Engineering Graphics MENG104 Lecture : Ali Vatankhah

INTRODUCTION:  The old saying that “necessity is the mother of invention ” is still true, and a new machine, structure, system, or device is the result of that need.  Why we need to learn this course :

Aim of the course  Knowledge of engineering drawing instruments.  Understanding and interpretation of technical drawings.  Ability to develop projections of a 3D object  Introduction to CAD

Engineering drawing  An engineering drawing, a type of technical drawing, is used to fully and clearly define requirements for engineered items. Engineering drawing (the activity) produces engineering drawings (the documents). More than merely the drawing of pictures, it is also a language —a graphical language that communicates ideas and information from one mind to another. Most especially, it communicates all needed information from the engineer who designed a part to the workers who will make ittechnical drawingengineered language

Classification of projection:

Instrument drawing

1. drawing board 2. T-square: drafting machine or parallel ruling 3. Set of instruments (Compass or drafting) triangle 5. 30*60 triangle 6. Ames lettering guide or lettering triangle 7. architects’ triangular scale 8. engineers’ triangular scale 9. Metric triangular scale 10. Irregular curve 11. Protractor 12. Mechanical pencils and thin lad mechanical pencils and HB, F, 2H 13. Lead pointer and sandpaper pad 14. Pencil eraser 15. Plastic drafting eraser or Artgum cleaning eraser

16. Erasing shield 17. Dusting brush 18. drawing paper(A4) 19. Drafting tape 20. Templates 21. Calculator 22. Cleansing tissue or dust cloth

For our class

Scale  1:1 full size  1:2 Half full size  1:5 one-fifth full size  1:10 one-tenth full size  2:1 Twice full size  5:1 five times full size  10:1 Ten times full size

Alphabet of lines 1: Visible lines: thick dark line use to show outline of object, visible and surfaces. 2: Construction: Very light and thin line use to construct layout work 3: Dimension line: Thin and dark lines use to show the size of an object with a numeric value. 4: Hidden line: Short dash lines use to show non visible surface. Usually shows as medium thickness 5: Centre line: long and short dash lines. Usually indicates center of holes, circle and arcs. 6: extension line: thin and dark line use to show the starting and ending of dimension. 7: short and long break lines: short and long medium line use to show cutaway view of long section. 8: phantom line: long line followed by two short dashes use to show alternate position of moving part. 9: Section line: medium lines at 45 degrees use to show interior view of slid areas of cutting plane line.

Drawing a Horizontal line

Drawing a Vertical Line

The Triangle Wheel

Technique of lines

Example:

Example

Vertical Capital Letters and Numerals

Guide lines for Dimension

Example :

Example

Points and lines

Angles

Triangles:

Quadrilaterals:

Regular Polygons:

The Circle:

Bisecting a line or a Circular Arc

Bisecting a line with Triangle and T-square

Bisecting an Angle

Transferring an Angle :

Dividing a Line into Equal Parts :

Practical Applications of Dividing a Line into Equal Parts :

Dividing a Line into Proportional Parts

Drawing a Line Through a Point and Perpendicular to a Line

Drawing a Triangle with Sides Given:

Drawing an Equilateral Triangle

Drawing a Square

Drawing a Pentagon

Drawing a Hexagon

Drawing a Hexagon by triangular

Drawing an Octagon

Finding Center of Circle

Drawing a Circle Tangent to a Line

Drawing a Tangent to a Circle Through a Point

Drawing Tangents to Two Circles Steps of Construction: 1: join AB, With center B(in bigger circle), draw a third circle with radius equal to R 2- R 1. 2 : Bisect AB at X 3: with center X and radius AX, draw a semicircle to cut the third circle at R. 4: join BR and produce it to meet bigger circle at Q 5: Draw AP parallel BQ. 6: join PQ PQ=AR

Tangents

Drawing a Tangent Arc in a Right Angle

Drawing Tangent Arcs

Drawing an Arc Tangent to an Arc and a Straight Line

Drawing an Arc Tangent to Two Arcs

Drawing an Arc Tangent to Two Arcs and Enclosing One or Both

Drawing an Ogee Curve

Conic Sections

Ellipse Constructions

Types of Projection