal Size: Should be dimensioned in the view where they appear as circles. The letter R ALWAYS precedes the radius value. Is the measured size. Is the theoretical perfect size that limits are derived from. The size from which the limits of size are derived from. The maximum/minimum sizes permissible from a specific dimension. General information.

5 DIMENSIONING SETUP USING AutoCAD * First setup a new layer for dimensioning. * Change Dimensioning layer to red color. * Go to the Dimension Style Manager. Select Style Select Modify From this point change these areas for initial setup of a drawing: Lines Tab - Extend beyond dim lines to Offset from origin to.062 Symbols and Arrows Tab - Arrowheads size to.125 (use Architectural ticks for architectural drawings) Text Tab - Text height to.12 - Offset from dim line to.062 Fit Tab nothing to change Primary Units Tab - Precision. Set number of decimal places to 3 places for engineering drawings. - Zero suppression; check Leading Alternate Units Tab nothing ever changed here Tolerances Tab - Method; set if needed for GDT; set to BASIC and any other tolerances that will be used. * Once all parameters are completed exit by selecting OK. * Set Current * Close

6 RECOMMENDED ORDER to DIMENSION Drawings 1. Do interior dimensioning first; known as doing LOCATION dimensions: a. Locate center marks for holes. b. Locate center-to-center distances of holes (linear dimensioning). c. Locate any interior dimensions needed. 2. Create next size dimensioning. 3. Dimension outside areas needing dimensioning. 4. Dimension Holes (by DIAMETER) 5. Dimension Arcs (by R; RADIUS). 6. Edit individual dimensions as needed. Add notes like X2, etc. 7. Overall Dimensions are created LAST. Note: NO overall dimension(s) needed if either end of a view is in an arc or circular form. 8. Create local notes. 9. Create general NOTES. 10. Check for duplicate, unnecessary dimensions. 11. Check for missing dimensions. Do an imaginary check left to right and top to bottom to see if everything is dimensioned. DO S AND DON TS OF DIMENSIONING A. Dimensions should not interfere with the drawing. Number 1 rule is CLARITY. B. Dimensions should NOT be duplicated. C. Text and number height is normally.12 when plotted. D. Avoid dimensioning to hidden lines wherever possible. E. Never (with few exceptions) dimension inside the object (view). F. Never CROSS an extension line with a dimension line. G. An overall dimension is always the last or farthest dimension from a view. H. Keep distances of dimension lines equal throughout the views. Be consistent between the views. I. Dimensions side-by-side must be on the same plane for clarity purposes. They should line up in chain fashion. Do NOT stagger dimension lines. J. Dimensions should be attached to the view where the shape is best shown (contour rule). K. Leaders can be any angle EXCEPT 0, 90, 180 and 270 degrees in Engineering drawings. L. Leaders always point to the center of the circle or hole. M. Attempt to group together dimensions. Makes it easier to read the drawing. N. In an orthographic three-view drawing attempt to dimension most of the features between the three views.

7 BASIC RULES FOR DIMENSIONING 1. Only create views needed for dimensioning. 2. No unnecessary dimensions. 3. Leader lines should be directed to the center of circular objects. 4. Do not dimension to equal distance centers. 5. Leader lines are never vertical or horizontal in engineering drawings. 6. Omit leading zero s for inch measurements (known as zero suppression). Examples: Inch measure.33 NOT 0.33 Metric measure 0.44 NOT.44 Architectural 5 ½ NOT 0-5 ½ 7. Set up CAD dimensioning styles as needed; such as GDT, Limit, and Deviation as needed. Only necessary rule; Rule 1 is CLARITY Dimensioning Components

8 Dimensioning Symbols

9 Unidirectional Dimensioning Primary method to dimension engineering drawings. Numerals, figures, and notes lettered horizontally. Read from the bottom of the drawing sheet. Mechanical drafting for manufacturing. Aligned Dimensioning Used in Architectural and Structural drawings. NOT shown here; see the Architectural Standards Manual. Coordinate Dimensioning Known as ordinate dimensioning. Dimension values aligned with extension lines: - Dimension represents a measurement originating from datums or coordinates. Features such as holes sized using specific notes or a table. Popular for: - Precision sheet metal part drawings - Electronics drafting

10 Tabular Dimensioning A form of rectangular coordinate dimensioning without the dimension lines. The features are dimensioned in a table. Chart Dimensioning Used when a part or assembly has one or more dimensions that change depending on the specific application.

