ENGINEERING GRAFICS UNIT 1 FIRST YEAR PDF
- 1. Introduction Drawing Instruments Lines Dimensioning Scale Quadrant System
- 2. Graphical means of expression of technical details without the barrier of a language. Universal language for engineers Engineering Drawing Drawing Describing any object/ information diagrammatically
- 3. Graphical representation of an object – Drawing • Engineering drawing – A drawing of an object that contains all information -like actual shape, accurate size,manufacturing methods, etc., required for its construction. -No construction/manufacturing of any (man -made) engineering objects is possible without engineering drawing.
- 4. Computer has a major impact on the methods used to design and create technical drawings. Design and drafting on computer are cheap and less time consuming. Why we go for manual drawing? Engineering Drawing Manual Drawing CADD
- 5. Computer cannot replace the drafting board and equipment as a learning tool. Once you have learned the basics of mathematics, now after class 12, you are allowed the use of calculator and computer. If basic fundamentals are clear, better use can be made of the power of the software. To be an expert in technical drawing, this first course on Engineering (manual) Drawing is the first step. Why we go for manual drawing?
- 6. Instruments required for drawing Drawing board Drawing sheet Mini-drafter/drafting machine/ T- square Instrument box containing compass, divider, etc. Scales Protractor French curves Drawing pencils Eraser Drawing clip/pin/adhesive tape Sharpener Duster
- 7. Drawing Sheet : Standard size Trimmed paper of a size A0 ~ A4. Standard sheet size (BIS) A4 210 x 297 A3 297 x 420 A2 420 x 594 A1 594 x 841 A0 841 x 1189 A4 A3 A2 A1 A0 (Dimensions in millimeters)
- 8. Mini-drafter – a miniature version of the drafting machine
- 9. Mini-drafter fixed on drawing board
- 10. Lay out of a drawing sheet
- 11. Drawing Pencils Wooden pencils – are graded and designated by numbers and letters Mechanical clutch pencils – Not allowed • 7B, 6B, 5B, 4B, 3B, 2B, B - in decreasing order of softness and blackness • HB to F – Medium grade • H, 2H, 3H, 4H, 5H, 6H, 7H, 8H, 9H – increasing order of hardness. Drawings are done using 2H pencils and finished with H and HB pencils – to be practiced in this course.
- 12. Grades and designation of wooden pencils
- 13. Line types
- 15. Units of Measure International systems of units (SI) – which is based on the meter. Millimeter (mm) - The common SI unit of measure on engineering drawing. Individual identification of linear units is not required if all dimensions on a drawing are in the same unit (mm). The drawing shall however contain a note: ALL DIMENSIONS ARE IN MM. (Bottom left corner outside the title box)
- 16. Dimensioning Indicating on a drawing, the size of the object and other details essential for its construction and function, using lines , numerals, symbols, notes, etc. Dimensions indicated on a drawing should be those that are essential for the production, inspection and functioning of the object and should not be mistaken as those that are required to make the drawing of an object.
- 17. Extension Lines Dimension Text Dimension Lines Arrow Heads
- 18. Dimensions are represented on a drawing using one of two systems, unidirectional or aligned. The unidirectional method means all dimensions are read in the same direction. The aligned method means the dimensions are read in alignment with the dimension lines or side of the part, some read horizontally and others read vertically.
- 19. Dimension Text Unidirectional vs. Aligned Unidirectional dimensions are placed so they can be read from the bottom of the drawing sheet. This method is commonly used in mechanical drafting. Aligned dimensions are placed so the horizontal dimensions can be read from the bottom of the drawing sheet and the vertical dimensions can be read from the right side of the drawing sheet. This method is commonly used in architectural and structural drafting.
- 20. Chain Dimensioning Dimensioning from feature to feature is known as Chain Dimensioning.. It is commonly used and easy to lay out. It does have possible consequences in the manufacturing of a part. Tolerances can accumulate, making the end product larger or smaller than expected.
