Engineering Drawing in AutoCAD A Primer for TA101

Instructor – Dr. Anupam Saxena

Prepared by Mohit Singh 2nd Semester 2012-13

© Copyright 2013 Autodesk, Inc. All rights reserved

Commands can be entered into AutoCAD in two ways --

1. The Ribbon – Contains the graphical access to all commands and features, divided into intuitive headings and icons which are self explanatory.

2. The Command line – Present at the bottom of the interface, it is another way of interacting and using features in AutoCAD. It is considered to

be a faster method of inputting data.

While it is usually very convenient to enter commands using the icons in the ribbon, it is suggested that to take the full advantage of all features,

users must also have familiarity with command line input. In this tutorial, we will try to give instances of both the ways.

The CAD drawings we will be making will be saved in the standard .dwg file format. We will also learn how to create the layouts (top, front and

side views) and export them in pdf format.

First, let us have a look at some of the basic actions in AutoCAD which are used repeatedly. These same actions are also used in a number of

other software and many users might be already familiar with their usage.

1. The scroll of the mouse is used to zoom in and out of the drawing area

2. The middle button of a 3-button mouse is used to pan in the drawing area. Panning is similar to moving your drawing page horizontally

or vertically to adjust the view. Hold the middle button and drag the mouse to pan

3. Shortcuts like Ctrl+Z (undo the last step) and Ctrl+S (save latest) have the same usual meaning and are used extensively

4. Left click selects an object and right click shows a dropdown list with options depending on the context

5. Keep the mouse still for 2 seconds on an icon and AutoCAD will show a very useful quick-hint on what the command does

6. When you click a command button, the default pointer changes shape and becomes ready to accept input from the user. To revert to

the default pointer state, press Esc

For example :

Default pointer A pointer ready to accept input after clicking the ‘Line’ command

7. Whenever you enter or click on a command button, remember to look at the command line once. It gives you additional information

regarding what all can you do with that command. For example,

If we write : fillet <enter>

The command line reads : Select first object or [Undo/Polyline/Radius/Trim/Multiple]

Now if you wish to change the radius of the fillet, just type r (first letter of ‘Radius’) and hit enter.

Similarly, type u <enter> if you wish to undo or t <enter> if you wish to trim, and so on.

8. By default, AutoCAD uses Relative Referencing. This means that the present point is treated as the local origin. You will need this while

specifying the next point to draw the line to. Use relative co-ordinates, and not the absolute ones

9. Before you start drawing anything, type the SNAP command and hit enter. The command line asks for the snap size. Enter 0.5 and hit

enter. What you just did is that since your drawing contains mostly integral co-ordinates, you told AutoCAD to move in units of 0.5 only

(horizontal or vertical) when you drag the mouse over the drawing area

The Line Command

Perhaps the simplest and the most used design feature is a line.

Type Line <enter> or click line button

1. Click on the starting point in the drawing area, take the mouse to the finishing point and click

again to create a line segment.

2. Alternately, enter the starting co-ordinates separated by commas and hit enter. Now

AutoCAD asks you to enter the next point.

Remember that by default we are using relative referencing. So specify the co-ordinate of the

next point relative to the present point and hit enter.

Continue this process to create a path. Hit Esc when you are done making the lines.

Let us start with the top view of the assignment.

Here is the plan –

To create the rectangle with rounded corners that is

visible in the top view, we draw the right side figure.

We will connect points 1 and 4 using an arc (a

semicircle)

We will use fillet command to round off the sharp

edges at 2 and 3.

Can you figure what co-ordinates to enter in order to create this figure? Start from 1 and move to 2, 3, 4. Remember, to specify the next point relative to

the present point. For example – Point 1 -> (57,32) <enter>

Enter next point

Point 2 -> (-146,0) <enter> … and so on (Can you see how relative referencing is being used here ?)

1 2

3 4

The Fillet command

This command is used to round off a corner.

Type: fillet <enter>

The command line says :

Select first object or [Undo/Polyline/Radius/Trim/Multiple]

We need to specify the radius of the round that will be created

from the edge.

Type: r <enter> and enter a value of 32 <enter>

Now AutoCAD asks you to select which two edges need to be rounded into a corner. So, left click on edge 1-2 and then on edge 2-3 to select them and

hit enter. The fillet will execute and you will see the result.

Now repeat the fillet operation to round off the corner 3 yourself.

The Arc command

This is used to create an arc. There are many ways of specifying an arc. Click on the dropdown of the arc command in the ribbon to see a list of the ways

in which AutoCAD takes information regarding an arc. We will click the Start, Center, Angle mode of specifying the arc.

2 1

4 3

As the name suggests, we need to specify the starting point

first. Click on point 4 to demarcate it as starting point.

