As long as I am posting low tech jigs and tools, here is how I cut the longerons. One end has a 45 degree angle for the forward end of the longerons and the other end has a 30 degree angle for the longeron splices. At this point I have gotten good enough with the portable bandsawin the picto cut quite accurately with the pictured miter box requiring almost no filing or touch up after. I make plenty of these out of scrap mdf or plywood for accurate cutting of miters on tubes.