Dimensioning Flra Hajdu B 406 hajdflsze hu Content
Dimensioning Flóra Hajdu B 406 hajdfl@sze. hu
Content • Dimensioning systems 2021. 12. 17. Hajdu Flóra
Dimensioning • A working drawing is one from which a part can be produced • The drawing must be a complete set of instructions • A working drawing consists of • The views necessary to explain the shape • The dimensions needed for manufacture • Required specifications (e. g. material, quantity) 2021. 12. 17. Hajdu Flóra
Dimensioning • Dimension must be clear and concise and permit only one interpretation • Each surface, line or point is located by only one set of dimensions • These dimensions are not duplicated in other views • Deviations from the approved rules for dimensioning should be made only in exceptional cases, when they improve the clarity of the dimensions (arrowless and tabular dimensioning) • In industry drawings require some form of tolerancing on dimensions • Components can be properly assembled • Manufacturing and production requirements can be met 2021. 12. 17. Hajdu Flóra
Dimensioning • Dimensions are given on drawings by extension lines, dimension lines, leaders, arrowheads, figures, notes and symbols • They define geometric characteristics, such as lengths, diameters, angles and locations • Thin lines are used in dimensioning scan 2021. 12. 17. Hajdu Flóra
Dimensioning Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design 2021. 12. 17. Hajdu Flóra
Dimension and extension lines • Dimension lines are used to determine the extent and direction of dimensions • They are nomally terminated by uniform arrowheads • Recommended leght and width of arrowhead should be in ratio 1: 3 • The length of the arrowhead should be equal to the height of the dimension numeral 2021. 12. 17. Hajdu Flóra
Dimension and extension lines • Dimension is placed above the dimension line • Dimension lines are broken for insertion of the dimension 2021. 12. 17. Hajdu Flóra
Dimension and extension lines • When the space between the extension lines is too small the alternative method of placing the dimension line, dimension or both outside the extension lines is used 2021. 12. 17. Hajdu Flóra
Dimension and extension lines • Extension (projection) lines are used to indicate the point or line on the drawing to which the dimension applies • A small gap is left between the extension line and the outline to which it refers • Extesion lines are usually drawn perpendicular to dimension lines • Center lines may be used as extension lines in dimensioning • When extension lines cross other extension lines or visible lines they are not broken • When they cross arrowheads or dimension lines a break in extension line is recommended Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design 2021. 12. 17. Hajdu Flóra
Leaders • Leaders are used to direct notes, dimensions, symbols, item numbers to features on the drawing • Leader should be generally a single straight inclined line and is terminated by an arrowhead (dots should be used within the outline of the object and rest on a surface) Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design scan 2021. 12. 17. Hajdu Flóra
Notes • Notes are used to simplify or complement dimensioning by giving information on the drawing in a condensed and systematic manner • General notes refer to the part or the drawing as a whole • Examples • FINISH ALL OVER • ROUNDS AND FILLETS R 6 • REMOVE ALL SHARP EDGES • Local notes apply to local requirements only and are connected by a leader to the point to which the note applies • Examples • 4 xØ 6 • 2 x 45 o • M 12 x 1. 25 2021. 12. 17. Hajdu Flóra
Rules of dimensioning All dimensions must be given needed for manufacturing Dimensions should not be duplicated Dimension lines should not be crossed Avoid dimensioning of hidden lines (use sections instead) Place dimensions between the views possible Place dimension line for the shortest length, width or height nearest the outline of the object Parallel dimension lines are placed in order of their size, making the longest dimension line the outermost Place dimensions with the view that best shows the characteristic contour shape of the object On large views dimensions can be placed on the view to improve clarity Use only one system of dimensions either the unidirectional or the aligned Dimensions should be selected so that it will not be necessary to add or substract dimensions in odrer to define a local feature • Use the same unit in a drawing • Manufacturing method should not be given • • • 2021. 12. 17. Hajdu Flóra
Dual dimensioning 2021. 12. 17. Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design Hajdu Flóra
