Dimensioning Composite Solids Basic requirements for dimensioning Dimensioning of basic body, cutting and interpenetration bodies Dimensioning general composite solids Exercises

Basic requirements for dimensioning Correctness，integrity，clarity， reasonableness. Correctness: There should be no mistake with all dimensions and the national standard (GB) should be observed. Integrity : The dimension must fully define the size of the part and the relative locations of individual components. It can not be skipped, nor repeated. Clarity : The arrangement of the dimensions should be clear and clean. Reasonableness:The dimensions must be marked according to the requirements of design, manufacture and test.

Basic requirements for dimensioning 2. Basic rules of dimensioning The true size of the spare part is based on the dimension marked on the drawing and has nothing to do with the size of the drawing and the accuracy of the drawings. 2) There is no need to mark the unit of dimensions if it is “mm”. One only needs to mark the dimensions if the units are not “mm”, such as “cm” or “30º”. All dimensions marked on the drawing are dimensions of the final part. Otherwise one needs to clearly indicate on the drawing. Each dimension of the part should mark on the drawing only once. It should also be marked on a drawing that most clearly represents the corresponding constructs.

Basic requirements for dimensioning 3.Dimension construction 9 9 Φ18 Φ18 9 38 38 9 9 22 22 22 28 14 Orientation of linear dimensions ① It must be drawn using continuous thin line and can not be in coincident with any existing lines or drawn as extension of any lines. ①An extension line is drawn with a continuous thin line. An extension line originates from a feature outline, an axis line, or a center line. ① Dimension text should be marked above or left the dimension line. All linear dimensions should be marked heading upwards for horizontal dimensions, heading towards the left for vertical dimensions. Dimension line and its terminals Dimension text Extension line ② The dimension line must be parallel with line segment being dimensioned. The distance between the dimension line and the nearest feature should be about 8－10mm. All distances between neighboring dimension lines should be as consistent as possible and are usually between 6－8mm. ② Dimension line is usually drawn perpendicular to the extension lines and the extension lines should extend beyond the terminal of dimension line for about 2－3mm. ② Dimension text can also be entered in the breaking space of the dimension line. ③ When there is 30 for horizontal line, dimension text can also be placed somewhere else using a leader line. ③ Arrowhead is equal to 1b thick and 4b length. （b=the continuous thick line ）

Dimensioning of basic body,cutting and interpenetration bodies 1. Dimensioning the basic part One usually needs to mark all dimensions of length, width and height. For body of revolution, it only needs to mark its radial dimension (the diameter symbol “” is added before the dimension figure) and axial dimension.

Dimensioning of basic body,cutting and interpenetration bodies 2. Dimensioning of subtraction/cutting type solid When dimensioning cutting type composite solid, there are also dimensions for defining location of individual shape elements, such as cutting planes, in addition to the above shape dimensions. As the intersection curve is uniquely defined with basic shape dimensions and location dimensions, there is no need to dimension intersection curves. location of cutting planes location of cutting planes intersection curve    intersection curve intersection curve location of cutting planes location of cutting planes

Dimensioning of basic body,cutting and interpenetration bodies 3. Dimensioning of union/interpenetration type part There are also location dimensions in addition to shape dimensions for union/interpenetration type parts. With shape and location dimensions, the interpenetration curves are uniquely defined, and there is no need either to dimension interpenetration lines. interpenetration line R  location dimensions location dimensions

Dimensioning of basic body,cutting and interpenetration bodies 4. Dimensioning of supporting board elements All center-to-center spacing of holes, screw threads and grooves on the board should be dimensioned. Since the basic shape of the board and the distribution of holes and grooves are different, the formats of location dimensions for dimensioning center-to-center spacing are also different.

Dimensioning general composite solids 1.Selection of dimension datum （1） Dimension datum Dimension datum indicates common starting position of related dimensions. There should be at least one dimension datum for each of the three principal directions for length, width and height of the composite solid. Height datum （Z） Width datum（Y） Length datum （X）

Dimensioning general composite solids （2） Commonly datum of dimensioning Length datum： Symmetry plane or the end surface. 1）Datum face Width datum： Symmetry plane or back-end surface. Height datum： Symmetry plane or the bottom surface. error

Dimensioning general composite solids intersection curve 曲面轮廓不能 作为尺寸基准 intersection curve Center line 2) Datum line Center axes Center point 3) Datum mark Coordinates origin

Dimensioning general composite solids （3） Form of commonly dimensioning Parallel dimensioning a b c Chain dimensioning a b c Combined dimensioning a b c Combined dimensioning is suitable Avoidance of dimensions into a series with an overall dimensions！

Dimensioning general composite solids 2.Correctness and integrity in dimensioning Shape dimensions show sizes, such as length, width and height, of the basic part and its building elements. (2) Location dimensions show the relative location relationships between individual shape elements. (3) Overall dimensions show the overall length, width and height of the composite solid. Center of holes must be given clearly Overall length added as an auxiliary Overall length must be given clearly Over-dimensioned

Dimensioning general composite solids 3.Clarity and reasonableness in dimensioning (1) Dimensions should be marked in the view that most reflects the characteristics of the related shape and location. Radius symbol R Diameter symbol”” Marked in bevel Marked in bulge Dashed line extend  R overall dimensions 

Dimensioning general composite solids Dimensions should be marked in the view that most reflects the characteristics of the related shape and location. Dimensions should not be marked on dashed lines as far as possible. Marked in the same view as possible Symmetry 避免在虚线处注尺寸 2Φ Symmetry Marked it   symmetrically 

Dimensioning general composite solids 4×8 10 10 R8 40 45º 4×8  8 16 16 40 15º 60

Dimensioning general composite solids (3) All dimensions should be better arranged outside individual view in order to avoid possible overlap of dimension lines and feature lines of the drawing. They should also be arranged following the principle of “Larger dimensions placed outside smaller dimensions”. (4) For diameters of cylinders and cones, the dimension should be better marked in a non-circle view as far as possible. Φ Larger dimensions placed outside smaller dimensions      

interpenetration line Dimensioning general composite solids There should be no dimension for intersection lines. intersection curve interpenetration line   intersection curve  intersection curve

Exercises 1. Point out the dimension which one is incorrectly. 2. Dimension this drawing of components. 3. Point out the dimension which one is incorrect and correct it.

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1. Point out the dimension which one is incorrectly.

2. Dimension this drawing of components. 2×Φ

3. Point out the dimension which one is incorrect and correct it. × × × × × × × Omit. × R ×