Lines Dimension Ing

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Engineering Drawing Lines, Lettering Lines, Lettering and Dimensioning and Dimensioning - Dr. Ranadip K. Das Assistant Prof. MEMME Dept., ISM

Transcript of Lines Dimension Ing

Engineering DrawingLines, Lettering and Dimensioning

- Dr. Ranadip K. Das Assistant Prof. MEMME Dept., ISM

Syllabus Drawing instruments and their uses. Lettering, Lines and dimensioning. Scales: Plain scale, Diagonal scale, Vernier scale. Curves used in Engg. Practice: Conic sections, Ellipse, Parabola, Hyperbola, Cycloid, Epicycloid, Hypocycloid, Involutes, and Spiral. Orthographic projections: First angle and third angle projections, conventions used, orthographic projection of simple solids; Conversion of three-dimensional views to orthographic views. Isometric projections: Isometric views, conversion of orthographic views to isometric views. Free hand sketching.

Types of Lines (SP : 46-1998)

Types of Lines

Lines - ThicknessLine group Mediu m Thin Thicknes Uses s (mm) 0.2 Out lines, dotted line, cutting plane lines 0.1 Centre lines, section lines, dimension lines, extension line, construction lines, leader lines, short-break lines, and long-break lines

Lines - Thickness In the finished drawing, all lines except construction lines should be dense, clean and uniform.

Construction lines should be drawn very thin and faint in the finished drawings.

Types of Lines

Types of Lines

Types of Lines

Types of Lines

Dimensioning Terms & Notations

Placing of DimensionsTwo systems: (i) Aligned system dimensions are placed perpendicular to the dimension line in such a way that it may be read from the bottom edge or the right-hand edge of the drawing sheet. The dimensions should be placed near the middle and above, but clear of the dimension lines. (ii) Unidirectional system - dimensions are so placed that they can be read from the bottom edge of the drawing sheet. The dimension lines are broken near the middle for inserting the dimensions. This system is mainly used on large drawings - as of aircrafts, automobiles etc. where it is inconvenient to read dimensions from the right-hand side.

Aligned system Dimensioning

Unidirectional System Dimensioning

Unit of Dimensioning As far as possible all dimensions should be given in millimetres

Abbreviation mm is omitted, only the dimension figures are written. But a foot note such as all dimensions are in centimetres is inserted in a prominent place near the title block. The height of the dimension figures should be from 3 5 mm.

The decimal point in a dimension should be quite distinct and written in line with the, bottom line of the figure (such as 2.5). A zero must always precede the decimal point when

General Rules for Dimensioning Dimensioning should be done so completely that further calculation or assumption of any dimension, or direct measurement from the drawing is not necessary.

Every dimension must be given, but none should be given more than once. A dimension should be placed on the view where its use is shown more clearly.

Dimensions should be placed outside the views, unless they a clearer and more easily read inside. Mutual crossing of dimension lines and dimensioning between hidden lines should be avoided. Dimension lines should not cross another line of the drawing. An outline or a centre line should never be used as a dimension line. A centre line may be extended to serve as an extension line.

Aligned system of dimensioning is recommended.

Practical Hints on Dimensioning Dimension lines should be drawn at least 8 mm away from outlines and from each other. Two ways of placing dimensions in a series: (a) Continuous or chain dimensioning: Dimensions are arranged in a straight line. An overall dimension is placed outside the smaller dimensions. One of the smaller dimensions (the least important) is generally omitted.

Practical Hints on Dimensioning(b) Progressive or parallel dimensioning: All dimensions are shown from a common base line. Cumulative error is avoided by this method. This method is preferable.

Practical Hints on Dimensioning Smaller dimensions should be placed nearer the view and the larger further away so that extension lines do not cross dimension lines. Extension lines may cross each other or the outlines. When a number of parallel dimension lines are to be shown near each other, the dimensions should be staggered. Dimensions should be shown where the shape is easily identified.

