# SSS 2 (BASIC 11) Technical Drawing FIRST TERM e – LEARNING NOTES

SSS 2 (BASIC 11)

Technical Drawing

FIRST TERM e – LEARNING NOTES

SCHEME OF WORK

WEEK TOPICS

THEME: PICTORIAL DRAWING

1. Revision of last term’s work.

2. Auxiliary Views of Geometrical Solids:

(a) Uses and types of auxiliary views: (i) 1st auxiliary view (ii) 2nd auxiliary view

3. Auxiliary Views of Geometrical Solids:

(b) Draw the 1st and 2nd auxiliary elevation and plans of shaped blocks

4. Auxiliary Views of Geometrical Solids:

(c) Draw the auxiliary views of geometrical solids; full and truncated hexagon, pyramid, truncated cones, cylinders and prisms.

5. Computer Aided Drawing; Pictorial and Auxiliary Views:

(a) Use of the computer for isometric, oblique and perspective drawing of shaped blocks

6. Computer Aided Drawing; Pictorial and Auxiliary Views:

(b) Use of the computer for drawing shaped blocks

(c) (c) Use of the computer to draw the auxiliary elevations and plans of truncated geometrical solids.

7. MID-TERM BREAK

ASSIGNMENT

THEME: POINTS AND LINE IN SPACE

8. Traces of a Point and Line in Space: Projection of a point and a line in space.

9. True Lengths and Angles of a Line in Space: True lengths and angles of a line in space.

10. Planes and Views in Space: (a) Key terms in planes and views in space. (b) Line inclined to horizontal and vertical planes.

11. Revision.

12. Examination.

WEEK 1

REVISION OF LAST TERM’S WORK.

WEEK 2

TOPIC:Auxiliary Views of Geometrical Solids

CONTENT:(a) Uses and types of auxiliary views

(i) 1st auxiliary view

(ii) 2nd auxiliary view.

Sub-topic 1:

True lengths and auxiliary views

Isometric view of a rectangular block is shown in Fig. 11.1. The corners of the block are used to position a line DF in space. Three orthographic views in firstangle projection are given in Fig. 11.2, and it will be apparent that the projected length of the line DF in each of the views will be equal in length to the diagonals across each of the rectangular faces. A cross check with the isometric view will clearly show that the true length of line DF must be greater than any of the diagonals in the three orthographic views. The corners nearest to the viewing position are shown as ABCD etc.; the corners on the remote side are indicated in rings. To find the true length of DF, anauxiliary projection must be drawn, and the viewing position must be square with line DF. The first auxiliary projection in Fig. 11.2 gives the true length required, which forms part of the right-angled triangle DFG. Note that auxiliary views are drawn on planes other than the principal projection planes. A plan is projected from an elevation and an elevation from a plan. Since this is the first auxiliary view projected, and from a true plan, it is known as a first auxiliary elevation. Other auxiliary views could be projected from this auxiliary elevation if so required.

The true length of DF could also have been obtained by projection from the front or end elevations by viewing at 90° to the line, and Fig. 11.3 shows these two alternatives. The first auxiliary plan from the front

Plan

Plan

End elevation

Front elevation

End elevation

Front elevation

First auxiliary elevation

First auxiliary elevation

elevation gives triangle FDH, and the first auxiliary plan from the end elevation gives triangle FCD, both right-angled triangles.

Figure 11.4 shows the front elevation and plan view of a box. A first auxiliary plan is drawn in the direction of arrow X. Now PQ is an imaginary datum plane at right angles to the direction of viewing; the perpendicular distance from corner A to the plane is shown as dimension 1. When the first auxiliary plan view is drawn, the box is in effect turned through 90° in the direction of arrow X, and the corner A will be situated above the plane at a perpendicular distance equal to dimension 1. The auxiliary plan view is a true view on the tilted box. If a view is now taken in the direction of arrow Y, the tilted box will be turned through 90° in the direction of the arrow, and dimension 1 to the corner will lie parallel with the plane of the paper. The other seven corners of the box are projected as indicated, and are positioned by the dimensions to the plane PQ in the front elevation. A match-box can be used here as a model to appreciate the position in space for each projection.

Second auxiliary elevation

First auxiliary plan

Second auxiliary elevation

First auxiliary plan

The same box has been redrawn in Fig. 11.5, but the first auxiliary elevation has been taken from the plan view in a manner similar to that described in the previous example. The second auxiliary plan projected in line with arrow Y requires dimensions from plane P1Q1, which are taken as before from plane PQ. Again, check the projections shown with a match-box. All of the following examples use the principles demonstrated in these two problems.

Part of a square pyramid is shown in Fig. 11.6; the constructions for the eight corners in both auxiliary views are identical with those described for the box in Fig. 11.4.

Auxiliary projections from a cylinder are shown in Fig. 11.7; note that chordal widths in the first auxiliary plan are taken from the true plan. Each of twelve points around the circle is plotted in this way and then projected up to the auxiliary elevation. Distances from plane PQ

Second auxiliary elevation

Second auxiliary elevation

First auxiliary plan

First auxiliary plan are used from plane P1Q1. Auxiliary projections of any irregular curve can be made by plotting the positions of a succession of points from the true view and rejoining them with a curve in the auxiliary view.

