Could someone please please help me? I'm stuck on the seemingly simple matter of cutting some Vs in 6in pvc so I can taper it down to 5in for mating to 5in flex hose.

I feel dumb for not being able to figure it out. I read Bill Pentz's duct section and he says to cut some long Vs to taper the pipe down.

So I get out my coping and hack saws and start cutting Vs. I tried Vs as you're staring through the pipe, Vs as you look down on it, Vs pointed towards the pipe opening, and some pointed towards the middle of the pipe.

Nothing I do seems to work. I feel like there is some fundamental mechanical principal I'm missing here. I started thinking about the circumference of a circle and figured I had to remove about 3 inches to get from 6in down to 5in - but still got nowhere.

Could someone please offer me a tip before I run out of my expensive 6in pvc pipe?

Thanks so much!