Lab manual

Notes on "Graphics" (Mech 291), Dept. of Mechanical Engineering, McGill University
(prepared by A. Hemami)

As two necessary parts of this course you will learn AutoCAD and Pro/Engineer. Obviously, within the limited time available you cannot become a master of these, but the course shows you the start-up. Those who are more interested, then, can gradually learn the more advanced material by practicing (which is the only way to learn an application software).

Since the philosophy and structure of AutoCAD and Pro/Engineer are different, you must pay attention to the way each one works. Although both are menu driven and the current versions are made to work in a Microsoft Windows environment, you cannot (and should not) assume that they are alike.

AutoCAD is a drafting software, thus it is mainly based on drawing points (various ways that a point can be defined) and lines (parallel lines, perpendicular lines, different types of lines) and so on.

Pro/Engineer is a design software, thus one starts with a solid object and how that solid object can be made up of simpler geometrical objects, or from a process such as revolution of a 2-D geometry about an axis in order to create a cylindrical object.

Practice with AutoCAD:

The following lines give some general information that helps you learn the software faster:

When you start AutoCAD you have two sets of menus on the screen. One set is similar to and associated with Windows operations, such as file management and edit. You use these for loading, saving, renaming, copying, editing, printing files and so on, as you do in other windows applications. The second set is AutoCAD commands and menus. These are to create and manipulate drawing objects. A drawing object or entity is any of lines, arcs, circles, dimension lines, and other geometric elements that a drawing is made of.

For many commands there are short-cut buttons, meaning that instead of getting to the command from the top of the page menu you are able to directly select the command with mouse click. For instance, clicking on the line button, circle button, copy button, erase button and so on issues the corresponding command.

There is a command line, also, that is very useful. You see all the actions that take place when you choose a menu command in addition to the corresponding data on this line. For instance if you issue the command to draw a circle this is reflected in the command line; it, moreover prompts for the selection of radius and centre point. All the processes taken place are recorded, and you can later consult the records of the work for checking data, etc. You can see this by pressing F1 button.

Your practice with AutoCAD consists of the following menus and their submenus:

1. Draw
2. Modify
3. View
4. Format
5. Dimension

Each menu consists of a number of commands. When you select an item from a menu, you are issuing a command. For instance a line command is to draw a line. Then we have to provide the appropriate necessary means, such as two end points for a line.

Draw allows you draw a line, a circle, an arc (of circle), an ellipse, a spline and other entities. Now notice that in drawing a line, for instance, there are specifications that you define or select by menu, depending on what you want to do. You may want to draw a line from one point to another point (the simplest case for creating a line), but some other choices are: drawing a line from a given point perpendicular to another line or tangent to a circle or so, or parallel to another line, etc. Learning AutoCAD implies knowing all of these by heart, and for all the entities and much more.

Modify allows you to do a number of modifications or manipulations on an entity, such as copying, rotating, displacing, multiple copying, deleting, creating a mirror image and many more. All of these can be applied to all the objects. There are some commands that can be applied only to some objects. For example, extend is a command that can be used for extending a line, but it does not apply for a circle.

View allows you do a number of manipulations corresponding to how you want to see the drawing on the screen. Examples are zoom and pan, letting you do things clearly and precisely for items that otherwise are very crowded together.

Format allows you set or change certain specifications for an entity. For example changing the colour, type of a line (normal, dashed, centerline, etc.), text font, units for drawing (metric or imperial) are among the things that you can specify.

Dimension allows you put dimensions for you drawings. As you will learn later, you have many options that you must specify or choose from, such as dimensioning angles or lines, location of a dimension line, if you want horizontal, vertical or none, and so on.

One more item that you will use in your work is the "inquiry" that let you measure a distance, an angle, an area, or so. This is in Tools menu.