Figure 11.8 shows a front elevation and plan view of a thin lamina in the shape of the letter L. The lamina lies inclined above the datum plane PQ, and the front elevation appears as a straight line. The true shape is projected above as a first auxiliary view. From the given plan view, an auxiliary elevation has been projected in line with the arrow F, and the positions of the corners above the datum plane P1Q1 will be the same as those above the original plane PQ. A typical dimension to the corner A has been added as dimension 1. To assist in comprehension, the true shape given could be cut from a piece of paper and positioned above the book to appreciate how the lamina is situated in space; it will then be seen that the height above the book of corner A will be dimension 2.

Now a view in the direction of arrow G parallel with the surface of the book will give the lamina shown projected above datum P2Q2. The object of this exercise is to show that if only two auxiliary projections are given in isolation, it is possible to draw projections to find the true shape of the component and also get the component back, parallel to the plane of the paper. The view in direction of arrow H has been drawn and taken at 90° to the bottom edge containing corner A; the resulting view is the straight line of true length positioned below the datum plane P3Q3. The lamina is situated in this view in the perpendicular position above

the paper, with the lower edge parallel to the paper and at a distance equal to dimension 4 from the surface. View J is now drawn square to this projected view and positioned above the datum P4Q4 to give the true shape of the given lamina.

In Fig. 11.9, a lamina has been made from the polygon ACBD in the development and bent along the axis AB; again, a piece of paper cut to this shape and bent to the angle ^ may be of some assistance. The given front elevation and plan position the bent lamina in space, and this exercise is given here since every line used to form the lamina in these two views is not a true length. It will be seen that, if a view is now drawn in the direction of arrow X, which is at right angles to the bend line AB, the resulting projection will give the true length of AB, and this line will also lie parallel with the plane of the paper. By looking along the fold in the direction of arrow Y, the two corners A and B will appear coincident; also, AD and BC will appear as the true lengths of the altitudes DE and FC. The development can now be drawn, since the positions of points E and F are known along the true length of AB. The lengths of the sides AD, DB, BC and AC are obtained from the pattern development.

ACTIVITY 1:

Example 1

Examples 2:

Example 3:

Example 4:

EVALUATION:

1. Name the principal planes of a projection.

2. When auxiliary plane is placed at right angles to the direction of view what happens?

3. Auxiliary views projected from an auxiliary elevation are called?

Given the front elevation of a cube inclined to the horizontal plane, draw an auxiliary on the ground line x1 y1 at 600 to the horizontal axis.

Procedure:

(i) Draw the given views and locate the ground line.

(ii) Project lines perpendicular to the ground line x1 y1 from all the parts on the plan.

(iii) Transfer the dimensions abcd to the auxiliary plane line as shown.

(iv) Locate the points LMNO as shown.

(v) Join the points to get the auxiliary views.

REFERENCE TEXTS

1. Elements of Technical Drawing for Senior Schools and Colleges by Osuji,U.S.APh.d and Akano,E.O. M.sc

2. Technical Drawing manual with solved past questions School curricular 1 & 2

WEEK 3

TOPIC:Auxiliary Views of a Straight Line

Activity 1:

If a straight line is parallel to any of the three reference planes, its true length is shown by the view on that particular plane. Ifthe line is parallel to the V.P, its true length is shown by the elevation; if it is parallel to the H.P, its true length is shown by the plan; and if is parallel to the S.V.P., by the end elevation.

Furthermore, if it is parallel to the V.P. or S.V.P., its inclination to the H.P is correctly shown in the elevation or end elevation respectively, and if the line is parallel to the H.P, its true inclination to the V.P is shown by the plan.

When a line is not parallel to any of these planes, as in Fig.184, none of the views will show its true length or its true inclination to the H.P and V.P. These things can, however, be worked out in several ways. Two of these methods will be dealt with here: the orthographic method and the conical method.

(i) The Orthographic Method

This method will be discussed first because, though it may not appear so easy, it follows on from the work in the previous sections, an auxiliary plane being introduced parallel to either the elevation or the plan, and the true length worked out on this plane.

Fig. 185 (a) demonstrates this principle of introducing an auxiliary horizontal — it will now be called ‘inclined’ – plane parallel to the elevation. The distance of one end of the line (ai) from the ground line XY is transferred to this plane, as is the distance of the other end of the line (b i) from XY. When these two new points A and B are joined, an auxiliary view of the line is obtained, showing its true length.

Fig. 185 (b) shows the method of applying this principle to the views of the line on the drawing paper.

Introduce a new ground line parallel to ab in the elevation. Draw projectors from a and b at right angles to X1Y1. Transfer the distance of a1from XY (that is c1a1) to the projector aA, marking the distance from X1Y1. This will give point A. Then transfer the distance of b1 from XY (that is d1b1) to the projector bB, again marking the distance fromX1Y1. This will give point B. By joining AB the true length of the line is found.

Fig. 186 (a) demonstrates a similar principle, but in this case an auxiliary vertical plane is introduced, being parallel to the plan of the line. The distance of a from XY is transferred to this plane from X1Y1, and the distance of b from XY is transferred likewise. AB is then the true length of the line.

Fig. 186 (b) shows you how to work this out when given the two views of the line.

Draw a new ground line parallel to the plan. Extend projectors from a1 andb1 at right angles to X1Y1, then transfer the distance of the other end b from XY to its projector, working from X1Y1. Join A and B for the true length.

To Draw the True Length of a Line and Its Inclination to H.P and V.P. (Fig.187)

Let the elevation and plan of the line be as in the figure. Obtain the true length of the line from both views.

