Back before the turn of the year, I once again turned to painters tape in an effort to simplify the measurements and calculations required for cutting a couple of tubes. The difference this time being that these tubes were for multi-axis (3D) angled ends.
As before, lay out the desired tube path with tape. This time, with two pieces of tape forming the opposing sides. I found it to be much more accurate and stable by 'sticking' a small piece of scrap tube between the two pieces of tape near each end to help place the tape. Then wrap tape across the 3rd side to form the 'top' of the cut, as well as mark the two 'sides' for finished length as well. Hopefully this picture will be worth enough additional words to salvage my poor description.
Now the tape can be removed and wrapped over the actual tube being cut.
Trim the excess. Note that the 4th and final edge can be found by drawing a line between the 'bottom' edges on the two sides.
Now be careful how to set this up in the saw. If done wrong, it will cut off needed extra length. If done right it will indicate what needs to be ground off, as pictured below.
Color the excess material in with Sharpie (finally a good use for the Industrial Sharpies) and take it to the bench grinder until the Sharpie is all gone and the tube fits.
I must admit that this method and/or my execution are not as perfect as the 2D tape method. As the tubes move out of plane with each other, the 1" wide face of the tube being intersected becomes less-than 1" relative to the intersecting tube probably plays a part here. I'm sure that I also just need more practice. The end result was that the indicated grind area was a bit on the conservative side, and I actually just needed to grind off a little more metal than the tape line indicated...Which is great, because I really hate trying to grind metal back on to the tube.