Geometry For Technical Drawing Chapter 4 Sacramento City College EDT 300/ENGR 306 EDT 300/ENGR 306 1
Objectives Identify and describe geometric shapes and constructions used by drafters. Construct various geometric shapes using Points. Lines. Planes. 2
Objectives Apply geometric construction as a problem-solving tool in technical drawing. Use geometry to reduce or enlarge a drawing or to change the proportions of a drawing. 3
Vocabulary Bisect Chord Circumscribed Diameter Entities Geometric constructions Geometry Hypotenuse Inscribed Intersect Object snaps Ogee curves Parallel Perpendicular Polygon Regular polygon Right angle Tangent 4
Geometry Geometry is the study of the size and shape of things. 5
Geometry Geometry has always been important. It was used in ancient times for measuring land and making right-angle corners for buildings and other kinds of construction. Egyptian rope stretchers used rope with marks or knots at 12 equal spaces. 6
Geometry The rope was divided into 3, 4, and 5 space sections. A right angle was constructed by stretching the rope and driving pegs into the ground at the 3, 4, 5 space marks. Refer to figure in text. 7
The Use of the 3-4-53 5 Triangle The use of the 3-4-5 triangle for making right angles was proved by Pythagoras in the sixth century B.C. The proof is the Pythagorean Theorem. A 2 + B 2 = C 2 8
The Use of the 3-4-53 5 Triangle The Pythagorean Theorem works for triangles that have the same proportions as 3-4-5. 6-8-10 9-12-15 Etc. 9
Geometric Construction Geometric Constructions are: Drawings made of individual lines and points drawing in proper relationship to one another. 10
Geometric Construction Geometric constructions are used by Drafters. Surveyors. Engineers. Architects. Scientists. Mathematicians. Designers. 11
Geometric Constructions Everyone, in all technical fields, needs to know the geometric constructions explained in this chapter. 12
Solving Problems Using Geometry Geometric constructions are often used by drafters to help solve design problems. 13
Solving Problems Using Geometry A designer may be designing a complicated mechanical assembly that has moving parts. The designer must determine whether the design allows enough clearance for the parts to move freely. The drafter may need to construct accurate circles and various tangents, parallel and perpendicular lines to measure clearances. 14
Designing Within Parameters A designer may be given very specific design parameters (guidelines). Example: A part or assembly may have to fit within a specific area. The principles of geometric construction are used to meet the specification. 15
Accuracy Is Fundamental Remember, accuracy is a fundamental of drafting. Sloppy drafting may give the designer the wrong answer, which may lead to a part being manufactured incorrectly. 16
Accuracy Is Fundamental Sloppy drafting may result in: Lack of clarity and people may misread the information. Change orders. Parts not ordered correctly. 17
Geometric Shapes EDT 300/ENGR 306 18
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Geometric Shapes-Triangles Equilateral Triangle all sides equal. Isosceles Triangle. two sides have equal length. 3-4-5 Right Angle Triangle right angle in triangle. Scalene Triangle no equal sides or angles. 35
Geometric Shapes-Circles/Arcs Semi-Circle and Circle Components Chord Diameter Radius Segment Sector Quadrant Concentric circles Eccentric circles 36
Geometric Shapes-Four Sides Squares. Rectangles. Rhombus. Rhomboid. Trapezoid. Trapezium. 37
Geometric Shapes-Multisided Pentagon. Hexagon. Heptagon. Octagon. Nonagon. Decagon. Dodecagon 38
Geometric Shapes-3D Cube. Right Rectangle. Right Triangle Prism. Right Triangular Prism. Right Cylinder. Right Cone. Frustum of a cone Sphere. 39
Laying Out Your Drawing EDT 300/ENGR 306 40
Laying Out Your Drawing 1. Determine the width of the drawing space available. 2. Determine the height of the drawing space available. 3. Determine how wide the object to be drawn is. 4. Determine how high the object to be drawn is. 41
Laying Out Your Drawing 5. Find the center of your drawing area. 6. Divide the object width by 2. 7. Measure from the center point out to the left and right this same distance 42
Laying Out Your Drawing 8. Divide the object height by 2. 9. Measure from the center point out to the top and bottom this same distance. 43
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