Odd angles - Do I use a corner post or what?
It is not unusual to have an angle other than a 90 degree corner. You can use a corner post or a line post, depending on the angle. Basically, anything wider than 90 degrees, use a line post. Less than 90 degrees, use a corner post.
To better understand the use of a line post versus a corner post, study the drawing below. If in doubt, you can always order a blank post (one with no holes) or an end post with the intention of cutting the other holes on the job, when you can better assess which is best.
Most styles of ornamental aluminum fence have pre-routed holes in the posts for the section rails to slide into. That is the significant difference in a line post, a corner post, or an end post.
Since the posts and rails are made for 90 degree connections, it will be necessary to widen the post holes for the increased angle and shape the end of the rail slightly for a snug fit. When you slide the rail into the pre-routed post rail hole, it will fit snugly. As you 'swing' the rail around to get an angle, the rail will bind up inside the hole. By widening the hole a bit, the rail will be able to 'swing' to the angle you need. Some styles of ornamental aluminum have notched rails. Only part of the rail slides into the hole. The rest of the rail butts up against the post. Since this notch is a 90 degree cut, you will have to notch one side deeper so it will fit the post snugly when the angle is acheived. This sounds very complicated, but in reality it is very simple. The rails can be 'nipped' with a hack saw very easily and the holes in the posts can be filed or cut-out to the proper width.