Differential cut w/ down UQ

**east_stingray** · 11-09-2009, 15:46

For those of you who have made a DIY down UQ, I have one in the planning stages but need a little help figuring out just how differential my cut needs to be.

I'm planning on making 3.5" baffles and overstuffing to 4" for winter temperatures. It's going to be a 3/4 quilt.

I haven't found anything on HF yet about how to determine what the difference should be between the top and bottom layer, and I don't really want to just hack up material for trial and error.

Any suggestions?

**Dutch** · 11-09-2009, 15:50

I bet there is someone on here that could calculate the radius of your body and figure it out. I have been using 7 inches for the bottom for every 6 inches for the top. It has worked out well. i am of average radius.

**traftonm** · 11-09-2009, 16:03

You do not need to use a dirrerential cut on an UQ as it lays flat,or at least almost flat. The differential cut is used to make the outer shell larger then the inner shell as it raps around you. This is so if you push on the inner shell you do not compress you insulation. So sence the UQ is flat its not nessisary to go to the truble of a differential cut. Jusy make shure that any tention on the quilt is only on the faberic the is agenst the hammock. Then everythin else hangs down and can not get compressed as you move in the hammock. Good luck 4 in. should take you to around 0-5 deg.

**beep** · 11-09-2009, 16:08

My UQ shape when properly suspended in an occupied hammock is definitely not flat. A differential cut, seems to me, is vital to getting the loft and insulation that I paid for. YMMV.

**east_stingray** · 11-09-2009, 16:16

Originally Posted by Dutch

I bet there is someone on here that could calculate the radius of your body and figure it out. I have been using 7 inches for the bottom for every 6 inches for the top. It has worked out well. i am of average radius.

What kind of loft did you use that formula on? Correct me if I'm wrong, but more loft will require more of a differential, right? So if you were making a 3 season quilt with 2" of loft, maybe I need to make it 6/7.5 or something like that when aiming for 4".

**TinaLouise** · 11-09-2009, 16:20

When I started thinking about my UQ and then started putting my thoughts onto the fabric, well my UQ was diffinately not flat either. I think it looks sort of like 1/2 peel from a banana or a strange canoe. The way I got the outer layer larger than the inner layer was as I sewed it, I used clips (like clothespins) to work out the extra fabric on one side. I've go no idea what the math was and probably couldn't understand it anyway!!! Now my Top Quilt is based on a flat laying quilt but I've got draw strings on it to change that if I so want. Flat on the bottom just would not work for my hammock.

**Dutch** · 11-09-2009, 16:26

I think the loft depends more on the height of the baffle and the differential cut is the same. Althought there is a small factor that the outside will have a little further in distance than on a thinner quilt. the difference is very very small and my guess work has much more room for error. I used basically the same calculation (7"to6") for my 3 inch high and my sewn through. In order to come up with the ratio I made a mock up of grossgrain first and held it around me to see the effect on the chambers.
http://www.hammockforums.net/gallery...&cutoffdate=-1

**jeffjenn** · 11-09-2009, 18:00

It seems that adding a min. of 10% to the outer shell will work, but after my brain started to hurt from figuring it out for sure I went with the add an inch method. It turned out very well!

**JayS** · 11-09-2009, 18:25

I made a down differential 3/4 (or 2/3?) quilt last week with 2.5 inch baffles. Instead of calculating the arcs, I bent a small piece of molding marked to the correct length. I eyeballed the amount of curve, then moved the molding "out" 2.5" and marked where the end point of the curve would be. I came up with about 1/2" to 3/4" extra on the outer shell for each 8" of inner shell. I wouldn't argue a lot that this is optimal but it did okay and kept me warm to freezing over the weekend. It didn't seem to compress the down when suspended and loaded. I think the "add an inch" method (per 7 to 8" baffle spacing) should be good for 3.5" baffles.

**JerryW** · 11-09-2009, 18:32

I recently finished my underquilt. It has 3.5" baffles, slightly overstuffed to around 3.75-4" thick.

I laid in my hammock and measured the approximate curve at my midsection and then drew it out on my AutoCAD program. After laying out the offset for the thickness, I could measure the baffle width.

The baffles are sewn 6" apart on the inner layer and 6.75" on the outer layer. To lay it out on the fabric, I started in the center and worked my way towards each edge.

In use, these measurements worked real well. I can't detect any compression of the chambers at all when someone is in the hammock.

Jerry