You must now understand an important point. Just as an ordinary plan gives us the inclination to the V.P., so an auxiliary plan will give us the true inclination to the V.P. You know that you project from an elevation for an auxiliary plan, so it is this view which will give the inclination to the V.P.

The method can be followed easily from the figure. Produce the true length line to the new ground line X1Y1, and the angle between these lines is the true inclination to the V.P., namely, 250.

Similarly, just as an elevation of a line gives its inclination to the H.P., an auxiliary elevation will give the true inclination of the line to the H.P. So produce the auxiliary elevation to the new ground line X2Y2, and the angle between these lines will be the true inclination to the H.P., namely, 210.

To Find the True Length of a Line, its True Inclination to Both Planes, and also its Horizontal and Vertical Traces (Fig. 188)

Work out the true length and inclinations of the line as above.

The trace of a line is a point. In other words, it is what we see if we sight exactly along the line when it is at eye level. The horizontal trace of a line is the point where the line ( or more often, the line produced) meets the H.P. The vertical trace of a line is the point where the line or the line produced – meets the V.P.

To find the horizontal trace of Fig. 188, produce ab to the ground line XY, then drop a perpendicular to meet a1b1 produced. To find the vertical trace, produce a1b1 to the ground line XY, then erect a perpendicular to meet ab produced. The intersection of these lines will give the required trace in each case.

(ii) Conical method

Once this method is understood, it will probably be preferred to the previous one.

Suppose the elevation of a line is ab, the plan a1b1, and the true length AB, as in Fig. 190.

If the figure is studied carefully it will be seen that the line AB, the line a1b1 and their projectors to each other, form a quadrilateral ABb1a1. Imagine this quadrilateral to be now slowly turned round, with b1B as the hinge, until it is parallel to the V.P. The impression of this quadrilateral can now be cast on to the V.P., and the line A2bso shown will be the true length of ab, while the angle θ will be its true inclination to the horizontal plane.

What has really been done, is to make the line AB the slant side of part of a cone, with B as its apex. Hence the name conical method.

Activity 2:

To draw the auxiliary plan and elevation of a given block.

Activity 3:

To draw the auxiliary elevation of a given block.

EVALUATION:

1. Mention the three faces of orthographic.

2. Draw a rectangle block and bring out the three faces (the teacher goes round to assist the pupils).

WEEKEND WORK:

With the help of the teacher in the drawing studio, each of the students should practice the solids.

REFERENCE TEXTS

1. Elements of Technical Drawing for Senior Schools and Colleges by Osuji,U.S.APh.d and Akano, E.O. M.sc

2. Technical Drawing manual with solved REFERENCE TEXTS

WEEK 4

TOPIC:Auxiliary Views of Geometrical Solids

CONTENT:(c) Draw the auxiliary views of geometrical solids; full and truncated hexagon, pyramid, truncated cones, cylinders and prisms.

Activity 1:

To draw the auxiliary plan and elevation of a given hexagonal prism given the ground lines

Activity 2:

Two views of a hexagonal pyramid are given. Draw an auxiliary plan looking in the direction of the arrow K

Activity 3:

To draw the auxiliary plan of a cylinder

Procedure:

(i) Draw the elevation and the side elevation.

(ii) Divide the side elevation into a number of equal parts.

(iii) Project lines from all the divisions to the front elevation.

(iv) From the points of intersection of the lines and election project lines parallel to line of sight or 900 to the new ground line.

(v) At any convenient point draw the new ground line x1 y1.

(vi) Draw another line parallel to the new ground line x1 y1 to act as centre line for drawing the auxiliary plan.

(vii) Transfer the plans to get the view by picking the radii one after the other with the pair of compasses.

Activity 4: Auxiliary drawing of a cylinder.

To draw the auxiliary of a given cone.

EXERCISES:

Exercises

1. Construct an auxiliary elevation of the cube shown in Fig. 195 on the plane X1Y1

2. Fig.196 shows a hexagonal prism resting on the H.P. Construct an auxiliary plan on X1Y1.

3. Draw an auxiliary view on the ground line of Fig. 197.

4. A hexagonal pyramid is shown in Fig. 198. Draw an auxiliary plan of the pyramid on the ground line shown if its base is a 200 to XY.

5. A hexagonal prism 50 mm long rests with one edge on the H.P. as shown in Fig.199. Draw an auxiliary sectional elevation of the prism on X1Y1, when it is cut by a plane PP.

REFERENCE TEXTS

1. Elements of Technical Drawing for Senior Schools and Colleges by Osuji,U.S.APh.d and Akano,E.O. M.sc

2. Technical Drawing manual with solved past questions School curricular 1 & 2

WEEKS 5& 6

WEEKS 5- 7 AUTOCAD PRACTICAL WORKS FROM THE SOFTWARE

TOPIC:Computer Aided Drawing: Pictorial and Auxiliary Views

Sub-topics:

i. (a) Introduction to AutoCAD

(b) Use of computer for Isometric, Oblique,Perspective

ii. Use of computer for drawing shaped blocks

Sub-topics 1:Introduction to AutoCAD

Requirement: every student should have the AutoCAD software installed in his/her computer system with a mouse attached.

Introduction to AutoCAD

Welcome to the world of CAD – first, you will be learning the very basics of CAD. AutoCAD software is made used of precise technical drawings on the computer. Therefore, AutoCAD is design software that is user friendly and requires interaction through commands with the use of command prompts and a response is being received.

