When I was cutting all the gussets for the fuselage I used a trick that someone told me about and it worked very well. Whether the gusset has a single angle or compound angle you really don't care what that angle is, you just want to duplicate it on whatever you are using to cut , sand, etc. that angle.
Take an old hacksaw blade and brake a section off each end of whatever length you want. Place these two end pieces together and put a pop rivit through the hole. After the pop rivit is set, use a hammer to pound the rivit to a tightness that allows you to adjust the angle of the two pieces but will hold that angle once set. I made one tool from a red blade and another from a black blade. I used one color for horizontal angles and the other for vertical angles so I wouldn't get confused when I got to the saw. Simply open the tool to a greater angle that you will need and slide it into the position the gusset will fill. When pushed into place it will conform to the angle you need for the gusset. Now you can use the tool to set the saw, sander, or whatever. As I stated above, you really don't care what that angle is , you just want to duplicate it. How many of you don't have one or two hacksaw blades in your shop that should have been pitched years ago? Larry Flesner