Technical Drawing in AutoCAD
1) What is AutoCAD
2) Drawing a Square using Absolute Co-ordinates
3) Correcting Mistakes
4) Exercise One Absolute Checkerboard
5) Relative Co-ordinates
6) Exercise Two Relative Checkerboard
7) The Offset Command
8) Exercise Three Offset Checkerboard
9) Review Questions
What is Autocad?
AutoCAD is a program used to produce technical drawings that are used as plans for building and manufacturing. AutoCAD is a professional program that is used by engineers, designers, and architects, and technical illustrators. It is used in mechanical, electrical, and civil engineering.
AutoCAD produces drawings that are mathematically precise. AutoCAD files are often used by machines to cut, shape, drill and manufacture products. Some robots will accept AutoCAD files as instructions.
The process of using a computer to design and manufacture a product is called CAD/CAM (computer aided design/computer aided manufacturing)
Because AutoCAD files are mathematically precise a large portion of the drawing is produced using commands and numbers, rather than by using a mouse.
The starting and ending points of lines are specified using numbers. This numbers are located on one of two axes. The x axis indicates a point’s position in the left or right direction on the page. The y axis indicates the point’s position in the up and down direction on the page.
Try moving the cursor around yourself and watch the numbers change to get a feel for how the co-ordinates work.
Co-ordinate System Review Questions
Drawing a Square using Absolute Co-ordinates
Lets try to draw a square using x and y co-ordinates and the line command. Each side of the square will be 100 units long.
The next point will be 100 units to the right so the y co-ordinate will be the same but the x co-ordinate will be 100 larger. The next co-ordinate will be at 150,150.
The next point will be 100 units below. So the x co-ordinate will not change but the y co-ordinate will be 100 less. This brings us to 150,50.
The next will be 100 units to the left so the co-ordinate changes from 150,50 to 50,50. This makes sense since the first co-ordinate was 50,50.
Press enter to stop creating the line.
Drawing a Square using Absolute Co-ordinates Review Questions
Correcting Mistakes
What should you do if you make a mistake?
Pressing enter inside a line command will undo the last line and exit the line command.
Pressing control Z (shortcut for undo) will back up one line segment at a time.
Using the erase tool can erase specific line segments.
Lets say I want to erase the sides of the square.
Exercise One Absolute Checkerboard
Make a drawing of a Checkerboard. The bottom left side of the checkerboard should start at 50,50 and the squares on the checkerboard should be 20 by 20.
The finished checker board should look like this.
Let’s do a few lines to get you started.
If the squares are 20 units high then 8 of them would be 160 units high. Let’s do the first vertical line on the left.
Let’s do one more vertical line
Let’s do one horizontal line.
When co-ordinates are measured from the bottom left hand corner of the screen (0,0) the co-ordinates are called absolute. Save your checkerboard with the filename absolute.
Relative Co-ordinates
Co-ordinates are not always specified relative to the bottom left corner of the screen (absolute co-ordinates). Sometimes co-ordinates are measure relative to the last point drawn. These co-ordinates are called relative co-ordinates.
We will draw a 100 by 100 square using a mix of relative and absolute co-ordinates.
Now we will draw the second point in the right side of the square using relative co-ordinates.
Relative co-ordinates are different than absolute co-ordinates because they can be negative or positive.
Sign of x co-ordinate / Horizontal position of pointNegative / Left of last point drawn
Zero / Horizontal position same as last point drawn
Positive / Right of last point drawn
Sign of y co-ordinate / Vertical position of point
Negative / Below last point drawn
Zero / Vertical position same as last point drawn
Positive / Above last point drawn
Lets look at the square to calculate the relative co-ordinate of the top left corner of the square.
The relative co-ordinate of the top left corner of the square is @ 0,100
@ means this is a relative co-ordinate
0 means the top left corner is neither right nor left of the last point drawn
100 means the top left corner is 100 above the last point drawn
Let’s draw the top right corner of the square. The relative co-ordinate is
@ 100,0
@ means relative
100 means the top right corner is 100 to the right of the top left corner
0 means that the top right corner is at the same height as the top left corner
Let’s draw the bottom right corner of the square
@0,-100
@ means relative
0 means the bottom right corner is neither right nor left of the top right corner
-100 means the bottom right corner is 100 below the top right corner
Let’s draw the final line in the square. The relative co-ordinate is
@ -100,0
@ means relative co-ordinate
-100 means the bottom left corner is 100 units left of the bottom right corner
0 means the bottom left corner is at the same height as the bottom right corner
Relative Square Review Questions
Exercise Two Relative Checkerboard
Create the same checkerboard as you did in exercise one but use relative co-ordinates. The bottom left side of the checkerboard should start at 50,50 and the squares on the checkerboard should be 20 by 20.
Let’s do a couple of lines as an example.
Try to make almost all of the co-ordinates you enter relative. The only time you should enter an absolute co-ordinate is when you make a mistake. When you have completed your checker board get your teacher to mark it before you save it so he can check your co-ordinate list.
Have the teacher mark your checkerboard, then save it as relative.
The Offset Command
The Offset command allows you to copy a line a specified distance along the x or y axis. The offset tool is located on the toolbar
Let’s try some examples of using the offset tool.
Offset Review Questions
Exercise Three Offset Checkerboard
Create the checkerboard we drew in exercise one using almost entirely offset commands. You should only draw two lines one horizontal and one vertical. The rest of the lines should be copies. When you have completed your checker board get your teacher to mark it before you save it so he can check your co-ordinate list.
Have the teacher mark your checkerboard, then save it as offset.
Review Questions
Co-ordinate System Questions
Co-ordinate system questions
1. Name two types of careers that would require the use of auto cad?
2. Autocad is a m______precise program.
3. Which direction of movement on the screen is specified by the X axis?
4. Which direction of movement on the screen is specified by the Y axis?
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Absolute Co-ordinate Square Questions
1) X2 is greater than X3 (True/False)
2) X2 is equal to X1 (True/False)
3) Y4 is less than Y3 (True/False)
4) Y4 is equal to Y3 (True/False)
5) Y1 is equal to Y4 (True/False)
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Relative Square Review Questions
1) To move from X2 to X1 use a negative x co-ordinate True/False
2) To move from X3 to X2 use a negative X co-ordinate True/False
3) To move from Y1 to Y4 specify a zero for the Y co-ordinate True/False
4) To move from Y2 to Y1 use a positive Y co-ordinate True/False
5) To move from Y3 to Y4 use a negative Y co-ordinate True/False
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Offset Review Questions
1) The Offset command is used to move a line a specific distance (True/False)
2) The Offset command is used to make a copy of a line a specific distance away from the original along the x or y axis (True/False)
3) You can only create one copy of a line per Offset command. (True/False)
4) The cursor is shaped like a square when it is ready to select the object to Offset.
(True/False)
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