1. Isometric Projection Drawing
CHAPTER 6
Isometric Projection Drawing

2. Content Overview Isometric projection
Pictorial projection
Parallel projection
Axonometric projection
Isometric projection
Axes and selection
Isometric lines and planes
Isometric scale
Isometric projection & Isometric drawing
Producing Isometric sketches & drawing
Isometric lines & non-isometric lines
Circles and arcs
Irregular curves
Oblique projection drawing

3. 6.1 Pictorial projection Pictorial projection:
Not intended to give exact or true view.
Not intended to transmit dimensions, although sometimes dimension is useful.
Useful when the information and instructions to be given to non-technical and untrained people.
Hidden lines are not shown in isometric drawing.

4. 6.1 Parallel projection technique

5. 6.1 Axonometric projection
axon = axis; metric = measure, in Greek
Axonometric projection is a parallel projection technique to create a pictorial drawing of an object by rotating the object on an axis relative to a projection or picture plane

6. 6.1 Axonometric projection
Trimetric
Dimetric
Isometric

7. 6.1 Axonometric projection

8. 6.2 Isometric projection
Isometric projection is a true representation of the isometric view of an object
Isometric view is created by rotating the object 45 degree about vertical axis, and tilting it forward 35 deg 16’

9. 6.2 Isometric projection: axes
The 3 axis meet at A,B form equal angles of 120 deg and they are called Isometric Axes
OA is vertical, OB is inclined at 30deg to the right, OC is inclined at 30deg to the left
Any lines parallel to these – Isometric Line
Any planes parallel – Isometric Planes

10. 6.2 Selection of Isometric Axes
Main purpose of isometric view is to provide a pictorial view which reveals as much detail as possible
Selection of principal edges is important
Figure shows different isometric views of the same block

11. 6.2 Isometric projection: scale
The tilt causes the edges & planes to become foreshortened
The projected length is approximately 80% of the true length

12. 6.2 Isometric projection & drawing
Isometric projection & Isometric drawing
Isometric projection: drawn at scale of 0.816
Isometric drawing: drawn at full scale

13. 6.2 Iso-lines & Iso-planes: examples

14. 6.3 Non-isometric lines
Non-isometric lines are the lines that are not parallel to any of the iso-lines.
They are drawn by transferring the distance of X or Y from multi-view to iso-view, not the actual length itself. L L
L is orthogonal not equal to L in isometric

15. 6.3 Isometric angles & non-iso lines
Example of producing non-isometric lines.
The position of point Z is obtained in the isometric view, by transferring the distance of X and Y.

16. 6.3 Iso-circles and arcs
Isometric circles or iso-circle cannot be simply drawn using compass.
Any iso-circle may lie on either top plane, left (front) plane or right (profile) plane.
Iso-circle looks slightly oval and skewed.

17. 6.3 Iso-circles and arcs: draw
Drawing isometric circles and arcs using four-centre method

18. 6.3 Producing isometric circle
Draw centre lines AOB and COD, O is centre of circle, AO=OB=CO=OD = radius of circle.
Draw FCG and EDH parallel to AOB, draw FAE and GBH parallel to COD.
Draw diagonal FOH, mark points J and K where FJ = HK = radius of circle.
With centre G and rad. R1 = GA, draw an arc between GJ produced at L and GK produced at M. Similarly with centre E.
With centres J and K and radius R2 = JL and KM, complete the figure.

19. 6.3 Iso-circles and arcs: draw
Drawing isometric circles using ordinate method.

20. 6.3 Drawing iso-circles 5 2 1 6 4 (a) (b) 3 (c) 5 5 2 7 6 8 4 (e) (f)
To draw an iso-circle, on left plane, Diameter 20mm
Draw centre lines, vertical & 30deg to left.
Draw (construction line) 20mm “square box”. The centre lines should divide each side by half.
(a)
(b) 3
(c) 5 5 2 7 6 8 4
(e)
(f)
(d)
(c) Draw straight lines; 1-2 & 1-3 and 2-5 & 2-6.
(d) Point 7 is the intersection between line 1-2 & 2-5, and similarly point 8, 1-3 & 2-6 on the other side.
(e) Set your compass to the distance 7-2, draw an arc with centre at point 7, from point 2 to point 5. Do the same on the other side.
(f) Set your compass to the distance 1-2, draw an arc with centre (1), from (2) to (3).

21. 6.3 Irregular curves in isometric
Irregular curves in isometric are produced by transferring the coordinates from orthogonal view.
A fixed distance is set, A, and the distance in B direction are obtained.
These values are then transferred to the isometric view.

22. 6.3 Producing Isometric Sketches
Isometric drawing starts with isometric sketches.
Begin with defining isometric axis.
Begin sketch by extending axes – vertical lines, 30deg left & right.

23. 6.3 Producing Isometric Sketches
Sketch an isometric ‘box’.
Sketch the view on each faces, starting with isometric lines.
Add in non-iso lines and other details
Darken all visible lines.

24. 6.3 Iso-circles and arcs: sketch
Sketching iso-circle is simpler than drawing.
Create isometric square, each side=diameter.
Find the centre point and midpoints of each side.
Use the construction lines and point to sketch each quarter of the circle.

25. 6.3 Sketching isometric cylinder
Start by drawing the bounding box.
The front end of the cylinder is sketched using the previous technique.
The far end of the cylinder is a partial iso-circle. Sketch until meeting the tangent with the two straight lines.

26. 6.3 Sketching partial arcs

27. 6.4 Producing Isometric drawing
Read the orthogonal drawing carefully,
observe the scale,
choose the best point where isometric axes meet to reveal as much detail as possible
draw an 'isometric box' enclosing the object
draw in light construction lines
draw arc & curves in thick, remove excess..
line in 30 right lines
line in 30 left lines
line in vertical lines to complete the view

28. 6.4 Producing Isometric drawing
Read multi-view dwg given.
Observe scale, dimension, proj. angle
Determine front, side & top view.
Try to visualise how the object looks like.
Start with sketching, do not draw straight away.
If not sure, start with sketching an isometric box, enclosing the whole object.
You can label points, lines and surfaces on multi-view to help visualisation.

29. 6.4 Producing Isometric drawing
You can start drawing, once you’re able to visualise how the object looks like, or finish sketching.
Start with drawing construction line – draw the iso-box, and fill up with other lines.
Line in (darken) arcs & circles.
Line in iso-lines.
Line in all other lines.

30. 6.4 Producing Isometric drawing

31. 6.5 Isometric dimensions
Although isometric drawing is not intended to transmit dimension, sometimes dimensions are placed to indicate the size.
Two types:

32. 6.5 Isometric features Common feature shown in isometric drawing.
Screw thread (external)
Fillet and rounds
Isometric section view

33. 6.5 Isometric assembly: 3D render

34. 6.5 Isometric exploded assembly

35. 6.6 Oblique projection drawing
Oblique projection – parallel projection where the projectors are parallel to each other but not perpendicular to the projection plane

36. 6.6 Oblique projection drawing
The actual angle that the projectors make with the plane is not fixed, but preferably between 30deg – 60deg
Most common 45 degree

37. 6.6 Oblique projection drawing
3 types:
Cavalier projection: true length along axis
Cabinet projection: half true length
General: any from half to full true length

38. 6.6 Oblique projection drawing
Place complex surfaces (arcs, holes, irregular curve, etc.) parallel to front plane
The longest dimension should be parallel to frontal plane

39. 6.6 Oblique projection drawing

40. 6.7 Producing oblique sketch
First, sketch the front face.
Project 45 deg line to the back.
For holes, determine the visibility.
Line in all object lines.

41. End of Chapter 6
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