Dimensioning of Circle in Engineering Drawing

Alphabet of Lines

What is the main image, which we are using in all our projects, designs, drawings?

It is a line!

In Graphics Advice practise in that location is the whole collection of different lines, which are used for drawing purposes.

The alphabet of lines is a set of standard line types established by the American National Standards Establish (ANSI) for technical drawing. The alphabet of lines and the approximate dimensions used to create dissimilar line types, are referred to as linestyles when used with CAD.

The standard line types used in technical drawings are

Eye lines are used:

• to represent symmetry,
• to stand for paths of move,
• to mark the centers of circles and the axes of symmetrical parts, such as cylinders and bolts.

Break lines are used to prove where an object is broken to save drawing space or reveal interior features.

Break lines come in two forms:

• a freehand thick line, and
• a long, ruled thin line with zigzags.

Dimension and extension lines are used to indicate the sizes of features on a cartoon.

Section lines (hatching) are used in department views to stand for surfaces of an object cut past a cutting aeroplane.

Phantom lines are used to represent a movable feature in its unlike positions.

Sew together lines - to point a sewing or stitching process.

Visible lines are used to represent features that can be seen in the electric current view.

Hidden lines, equally you lot already know, are used to stand for features that cannot be seen in the current view.

Cutting plane lines are used in section drawings to show the locations of cut planes.

In that location are besides lines used in some particular cases:

Chain lines - to indicate additional treatment for a surface.

Symmetry lines - equally an centrality of symmetry of a particular view.

While preparing drawings you must follow the rules established for the line technique.

Each line should have one of the two thicknesses, thick or thin, and the ratio of the thicknesses must be not less than two:ane. In many textbooks (peculiarly, of the US authors) yous volition come across the thicknesses of lines: 0.3 mm and 0.6 mm. In general cases it is adept plenty in practical work.

The alphabet of lines assigns specific thickness to each line and it cannot be inverse arbitrarily.

In cases where other than shown types of lines are used for special drawings (for instance, electrical drawings, pipeline diagrams, or building drawings) the conventions adopted must be clearly indicated by reference to specific standards or by notes on the drawings.

For all views of one piece or assembly to the same scale, the thickness of the lines should exist the same. Medium and extra-thick lines should be used only in special cases.

The minimum space between parallel lines should never be less than twice the thickness of the heaviest line. Information technology is recommended that these spaces exist 0.vii mm or greater.

In end views of round features the point of intersection of ii centre lines should be shown by two intersecting brusque dashes, except for very small circles, as shown:

Break Line are used to shorten the view of long uniform or tapered sections, or when only a partial view is necessary, and are used on both detail and assembly drawings.

The thin line with freehand zig-zags is recom­mended for long breaks and may be used for solid details or for assemblies containing open space.

Thick freehand lines are used for short breaks

and the jagged line for forest parts.

The special thick pause lines shown for cylindrical and tubular parts are useful when an end view is not shown, but otherwise the thick freehand break line is adequate.

Note that all these break lines were designed for preparing drawings in the erstwhile-fashioned manner by using a draft board. Sometimes engineers and designers still piece of work on drawings with pencils and rulers. All the same, modern 3D CAD software, which prevails in our days, can offer other line types for the break lines in the computer-based drawings.

Dimensioning practise

Once the shape of a role is defined with an orthographic drawing (i.e., in projections), the size information is added in the course of dimensions.

Dimension elements

Dimensioning a drawing likewise identifies the tolerance (or accurateness) required for each dimension.

1. Dimension — the numerical value that defines the size, shape, location, surface texture, or geometric characteristic of a feature.
2. Basic dimension — a numerical value defining the theoretically exact size, location, or orientation relative to a coordinate system. Basic dimensions are enclosed in a rectangular box & take no tolerance.
3. Reference dimension — a numerical value enclosed in parentheses, provided for information only.
4. Dimension line — a thin, solid line that shows the extent and direction of a dimension.
5. Arrows — symbols at the ends of dimension lines showing the limits of the dimension, leaders, and cutting plane lines.
6. Extension line — a thin, solid line perpendicular to a dimension line, indicating which feature is associated with the dimension.
7. Visible gap — there should be a visible gap of 1 mm between the feature's corners and the finish of the extension line.
8. Leader line — a thin, solid line with arrow drawn nether an bending & indicating the feature with which a dimension or note is associated.
9. Limits of size — the largest acceptable size and the minimum acceptable size of a feature.
10. Plus and minus dimension — the commanded positive and negative variance from the specified dimension.
11. Diameter symbol — a symbol indicating that the dimension shows the diameter of a circle. The symbol used is the Greek letter phi Ø.
12. Radius symbol — a symbol indicating that the dimension shows the radius of a circle. The radius symbol used is the uppercase letter R.
13. Tolerance — the amount that a item dimension may vary.

Basic concepts and principles

• The unit of measurement for dimensioning should exist in accordance with the policy of the user. On a drawing for utilize in American industry for manufacturing, all dimensions are in inches, unless otherwise stated.
• Most countries outside of the United States, including Canada, apply the metric system of measure out, or the international system of units (SI), which is based on the meter.

The mutual metric unit of measurement of mensurate on engineering drawings is the millimeter, abbreviated as mm.

Sometimes, you will have to place dimensions in two units simultaneously!

Dimensions should be placed in the most descriptive view of the feature.

If the view is overcrowded with different dimensions, two and more separate drawings with the aforementioned view can be produced.

Dimension text placement

Text of the dimensions tin be placed in unlike ways:

• dimension inside the extension lines, with arrows inside or outside; and
• dimension outside the extension lines, with arrows again inside or exterior.