Now AutoCAD needs to know the center of the arc. You

know it to be 32 mm above the point 4, so go to that point

and click.

Now AutoCAD need to know the angle that the arc subtends

at its center. Since it is a semicircle, enter 180 <enter>. You

can also drag the mouse till the arc meets point 1 and then

left click.

The Circle command

Again, there are a number of ways of creating a circle. Let us use Center, Radius method.

Type : circle <enter>

Command line says : Specify center point for circle or [3P/2P/Ttr (tan tan radius)]:

Type : (57,0) <enter>

Command line says : Specify radius of circle or [Diameter] :

Type : 11 <enter>

Similarly, create the other circle

Now using all that you have learnt till now, you should be able to create the following figure, which happens to be the top view !

We will see in a moment how to construct the hidden lines, the construction lines and the auxiliary lines using a very important concept known as layers.

First, zoom out of the drawing area using you scroll. To zoom out more, go to View-> Extents (in Navigate group) -> Zoom out

USING LAYERS

As you must know, a drawing also contains many elements like hidden lines or construction

lines. AutoCAD also has such features which are implemented by using a fairly simple concept

of layer. Imagine that you have just finished your class assignment in TA lab. In order to keep

your drawing neat, you have deliberately not shown the hidden lines or construction lines on

the drawing sheet. So you decide to bring in a transparent drawing sheet and put it exactly

over the sheet in which you have your drawing. Now you pick up a marker and start drawing

only the hidden lines on this transparent sheet. If we call your original sheet as the Layer 0,

then this transparent sheet will be called Layer 1.

Do you now understand what layers are? Nothing but a way of presenting information

conveniently.

AutoCAD uses a different layer for each of such lines.

Click on the dropdown of the layer button. Click on the Centerline layer to activate it. Now

draw the + symbol depicting the center of the circle. The lines that you make in this layer will

have a different color and style. If you zoom in, you will find that the line is of dash-dot type.

Change back to original layer by clicking the first Contour layer when you are done.

Similarly, we will draw the hidden lines and the auxiliary line (Hinge line).

Construct the hinge lines by jumping to the auxiliary layer. Do not

forget to switch back to first contour layer when you are done!

The Construction lines

Construction lines are useful for alignment and quick measurements. Click on the construction line button and select the kind of construction line. At

present we use only 3 types – horizontal, vertical and tangents to circle (find them yourself in the construction line dialog box)

STEP 1 : use the vertical construction line and carry the pointer to STEP 2 : Click to create the construction line (seen in red)

the left end point of the top view. The autoCAD confirms Similarly draw other construction lines as and

that the point is indeed the end point (green square box) when you need them

Using the Construction lines to draw front and profile view

You will see that drawing becomes much easier when you have drawn required construction lines. Here is how you use them to draw line in

front and side view.

1. Start making a line in the front view by clicking the line command. You will see that at first autoCAD does not give you hints to start the

drawing of the line

2. Now, to make autoCAD give you inferences, just carry the pointer to the square green box you encountered while drawing the

construction line earlier. AutoCAD will now understand that you need to make a line using the present construction line.

3. Slowly bring the pointer vertically down along the construction line and once you have reached the desired point, click to define the

starting point of your line.

The Trim Command

Look at the situation shown on the right side. I have drawn the front view using the construction lines. But notice that the middle part of the

upper line in the front view needs to be deleted. We do this by using the trim command.

This command requires following 2 inputs from you –

1. The cutting edges – These are the edges between which the line has to be deleted. Select the 2 innermost construction lines and hit

enter. (Can you see why these are the cutting edges ?)

2. The object to be deleted – Obviously, here you select the line which has to be deleted. Select the line and hit enter, and you are done

Now in principle, you know everything required to draw the complete third angle projection given on the next page. Use all the steps laid down

till now and apply them. Remember following 2 points –

1. The construction lines can also be trimmed. You may need to do this to draw the hidden lines in the front view. Also, once the feature

has been drawn, the construction lines can be selected and deleted.

2. Do change the layer to Hidden Layer while drawing the hidden lines. Change back to the contour layer when you are done

Creating the Layout

Now that we have created the views, we need to print them to share with others. Let us see how to do this.

Click the layout tab just above the command line window. The view changes to layout view from model view.

Now you just need to tell AutoCAD the view of your drawing you wish to print. Go to the View tab above the ribbon and click on the

Viewport/Scale Area command. Just as you click, AutoCAD will now expect you to draw a rectangle in the layout page which will contain the drawing.

So, click on the upper left corner of the page and then on the right bottom corner. Select a scale factor of 1:1

Now double click inside the page and zoom/pan till you have a desired view of your drawing.

Go to the file menu and Export the view to a pdf file. The output looks like this.

ASSIGNMENT – Go back to the model view. Go to the Annotate menu and try to dimension the drawing.