# Thread: Rule of thumb for the differential cut??

1. ## Some preliminary numbers

courtesy of doodling with my CAD program. For 3.5" baffles, and 44 inches inside measurement the outside appears to be 55 inches wide. Of course, this is without tapering the edges (leaving them square for simplicity's sake).

Jim

2. Originally Posted by Jsaults
courtesy of doodling with my CAD program. For 3.5" baffles, and 44 inches inside measurement the outside appears to be 55 inches wide. Of course, this is without tapering the edges (leaving them square for simplicity's sake).

Jim
Ok, but whats the spacing of those baffles in the inner and outer layers?

3. ## it's deja vu all over again --Yogi Berra

Familiar discussion! I did some googling and found a thread I started---I did the "My backside is circular" model too.

TiredFeet and TeeDee have a discussion here, he did something almost parabolic, a bit more complex.

now back to your regularly scheduled programming...

Familiar discussion! I did some googling and found a thread I started---I did the "My backside is circular" model too.

TiredFeet and TeeDee have a discussion here, he did something almost parabolic, a bit more complex.

now back to your regularly scheduled programming...
Thanks for that Grizz, thats a great thread.

5. Originally Posted by Jsaults
courtesy of doodling with my CAD program. For 3.5" baffles, and 44 inches inside measurement the outside appears to be 55 inches wide. Of course, this is without tapering the edges (leaving them square for simplicity's sake).

Jim
3.1416*3.5 + 44 = 54.9956 My equation seems close enough for me

Familiar discussion! I did some googling and found a thread I started---I did the "My backside is circular" model too.

TiredFeet and TeeDee have a discussion here, he did something almost parabolic, a bit more complex.

now back to your regularly scheduled programming...
Interesting threads, but isn't my formula simpler? :P
Like I said, I was trying to simplify things. Since I get the same number as the CAD program, I'm callin' it good.

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OK I read TeeDee's work again. I see he was trying to computer the volume of the chambers. I suspect to know the amount of down to put in each one. If I ever make a a quilt like that, I'll certainly reference that thread. I think his method works well!

I haven't made a bridge hammock... yet.

I haven't made an UQ... yet.

When I do make an UQ, I have a real easy solution to calculate the amount of down needed. Using my same, over simplified, logic as above. I'll calculate the area of that semi circle of width B, then multiple by the length of my quilt, then divide by the fill power of down I'm using. Now I know the weight of down I want for a given loft.

How much for each chamber? Even easier! I'm planning to use a Karo variation, so it's all one big chamber.

6. why couldnt you just make them the same length???? like a blanket or sleeping bag shouldnt that work just as well or am i missing something important??

7. Originally Posted by twsmith001
why couldnt you just make them the same length???? like a blanket or sleeping bag shouldnt that work just as well or am i missing something important??
Because the quilts are curved. Since a down quilt has a specific loft, ie 2", 3" etc, there are 2 different radius curves. One against your body at the hammock, and a larger curve the distance of the baffle away. Since the 2 pieces of fabric have to meet at the same place, the lower piece needs to longer as it travels a long path. Another way to think about it... One piece is pulled tight against you. The other needs to hang loose to leave room for the down to loft.