Where infinite is limited extension lines may be fatigued at an angle:

Extension lines should non cross dimension lines, and they should avoid crossing other extension lines whenever possible. When extension lines cross object lines or other extension lines, they should non exist broken. When extension lines cross or are close to arrowheads, they should be broken for the arrowhead.

Arrowless dimensioning

To avert having many dimensions extending away from the function, arrowless dimensioning may be used.

1. the "nix" lines represent the vertical and horizontal datum lines,
2. each of the dimensions shown without arrowheads indicates the distance from the zero line.

• There shall never be more 1 zero line in each management.
• Arrowless dimensioning is used for locational dimensions for a series of features such as holes and slots.

All dimensions and note text must be oriented to read from the bottom of the drawing. This is called unidirectional dimensioning.

The aligned method (where text is placed parallel to the dimension line) may be seen on older drawings or on architectural drawings only is not approved by the current ANSI standard.

Grouping dimensions

In standard practice, dimensions are grouped on a cartoon for uniform advent.

Avoid using object lines every bit extension lines for a dimension.

Dimensions must be kept exterior the boundaries of views, wherever applied.

Dimensions can be placed in serial and parallel.

• When a series of dimensions is applied on a point-to-betoken basis, information technology is referred to as chain dimensioning .

The outset dimension in a raw should be stuck to a base line.

Disadvantage of this system: it may result in an undesirable accumulation of tolerances between individual features.

• When several dimensions beginning from a common reference point or line, the method is referred to every bit common-point, or parallel, dimensioning .

The reference line may exist an extension of the outline of the origin, a base of operations line, or a system line.

The base surface is the external surface of the part, which must be machined first.

Dimensions can be placed in parallel or in series, but in all cases, they should be related to the base (datum) surface.

Stagger dimensions

The general practice is to stagger the dimension text on several parallel dimensions.

Size dimension

The dimensions tin can be classified by types of size:

• Horizontal — the left-to-right distance relative to the drawing sail. Hither the width is the only horizontal size dimension.
• Vertical — the upward and down distance relative to the drawing canvas. Here the height and the depth are both vertical dimensions, fifty-fifty though they are in two different directions on the function.
• Diameter—the full distance across a circle, measured through the center.
• Radius—the altitude from the heart of an arc to any point on the arc. Radius is usually used on arcs less than half circles.

Location and orientation dimensions

The dimensions can be classified by blazon of location or orientation:

• Horizontal position – locates the position of the feature in horizontal direction with respect to a base;
• Vertical position – locates the position of the feature in vertical direction with respect to a baseast;
• Angle – gives the bending between the horizontal airplane and the sloping surface.

Athwart units

1. Athwart dimensions are shown either in decimal degrees or in degrees, minutes, and seconds.
2. Where simply minutes and seconds are specified, the number of minutes or seconds are preceded by the 0⁰.

Information technology is also good to have an isometric view of the part on its drawing. Non mandatory but preferable for complex parts.

No dimensions should be shown on isometric view. Scale must exist shown if it differs from the full general i.

Detail dimensioning (How to dimension various features)

• Holes are typically dimensioned in a view which best describes the shape of the pigsty. Diameters must exist dimensioned with the bore symbol preceding the numerical value. When holes are dimensioned with a leader line, the line must exist radial.

A radial lin e is one that passes through the middle of a circle or arc if extended.

• Symbols may exist used for spotface, counterbore, and countersunk holes. These symbols e'er precede the diameter symbol.

The depth symbol may exist used to indicate the depth of a hole. The depth symbol is placed preceding the numerical value.

• When the depth of a blind hole is specified, it refers to the depth of the full diameter of the hole.

• Chamfers are dimensioned by providing either an angle and a linear dimension or by providing two linear dimensions.

Chamfers of 45⁰ may be specified in a note.

• Slotted holes may be dimensioned any of several ways depending on which is nigh appropriate for the application.

• The gradient of a line or flat surface can exist specified:

(a) every bit a ratio combined with the gradient symbol; (b) by the angle; (c) by the dimensions showing the deviation in the heights of two points from the base line and the distance between them.

• Dimensioning chords, arcs and angles

• Keyseats and keyways, which are fastening devices, are dimensioned in a particular way, considering they nowadays some unusual problems.

The height of the keyseat itself is not dimensioned because, once the peak of the shaft is cutting away, there is no feature left to mensurate.

Also the dimensions are unilateral:

• for the keyseat, the dimension is a minimum;
• for the keyway, the dimension is a maximum.

This is to ensure an interference in one case the key is inserted between the parts.

Dimensioning repetitive features

• Repetitive features and dimensions may exist specified by the utilize of an "10" in conjunction with the numeral to indicate the " number of times " or " places " they are required. A total space is left between the "Ten" and the feature dimension.

An "X" is sometimes used to bespeak " BY " between coordinate dimensions specified in note form. A half space is left in this example between the "X" and the dimensions.

To avoid repeating the same dimension or to avoid long leader lines, nosotros may employ reference letters in conjunction with an explanatory table or note.

• Identification of similar sized holes

• Dimensioning gears

A gear is a toothed-bicycle mechanical device used to transit power and motility betwixt machine parts. Typically a shaft is used to both use and receive power from the gears.

When two gears of different sizes mesh, the larger is chosen the gear and the smaller is the pinion.

Normally, gear drawings include a tabular array of information, called cutting information, for manufacturing. A detail drawing of a gear would also include other dimensions non found in the table (root bore, bore diameter, keyway dimensions).

Alternatively, gears and splines may be shown with a solid line representing the basic outline of the part, and a lighter line representing the root of the teeth.

The pitch line may be added using the standard heart line. This is the same convention every bit used for spiral threads.

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Source: https://www.mcgill.ca/engineeringdesign/engineering-design-process/basics-graphics-communication/principles-dimensioning