I sometimes find that the trim command doesn’t function properly as it leaves little bits behind or the items I trimmed don’t trim to the cutting edges I selected. What is the reason for this?
An option to watch out for within the Trim command is the EDGE modifier...which is located on the right-click menu...this can work FOR or AGAINST you...When set to EXTEND It’s used to infinitely extend a cutting edge invisibly across the drawing... so that the cutting edge doesn’t have to physically cross the objects to trim. However, if left ON, it can produce unwanted results...especially if you are using the Auto-Trim mode.
Note! The Extend command also has these same options! Therefore, setting the Edge>Extend option in the Trim command also initiates it for the Extend commandand vice-versa, so, the golden rule when using the Edge mode, is to Turn It Off after using it...set it back to No Extend!