This course is designed so that the commands and instructions should work on almost any version of AutoCAD, although this lesson is designed specifically for AutoCAD 2010 and will work great for 2012. By the end of this level you will have the skills to develop basic 2D drawings.

The X,Y coordinate system

Everything that you draw in AutoCAD is exact. It will be more accurate than you will ever need it to be. We’re talking 14 decimal points accurate. All objects drawn on the screen are placed there based on a simple X,Y coordinate system. In AutoCAD this is known as the World Coordinate System (WCS). You must understand this to know how to put things where you want them. (3-D work has an added axis, the Z-axis, but this is not covered in this lesson.)Above is a diagram showing you how this system works.

Here is how it works

AutoCAD uses points to determine where an object is located. There is an origin where it begins counting from. This point is (0,0). Every object is located in relation to the origin. If you were to draw a line straight out to the right from the origin, this would be considered the positive X-axis. If you were to draw a line straight up, this would be the positive Y-axis. The picture above shows a point located at (9,6). This means that the point is 9 units over in the X-axis and 6 units up in the Y-axis. When you are working with points, X always comes first. The other point shown is (-10,-4). This means that the point is 10 units in the negative X-axis (left) and 4 units in the negative Y-axis (down).

A line has two points, a start point and an end point. AutoCAD works with the points to display the line on the screen. Move your cursor over the picture above and you will see line drawn from the absolutepoints of (-10,-4) to (9,6).

Most of the time you will not have an indication of where the origin is. You may need to draw a line from the endpoint of an existing line. To do this you use relative points. These work the same way, but you have to add [email protected] symbol (shift+2) to tell AutoCAD that this next point is relative from the last point entered.

Review:

ABSOLUTE POINTS are exact points on the drawing space.

RELATIVE POINTS are relative to an OBJECT on the drawing space.

It’s a simple system, but mastering it is the key to working with AutoCAD and is explained in more detail further below. In order to work effectively with AutoCAD, you have to work with this system. Until you are comfortable and familiar with it, learning AutoCAD will be more of a chore. From experience, the better a student is with coordinates, the faster they will learn.

Angular Measurement

AutoCAD measures angles in a particular way also. Look at the diagram below:

When drawing lines at an angle, you have to begin measuring the angle from 0 degrees, which is at the 3 o’clock position. If you drew a line at 90 degrees, it would go straight up. The example above shows a line drawn at +300 degrees (270+30), or -60 degrees.

You might not always have an obvious reference point for 0 degrees. Look at the example below and find out the angle in question.

In this example, you are given information about the lines, but not the angle AutoCAD needs to draw the line from the start point. What you are given though, is (a) the knowledge that 0° is at the 3 o’clock position (b) the knowledge that 180° is at the 9 o’clock position and (c) the angle between 180° and the line you want to draw is 150°. With this information, you can figure out what angle you need.

Here is a fool-proof way of getting the angle you need:

1.) Start at the 0° position and measure counter-clockwise (+) to 180°.

2.) From 180°, measure clockwise 150° (-)

3.) Consider that you just went +180-150 and use that as an equation: +180-150=30

4.) Now you can draw your line using polar coordinates (discussed below)

Entering Points in AutoCAD

You can enter points directly on the command line using three different systems. The one you use will depend on which is more applicable for the situation. The first assignment will get you used to this. The three systems are as follows:

ABSOLUTE CO-ORDINATES – Using this method, you enter the points as they relate to the origin of the WCS. To enter a point just enter in the exact point as X,Y.

RELATIVE CO-ORDINATES – This allows you to enter points in relation to the first point you have entered. After you’ve entered one point, the next would be entered as @X,Y. This means that AutoCAD will draw a line from the first point to another point X units over and Y units up relative to the previous point.

POLAR CO-ORDINATES – You would use this system if you know that you want to draw a line a certain distance at a particular angle. You would enter this as @D<A. In this case, D is the distance and A is the angle. Example: @10<90 will draw a line 10 units straight up from the first point.

The three ways of entering coordinates shown above are the ONLY way AutoCAD accepts keyboard input. First decide which style you need to use, and then enter as shown. Remember that X is always before Y (alphabetical). Don’t forget the ‘@’ symbol when you are entering relative points. Any typing error or omission will give you results you don’t want. If you make a mistake and need to see what you typed, press F2 to bring up the text screen and check your typing. (pressF2 to get back to your drawing.)

The AutoCAD screen, Workspaces, Starting Commands, Terminology

The AutoCAD Screen

• Application Button- This button displays commands for printing, saving, drawing utilities and other non-drawing tool.

• Quick Access Toolbar- This is for quick access to common commands like New, Open, Save, Plot

• Filename – The name of the current file you are working on.

• Search Bar- Search for text in your drawing or search the help files.

• Ribbon – The Ribbon has most of the commands/tools that you will use while you are working.

• Tabs- A series of Tabs make up the Ribbon (Home, Insert, Manage, etc) and organize the Tools into common groups.

• Panels- Contain a group of tools

• Tools – These are the icons that start the commands you use to draw, modify, etc.

• Tool Tip- If you hover your mouse over a tool, a tool tip will appear to give your more information. Hold it longer for more info.

• Drawing Space- These is where you draw your designs.