Important Notes

For sure before you learn AutoCAD there are many situations that you do not know what to do next for what you want to do. Knowing the following facts can help you a lot in such a situation:

1. Whenever you need to terminate some command, either because you made a mistake, chose the wrong choice, etc., you can hit the Esc. Key.
2. Many commands need pressing the Return key to be terminated. Thus, for instance, in drawing a line, until you press Return the process of drawing a line is not terminated and you get a new line each time you press the left mouse key.
3. Pressing the right mouse key is equivalent to a keyboard Return
4. You can always issue a command by typing on the command line. For instance if you type "circle", it is as you have selected a circle command from the menu.
5. Some commands have an abbreviation, for example "e" represents "erase" and "rec" denotes "rectangle".
6. Whenever you press "Return" in the command line the previous command is repeated. This makes it easier when you want to draw an entity for a number of times. For example, drawing a number of circles.
7. When you issue a command, the corresponding parameter is automatically chosen as that of the latest use of the command, as a default value. You can always enter a new value. For example, when drawing a circle, you need to enter the radius. If you press "return" without entering any value for radius, the default value is used.
8. Like many other applications, you need to save your file somewhere in a directory or on a floppy disc. AutoCAD files automatically are assigned an extension ".dwg". Therefore, you do not need to add that to your file name.
9. For copying an entity DO NOT use the cut and paste of Windows. You must use the copy command.
10. You can use the "Undo" for canceling what you have done. Be careful if now you press "Return" at the command line a new "Undo" will be issued and cancels one more operation that you have completed.
11. You can get "Help" by F1 for AutoCAD commands

Lesson 1:

Practice with points, lines and circles, various ways of drawing points, drawing lines with various specifications. Effects of F8 and F9 on line drawing, grid and effect of F7.

Lesson 2:

Practice with other geometric entities. Practice with copy, mirror image, extend, trim, fillet and chamfer. Working with array and break, move and rotate, offset and explode.

Lesson 3:

Practice with pan, zoom and print. Changing colour, line type, etc. Working with text and font.

Lesson 4:

Practice with dimensioning.

Lesson 5:

Practice with layers, hatch and setting parameters.

Descriptive geometry:

In order to understand descriptive geometry you must first have a good knowledge of ordinary geometry and geometrical rules. These are very simple, and more often common sense, rules that an engineer must know. For instance, when two lines are parallel they do not intersect (and thus, they do not have a common point); or if a line is perpendicular to a plane its angle with any line in that plane is 90 degrees, no matter whether or not they intersect each other.

Descriptive geometry is, in fact, an intelligent way of describing the 3-D geometrical relationships in two planes. In addition to a good knowledge of geometry, you need to have a good visualization ability for 3-D objects. This course helps you to develop such a capability. Also it helps you to recall your knowledge of geometry.

The main application of the knowledge of descriptive geometry in mechanical engineering is for design, manufacturing and assembly of parts that must be jointed, welded and put together. For instance, in order to make a box of a given geometry from sheet metal we need to cut and fold the metal taking into account the necessary overlaps and bending allowances. We should know the shape and sizes for cutting or stamping from a flat sheet to begin with. Or, for two pipes to intersect each other one needs to know the form of the cross section on each pipe in order to correctly cut and prepare it.

The course starts with the representation of a point, a line and a plane. If you understand the philosophy behind descriptive geometry and the way these principal geometrical elements are represented, you will follow the rest in a natural and easy way.

Pro/Engineer

The philosophy and the structure of Pro/Engineer are different from that of AutoCAD. Thus, in working with Pro/Engineer you must avoid thinking the same way as when you use AutoCAD. In using Pro/Engineer you start with the idea of creation (manufacturing) of a 3-D physical entity. You start with a "part" or the "assembly" of parts and the way a part is going to be developed. For instance, a solid piece can be made up by adding components to and taking away (cuts and holes) from a solid block.

One feature of Pro/Engineer is that the sizes are parametric and you do not have to undo and redo operations in order to change a design. Moreover, certain things that can help us are automatically done (we can make changes and corrections, of course).

The engineering drawings of a part that is designed by Pro/Engineer can be extracted from the part data. Thus, you do not need to design the 3-D object and then draw the 2-D drawings, too. Within the limited time that we have, you practice with "part" and "drawing" of Pro/Engineer.