- 21. Chain Dimensioning This is a general note. It indicates that all two place decimal dimensions have a tolerance of plus or minus .01 inch unless otherwise specified.
- 22. Datum(parallel) Dimensioning The accuracy of the final product is determined by the dimensions on the drawing. If all the dimensions originate from a common corner of the part, the object will be more accurate. This is referred to as Datum Dimensioning. Datums insure the tolerance or errors in manufacturing do not accumulate.
- 23. Datum Dimensioning The dimensions originate from a common edge (DATUM) of the part.
- 25. Dimensioning Curved Features and Arcs Use a capital “R” for dimensioning arcs. Large Arcs use center marks. Small arcs do not need center marks. Arrow can be outside. The arrow can be inside for small arcs.
- 26. Diameters A full circular object should be dimensioned using its diameter. Holes should use hole notes. This specification calls for a hole with a .5 diameter and 1.00 deep.
- 27. Diameters Cylindrical parts may show their diameters in this manner. Dimensioning on the right side view could be too crowded. Note that the diameter symbol is used so it is not confused with a linear dimension.
- 28. Chamfers External chamfer for 45 degree chamfers only. There are two options. External chamfer for angles other than 45 degrees. Internal chamfers.
- 29. Drawing Scales : Definition Drawing Actual Length, size : Scale is a ratio between the linear dimension of a drawn representation of an object and the actual object. 1 2 20 10
- 30. Designation of a scale consists of the word “SCALE” followed by the indication of its ratio, as follows SCALE 1:1 for full size SCALE X:1 (X > 1) for an enlargement scales SCALE 1:X (X > 1) for a reduction scales Drawing Scales : Designation Drawing scale is commonly found in a title block.
- 31. Standard reducing scales are 1:2, 1:5, 1:10, 1:20, 1:50, 1:100 Drawing Scales : Standard scale Standard enlarging scales are 2:1, 5:1, 10:1, 20:1, 50:1, 100:1
- 33. X Y 1ST Quad. 2nd Quad. 3rd Quad. 4th Quad. X Y VP HP Observe THIS QUADRANT PATTERN, IF OBSERVED ALONG X-Y LINE ( IN RED ARROW DIRECTION) WILL EXACTLY APPEAR AS SHOWN ON RIGHT SIDE AND HENCE IT IS FURTHER USED TO UNDERSTAND ILLUSTRATION PROPER
- 35. FOR T.V. FIRST ANGLE PROJECTION IN THIS METHOD, THE OBJECT IS ASSUMED TO BE SITUATED IN FIRST QUADRANT MEANS ABOVE HP & INFRONT OF VP. OBJECT IS INBETWEEN OBSERVER & PLANE. ACTUAL PATTERN OF PLANES & VIEWS IN FIRST ANGLE METHOD OF PROJECTIONS X Y VP HP PP FV LSV TV
- 36. FOR T.V. IN THIS METHOD, THE OBJECT IS ASSUMED TO BE SITUATED IN THIRD QUADRANT ( BELOW HP & BEHIND OF VP. ) PLANES BEING TRANSPERENT AND INBETWEEN OBSERVER & OBJECT. ACTUAL PATTERN OF PLANES & VIEWS OF THIRD ANGLE PROJECTIONS X Y TV THIRD ANGLE PROJECTION LSV FV
- 37. Methods of Drawing Orthographic Projections First Angle Projections Method Here views are drawn by placing object in 1st Quadrant ( Fv above X-y, Tv below X-y ) Third Angle Projections Me Here views are drawn by placing object in 3rd Quadrant. ( Tv above X-y, Fv below X-y ) FV TV X Y X Y G L TV FV SYMBOLIC PRESENTATION OF BOTH METHODS WITH AN OBJECT STANDING ON HP ( GROUND) ON IT’S BASE. NOTE:- HP term is used in 1st Angle method & For the same Ground term is used in 3rd Angle method of projections