Practical Hints on Dimensioning Arrowheads should ordinarily be drawn within the limits of the dimensioned feature. But when the space is too narrow, they may be placed outside. A dot may also be used to replace an arrowhead. Due to lack of space, the dimension figure may be written above the extended portion. of the dimension line, but preferably on the right-hand side.

Practical Hints on Dimensioning Dimensions of cylindrical parts should as far as possible be placed in the views in which they are seen as rectangles. The dimension indicating a diameter should always be preceded by the symbol . Dimension of a cylinder should not be given as a radius. Dimensions should be shown in one view only, the same dimension must not be repeated in other view.

Practical Hints on Dimensioning Various methods of dimensioning different sizes of circles as shown in the following figure.

Practical Hints on Dimensioning Holes should be dimensioned in the view in which they appear as circles. They should be located by their centre lines. As far as possible, all dimensions for one particular operation, such as diameter and depth of a drilled hole, or size and depth of a threaded hole should be given in one view only.

Practical Hints on Dimensioning In case of a large-size bore or a pitch circle, the dimension may be shown by a diagonal diameter. But, in aligned system, a dimension should not be placed within 30 zone of the vertical centre line as shown by the shaded space.

Practical Hints on Dimensioning Holes on pitch circles when equally spaced should be dimensioned as shown in the previous figure. When holes are not equally or uniformly spaced on the pitch circle, they should be located by angles with one of the two main centre lines.

Practical Hints on Dimensioning Arcs of circles should be dimensioned by their respective radii. Dimension line for the radius should pass through the centre of the arc. The dimension figure must be preceded by the letter R. The following figure shows different methods of showing the radii of arcs.

Practical Hints on Dimensioning Angular dimensions may be given by anyone of the methods shown in the following figure.

Practical Hints on Dimensioning A slope or taper is defined as unit alteration in a specified length. Slope on a flat piece is written parallel to the sloping line The taper on a shaft is indicated along the centre line and is accompanied by one or both the diameters.

Incorrect & Correct way of Dimensioning

Incorrect & Correct way of Dimensioning

Incorrect & Correct way of Dimensioning

Lettering The Bureau of Indian Standards (IS : 9609-1990) recommends single-stroke lettering for use in Engg. Drawing. It should not be taken to mean that the letters should be made in one stroke without lifting the pencil. It means that the thickness of the line of the letter should be such as is obtained in one stroke of the pencil. The horizontal lines should be drawn from left to right and vertical or inclined lines from top to bottom. Two types of single stroke letters: Vertical and inclined Inclined letters lean to the right, the slope being 75 with the horizontal. The size of a letter is described by its height.

Vertical Capital Letters & Figures

Inclined Capital Letters & Figures

Vertical & Inclined Lower-Case Letters & Figures

Lettering ProportionsCharacteristics Height of capitals Height of lower-case letters Spacing between characters Min. spacing of base lines Min. spacing between words Thickness of lines Ratio h h(14/1 4) c h(10/1 4) Dimensions (mm) 2.5 5.0 3.5 0.7 7.0 2.1 0.3 5 10 20 7 1. 4 14 2. 8

a h(2/14) 0.3 5 b h(20/1 4) 3.5

14 28 4. 2 0. 7 8. 4 1. 4

e h(6/14) 1.0 5 d h(1/14) 0.1 8

Vertical Capital Letters with Correct Proportions

Few Points about Lettering Lettering id generally done in capital letters. Different sizes of letters are used for different purposes. The main titles are generally written in 6 8 mm size, subtitles in 3 6 mm size, while notes, dimension figures etc. in 3 5 mm size. The drawing number in the title block is written in numerals of 10 12 mm size. All letters should be uniform in shape, slope, size, shade and spacing. Thin, light guidelines may be drawn, and lettering may then be done between them. H or HB pencils are recommended for lettering. Lettering should be so done as can be read from the front with the main title horizontal.

Engineering DrawingEnd of Lines, Lettering and Dimensioning- Dr. Ranadip K. Das Assistant Prof. MEMME Dept., ISM