• Command line- When you type a command, you will see it here. AutoCAD uses this space to ‘prompt’ you for information. It will give you a lot of information and tell you where you are in the command. Watch this line while learning.

• Status bar- This allows to see and change different modes of drawing such as Ortho, Osnaps, Grid, Otrack, etc. You can right click this area to toggle between icons and text for this area.

Workspaces

Within this lesson you will want to be in the 2D Drafting & Annotation workspace. Set this by clicking in the bottom right of the AutoCAD screen on the ‘gear’ icon as shown in the image below. In AutoCAD 2012, this is at the top of the screen.

Icons, Keystrokes and Menus

There are many ways to do things in most Windows programs. AutoCAD is no exception. Everyone will develop a way that works best for him or her. In this course, we will primarily be working with the keystroke commands. The reason for this is because they will work in most AutoCAD versions (including DOS versions), and in some other CAD programs. The icons work well, but as you will see, icons can be placed anywhere on the screen and can be difficult to find quickly. You may be working on another employee’s computer that is set up differently than what you’re used to. The pull-down menus will access almost all commands, but are a slower way of doing things. Icons in AutoCAD 2010 are found on the ribbon, divided into panels – just click on the appropriate tab to open the panel you need.

Example: If you want to draw a line, you can do it a few ways:

• At the command line type: LINE (or) L and press the ENTER key.

• Select the line icon from the DRAW Panel.

• Another way is to Right-Click on the drawing space and choose “Recent Input” from the menu. This will give a list of the most recent command that you have used.

AutoCAD is a popular program because it can be customized to suit an individual’s needs. The toolbars are a good example of this. You can have the toolbars you use most often on the screen all the time. You can easily make them go away so that you have more drawing space. You can also customize them so you have the most common commands on one toolbar. For example, the dimensioning toolbar is one that you will not want taking up space on your screen while drawing, but is very handy when you’re dimensioning your drawing.

To remove the ribbon and have the most drawing space available, click on the “Clean Screen” icon in the bottom right corner of the screen (or press CTRL+O [letter O]). To go back the to the standard display, click again on the same icon.

Basic AutoCAD Terminology

Here are some basic terms that you will want to review before using AutoCAD

Absolute coordinates

A way of inputting points based on AutoCAD’s origin.

Acad.dwt This is the default template that automatically loads whenever you start a drawing session. It can be customized to suit your needs.

Associated Dimensioning Dimensions that are associated with specific points will update as that point is moved.

Backup file AutoCAD can be set to automatically backup your drawing and save it. This is a safeguard in case your file gets corrupted. It is saved with a .BAK extension

Block

A pre-drawn image you can insert in your drawing to save time and make your file size smaller.

Clean Screen A display setting that gives you maximum drawing space.

Crosshairs This is your cursor when it is in the drawing space.

Cursor Your cursor will change depending on what function it is performing in the program.

Database An AutoCAD drawing file is actually one large database containing all the information needed to reproduce the objects when the file is opened. Info for layers and linetypes, etc.are stored in this manner.

Dialog box AutoCAD uses a large number of dialog boxes to get information from you. You must know how input the information that it asks for.

Drawing template file

This is a file that contains preset values for frequently used settings. AKA a prototype drawing. The file extension is DWT.

Extents The outer boundaries of the objects you have drawn.

Grid This is pattern of dots displayed on the screen to guide you. It can be toggled on and off by pressing the F7 key.

Grips

Small ‘handles’ on objects that allow for quick editing.

Layer All objects are drawn on a layer. You can group objects (such as electrical) on a single layer and organize your drawing.

Layout Tabs

A space used for plotting your drawings (formerly called Paper Space).

Limits (Grid) A setting to impose an ‘artificial’ boundary on your drawing that sets the area of the grid, and when turned on, limits you to drawing in the grid area.

Linetype

All objects are drawn with a particular line type. Examples would be solid, center, dashed, etc.

Model space The drawing space where you ‘model’ the objects.

Modify A generic term used for changing your objects

Object Any item that is in the AutoCAD database. Also known as an entity.

Origin

The (0, 0) point of your current coordinate system.

Ortho mode This is a drawing mode that allows you to draw only perpendicular lines. It is toggled on and off by pressing the F8 key.

Orthographic Projection

A standard drawing method that shows 2 or more views of the same part.

Osnap – Object Snap

This is a method of ‘snapping’ to certain, precise points on an object.

Pan

To move around drawing by dragging the drawing area around your screen.

Panel A grouping of commands on the ribbon

Path The specific folder where AutoCAD looks for, or saves files.

Pick To select an object by ‘left-clicking’ on it.

Plot Also known as print. To make a hard copy of your drawing.

Polar coordinates

A way of inputting points based on distance and angle.

Property Any specific characteristic of an object such as layer, scale, linetype, start point, etc.

Ribbon The Ribbon runs across the top of the drawing space and contains panel – each panel has a group of associated tool. Switch to different panels by clicking on the tabs at the top of the ribbon.

Relative coordinates

A way of inputting points based on a starting point.

Section View

A drawing that represents a cross section of a part or assembly.

Selection set

The current group of objects selected for modifying.

Snap This is a drawing mode that allows you to snap your cursor to precise points laid out in a grid pattern. Toggle with the F9 key.

Styles Formatting that defines the look of text, dimensions, etc.

Units

The basic drawing unit set for you drawing. For example, you can use inches or millimeters depending on your needs. You can also set the precision you want displayed, such nearest 1/4″, 1/2″ 1/64″, etc.

