Dimensioning & Projections. 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.
Dimension line, Extension line, Leader, Dimension offset or gap, Centerline,
Finish mark, Dimension value
Baseline dimensioning, Chained dimensioning
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.
use thin, dark, lines (HB lead)
make object stand out clearly!Dimensioning Technique
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.Choosing Which Dimensions to Show
each dimension is specified from a common baseline
tolerances do not stack
each dimension continues from the previous one
tolerances stackEffect of Tolerance on Dimensioning
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.Placement Practices
a system of drawing views of an object using perpendicular projectors from the object to a plane of projection
LEFT FRONT RIGHT
Why must views be arranged so that they align?
To make it possible for someone to interpret the drawing.
Draw miter line at 45 degrees
at a convenient distance to produce the desired view.
Sketch light lines projecting depth locations for points to miter line and then down into side view as shown.
Project additional points, surface by surface. miter line and then down into side view as shown.
4. miter line and then down into side view as shown.
Draw the view locating each vertex of the surface on the projection and miter line.
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
An alternative postion for the side view is
rotated and aligned with the top view.
Third angle projection is used
in the U.S., and Canada