Me too. I like to insert a piece of styrene rod into the tubing to support it a bit, but you can do it without, just work a little slower. Use a good blade, square it up to the tubing, and just slowly roll the tubing with the blade, as if you were sawing it. Using nearly the full length of the blade (long strokes) seems to work better for me. This tends to taper the end inward, as others have noted, so after you cut, you'll want to ream out the end to open the diameter to what you want. I usually just use another Exacto with a worn blade, this actually shaves a little of the aluminum along with the "burr" from the cut, leaving a nice scale thickness. you can use any number of pointed objects to flare the end if you want; I've tried pencils, nails, bamboo skewers, and more with satisfactory results. Use what you have!