11 Millimeter Dimensions Millimeters (mm) - Common International System of Units (SI) unit of measure. GENERAL NOTE: UNLESS OTHERWISE SPECIFIED, ALL DIMENSIONS ARE IN MILLIMETERS. Follow any inch dimensions with IN. Popular use of Metric Units Omit decimal point and 0 when dimension is a whole number. Precede a decimal value that is less than 1 with a 0. (EX: 0.5) When the value is greater than a whole number by a fraction of a mm, do not place a 0 next to last digit. - Exception: when displaying tolerance values Plus and minus tolerance values have same number of decimal places. Limit tolerance values have same number of decimal points. Unilateral tolerances use a single 0 without a corresponding + or sign.

12 Inch Dimensions Decimal inches (IN) - United States (U.S.) customary unit of measure GENERAL NOTE: UNLESS OTHERWISE SPECIFIED, ALL DIMENSIONS ARE IN INCHES. Follow any millimeter dimensions with mm. Proper Use of Inch Units Do not precede a value that is less than 1 inch with a 0. Express a specified dimension to the same number of decimal places as its tolerance. Fractional inches generally indicate larger Tolerance. Plus and minus tolerance values have the same number of decimal places. Unilateral tolerances use the + and sign - The 0 value has the same number of decimal places as the value that is greater or less than 0. Limit tolerance values have the same number of decimal points. Proper Use of Angular Units Use decimal or degrees minutes seconds format. Angle and tolerance values have the same number of decimal places. Include 0 or 0 0 when specifying only minutes or seconds, as applicable.

13 Using Fractions Not as common as decimal inches or millimeters. Used in Architectural and structural drawings; see the Architectural Standards Manual. Arrowheads Terminate dimension lines and leaders. Three times as long as they are wide; generally.125 long plotted on prints. Consistent size. Filled in solid or open. Dimension Line Spacing First dimension line: - Uniform distance from the object.375 in. (10 mm) minimum in. (12-24 mm) preferred Succeeding dimension lines: - Equally spaced.25 in. (6 mm) minimum in. (12-20 mm) preferred

14 Dimension Numbers:

15 Chain Dimensioning Creates tolerance stacking (tolerance buildup) - Omit one intermediate dimension or the overall dimension Baseline Dimensioning Size or location of features controlled from a common reference plane. Reduces possibility of tolerance stacking Direct Dimensioning Results in the least tolerance stacking.

16 Dimensioning Symmetrical Objects Dimensioning Cylinders Dimensioning Square Features

17 Dimensioning Angular Surfaces Dimensioning Chamfers Dimensioning Conical Shapes

18 Dimensioning Hexagons and Other Polygons Dimension across the flats. Dimension Arc Radius Dimension Arc Length Additional Radius Dimensioning Applications True radius - TRUE R followed by the actual radius Controlled radius - CR followed by the radius Spherical radius - SR followed by the radius Dimensioning Contours Not Defined as Arcs Dimension coordinates or points along the contour from common surfaces. Series of dimensions on the object and along the contour. Tabular dimensioning.

19 Locating a Point Established by Extension Lines Dimensioning Circles and Thru Holes Dimensioning Blind Holes

20 Dimensioning a Counterbore A counterbore is often used to machine a diameter below the surface of a part so a bolt head or other fastener can be recessed. Dimensioning a Spotface A spot provides a flat bearing surface for a washer face or a bolt head.

21 Dimensioning a Countersink or Counterdrill A countersink is a conical feature in the end of a machined hole. Dimension Multiple Features Number of features, X, a space, feature specification. Dimension to one of the features only. Examples: - 4X Ø6 THRU or 4X Ø6-2X R.50-3X 8X45 Dimensioning Slots

22 Dimensioning Keyseats and Keyways Keyseats are a groove or channel cut in a shaft. A keyway is a shaft and key that are inserted in a hub, wheel, or pulley where the key mates with a groove called a keyway. Dimensioning Knurls A knurl is a diamond or straight pattern created on a cylindrical or flat surface. It generally provides a gripping surface for the user of a device that is knurled.

23 Dimensioning Necks and Grooves Rectangular Coordinate Dimensioning

24 Polar Coordinate Dimensioning Dimensioning Repetitive Features Locating Multiple Tabs in a Polar Orientation

25 Locating Multiple Features of Nearly the Same Size Specifying Dimension Origin Clearly identifies from which feature the dimension originates Dimensioning Auxiliary Views