Reference dimension • A reference dimension is shown for information only and is not required for manufacturng or inspection purposes • It is enclosed in parentheses 2021. 12. 17. Hajdu Flóra
Not-to-Scale dimensions • When a dimension is altered making it not to scale it should be underlined with a straight thick line, except when the condition is clearly shown by break lines 2021. 12. 17. Hajdu Flóra
Symbols for different shapes • • • 2021. 12. 17. : Diameter SR: Spherical radius R : Radius S : Spherical diameter � : Square Hajdu Flóra
Rounded ends • • Overall dimensions should be used for parts or features having rounded ends Fully rounded: radius R is shown but not dimensioned Partial rounded: radius is dimensioned When a hole and a radius have the same center and the hole location is more critical: radius of the overall length should be shown as a reference dimension scan Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design 2021. 12. 17. Hajdu Flóra
Dimensioning chords, arcs and angles 2021. 12. 17. Hajdu Flóra
Holes • Plain, round holes are dimensioned in various ways, depending upon design and manufacturing requirements • With small holes a leader can be used to specify sizes • The size, quantity and depth may be shown on a single line 2021. 12. 17. Hajdu Flóra
Repetitive features and dimensions • Repetitive features and dimensions may be specified on a drawing by the use of an X in conjunction with the numeral to indicate the , , number” they are required 2021. 12. 17. Hajdu Flóra
Slopes • A slope is the slant of line representing an inclined surface • It is expressed as a ratio of the difference in heights at right angles to the base line at a specified distance apart • Specified as a ratio combined with the slope symbol 2021. 12. 17. Hajdu Flóra
Tapers • Taper is the ratio of the difference in the diameters of 2 sections (perpendicular to the axis of a cone to the distance between these 2 sections) • When the taper symbol is used the vertical leg is always shown to the left and precedes the ratio figures 2021. 12. 17. Hajdu Flóra
Undercuts • The operation of undercutting or necking (cutting a recess in diameter) is done to permit 2 parts to come together • It is indicated by a note listing the diameter and the width Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design scan 2021. 12. 17. Hajdu Flóra
Dimensioning methods • The choice of most suitable dimensioning method depends on how the part will be produced and wether the drawings are intended for unit or mass production • Unit production: refers to cases when each part is made separately using general purpose tools and machines • Mass production refers to parts produced in quantity, where special tools and gages are usually provideded • Systems of dimensioning • • • 2021. 12. 17. Rectangular coordinate dimensioning Polar coordinate dimensioning Chordal dimensioning True-position dimensioning Chain dimensioning Common-Point dimensioning Hajdu Flóra
Rectangular coordinate dimensioning • Method for indicating distance, location and size by means of linear dimensions measured parallel or perpendicular to reference axes or datum planes, that are perpendicular to one another • Regular coordinates for arbitrary points • Rectangular coordinate dimensioning withouth dimension lines • Tabular dimensioning 2021. 12. 17. Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design Hajdu Flóra
Polar coordinate dimensioning • Commonly used in circular planes or circular configuration of features • Indicates the position of a point, line or surface by means of linear dimension and an angle other than 90 o Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design scan 2021. 12. 17. Hajdu Flóra
Chordal dimensioning • Used for spacing of points on the circumference of a circle relative to a datum, when manufacturing methods indicate that this will be convenient Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design scan 2021. 12. 17. Hajdu Flóra
True-Position dimensioning • Geometric dimensioning and tolerancing scan 2021. 12. 17. Hajdu Flóra Source: C. Jensen, J. D. Helsel, D. R. Short: Engineering Drawing&Design
Chain dimensioning • When a series of dimensions is applied on a point-to-point basis • Disadvantage: it may result in an undesirable accumulation of tolerances between individual features 2021. 12. 17. Hajdu Flóra
Common-point dimensioning • When several dimensions emanate from a common reference point or line • Parallel • Superimposed running dimensioning (simplified parallel dimension, when there are space problems) 2021. 12. 17. Hajdu Flóra
Summary • Dimensioning • Dimension lines, extension lines, dimensions • Rules of dimensioning • Dimensioning systems Next week: Sections
Thank You for Your attention!
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