I found this cheap compass at Michaels Craft Supply, it uses a 1/2" dowel as the bar and is adjustable to as large as you need. This is the first time that I used it and it really worked well. With the compass I created two lines at 90 degrees on the workbench. To support the wing tube I make two stands out of scrap wood, these pieces were left over from the engine box. The stands were drilled together so that both holes are the exact distance above the working surface.