While making the bends for the front and rear center spar uprights, I had a problem trying to take measurements with any of the numerous protractors I had. The angles I was trying too measure were to acute for any of my protractors to fit. So I decided to make a set of simple angle gages.

The gages were made using .025 aluminum scraps that I had laying around. The key to setting up the angle is to use a machinist tool called a sine bar. Referring to the picture below, the sine bar is the bar with the cylinders attached. The distance between the cylinders is 5 inches.The stack on the right is from a gage block set.  When the stack size is set to (5 inches) * sin(angle). This sets the angle relative to the straight edge at the bottom. If your trig is a little rusty for why this works you can find numerous demonstrations on youtube for how to use a sine bar.

A parallel was aligned to the sine bar and slid down the side until it touches the straight edge. The sine bar is removed and the hypotenuse is drawn using the parallel as a guide. The vertical line is then drawn. Being exactly perpindicular on the vertical line is not important because I am only intersted in the angle defined by the sine bar.

Below is a set of completed angle gages that were used when I was fabricating my center spar uprights.