Drafter Kathy Bracisco shares a tip that expands on Cadalyst CAD Tip No. 3739.
"In addition to David Gaskill's 'Leverage the Trim and Extend Commands' tip, I find that the EdgeMode system variable is a great help to me. I set the EdgeMode variable to 1, and this allows lines that do not extend for use in the Trim/Extend command to become implied. When I press the Enter key the second time, the implied edges become available."
Notes from Cadalyst Tip Patrol: Using the Trim and Extend commands in AutoCAD takes up a lot of time. Finding a way to use the commands in more efficient ways, such as with EdgeMode, will reduce your drafting time. EdgeMode comes turned off (set to 0) out of the box; this means that AutoCAD cannot trim or extend a line that does not actually intersect the line to be altered. Users will have to extend the trimming line, create a construction line, or go to a few extra steps to get the job done. Turning EdgeMode on (by setting it to 1) can save you much time and effort.