Here's how I made my first down underquilt. I've built 8 synthetic underquilts - made from IX and Thinsulate, but always thought a down UQ would be a major undertaking. Surprisingly it wasn't. So here's the my version of step by step instruction for those who are hesitating on making one.
First thing I did was search the forums and ask lots of silly questions. MAD777 was kind enough to answer most of them - Thanks MAD777! Next I took a look at an underquilt calculator - I used CatSplat's Differential Underquilt Calculator. Next, I went shopping at D.I.Y. Gear Supply and got 3 yards each of 2nd's 1.1 ripstop in olive green and foliage gray, 20 feet of 1/8" shock cord, 3 yards of NoSeeUm and 8 yards of 1" grossgrain. Last and most importantly - Thread for the injector - GŁtermann Mara 70 Tex40.
The down I got from a KMart pillow - Cannon King Size with Duck Down. It was on sale in it's own bin. I was hoping to just get some decent down even if it was low grade. I got 44oz of duck down with only a handful of feathers out of it. The calculator said I needed close to 28oz for my UQ. Cost of the pillow was $16.00 exactly and now that I know what's inside, I will be getting 2 more just for projects and give away's to friends and family.
I decided on a 76 x 46 size with 9 baffles. I used 500 in place of the quality of down (guessing) so each baffle needed 3 oz - that's with a 20% overstuff. Due to some errors that creeped in and my inability to cut straight, my finished dimensions were 72 x 44, which is just fine for me.
The thing I came across once I started was that it's not an exact science, but close enough. I also didn't initially trust the calculator and measured things over and over when I should have just started sewing the silly thing. I wasted probably 4 hours out of the 16 it took to sew on worrying about the calculations. Don't worry - Be sewing!
Ok - on to the pics.