內(nèi)容lecture slides英文課件posite solids

1、Chapter 4 Composite Solids-DimensionPresented by YANG Zhi-LingContentsBasic Knowledge of DimensionRequirement for DimensionShape Analysis for DimensioningPlacement of DimensionsDimensions in Engineering PracticeBasic Knowledge-International System of UnitsAll standards of the Chinese National Standa

2、rds Institute adopt an international system of units in conformity with the International Standards Organization standards.The basic units of measurement are the millimeter in Mechanical engineering.Basic Knowledge- Size DescriptionDimensions describe the size and location of features of an object.T

3、he responsibility for size control has been shifted to the designing engineer and the drafter. The production worker no longer exercise judgment in engineering matters, but only in the proper execution of instruction given on the drawings.A drawing submitted to production should show the object in i

4、ts completed condition and should contain all necessary information to bring it to that final state.Dimensions should not be duplicated or superfluous; that is, the same information is given in two different ways.Basic Knowledge- Scale of DrawingObjects in engineering drawings are created to scale.

5、Large objects are drawn smaller than life size; small objects are drawn larger than life size.The ratio of drawn size to life size is the scale.the scale should be indicated in the title block even though the worker is never expected to scale the drawing or print for a needed dimension.Basic Knowled

6、ge- Leaning to DimensionThe student must learn the technique of dimensioning: the character of lines, the spacing of dimension, the making of arrowheads, and so forth.The students must learn the rules of placement of dimensions on the drawing . These practices assure a logical and practical arrangem

7、ent with maximum legibility.The student should learn the choice of dimensions. Now the function is considered first and manufacturing process second. A “geometric breakdown” will assist the beginner in selecting dimensions.Requirement for DimensionCorrectness. There should be no mistake with all dim

8、ensions and the National Standard should be observed. Each dimension should be given clearly so that it can be interpreted in only one way.Integrity. The drawing should be given the complete size description, and dimension should not be duplicated or the same information given in two different ways.

9、Legibility. The arrangement of dimensions should be logical and practical so that the drawing has maximum legibility.Function. No dimensions should be given except those needed to produce or inspect. Dimensions should be given between points or surfaces that have a functional relation to each other

10、or that control the location of matting parts.Requirement for Dimension- Review of Chapter 1Example 1: Correct the dimensions in the drawing.Requirement for Dimension- Review of Chapter 1Example 1: Correct the dimensions in the drawing.Shape Analysis for DimensioningEngineering structures are compos

11、ed largely of simple geometric shapes, such as the prism, cylinder, pyramid, cone, and sphere. They may be exterior(positive) or interior(negative) forms.The dimension of engineering structures involves two basic step:Give the dimensions showing the sizes of the simple geometric shapes, called size

12、dimensions.Give the dimensions locating these elements with respect to each other, called location dimensions.The process of geometric analysis is very helpful in dimensioning any object, but it must be modified when there is a conflict either with the function of the part or with the manufacturing

13、requirements.Size Dimensions of Simple Geometric Solids Size Dimensions of Simple Geometric Solids Dimensions of a Simple Geometric Solid with Cuts181820565020525220565020When dimensioning the geometric solid with cuts, the dimensions for locations of cutting planes should be given, instead of the s

14、ize of intersection.Dimensions for Two Intersected SolidsR84030252016403016When dimensioning two intersected solids, dimensions for locations of two solids should be given, instead of the size of intersection.Dimensions for Two Intersected SolidsLocation DimensionsAfter the geometric shapes composin

15、g a structure have been dimensioned for size. Location dimension must be given to show the relative positions of these geometric shapes.20153015Size Dimensions for HolesLocation DimensionsThe rectangular shapes, whether in the form of solids or of recesses, are located with reference to their faces.

16、The cylindrical or conical hole or bosses, or other symmetrical shapes, are located with reference to their center lines.20153015Location Dimensions-DatumIn general, location dimensions should be built from an important surface as a datum plane, or form an important center line as a datum line.A dat

17、um indicates the starting position of related dimension.Location Dimensions-DatumThere should be at least one dimension datum for each of the three principal directions for length, width and height of the composition solid.Some geometrical elements, such as the symmetry plane, the bottom surface of

18、base board, end surfaces, axes, and center of a circle are usually selected as the datum.Datum for LengthDatum for WidthDatum for HeightProcedure of Dimensioning by Shape Analysis Mentally break the object down into its elementary units by shape analysis.Select the datum for each of the three princi

19、pal directions for length, width and height.Mark the size dimensions of each geometrical shape.Mark the location dimensions of each geometrical shape.Adjust the dimensions for the overall length, width and height.Example for Dimensioning by Shape AnalysisNO!NO!NO!Placement of DimensionsThe shorter d

20、imensions are nearest to the object outline. Dimension lines should not cross extension lines.It is perfectly satisfactory to cross extension lines, but they should never be shortened.A dimension line should never coincide with, or form a continuation of, any line of the drawing.CORRECT!NO!Placement

21、 of DimensionsDimensions should be lined up and grouped together as much as possible.CORRECT!NO!Placement of DimensionsDimensions should be given where the shapes are shownThat is, in the views where the contours are delineated.RRRRRRPerfect！No!Placement of DimensionsPlace dimensions outside the vie

22、ws where possible.Placement of DimensionsPerfect!No!44The diameters of numbers of cylinders that have same axis should be dimensioned in the view that is not circle.Placement of DimensionsPerfect!No! Place the outside dimensions and the inside dimensions to different sides of the view.Dimensions in

23、Engineering PracticebcdebcdNo!Correct! All necessary dimensions must be shown, but the designer should avoid giving unnecessary or superfluous dimensions. Dimensions should not be repeated on the same drawing; nor should the same information be given in two different ways.Dimensions in Engineering P

24、racticecbcdPerfect!No! The important functional dimensions should be marked directly.Dimensions in Engineering PracticePerfect!No! The marked dimensions should be convenient for measurement.Dimensions in Engineering Practice. Holes equally spaced (EQS) about a common center may be dimensioned by giving the diameter of the circle of centers. Repetitive features or dimensions may be specified by the use of an preceded with a number to indicate the number of times. Dimensions in Engineering Practice. The method used for dimensioning round-end shapes depends on t