1. Dimensioning & Projections

2. Dimensions
Dimensions are used to describe the sizes and relationships between features in your drawing.
Dimensions are used to manufacture parts and to inspect the resulting parts to determine if they are acceptable.
Drawings with dimensions and notes often serve as construction documents and legal contracts.
ANSI Y14.5M-1994 is the current standard. Other standards may apply.
ANSI – American National Standards institute

3. Standards for Your Career Field
Standards are different in different career areas.
Most of the examples in this lecture will be of mechanical parts.
Civil, Electrical, Construction, and other areas follow similar practices, but sometimes with less need for precision in measurements.
Dimensioned drawings are a part of a contractual document.

4. Vocabulary
Dimension line, Extension line, Leader, Dimension offset or gap, Centerline,
Finish mark, Dimension value
Baseline dimensioning, Chained dimensioning

5. Tolerance
Definition: The total allowable variation an acceptable part can have from the specified dimension.
The less variation allowed, the more the part will cost to make.

6. 3 Things for Good Dimensioning
Good technique of dimensioning
Good choice of dimensions
Good placement of dimensions

7. Dimensioning Technique
describes how the dimensions in your drawing should look.
defined by various standards like ANSI Y
help you create dimensions that are plainly visible and can be easily interpreted.
specifies sizes for creating dimensions relative to the paper size of your final plot.

8. Dimensioning Technique
arrowheads
extension lines
dimension lines
sizes
use thin, dark, lines (HB lead)
make object stand out clearly!

9. Dimension Values

10. Dimensioning Symbols

11. Leaders

12. Orientation for Dimension Values
Unidirectional:
read horizontally from bottom of sheet
Aligned:
align with dimension line and read from bottom or right side of sheet

13. Unidirectional Orientation

14. Aligned Orientation

15. Aligned Dimensions

16. Stagger Dimension Values

17. Dimension & Extension Lines

18. Choice of Dimensions
the dimensions you specify determine the way the the part is manufactured and the way the tolerance is applied
consider the purpose of the part and its function in the assembly
consider how easy it will be to check the measurement on the actual part
fully dimension each part
do not overdimension, each dimensions should appear only once

19. Choosing Which Dimensions to Show
Don’t over dimension
Give the diameter of circular shapes, the radius of arcs.
No redundant or superfluous dimensions
Give size dimensions for features.
Give location dimensions to show how features relate to one another.

20. Mating Dimensions

21. Effect of Tolerance on Dimensioning
Chained
each dimension continues from the previous one
tolerances stack
Baseline
each dimension is specified from a common baseline
tolerances do not stack

22. Units
Fractional Inch
Decimal inch dimensions are typically specified to 2 decimal places.
Metric values are typically given in whole millimeters or to one decimal place.

23. Placement of Dimensions
Rules-of-thumb for dimension placement help ensure that others will be able to interpret your drawing
Where placement practices conflict, remember that your goal is to clearly communicate the purpose of the drawing. Use the practice you feel will make the drawing easy to understand.

24. Placement Practices Place dimensions where feature shows shape.
Avoid dimensioning on object (face of part).
Avoid dimensioning to hidden lines.
Place dimensions between views when possible.
Don’t “float” dimensions.
Place dimensions where feature shows shape.
Give overall dimensions where possible.
Group dimensions around a central view.

25. Dimensioning Prisms

26. Dimensioning Cylinders

27. Dimensioning Holes

28. Using Diameter Symbol

29. Locating Holes

30. Coordinate Dimensioning

31. Summary
Good dimensioning is a combination of choosing dimensions which reflect your design intent, proper technique in creating the details of the dimension line, extension line, arrowheads and dimension values, and placing the dimensions on the drawing so that they can be read clearly.
Dimensioning drawings correctly can be as important or more important than drawing the shapes correctly.
Good dimensioning requires practice and thought!

32. Orthographic Projection – Multi-View Drawing

33. Orthographic Projection
a system of drawing views of an object using perpendicular projectors from the object to a plane of projection

34. Revolving an Object to Produce the Six Basic Views

35. Projection of an Object

36. The Glass Box
Imagine that the object you are going to draw is positioned inside a glass box, so that the large flat surfaces of the object are parallel to the walls of the box.
From each point on the object, imagine a ray, or projector perpendicular to the wall of the box forming the view of the object on that wall or projection plane.

37. The Glass Box

38. Unfolding the Glass Box

39. Unfolding the Glass box
For Third Angle Projection (the method in the U.S.)
Imagine that the walls of the box are hinged and unfold the views outward around the front view.
This will give you the standard arrangement of views for 3rd Angle Projection which is used in the US, Canada, and some other countries.

40. The Six Basic Views

41. The Standard Arrangement of Views
TOP
LEFT FRONT RIGHT
BOTTOM
REAR
Why must views be arranged so that they align?
To make it possible for someone to interpret the drawing.

42. Transferring Dimensions

43. Using a Miter Line to Transfer Depth1.
Draw miter line at 45 degrees
at a convenient distance to produce the desired view.

44. Sketch light lines projecting depth locations for points to miter line and then down into side view as shown. 2.

45. Project additional points, surface by surface.3.

46. 4.
Draw the view locating each vertex of the surface on the projection and miter line.

47. Necessary Views
A sketch or drawing should only contain the views needed to clearly and completely describe the object. Choose the views that show the shape most clearly, have the fewest hidden lines, and show the object in a usual, stable, or operating position.
One view drawing
of a shim
One view drawing
of a connecting rod

48. Position of Side Views An alternative postion for the side view is
rotated and aligned with the top view.

49. First Angle Projection

50. Symbols for 1st & 3rd Angle Projection
Third angle projection is used
in the U.S., and Canada

51. Summary
The six standard views are often thought of as produced from an unfolded glass box.
Distances can be transferred or projected from one view to another.
Only the views necessary to fully describe the object should be drawn.