Originally Posted by hammock_monk
CatSplat, I'm so glad you joined the discussion. I almost PM'd you yesterday to ask for your input. The accuracy of Sketch up is, I think, to the hundredth of an inch—more than adequate for my purposes. But, as you observe, the more critical element is the curve profile. You and Wolfman both note that the differences in the width of the outer fabric layer will depend entirely on the profile of the curve of the arc.
I love the direction this discussion has taken. I'm a bit of a math geek, though more on the drafting side than computation.
In any event, I am planning to approach the question from the opposite direction: I am going to use 6 inches as the width of the fabric for the outer layer of each chamber and let the curve profile take care of itself. I figured that each chamber will end up with somewhere between 2 3/4 and 3 1/4 inches of height. With 850fp down, I expect that will keep me comfortable down to 20° and maybe even the teens.
I'm more than happy to chat about it, the more folks stitching their own insulation, the better! It sounds like you have a good plan for construction, I think you'll find that the curve shape and chamber height will vary greatly between baffles when the UQ is hung, so as long as you have enough fabric to maintain loft when wrapped around the quilt, you're in good shape. Looking forward to seeing the finished product!