Top quilt baffle volume question

[Monkeyboy42]

I may be over thinking this, but... I'm planning a build of a set of 20 degree quilts. For the top quilt most of my reading has you calculating the volume needed by mutipling the area of the quilt by the baffle height. My 55x78" quilt with 2 1/2" baffles comes out to 10,725cu", and with 850 fill power down I need 12.6oz (x 1.1 for 13.86oz). Most people divide the quilt into an equal number of baffles and divide the down up by volume. for my square quilt that's pretty easy, and comes out to 12 chambers sized 6.5"x55"x2.5" that each hold 1.155oz.

When I started really thinking about this I realized an issue. Most people don't do a differential cut on a topquilt. That seems fine on the sides where the down get compressed equally, and just adds a little overstuff. For the foot and head end though, the baffle chambers don't hold the same volume as all of the rest of the baffles. Without a differential cut they have half the volume; in this case 1/2oz of down instead of 1oz. Normally an oz here or there on my equipment doesn't matter, but with down that's a full extra ounce stuffed between two chambers.

This also seem that when the down lofts that the quilt would shrink a few inches as the foot and head round out from a triangle to more of a box shape.

I haven't found anyone mentioning this in their build threads.. Are most people just way over stuffing the foot and head end of their topquilts, or are they actually taking this into account and halving the down in those chambers. I suppose they could also be doing a differential cut, but I haven't seen that either.

Here's a drawing to illustrate:


Thanks,

Just trying to figure this out before ordering materials!

[jwright]

I think I get what you are asking.

I added the height (2.5") to the length of each end of one of the shells. I didn't think of this as a 'differential', but simple as adding in the wall height, providing the same vol as the other chambers. In reality, the chamber still took on a rounded shape but in theory would appear as another rectangle 6.5 x 2.5.
Hope that helps.
I did add a bit of over stuff to the last head end chamber to give it a bit of draft collar effect

[Randerson]

I think I get what you are asking.

I added the height (2.5") to the length of each end of one of the shells. I didn't think of this as a 'differential', but simple as adding in the wall height, providing the same vol as the other chambers. In reality, the chamber still took on a rounded shape but in theory would appear as another rectangle 6.5 x 2.5.
Hope that helps.
I did add a bit of over stuff to the last head end chamber to give it a bit of draft collar effect

+ 1 on adding baffle height to end chambers

[Monkeyboy42]

+ 1 on adding baffle height to end chambers

Thank you! I thought I might be crazy, since I can't find anyone doing this in a build thread or tutorial.

[jjr]

This also seem that when the down lofts that the quilt would shrink a few inches as the foot and head round out from a triangle to more of a box shape.

Your finished quilt will be shorter in length than the shell material. The inches added to the head and foot ends to make up for the "baffle height" will not show up in the finished quilt's length. Unlike your drawing (triangle), you can think of the end like a rectangle (box baffle). Also, when the quilt lofts higher than the baffle height, there is a dome effect on the shells which effectively shortens the distance between the baffles. You can count on losing about 6-8 inches or so of length on a quilt from this effect.

I suggest you go to the hammockgear website and study the specs on their topquilts. This should give you a good idea of how long to cut your shells for your height.


Good luck!