1SheetCourse: Engineering Graphics 1504 Memorial University of Newfoundland

Engi 1504 – Graphics

Lecture 6: Descriptive Geometry Properties of lines Properties of planes Auxiliary planes Midterm hints Class assignment 6

2SheetCourse: Engineering Graphics 1504 Memorial University of Newfoundland

Points and Lines

The point is the basic building block for an object.

3SheetCourse: Engineering Graphics 1504 Memorial University of Newfoundland

Points and Lines

Standard notation – AF is the view of point A on the frontal plane– The height, width, and depth are specified with

reference to the reference (folding lines)

4SheetCourse: Engineering Graphics 1504 Memorial University of Newfoundland

Points and Lines

Note: – The distance behind a plane (say the front plane) is seen in all

other adjacent views.– If the distance to point A from the folding line is known in one

adjacent view, point A can be located in another adjacent view

5SheetCourse: Engineering Graphics 1504 Memorial University of Newfoundland

Lines A line is made up of two points 3 views of line AB are shown

6SheetCourse: Engineering Graphics 1504 Memorial University of Newfoundland

Lines Vertical line – shows as a

point in top view, parallel to front and right side planes

Horizontal – infinite positions, but all points must have equal elevation

7SheetCourse: Engineering Graphics 1504 Memorial University of Newfoundland

Lines Inclined line – parallel to

front or right plane. Always parallel to one plane and inclined to the others

Oblique line – inclined to all principal planes

8SheetCourse: Engineering Graphics 1504 Memorial University of Newfoundland

Auxiliary Planes

The length of a line can only be measured if it is seen in true length

Recall: A line can be seen true length if projected onto a plane parallel to it

So to find the true length of a line we draw an auxiliary folding line parallel to it.

9SheetCourse: Engineering Graphics 1504 Memorial University of Newfoundland

Auxiliary Planes

Consider the front and top view of oblique line ab

We can draw an auxiliary plane parallel to either line aFbF or aHbH

10SheetCourse: Engineering Graphics 1504 Memorial University of Newfoundland

Auxiliary Planes

Auxiliary plane parallel to line aHbH

The line is perpendicular to horizontal (top) view

H2

H2

H1

H1

TL

11SheetCourse: Engineering Graphics 1504 Memorial University of Newfoundland

Point View of a line

Recall: A line can be seen as a point if projected onto a plane perpendicular to it

So an auxiliary plane perpendicular to a line that shows true length will show as a point.

Note: to show line as a point, need a view that shows true length first.

12SheetCourse: Engineering Graphics 1504 Memorial University of Newfoundland

Point View of a line Recall: A line can be seen

as a point if projected onto a plane perpendicular to it

So an auxiliary plane perpendicular to a line that shows true length will show as a point.

Note: to show line as a point, need a view that shows true length first.

D3

D3

aobo

A O

13SheetCourse: Engineering Graphics 1504 Memorial University of Newfoundland

Slope of a line

The slope (or grade) of a line is the inclination of the line with the horizontal

Slope can be measured in a view that shows vertical height and the line in true length

So we draw a folding line in the horizontal (top) view.

14SheetCourse: Engineering Graphics 1504 Memorial University of Newfoundland

Slope of a line So we need an

auxiliary view (folded from the top view), that shows the line as true length

Slope is the angle between the true length line and a line parallel to the folding line

15SheetCourse: Engineering Graphics 1504 Memorial University of Newfoundland

Direction of a line The direction of a line (given

as a compass reading) is seen only in the top view. Think of holding a compass.

A bearing is measured from either north or south, with north usually at top of page

Azimuth is measured from north and specified as an angle from 0-360º

Bearing

Azimuth

16SheetCourse: Engineering Graphics 1504 Memorial University of Newfoundland

Summary

Find true length of a line:1. Place an auxiliary view parallel to the line and project two points

on the line onto the auxiliary view

Find point view of a line:1. Need a true length line first2. Locate an auxiliary view perpendicular to the true length line and

project endpoints

Find slope of a line1. Need a true length line and an edge view of the horizontal2. Find an auxiliary view (folded off the top view) that will show true

length

17SheetCourse: Engineering Graphics 1504 Memorial University of Newfoundland

Summary Continued …

Things to remember about lines: If a line is parallel to a folding line, it will appear true length in

the adjacent view Bearing and azimuth are seen only in the plan (top) view If two lines intersect, the intersection point will correspond in

all views The shortest distance between two lines is seen where one of

the lines appears as a point Perpendicular lines appear perpendicular in any view in which

one or both of the lines appear in true length A line will appear true length in any view folded off a point

view of the line.

18SheetCourse: Engineering Graphics 1504 Memorial University of Newfoundland

Break Time

Take 5 minute break

19SheetCourse: Engineering Graphics 1504 Memorial University of Newfoundland

Midterm Hints and Topics

Midterm exam is November 2nd

Lectures 1-5 are covered (Chapters 1-4 in text) Review your assignments Review visualization exercises Practice as many problems as you can Contact me if you are stuck. My office hours are 1-2

pm on Tuesdays and 9-10am on Thursdays Student Questions?

20SheetCourse: Engineering Graphics 1504 Memorial University of Newfoundland

Class Assignment #6

Point A is 15 m behind the frontal plane and 30 m below the horizontal plane. Point B is 33 m behind the frontal plane and 12 m below the horizontal plane. The line AB bears N 65º E. Using an appropriate scale draw a point view of line AB.