I was screwin' around with buzzsaw weaves today (buzzsaw inserted into a weave every time you change sides), and realized that the motions for that are exactly what you need for a clean buzzsaw fountain.
I see a lot of buzzsaw fountains which start to break up the buzzsaw in the middle and then put it back together on the other side, very few that keep a nice clean circle all the way around the cycle- understandably so, 'cause it's really hard to keep things lined up while you're tryin' to switch which side of your arms your swinging on and get your arm positions swapped at the same time, but post-epiphany, I'm suddenly finding this really easy. If this is really well-known, well, just ignore me I guess, but I've never seen it explained in a tutorial, so, hey, maybe it'll be worth something to throw it out there.
So, arm motions:
1. Start raising the buzzsaw above your head / lowering it in front of you. Obvious. Normal start of a fountain.
2. Cross your arms so that each hand is spinning on the outside, on the opposite side. If you're spinning forward, your back hand needs to cross over your front hand; if you're spinning reverse, your back hand crosses under your front hand. Exactly the same as going from a buzzsaw into a weave.
3. Arms uncross as you rotate to the other side, and your new back string switches which side of your arm it's on so it's back in buzzsaw mode.
4. Switch your front string back into buzz-saw mode, exactly like going from a weave to a buzzsaw, and ta da, you're done.
I'm certain there're other ways of doing it, but this just worked out amazingly well for me, and I wish I'd discovered it / had somebody tell me about it sooner.
Might make a tutorial if I can get hold of a decent camera.