AutoCAD - Enhancing Drawing Accuracy

Note: Classic view screenshots used in this module are taken from AutoCAD 2000i, whose interface closely reflects the AutoCAD 2009 'Classic' interface.

RULE NO 1 - NEVER, EVER, "EYEBALL" THE LOCATION OR LENGTH OF A LINE (OR OTHER AUTOCAD ENTITY). ACCURACY IS A MUST!!! ALWAYS!

Grid and Snap

Using the Grid and Snap commands in combination enhances the accuracy of your drawings by "constraining" the cursor within a standardized grid system. Note the following;

• The Grid and Snap settings need to be setup before they will work properly.
• The Grid and Snap systems need to be switched ON to activate them (Uee the buttons on the Status Bar).
• The Grid and Snap settings can be changed at any time - changing the settings will not effect anything that you have already drawn.
• The grid will be displayed throughout the Limits of your drawing.
• If the Grid or Snap doesn't seem to be working, check your drawing Limits. Also do a Zoom>All so that you can see the entire Limits of your drawing.
• The Grid and Snap method of drawing will not work for all projects - it requires that the item(s) to be drawn follow a regular grid pattern.

Classic View Samples	Access the Drafting Settings through the Tools Menu or by right-clicking one of the icons.	AutoCAD 2009 Samples
	Alternatively, Right-Click over the Grid or Snap button on the Status Bar, then Choose Settings . . .
	Change the Grid and Snap setting then OK.
	Switch Grid and Snap ON/OFF using the buttons on the Status Bar

Object Snapping

Drawing accuracy is greatly enhanced through the ability to attach a line (or other entity) onto an existing point in a drawing, such as the end point of a line. This is known as object snapping (Osnap).

When prompted to provide a point, do one of the following

	Use the keyboard/mouse combination of Shift+Right-Click to bring up the Osnap Menu OR
	Pick the Osnap setting from the Object Snap Toolbar

Common Object Snap Settings
	To snap onto the end point of a line or other entity
	To snap onto the mid point of a line or other entity
	To snap onto the intersection point where two entities cross
	To snap onto the centre point of a circle or arc
	To snap onto aquadrant point of a circle
	To connect a line perpendicular to another line

Running object snapping programs AutoCAD to ALWAYS look for particular snap settings whenever it is looking for a point. Running object snaping can be switched ON/OFF. Note the following;

• The Running Object Snap settings needs to be setup before it will work properly.
• The Running Object Snap system need to be switched ON to activate it (Use the buttons on the Status Bar).

Running Object Snap
	Access the Drafting Settings through the Tools Menu
	Alternatively, Right-Click over the OSNAP button on the Status Bar, then Choose Settings . . .
	Check-off the Osnap modes you wish to program AutoCAD to look for.
	Switch Osnap ON/OFF using the buttons on the Status Bar

Polar Tracking

Polar tracking constrain (snap to) the exact angle that lines will be drawn when they are close to a given angle. Note the following;

• The Polar settings need to be setup before they will work properly.
• The Polar system need to be switched ON to activate it (Use the buttons on the Status Bar).

Polar Settings
	Access the Polar Settings through the Tools Menu
	Alternatively, Right-Click over the POLAR button on the Status Bar, then Choose Settings . . .
	Set the angle to constrain linework. Note if 30 is chosen, lines will be constrained for the following angles; 0, 30, 60, 90, 120, 150,180, 210, 240, 270, 300, 330, 360.
	Switch Polar Tracking ON/OFF using the buttons on the Status Bar

Direct Distance Entry

When used in conjunction with Polar Tracking, Direct Distance Entry (DDE) is a quick and accurate method for drafting. Note the following;

• With Polar Tracking activated and defining the exact direction of a line (#1 on the illustration below), type the length of the line in the command prompt area (#2 on illustration below) - that's all there is to it!
• Note how the tool tip display changes as you move the cursor.
• DDE will NOT work for the first point of a line.

Coordinate Systems

Absolute

The absolute coordinate system requires input of coordinates as they relate to the origin or 0,0. The coordinate is made up of two values. (There actually is a third value - the z component - but in 2D drafting it is always zero)

Relative

The relative coordinate system requires input of the change in direction of x, and the change of direction of y from the point you are currently at. There is a special character used to distinguish this coordinate from the absolute coordinate system. That symbol is the @ character. (i.e. @ delta-x, delta-y or @3,0 to move 3 in the x and zero in the y).

 

 

Drawing the Triangle using Relative Coordinates
Task	Command Line Prompt:	You type:
Start line command	Command:	LINE
Start the line at point A	Start Point:	2,1
Draw line from A to B	Next Point:	@4,0
Draw line from B to C	Next Point:	@0,3
Draw line from C to A	Next Point:	@-4,-3
End the command	Next Point:	ENTER

Relative Polar

The relative polar coordinate system borrows the @ symbol from the relative coordinate system but uses a vector to determine the next point to use. This vector is specified by a distance and an angle. (i.e. @ distance < angle or  @5<45 to draw a line 5units long at 45 degrees.) Remember;

• 0 (zero) degrees is in the direction of the positive X-axis.
• Positive angles are measured counter-clockwise from the direction of the positive X-axis.
• Negative angles are measured clockwise from the direction of the positive X-axis.

Drawing the Triangle using Relative Polar Coordinates
Task	Command Line Prompt:	You type:
Start line command	Command:	LINE
Start the line at point A	Start Point:	2,1
Draw line from A to B	Next Point:	@4<0
Draw line from B to C	Next Point:	@3<90
Draw line from C to A	Next Point:	@5<216.87
End the command	Next Point:	ENTER

Copyright Sheridan College Institute of Technology and Advanced Learning 2008