# Mechanical Drawings By: Mr. Lua 09/09/2013.

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Mechanical Drawings By: Mr. Lua 09/09/2013

Multi- View Drawings What is Multi-View Drawings?
More than one view is needed to give an accurate shape and size description of the object being generated.

Which views? Front Top Right side Left side Rear And bottom View

Is there a method? Orthographic Projection
Permits 3D objects to be shown on a flat surface having only two dimensions. Reveals width, height and depth

Two Methods to Project Third Angle Projection First Angle Projection
Views are projected to the six sides of the box. First Angle Projection Viewed as if the object is placed on each side of the box.

Selecting Views Only those views needed to give a shape description.
Many times only 2 or 3 views are required. Views that display too many hidden lies are typically avoided.

Transferring Points Used to avoid duplicating dimensions.
Typically what construction lines are used for.

Example

Class Work Draw each problem on a separate sheet and complete as indicated.

Dimensioning and Notes
What is Dimensions? Define the size of the geometrical features of an object. What are notes? Provide additional information not found in the dimensions. Usually presented in inches or millimeters using decimals to make it easier.

Unidirectional Placed to read from the bottom of the drawing. Aligned Placed parallel to the dimension line

Rules for Dimensioning
Place dimensions on the views that show the true shape of the object. Unless absolutely necessary, dimensions should not be placed within the views. If possible dimensions should be grouped together rather than scattered about the drawing. Dimensions must be complete, no scaling of the drawing is required. Possible to determine size and shapes w/o assuming any measurements.

Rules for Dimensioning (Cont.)
Draw dimension lines parallel to the direction of measurements. If there are several parallel dimension lines, stagger the values. Dimensions should not be duplicated unless they are absolutely necessary to the understanding of the drawings. Plan your work carefully so the dimension lines do not cross extension lines. When all dimensions on a drawing are in inches, the inch symbol (“) should not be used. Dimensions on metric drawings are in millimeters unless otherwise noted.

Rules (cont.) Rule 5: Stagger Numerals (Values) Rule 1: Stay true
Rule 3: Keep Grouped Rule 6: Avoid duplicates omit unnecessary dimensions. Rule 7: Plan

Circles, Holes and Arcs ANSI (American National Standards Institute)
“fi” Φ, Greek symbol, indicates the dimension is a diameter. And is placed before the dimension. Symbols of depth of a hole.

Leaders Employed to direct attention to a note or to indicate size of arcs and circles. When used on a circle or arc, the leader should always point to the center of the diameter.

Arcs Dimensioned by giving the radius and placing a capital R in front of the dimension.

More on Circular Dimensioning
Equally Spaced Holes Always from the centers.

More on Dimensioning Dimensioning Angles
Expressed normally in Degrees (°) Dimensioning small portions of an Object Extension lines indicate object being dimensioned but value written off to the side

Sectional and Auxiliary Views
Sectional Views How an object would look if a cut were made through it perpendicular an exact right angle) to the direction of sight. Necessary for a clear understanding of the shape of complicated parts.

Types of Sectional Views
Full section Made thru the entire object. Half Section Shape of ½ of the interior & ½ the exterior features. Normally suited for Symmetrical Objects- objects having same size, shape and relative position on opposite sides of a dividing line or plane. Revolved Section Primarily utilized to show shape of objects as spokes, ribs and stock metal objects.

Types of Sectional Views (cont.)
Aligned Section Removed Section Used when it isn't possible to draw a needed sectional view on one of the regular views. Offset Section Uses cutting plane that is stepped or offset to pass through the required features. Broken-out Section Employed when a small portion of a sectional view will provide required information

Types (Cont.) Full Section Half Section Revolved Section

Types (Cont.) Removed Section Offset Section

Auxiliary View Needed to show the true length and true width of the angular surface. Can be projected from any view that shows the angled surface as a line. Front Auxiliary taken from the Front View Top Auxiliary taken from the Top View Right Auxiliary taken from the Right View.

Auxiliary View (Cont.)