lines & lettering on technical...

LINES & LETTERING ON

TECHNICAL DRAWINGS

Text on Technical Drawings

Standard engineering lettering uses single stroke, Gothic, upper case letters.

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

I 2 3 4 5 6 7 8 9

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

I 2 3 4 5 6 7 8 9

Drawing Line Types & Weight

• Construction Line

• Object Line

• Hidden Line

• Centre Line

Centre Lines on Cylindrical Objects Centre lines are used to represent:

– the centre of circular features, & – the axis of cylinders & holes.

Centre lines extend 5 mm beyond the feature’s boundaries.

MULTIVIEW DRAWING

Various Projection Types

Pictorial Drawing

A pictorial drawing of an object suggests the 3-dimensional character of the object in a single image.

Multiview Drawing A multiview drawing

shows the 3-dimensions of an object in an arrangement of flat, 2-dimensional views of different sides of the object – front, top, side, and so on.

Only 2 of the 3

dimensions can be seen in each view.

Why Use a Multiview Drawing?

• Most features are shown in their true size and shape.

• Dimensions can be shown easily and

clearly.

Theory of Multiview Projections (Glass Box Theory)

Alignment of Views Views in multiview drawings are aligned according

to the dictates of the glass box projection planes

Front Views of Multiview Drawings Select: -the most descriptive view of the object,

-the most common orientation, -the longest principal dimension, & -the view with the fewest hidden lines.

First & Third-Angle Projection Symbols

Both the first & third-angle symbols show 2 views (front & right views) of a truncated cone.

PROPORTIONS