User coordinate system (UCS)

Modifications made to the World Coordinate System (WCS) results in a User Coordinate System (UCS)

View A particular area of your drawing.

Viewport

A separate ‘window’ on your drawing. You may have more than one viewport visible to see different areas of your drawing at the same time.

Wizard

An easy step-by-step instruction set to help you set-up certain aspects of your drawing.

World Coordinate System (WCS)

This is the common X-Y coordinate system that is the default. If it is modified, it becomes a User coordinate System (UCS)

Zoom

To view either a smaller section of your drawing (zoom in) or a larger section (zoom out)

Line,Circle , Erase & Undo

AutoCAD allows you to have access to a large number of commands. A general rule is that you will use 20% of the commands 80% of the time. I will start by introducing you to the most common drawing commands. When you combine these with the basic modify commands, you will be able to make elaborate drawings quite quickly. In other words, most of the commands you will use while using AutoCAD are taught here.

The important thing to remember is that AutoCAD will expect you give it information in a very particular order. The most frustrating thing when you begin using this program is that you will try to do something, but AutoCAD will ‘not work’. In most cases, it means that you are trying to input information at the wrong time. This is why it is veryimportant to be in the habit of looking at the command line.

The command line tells you what information AutoCAD requires to continue.

Your first drawing assignment will be to use the drawing commands in conjunction with the co-ordinate system defined in earlier. This is a basic assignment, but it is very important to understand how to give the program accurate information. You will use the following commands:

Command Keystroke Icon Location Result

Line Line / L Home >LIne Draw a straight line segment from one point to the next

Circle Circle / C Home>Circle >Center, Radius Draws a circle based on a center point and radius.

Erase Erase / E Modify >Erase Erases an object.

Undo U / CTRL+Z Quick Access Toolbar>Undo Undoes the last command.

EVALUATION:Duplicate the drawing below. You will not have to worry about the title block or text, or dimensioning

Sub-topics 2:Use of computer for Isometric, Oblique, Perspective

Objective: On the completion of this section student should be able to:

• Understand and explain Isometric Projection.

• Create an Isometric sketch using the computer

• Identify and draw the three main projection divisions in engineering sketches and drawings:

Axonometric (Isometric, Dimetric and Trimetric)

Oblique

Perspective

Isometric Projection

Isometric projection is a method of visually representing three dimensional

objects in two dimensions, in which the three coordinate axes appear

equally foreshortened and the angles between them are 120 º.

Consider the point below for 3D workspace

Circles drawn in isometric view:

A circle drawn on a sloping surface in Axonometric projection will be drawn as an

ellipse. An ellipse is a circle turned through an angle. All the examples shown above

were box shapes without any curved surfaces. In order to draw curved surfaces we need

to know how to draw an ellipse.

If you draw a circle and rotate it slowly, it will become an ellipse. As it is turned through

90º – it will eventually become a straight line. Rotate it 90º again, and it will eventually

be back to a circle.

An ellipse has a major axis and a minor axis. The major axis is the

axis about which the ellipse is being turned. The minor axis

becomes smaller as the angle through which the ellipse is turned

approaches 90º.

You can draw a cylinder using the technique shown below. The

ellipses can either be sketched freehand or drawn using an ellipse

template found on your screen.

Oblique Projection:

In Oblique projections; the front view is drawn true size, and the

receding surfaces are drawn on an angle to give it a pictorial appearance.The direction of projection can be top-left,top-right, bottom-left, or bottom-right. The receding axis is typically drawn at 600, 450 or 300.

Exercise: Use your computer to draw the above drawings

In the oblique pictorials coordinate system, only one axes is at an angle. The most

Commonly used angle is 45º.

Drawing cylinders in Oblique projection

Step One:Draw vertical and horizontal center lines to indicate

the center of a circle and then with a reasonable radius draw a circle.

Step Two:Draw a 45º line to match the length on the

cylinder. At the end of this line, draw vertical and

horizontal centerlines.

Remember the general rule for Oblique is to half all

distances projected backwards. If the cylinder is 100mm

in length the distance back must be drawn to 50mm.

Step Three:Draw the second circle as illustrated.

Step Four:Draw two 45º lines – to join the front and

back circles.

Perspective Projection

If you look along a straight road, the parallel sides of the road appear to meet at a point in the distance. This point is called the vanishing point and has been used to add realism. Suppose you want to draw a road that vanishes into the distance. The rays from the points a given distance from the eye along the lines of the road, are projected to the eye. The angle formed by the rays decreases with increasing distance from the eye.

The above point/ statement is for 3D workspace

One point Perspective Drawing:

Exercise: Use AutoCAD to draw the above one perspective drawing

Two-point Perspective Drawing

Exercise: Use AutoCAD to draw the above two-point perspective drawing

WEEKEND ASSIGNMENT:

1. Duplicate the drawing below

The following tools will be useful

Command Keystroke Icon Location Result

Rectangle RECTANGLE /

REC H ome> Draw >

Rectangle Draws a rectangle after you enter one corner and then the second.

Trim TRIM / TR Home > Modify >

Trim Trims objects to a selected cutting edge.

Extend EXTEND / EX Home > Modify > Extend Extends objects to a selected boundary edge.

Offset OFFSET / O Home > Modify > Offset Offsets an object (parallel) by a set distance.

