Modifying Commands and Object Snaps

The previous lesson dealt with drawing commands. This lesson will introduce some common modifying commands. In AutoCAD, you may actually use modifying commands more often than drawing commands. Now that you know the basics, here's some more commands to add to your collection. Three commands, Trim, Extend and Offset are used often in 2D AutoCAD work.

Command	Keystroke	Icon	Location	Result
Rectangle	RECTANGLE / REC		Home > Draw > Rectangle	Draws a rectangle after you enter one corner and then the second.
Trim	TRIM / TR		Home > Modify > Trim	rims 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		Tools > Object Snap Settings	Brings up the OSNAP dialog box.

Assignment #2 - Modifying Commands

The purpose of this assignment is to use the commands learned in the previous lesson and learn some new ones.
Duplicate the drawing called Assign_2.
Click HERE to download the DWG file

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

Start AutoCAD and begin the the drawing by opening up the template file like you did in Lesson 1-2. 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 your 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.
This is what you saw on the command line:

Command: TR TRIM
Current settings: Projection=UCS, Edge=None
Select cutting edges ...
Select objects: <Select the Horizontal line> 1 found
Select objects: <enter>
Select object to trim or shift-select to extend or [Fence/Crossing/Project/Edge/eRase/Undo]: <Select the vertical line>
Select object to trim or shift-select to extend or [Project/Edge/Undo]: <enter>

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.

BREAK TIME: You won't believe me now, but I use the Offset A LOT when I am drafting. As you watch the videos in the next level, you'll see what I mean. I would be lost without my Offset. You will be too, so learn how to use it and be quick with it. You'll get more practice.

Object Snaps

Suppose you want to draw a line from the center of the circle to the middle of the vertical line you extended earlier. AutoCAD has a feature that makes this very easy. These are the Object Snaps (or Osnaps "Oh-Snaps"). Type OS <ENTER> . You will see this dialog box appear.

Icon	Setting	Icon	Setting
	Endpoint		Insertion Point
	Midpoint		Perpendicular
	Center		Tangent
	Node		Nearest
	Quadrant		Apparent Intersection
	Intersection		Parallel
	Extension	M2P	Mindpoint between 2 points

You may select whichever points you want to 'snap' on an object. Here is a list of your options. Followed by the command entry to invoke the needed Osnap.

Endpoint - snaps to either the beginning or the end of an object such as a line - END
Midpoint - snaps to the exact middle of a line or an arc - MID
Center - snaps to the center-point of a circle or arc - CEN
Node - snaps to 'nodes' (not covered in this course) - NOD
Quadrant - snaps to any of the four quadrants of a circle - QUA
Intersection - snaps to the point where two object cross - INT
Extension - Snaps to the phantom extension of an arc or line - EXT
Insertion - snaps to the insertion point of an object (such as a block or text) - INS
Perpendicular - will snap so that the result is perpendicular to line selected - PER
Tangent - snaps to create a line tangent to a circle or arc - TAN
Nearest - will find the closest point an object and snap to that point - NEA
Parallel -Snaps parallel to a specified line - PAR
M2P - This isn't technically an 'Object Snap' as you are not snapping to specific point on an object, but it allows you to select 2 points and it will calculate the midpoint between those 2 points. This is a very handy option to have.

Note: Beside each checkbox is a symbol. That symbol will show up on the screen when you have found a valid snap point. (An endpoint will show a small square). If you select the "Options" button, you can change the aperture size and the color of the Osnaps. Depending upon the background you are drawing on, this may be needed. Osnaps are explained in more depth in tutorial 4-2, but this will be enough for you now.

Check off the boxes as shown in the dialog box above (Object Snaps On, Endpoint, Midpoint, Center) and press OK.

Begin the LINE command. Move your cursor around the screen and you'll see that as you get close to an object, it will 'snap' to one of the points that you had checked off in the dialog box. Place your cursor on the circle (not the middle of the circle) until you see a small purple circle appear at its center. Left-click to make this the start point of the line. Move the cursor towards the middle of the vertical line until you see a small triangle appear. (Remember this is the symbol for 'midpoint'). When you see it left-click to accept this as your endpoint. Press <ENTER> to end the line command.

Save your drawing.

Print your drawing with the same settings as in Assignment #1. Don't forget to use the preview.

Video: Assignment 2

TIP: Before you select the Osnap you want, you can press the TAB key on your keyboard to cycle through the available Osnaps in the area of your cursor.
CAUTION: Although it may seem tempting to turn 'all' the Osnaps on when drawing, you can have too much of a good thing. For example, in shorter lines, Midpoint, Nearest and Perpendicular could all be very close to each other, and you could select the wrong point. When you have finished the assignment, continue practicing with these commands until they are mastered. These are common commands that you will use in everyday drafting.

Extra Practice: Copy this drawing, using lines, offset, osnaps - click to view extra_003.gif

Video: Exercise 3

Extra Practice: Copy this drawing, it could a little to figure out, but still uses the commands you have learned so far. - click to view extra_004.gif

Video: Exercise 4

Extra Practice: Have a look at this drawing of a simple reflected ceiling plan (RCF) and see how the offset, trim and extend commands might be used. If you know how to change units to Architectural, try drawing it. Here's how to change units

Video: Bonus 1