lines & lettering on technical...
TRANSCRIPT
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