Object Snaps

OSNAP / OS / F3 CLICK

Tools > Object

Snap Settings Brings up the OSNAP dialog box.

PROCEDURE:

Once again, do not worry about title blocks, text or dimensions; draw only the geometry (in green).

Start AutoCAD and begin the drawing.

Draw a LINE from 1,2 to 3,2 to 3,4 to 1,4 (*Remember to watch the command line as you do this.) For the last line’s endpoint, you can either type in 1,2 or C to close the line back to the first point you entered. These are absolute coordinates. Make sure you understand what the points you just entered represent.

Draw the next square using the RECTANGLE command. A rectangle is created by specifying 2 points to represent the opposite corners. Enter the first point as 4.5,2 and then make the opposite corner 2 inches over and 2 inches up @2,2 using relative coordinates. This is much faster and also makes the square one object and not 4 separate lines.

ERASE the rectangle. You will see that all of it is gone with one pick. Redraw it and continue.

For the 3rd square, draw a 1.5 x 1.5 unit square using any of the methods you know. The bottom left corner must be at 8,2.

Draw a line from 2,5 to 2,6.5 Draw another line from 1,6 to 3,6 You should now have two perpendicular lines. What you want to do is trim off the top of the vertical line and create a T.

Start the TRIM command. It will first ask for a cutting edge. Select the horizontal line and press <ENTER>. It will now ask for the object to be trimmed. Select the vertical line anywhere above the horizontal (cutting) line and press <ENTER> to finish the command.

Once again, it is important to keep your eye on the command line as it will guide you through most commands.

Draw a LINE from 4,6.5 to 6,6.5 Draw another line from 5,5 to 5,6 What you want to do now is extend the vertical line up to the meet horizontal line. Start the EXTEND command. AutoCAD asks for a boundary edge; select the horizontal line press <ENTER>. It then asks for an object to extend; select somewhere in the top half of the vertical line. Press <ENTER> to end the command. Your command line history should match what is shown below.

Command: EX <enter> EXTEND

Current settings: Projection=UCS, Edge=None

Select boundary edges …

Select objects: <Select the horizontal line> 1 found

Select objects: <enter>

Select object to extend or shift-select to trim or [Fence/Crossing/Project/Edge/Undo]:<Select the top half of the vertical line>

Select object to extend or shift-select to trim or [Project/Edge/Undo]: <enter>

Draw a CIRCLE with a center point of 7.5,5.5 with a radius of .5 Now you will use to offset command to make another circle 1/4″ larger. Start the OFFSET command (watch the command line) and enter .125 as the offset distance (1/2 of 1/4″). Now select the circle and pick anywhere outside the circle. Press <ENTER> to end the command.

2. Draw a cuboid having length = 60mm, width = 40mm and height = 30mm in an isometric view and draw its perspective views (one point and two-point) from a point 70mm away.

3. Identify the number of vanishing points for each picture.

i. Number of vanishing points for the first picture.__________________

ii. Number of vanishing points for the second picture._________________

iii. Number of vanishing points for the third picture. __________________

SUB-TOPICS 2:Use of computer for drawing shaped blocks

In this topic emphasis is laid on perfecting students’ skill in the use of the AutoCAD in drawing shaped blocks. The following exercises will do: With that assistance of the teacher

a. Use your system to draw two of the following shaped blocks

b. Draw two out of the isometric blocks below

EVALUATION: Draw one of the untouched isometric blocks

WEEKEND ASSIGNMENT: Draw all the remaining untouched blocks above.

WEEK 7

TOPIC:Computer Aided Drawing: Pictorial and Auxiliary Views

Sub-topics: Use of the computer to draw the Auxiliary elevations and plans of truncated geometrical solids

BACKGROUND: ISOMETRIC PROJECTION AND MULTI VIEW DRAWINGS

EXERCISES:

1. With the assistance of the teacher draw using AutoCAD the following auxiliary views of the truncated geometrical solids below:

2.

Evaluation: Draw, using your system, the auxiliary views shown below:

General Evaluation:

1. When using the TRIM command, which do you select first?

The cutting edges

The object to be trimmed

Everything

Nothing

2. What is the best way of drawing a rectangle?

Using the Line command

Using the Polyline command

Using the Rectangle command

Using the Multiline command

3. What is the best way of drawing a rectangle?

Using the Line command

Using the Polyline command

Using the Rectangle command

Using the Multiline command

4. From which direction does AutoCAD start measuring angles?

12 o’clock

3 o’clock

6 o’clock

9 o’clock

5. What does WCS stand for?

Western CAD System

Worldwide Coordinate Sectors

World Coordinate System

Wrong CAD Settings

6. When drawing in 2D, what axis do you NOT work with?

X

Y

Z

WCS

7. 1s 300 degrees the same as -60 degrees in a drawing?

Yes

No

Not always

Never

8. Reproduce the drawing below:

WEEKEND ASSIGNMENT:

Reproduce the drawing below:

REFERENCE TEXTS:

Teach Yourself AutoCAD by OcheAmuta; Engineering Graphics with Solid Works 2013 at www.sdcpublications.com/pdfsample/978-1-58503-780-3-2.pdf; www.mycadsite.cotm.

WEEK 8

TOPIC:Traces of a Point and Line in Space

SUB-TOPIC:Projection of a point and a line in space.

