Geometric Construction & Modeling Basics

1. Geometric Construction& Modeling Basics

2. Points • A point represents a location in space or on a drawing. It has no width, height or depth. • Sketch points by a short crossbar on a line, or by a small cross.

3. Lines • A straight line is the shortest distance between two points. • Parallel lines • Intersecting lines • Perpendicular lines

4. Drawing Straight Lines • Always use some sort of straight edge (Triangle, ruler, credit card, etc.) • Line weights must be consistent. Rotating the pencil as you draw the line keeps the lead tip width consistent. • Lines need to begin and end crisply. • Line intersections must connect and not overshoot. • Good Lighting is essential to seeing where to draw lines when using mechanical tools.

5. Drawing Parallel & Perpendicular Lines • Parallel lines are drawn using a straight edge (can be a triangle) and a triangle. See Figure 12.19 (pg 146) of text. Straight edge must not move. • Perpendicular lines are drawn with same instruments.

6. Practice! • Draw 3 parallel lines 6” long and 1.5” apart, p146 • Construct a perpendicular bisector to the bottom line using a compass, p144 • Connect them at the ends and midpoint with a perpendicular line using a triangle • Draw a random angle 30 – 170 degrees and construct its bisector, p145 • Do Worksheet 7, parts 1, 2, 5, 6

7. Drawing Lines at Angles that are a Multiple of 15 degrees • Using a horizontal reference and the two basic triangles, any angle that is a multiple of 15 degrees can be drawn. • The angles are the sum or difference of 30, 45, or 60 degrees which can be obtained by the combination use of the two standard triangles. • A protractor may be used to assist in constructing lines at other angles.

9. Drawing Curved Lines • General curves are drawn by plotting points along a line then using an irregular curve (normally a French curve) or a Spline to connect the points.

10. Scales • Scales are used to measure distances. • Drawings are often not done at the same size, or “scale”, as the object being drawn. • There are many types of scales available. • The text (p123-128) has a good discussion (with illustrations) on how to read a scale.

12. Polygons • A polygon is any plane figure bounded by straight lines. A Pentagon

13. Regular Polygons • Regular polygons have equal angles and equal sides. • They are often created and described by inscribing them in a circle, or circumscribing them about a circle. • Hex head bolts are a typical example

14. Circles • A circle is a closed curve, all points of which are equally distant from the center. • Circumference equals pi times the diameter C =p d

15. Practice! • Do Worksheet 6 (see p143, 144) • Do Worksheet 8 (see p147-149) • Do Worksheet 9 (see p150-151) • Do Worksheet 10 (see p152)

16. Solids

17. Extruded Solid • CAD construction for a 3D part having a uniform cross section. • Named for the manufacturing process of forming material by forcing it through a shaped opening.

18. Revolved Solid • construction by revolving a uniform cross-section along a circular path.

19. Boolean Operators • Venn diagrams can be used to show Boolean operations. • Union (addition) • Difference (subtraction) • Intersection

20. Boolean Operationsof Solids

21. Summary • Points, lines, and circles are the basic geometric elements used to make 2D sketches. • Using CAD you can create 3D models. • Understanding geometric solids can help you create CAD models and interpret and visualize from 2D sketches and drawings.