This command is similar to Break command but the only difference is the way you cut the object. In Trim command the cutting edge is defined by other object. Objects that can be trimmed include arcs, circles, elliptical arcs, lines, open 2D and 3D polylines, rays, splines, floating viewports, regions, text, and xlines.
For example, first create a circle in the autocad drawing area. Then create another circle that overlaps the other circle ( See Fig. 1). In this point you have to select which of the two circle will be your cutting edge. In this exercise, we will choose circle #2. To invoke the command, got to the menu area and select MODIFY>TRIM then AutoCAD will prompt Select cutting edges…Select objects: which is asking you to select your cutting edge. Select circle #2. After selecting, right click you mouse or just press enter on the keyboard. Then it will prompt you again Select object to trim or [Project/edge/Undo]: and you will see the circle you selected highlighted. Autocad is asking you to select the edge of the object you want to cut or trim. In this example choose the overlapping edge of circle #1(See Fig.2) and it will immediately disappear ( See Fig. 3). Then press enter on the keyboard to terminate the command loop.
You can also use this command on many types of objects like circle to ellipse, line to arc, arc to circle, triangle to square.
Fig. 1 – Draw Circles that Overlap Each Other
Fig. 2 – Select and Overlapping Edge
Fig. 3 – The Circle was Trimmed