The window apron happens to be the easiest part of the window trim to install. A window apron can change depending on the persons taste. There are two main forms of it. One is where it will line up directly with the outside of the casing. In the other scenario, the apron will be just shy of the casing. After deciding which you would like to do you can prepare the apron for installation.
You will want to start by marking and cutting a 45 degree cut through the apron using a miter saw.
You will then want to take a scrap piece and do the same thing to the end of that.
Now take the scrap piece and cut off the tip that you just cut. You should end up with a small triangle.
Finally you will want to nail the apron into place and drill holes in to be able to attach the return to it.
Tips to Keep in Mind for Creating an Apron
You have to do these steps for each side of the apron.
Although time consuming, this method will allow for a smooth face with no grain exposed.