Differential cut UQ calculation

**Merganser** · 08-22-2011, 21:43

I am making a torso length UQ with a differential cut. My previous attempts at this have turned out nicely but under performed. I believe this to be in part due to not getting correct the radii values and winding up with a bit of compression.

On an old thread Grizz suggested 14" as a radius for the side to side arc. That was based on his bridge. Anyone try this value on UQ with a gathered end hammock or have thoughts on that? What about the end to end arc? Any one have any suggestions?

**Catavarie** · 08-22-2011, 23:42

I would think that if you wanted to use this method for designing an UQ for a gathered end hammock that it would end up being person specific. The reason is works for a Bridge hammock is that the hammock has a fixed curvature and length, while a gathered end varries with the person laying in it.

**MAD777** · 08-23-2011, 11:42

Originally Posted by Merganser

On an old thread Grizz suggested 14" as a radius for the side to side arc. That was based on his bridge. Anyone try this value on UQ with a gathered end hammock or have thoughts on that? What about the end to end arc? Any one have any suggestions?

I use about 14" radius for the fabric layer next to the hammock for gathered end hammocks. I don't use any end-to-end radius for my partial under quilts.
All this seems to work just fine.

**Merganser** · 08-24-2011, 07:21

I'm not getting much feedback here

so I decided to try to make a some measurements and see what I could come up with. The first thing I wanted to prove what that r=14in was right for the width. I placed a yardstick across the hammock, perpendicular to the angle I was laying at. Wouldn't you know it, the width (cord) was about 28in and the height was about 14in, a sort of semi circle and that would make r=14. Go Grizz...

With my current UQ attached for reference, I measured a chord, along the hammock axis, intersecting the hammock body about where my new UQ will end. That was about 50in. The height I measured as 12in. Finding r from that takes a little math, fortunately there are math geeks on the internet and I found the equation I needed quickly.

r = (h^2 + 1/4c^2)/2h

plugging in h=12 and c=50, r=~32 and that seems pretty reasonable. For the length of my UQ (54in) with 1.8in of insulation, that's an extra 3in and that also seems reasonable.

**MAD777** · 08-24-2011, 16:18

To have a longitudinal differential, not only would the outer fabric be 3" longer: the outer edge of the baffle needs to be 3" longer than the inner edge. In other words, the baffle must be cut on a curve having a 32' radius.

I'm just not that ambitious.

(All this assumes a down quilt with longitudinal baffles).