Part 1 of 3
The quick way to get a trapezoidal flat quilt out of a mummy bag is to sew across the hood where you want the edge of the quilt to be, cut off the hood (down everywhere, so be prepared) and do the same for the footbox.
Since I am certifiable (according to people who know me well) I had to do it the hard way since I have plans to make a dog bed out of some of the leftover pieces of this mummy. Maybe this will keep my dog from trying to hog my down bag when camping. Fat chance! Or I might make myself a nice down pillow.
This is what I did.
Removed the drawstring casing from the top of the bag. (I just cut it off and used most of it later to bind raw edges).
First attached pic of hood pre-removal. Arrow is the baffle seam I chose to cut next to.
Pinned the heck out of the bag just below the baffle between the hood and the bag. The goal was to keep most of the feathers in the sleeping bag side and keep the interior baffle out of the way of the pins. It worked best for me to pinch the seams of the baffle on the inside and the outside of the bag, pull the baffle tight, and use a couple of fingers to push the baffle out of the way toward the hood. Then pin the inside and outside of the bag together just shy of the baffle seams on the bag side of the seams.
Second attached pic - showing pinned baffle seam and beginning of cut. Netting baffle visible in cut.
Carefully cut the hood off. I have sharp scissors and, by keeping the fabric taut while I cut, I could just glide the scissors through the shell of the bag. I turned the whole thing over, and cut the other side.
Third attached pic - the hood is off!
.... more to come ......