Similar to AutoCAD, in working with Pro/Engineer you have menus that you must choose from. However, contrary to the drawing operations of AutoCAD, that consist of one, two or maximum three steps, in Pro/Engineer the operations have a tree-like structure consisting of a set of sub-menus and sub-sub-menus and so on. You must follow a branch and choose from the proper menu until you reach the end of the branch for each operation. At the end of a selection from each menu you need to notify the completion of your selection by pressing "done" in order to go up (or back) one step (This is the way the software works, even if it seems illogical).

In your practice with Pro/Engineer you work mainly with "part" and necessarily "sketching" which is necessary for creating a part. The following lines show a schematic of the more important components in the tree of operations for your use.

feature:

create:

solid:

hole
round
cut
protrusion
pipe
etc (other solid options)

surface:

revolve
sweep
blend
flat
offset
copy
etc (other surface options)

cosmetics:

sketch thread
groove

user defined:
style:
etc (other create options):

copy:
same ref
mirror
move

delete:
group:
reorder:

As can be seen the first selection menu is "feature" which consists of : Create, copy, delete, group and reorder.

For "Create" then you have the choice of : solid, surface, cosmetics and some more. For everything that you want to do you must know what the sequence of selection menus are. For instance, in order to make a hole, you must know that you should follow 1- feature 2- create 3- solid and 4- hole (After that you must also know how to define the size and location of the hole in a part).

When working with Pro/Engineer, on the screen you have a graphic area and a dialogue box. The dialogue box show you what action you must take next. It also keeps a record of operations. Anytime that you are stuck and do not know what to do, consult this box, bearing in mind that often it is necessary to hit the "done" button in order to be able to continue a task.

The time allocation of the course to AutoCAD, Descriptive Geometry, Engineering Drawings and Pro/Engineer is as follows:

Plan of material for Graphics (Mech 291)

(Chapter numbers refer to your textbook)

2 lectures a week

1	Introduction, principle views, Chapter 14
2	AutoCAD, Lesson one
3	AutoCAD, Lesson two
4	Descriptive Geometry, Chapter 26
5	AutoCAD, Lesson three
6	Descriptive Geometry, Chapter 26
7	AutoCAD, Lesson four (Chapter 20)
8	Descriptive Geometry, Chapter 27
9	AutoCAD, Lesson five
10	Descriptive Geometry, Chapter 27
11	Descriptive Geometry, Chapter 28
12	Descriptive Geometry, Chapter 28
13	Descriptive Geometry, Chapter 28
14	Descriptive Geometry, Chapter 29
15	Review, mid term.
16	Descriptive Geometry, Chapter 29
17	Descriptive Geometry, Chapter 31
18	Descriptive Geometry, Chapter 31
19	Introduction to Pro/Engineer
20	Getting started with Pro/Engineer
21	Pro/Engineer 1
22	Pro/Engineer 2
23	Fasteners and Gears, chs 17, 18
24	Pro/Engineer 3
25	Tolerances and welding chs 21, 22
26	Pro/Engineer 4

3 lectures a week

1	Introduction, principle views
2	AutoCAD, Lesson one (draw)
3	AutoCAD, Lesson one (draw)
4	AutoCAD, Lesson two (modify)
5	AutoCAD, Lesson two (modify)
6	AutoCAD, Lesson three (format)
7	AutoCAD, Lesson four (view)
8	AutoCAD, Lesson five (Dimension)
9	AutoCAD, example
10	Descriptive Geometry
11	Descriptive Geometry
12	Descriptive Geometry
13	Descriptive Geometry
14	Descriptive Geometry
15	Descriptive Geometry
16	Descriptive Geometry
17	Descriptive Geometry
18	Descriptive Geometry
19	Descriptive Geometry
20	Descriptive Geometry
21	Descriptive Geometry
22	Descriptive Geometry
23	Review
24	Mid term
25	Descriptive Geometry
26	Descriptive Geometry
27	Introduction to Pro/Engineer
28	Getting started with Pro/Engineer
29	Pro/Engineer
30	Pro/Engineer
31	Pro/Engineer
32	Pro/Engineer
33	Pro/Engineer
34	Pro/Engineer
35	Pro/Engineer
36	Pro/Engineer
37	Fasteners and Gears, chs 17, 18
38	Tolerances and welding ch. 21
39	Tolerances and welding ch. 22