Lecture 3 1

Lecture 4

Foundation in CAD

Lecture 3 2

What we cover

Coordinate System

Principle governing the position of CS axis, type of CS

World CS and Local CS

Why WCS and LCS, the number of CS required to model

Basic Part Modeling

Sketches, extrude, swept and loft bodies

How to model

Modeling approaches

Lecture 3 3

What we need to know?

Coordinate System (CS)

Rule governs the standard convention

Type of CS

World CS (WCS) and Local CS (LCS)

Lecture 3 4

Axis

Right Hand Rule:

Lecture 3 5

Axis of rotation

+ve angle

Lecture 3 6

2D & 3D Coordinate Systems

Foundation in CAD software: to label certain entities in space for the purpose of movement, position and orientation

Absolute and Relative Cartesian and Polar Coordinate System.

Lecture 3 7

Absolute Cartesian CS

Using the usual (x, y) for 2D and (x, y, z) for 3D.

Lecture 3 8

Relative Cartesian Coordinate System

Similar to absolute Cartesian Coordinate System.

The coordinates is referred to a local origin point

The relationship between origin of absolute CS and local one must be known.

Lecture 3 9

Polar Coordinate System

Cylindrical CS

2D: ( R , q) x = R cos q, y = R

sin q

3D: (R , q , z) x = R cos q, y =

R sin q, z = z

* cylindrical

Spherical CS

3D: ( r, j, q)

x = r sin j cos q, y = r sin j sin q, z

= R cos j

L

q

Lecture 3 10

Why?

Fill in the blanks below to complete the Cartesian -Cylindrical Polar Coordinates Conversion Table. (10 marks)

Lecture 3 11

Cartesian Coordinate Cylindrical Polar Coordinate

( 1 , 1) (1.414, 450)

( 10, -4) (a)

(b) (30, 2700)

(-6, -5, 10) (c)

(d) (6, 2000, 7)

(e) (3, ___ ) (f) (5, ____)

Lecture 3 12

Right Hand Rule ( 1& 2)

To maintain the position of x, y and z axis.

Lecture 3 13

Right Hand Rule ( 1& 2)

To determine whether the rotation is positive or negative, e.g why ccw for moment is positive???

14

CS in CAD software

Employ various CSs to ease the process modelingie: plane independent/dependent entities

Not all entities can use one reference World CS (WCS): circle, ellipse

CIRCLE Layer: "0"Space: Model spaceHandle = 216center point, X=2199.2165 Y= 0.0000 Z=-

1378.7312radius 302.0956Extrusion direction relative to UCS:

X= 0.0000 Y= 1.0000 Z= 0.0000

circumference 1898.1224area 286707.1852

CIRCLE Layer: "0"Space: Model spaceHandle = 217center point, X=3558.5155 Y=1688.3192 Z=

0.0000radius 210.5250

circumference 1322.7674area 139237.7886

Lecture 3 15

Why we need multiple CSs

Not all entities are CS independent i.e circle, arc and ellipse

Information we have to draw require multiple CSs

Lecture 3 16

Indicate the missing principle axes (X, Y, Z) on theCoordinate System shown in Figure 1a(i) and (ii).

Ans: 1. A 2. D 3. A 4. B

Lecture 3 20

Determine the axis and angle rotation required to transform

model in (I) to new position in (II) for Figure 1b and 1c.

The answer must in sequence