DIY Differential Cut UQ Calculator

[Aardvark]

Think of it like a loaf of bread, OWB is the top of the bread, IWB is the bottom of the loaf. OWB > IWB cause the loaf stretches out of the pan when the bread rises. HC and HB are just the sides of the pan (represents the baffles).
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[chickenwing]

Think of it like a loaf of bread, OWB is the top of the bread, IWB is the bottom of the loaf. OWB > IWB cause the loaf stretches out of the pan when the bread rises. HC and HB are just the sides of the pan (represents the baffles).
Capture.JPG

Preaching to the choir brother. This is how I did my last UQ and topquilts. I used a differential cut based on a 29" inner diameter and a 31" outer diameter.

[MAD777]

.... I used a differential cut based on a 29" inner diameter and a 31" outer diameter.

In contrast, I use a 14" inner radius and 40" finished inside width for all my UQ's.
This goes to show you how much variation in designs there are out there. Still, they all keep us warm.
(For reference, I'm a 200 pound guy).

[Boston]

In contrast, I use a 14" inner radius and 40" finished inside width for all my UQ's.
This goes to show you how much variation in designs there are out there. Still, they all keep us warm.
(For reference, I'm a 200 pound guy).

For the record, a 14" inner radius is a 28" diameter. So you're only an inch off from chickenwing.

[MAD777]

For the record, a 14" inner radius is a 28" diameter. So you're only an inch off from chickenwing.

Ha-ha! Yep, read that wrong :embarassed:

[chickenwing]

Mad777. How did you come to the decision to use the 14" radius? I chose my dimension based on measuring shoulder to shoulder and then adding a few inches for where the hammock had a tendency to flare out.

I am just a little bit heavier than you are (now down to 204 from 225 @ 6' 1")

[Wolle]

..... 40" finished inside width .....

are the 170 degree?

[chickenwing]

are the 170 degree?

My design was based on 180 degrees of the circle.

[CountryRoads]

When I started out making my DIY down-filled underquilt, I knew I would need to calculate my overall material size to have a sufficient amount of outer shell material to accommodate the "lumps" inherent in the differential design, as well I would have to calculate the required amount of down to fill the baffle volume. The Red River Gorge Underquilt How-To provides some nice starter calculations for fill volume but lacks the means to calculate the outer shell area. As tends to be habitual for engineers, I fired up Excel and created a spreadsheet for calculating material requirements and down fills for underquilts based on the cross-sectional area of the baffles.

The sheet allows you to specify your finished quilt dimensions and baffle design, and will return material dimensions for construction and the amount of down (for an input fill power) required to fill it. Down fill can be adjusted via the Over/Understuff field or by directly altering the "Total Oz. of Down" field.

Two experimental features are also included:
- An approximation of the quilt's overall weight (minus suspension) based on the material sizes, fabric weights, and down, with 15% allowance for stitching and seams.
- A VERY experimental calculation of the quilt's theoretical temperature rating, based on the published design specs for some Underground and HammockGear quilts.

I've attached the sheet for the community's perusal, please give it a look and feel free to suggest any improvements to be made. If you want to un-protect the sheet to play with the formulas, the password is "hammockforums".


-Trevor

Thanks CatSplat, about to start an UQ project and just spent half an our studying your spreadsheet to make sure I have enough materials. Thanks a bunch! I had been putting this off because I was a bit overwhelmed by all the math involved. Do you have pictures of your underquilt?

[bootstick]

Wow thanks for this, A user recommended I check this out, not sure If i want to put in all the work now lol