Lecture 3 Dimensions and tangent complete-21.pptx

...

1. Engineering Drawing & Graphics Lecture 03 Dimensioning by Engr. Ismail Khan Lecturer Mechanical Engineering Department UET Peshawar

2. Dimensioning Dimensioning is the process of specifying an object’s information by lines, numbers, symbols and notes. We locate the length, breadth, height, sizes and positions of objects and their other detail in this process.

3. Dimensioning

4. Terms Used in Dimensioning 1. Dimension line: These are thin continuous lines, located between extension lines, terminated by arrowheads. These show the direction and extent of dimension. It includes a numeral value at the middle.

5. Term Used in Dimensioning 2.Extension line: These are thin continuous lines drawn in extension from the point of interest. These are used to indicate the extension of an edge to a location outside the drawing. There is always a space between the reference point and the extension line, this space tells the reader that the extension line is not the part of the object being dimensioned.

6. Term Used in Dimensioning 3. Arrowhead: It is placed at each end of a dimension line, the pointed end touches the extension line. The length of the arrowhead should be three times its maximum width. Arrowheads may appear as solid or hollow. Careless arrowheads shall be avoided. Arrowheads may also appear as dots or ticks.

7. Term Used in Dimensioning 4. Leader line: It is a thin continuous line, connecting a note or a dimension to which it applies. It may touch the figure Only (with arrowhead) or may go inside the figure (with a dot).

8. Some Basic Rules for Dimensioning Always place shorter dimensions nearest to the object lines. Dimension lines should never cross. However, extension lines may cross each other.   Make sure that no object is left un-dimensioned. But remember not to repeat a dimension, it will confuse the reader.   Don’t put dimensions inside the drawing (unless absolutely necessary). Do not change the direction of the leader line inside the drawing.

9. Some Basic Rules for Dimensioning All dimensions shall be evenly spaced. Use either decimals or fractions; do not mix the two systems. Use either the unidirectional system or aligned system; do not mix the two systems. Hidden lines are never dimensioned; rather they are dimensioned in another view in which they are directly visible.

10. Methods of Dimensioning Datum/Ordinate/Baseline dimensions: The dimensions originate from the same reference point and same extension line, called as the baseline (may also be called as reference line or datum line). This system takes more drawing space, but is more accurate because the location of each feature is independent of other features. This system is also easy to follow.

11. Methods of Dimensioning Chain/Continuous dimensions: These are placed end-to-end, i.e. next dimension line starts as soon as the previous dimension line ends. It takes lesser space compared to the first system, but is not accurate because the location of each feature is dependent upon neighboring features, and measurement of current object to be dimensioned relies on the accuracy of the previous measurement.

12. Sheet No. 2 Dimensioning: To draw the given two shapes and dimension them by both the methods. Instruments required: Soft and hard pencils, eraser, sharpener, drawing sheet, t square, set squares, compass and masking tape.

13. Sheet No. 2 Dimensioning: To draw the given two shapes and dimension them by both the methods. Instruments required: Soft and hard pencils, eraser, sharpener, drawing sheet, t square, set squares, compass and masking tape.

14. Final Output

15. Methods of Dimensioning More Detail are available in ND Bhatt and James Bethune, please study them .

16. Engineering Drawing & Graphics Geometric Constructions How to Draw a Regular Polygon

17. Problem : To draw a regular polygon, given the length of its side. Draw a line AB equal to the given length.

18. Problem : At B, draw a line BP, perpendicular and equal to AB.

19. Problem : With center B and radius AB, draw the quadrant AP.

20. Problem : Draw a line joining A with P.

21. Problem : Draw the perpendicular bisector of AB to intersect the straight line AP at point 4 and the arc AP at point 6.

22. Problem : Draw the perpendicular bisector of AB to intersect the straight line AP at point 4 and the arc AP at point 6.

23. Problem : Draw the perpendicular bisector of AB to intersect the straight line AP at point 4 and the arc AP at point 6

24. Problem : Draw the perpendicular bisector of AB to intersect the straight line AP at point 4 and the arc AP at point 6

25. Problem : To draw a regular polygon, given the length of its side.

26. Problem : To draw a regular polygon, given the length of its side.

27. Problem : To draw a regular polygon, given the length of its side.

28. Problem : A regular hexagon of side = AB can be inscribed in the circle drawn with center as point 6 and radius = A6.

29. Problem : Similarly, a regular octagon can be drawn with center as point 8 and radius = A8, and so on.

30. Problem : To draw a regular polygon, given the length of its side.

31. Problem : To draw a regular polygon, given the length of its side.

32. Problem : To draw a regular polygon, given the length of its side.

33. Problem : To draw a regular polygon, given the length of its side.

34. Problem : To draw a regular polygon, given the length of its side.

35. Problem : To draw a regular polygon, given the length of its side.

36. Geometric Constructions Chamfer: A chamfer is the cutting away the sharp external or internal corner of an edge with a straight line. Fillet: A fillet is an arc of small radius formed between the inside angle of two surfaces. These are often used to help to smoothen inside corner. 3. Round: Round is a small-radius outside corner formed between two surfaces. Rounds are used to refine sharp corners.

37. Geometric Constructions 1.Chamfer: 2.Fillet: 3. Round:

38. Sheet No. 3 Geometric shapes: To draw the given different geometric shapes. Instruments required: Soft and hard pencils, eraser, sharpener, drawing sheet, t square, set squares, compass and masking tape.

39. Sheet No. 3 Geometric shapes: To draw the given different geometric shapes. Instruments required: Soft and hard pencils, eraser, sharpener, drawing sheet, t square, set squares, compass and masking tape.

40. Final Output