Projection of a point and a line in space

It is stated in orthographic projection that the projection of line will only show its true length if the line is parallel to the plane on which it is projected. Therefore, if a straight line is parallel to any of the three reference planes, its true length is shown by the view on that particular plane or side vertical plane, its true length and angle of inclination will be shown on the elevation or end deviation respectively. But when the line is not parallel to any of the planes, none its views will show the true length of the angle of inclination. These can be worked out in different ways. True lengths of lines are very important aspects of engineering drawing. Note that if a line makes an angle to a plane, it will penetrate the plane if produced. The point where it penetrates the plane is called trace.

Activity 1:

To find the traces of a line given the plane and elevation.

Procedure:

1. Draw the given plan A,B, and the elevation AB

2. Extend line AB to intersect the base line at x, while A,B, will intersect the base line at y.

3. Draw vertical lines from y and x to intersect with the extended lines to get the vertical trace V.T and horizontal trace H.T

EVALUATION

1. When can we have true length and angle?

2. Where is the true length and angle most needed?

3. What do you understand by trace?

READING ASSIGNMENT: Elements of Technical Drawing by Osuji and pages(75-78)

WEEK 9

DATE

TOPIC:Traces of a point and line in space continues.

Activity 1:

To find the true length and true angle of inclination of a given line using the conical method.

Procedure:

1. Draw the given views AB and A1B1

2. Draw horizontal lines at A and B1

3. Centre at B1 radius B1A1 describe an arc to cut the horizontal line from A at C1. Join C1B to get the true length and angle.

Activity 2:

To find the true length and angle of a line using the triangulation method.

Procedure:

1. Draw the given views of the line B and A1 B1

2. Draw horizontal lines from A ad B1 as shown

3. At any point, draw a vertical line OP showing the vertical difference between points A and B.

4. Centre at P1 radius A1 B1 cut the horizontal line at q.

5. qo is the true length while is the true angle of inclination.

Activity 3:

To find the true length and angle of a line and angle of a line using the auxiliary views method.

Procedure:

1. Draw the given views of the given line AB and A1 B1

2. introduce an auxiliary plane X1Y1 parallel to A1 B1

3. Look in the direction of arrow K and project lines from A1 B1 parallel to the direction of sight K

4. Make X1A2 = XA and Y1 B2=YB

5. A2 B2 is the true length while ᶿ is the true angle .if you want to use the elevation AB, project lines from A and B parallel to K the line of sight. At any point convenient , draw a line X1 Y1 parallel to AB. Make X1A2 = XA1 and y1B2 = YB1. A2B2 is the true length.

EVALUATION

i. State three ways of how true length and true angle can be shown?

ii. Sketch any one of the ways stated above?

WEEK-END ASSIGNMENT

Follow the procedure as outlined in your e-note, and draw the true length and true angle of a line using the triangulation method.

WEEK 10

TOPIC:Planes and Views in Space

CONTENT:(a) Key terms in planes and views in space.

(b) Line inclined to horizontal and vertical planes.

Sub-topic 1:Key terms in planes and views in space.

The key terms in views and planes in space include: vertical plane, horizontal plane, triangular laminar, hip rafter, roof rafter etc.

1. vertical plane

2. horizontal plane

3. triangular laminar

4. hip rafter

5. roof rafter .

Activity 1:

To find the true shape of a given inclined triangle.Q1 given the elevation a1 b1 c1 and the plan a b c of a triangle as follows: ab=35mm, bc=60mm, ac=70mm and is parallel to the vertical plane. On the elevation b1 is 40mm above the horizontal plane. Find the true shape of the plan.

Procedure:

(i) Draw the views of the triangle.

(ii) Find the true lengths of a1 b1 =XZ and c1 b1 = XZ1

(iii) Centre at a1 radius XZ describe an arc.

(iv) Centre at c radius XZ1, cut the arc at b2. ab2c is the true shape.

Activity 2:

Given a triangular laminar lying at an angle to the vertical plane and at right angles to the horizontal plane, find the true shape of the elevation.

Procedure:

(i) Draw the view of the triangle.

(ii) With centre at B1, radii B1 A1 and B1 C1 describe arcs to cut a horizontal lines from B1 at D and E respectively.

(iii) Draw a vertical line from A to A2.

(iv) Draw a vertical line from E to intersect BC produced at C2.

(v) Join B C2 A2 to get the true shape of the elevation.

Activity 3:

Given the plan and elevation of hip rafters of a roof, find the true lengths of the roof raters.

Procedure:

(i) Draw the given view of the hip rafters xyz and x1 y1 z1.

(ii) Centre at x1 describe an arc to cut a horizontal line from x1 at a.

(iii) From a draw a vertical line to intersect with a horizontal line from z at b.

(iv) xb is the true length of xz.

(v) Centre at x radius xy describe an arc to intersect with a horizontal line from x at a1.

(vi) From a1 drop a vertical line to intersect with z1 y1 produced at b1.

(vii) x1b1 is the true length of x1y1.

EVALUATION:

1. mention the key terms in planes and views in space.

2. Make a free hand sketch of triangular laminar showing the true shape.

WEEKEND ASSIGNMENT

Following the procedure in your system draw plan and elevation of hip rafters of a roof.

REFERENCE TEXTS

1. Elements of Technical Drawing for Senior Schools and Colleges by Osuji,U.S.APh.d and Akano, E.O. M.sc

2. Technical Drawing manual with solved past questions School curricular 1 & 2.