The drive horn shown in the plans has no dimensions but is drawn full scale. I decided that the quickest way to make this part was to start with a template. I used a piece of drafting paper to trace the drive horn from the plans. I then glued the drafting paper to a piece of bristol board and cut it out. This provided a rigid template that I could trace for the final shape on the aluminum.<br /><br /> I traced the shape onto the aluminum and used the band saw to cut out the rough shape. Next, I started the sanding.