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Track Geometric Points in AutoCAD
17 Jun, 2010 By: John HackneyAvatech Tricks Tutorial: Find points in relation to existing geometry without extra geometry.
Editor's note: This tutorial courtesy of Avatech Solutions.
While designing in AutoCAD, you often want to sketch to coordinates that are referenced from existing geometry. AutoCAD offers a few tools that can help with this task and avoid the addition and management of construction lines. Most AutoCAD users are familiar with the object snap (osnap) Extension function — which can be combined with object snap tracking to find needed coordinates from existing geometry — but there are a few more commands and sub-commands that not all users are as familiar with. These commands include From, Point Filters, Temporary Tracking Points, and Tracking. This Tech Tip will explain the use of the last two.
To illustrate these commands, we will use a simple design of a bearing and the machine side plate to mount two of these bearings on. 
We want to make sure our AutoCAD osnap settings are correct. For this exercise, make sure Endpoint, Center, Midpoint, Intersection, and Extension are selected as running osnaps. Also be sure the Object Snap Tracking option is enabled on the status bar. For this exercise we will turn off Dynamic Input, either by selecting the icon on the status bar or by pressing the F12 key.
The first task is to place the bolt holes on the bearing flange. These holes are 3 inches from the center of the bearing in both directions. We will use the Temporary Track Point sub-command to place one hole, and then we will pattern the remainder. We want to find the bolt hole center by "temporarily" tracking in two directions from the center of the bearing. Select Center, Diameter from the circle command menu. Hold down the Shift key and press the right mouse button (RMB) to display the osnap override dialog box. Select Temporary Track Point.
If you use keyboard shortcuts, press T + T + Enter instead of using the dialog box.
Next is the point in the process where you probably will need to slow down until you can master the process. Do not click the center of the bearing; just hover over it and the center osnap icon, and then move away. You will leave an acquisition point behind. If you hover over the point again, it will be removed — it is a toggle.
Move your cursor along a horizontal line to form the extension dotted line. Best practice is to move either beyond the dimension you want. Enter the first dimension from the keyboard and press Enter. Another acquisition point will show up; resist passing your cursor over it, because that will erase the point. Move your cursor directly above this acquisition point to form a second extension dotted line.
Acquiring the first point (left) and the second point (right).
Enter the second dimension from the keyboard and press Enter. You can now specify the diameter of the circle. Use either a polar or rectangular array to create the remaining holes.
Next we will draw the side plate on top of the base plate. Imagine that you know the plate is 24 units tall, but you do not know the length of the base plate. You do know you want it 2 units from each end of the base plate. This is a perfect situation for the Tracking sub-command. This sub-command does not exist on the ribbon, in a toolbar, or a pop-up dialog box, but if desired can be programmed by using the AutoCAD CUI (Custom User Interface) to a location of your choice. A good location is Ctrl + RMB, since it is just as easy to access as the Shift + RMB combination used for the Temporary Tracking Point sub-command. If you want to use keyboard input, type T + K + Enter to start the sub-command.
Start the Rectangle command and hover over the top left corner of the base plate to acquire the extension tracking point. Move your cursor along the extension dotted line pass 2 inches. Enter 2 on the keyboard and press Enter. You now have the lower corner of the rectangular side plate. Type T+ K + Enter to start the Tracking sub-command.
Two things happen that the user should be aware of. First of all, the command automatically turns off Polar Tracking and turns on Ortho Mode. When you finish the sub-command, it will automatically return to the original settings. The second thing is the rectangle disappears and you will notice it is asking to select First Tracking Point. During this sub-command, you do not hover, you select points using the pick button on your mouse. Pick the top left corner of the base plate.
Picking the first tracking point.
Move your cursor left to right to see the horizontal rubber band line. Move your cursor up and down, from the original pick, to see the vertical rubber band line. The Command line is asking for Next Point or Enter to end the tracking. Move the cursor to the left and enter 2 on the keyboard and press Enter. Move the cursor up from this point to show the vertical rubber band line, and type 24 on the keyboard and press Enter. At this point we are at the top right hand corner of the side plate, so press Enter to end the tracking sub-command and place your finished rectangle.
Tracking the second point.
Placing the two bearings in place using the Copy command will be good practice using either of the two methods outlined above.
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