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Thread: Why Dart?

  1. #1
    Senior Member Str1der's Avatar
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    Why Dart?

    Maybe I'm missing something obvious, but why make darts at all? Why not simply cut the shells as non-rectangles with the head end width being wider than the foot end with and the sides tapering accordingly? The only reason I can think of is to allow to pattern to be cut from a perfect ractangle which would allow for the natural weaving pattern to remain intact, but that also very slightly increases the total material (and therefore the weight) in the quilt. Is that worth it?

    I guess essentially, I'm asking why use the pattern in the attached image on the left with darts instead of the one on the right that is simply tapered? They both seem to yield the same final product dimensions, but the pattern on the right would weigh slightly less.
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    Senior Member Ramblinrev's Avatar
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    Generally speaking the darts are only on the inside layer. That effectively makes the inside layer smaller than the outside layer. Thus giving a "differential" cut. That means as the inside layer takes the weight the outside layer remains the same giving you a good insulation chamber for the down w/o compressing it. while it is possible to do the same thing with a different set of measurements inside and out the math becomes somewhat more daunting when trying to line up and place the baffles. This way the baffles are, for lack of a better term, self-indexing.
    I may be slow... But I sure am gimpy.

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  3. #3
    Senior Member JerryW's Avatar
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    The darts do one very important thing - they give the shell a 3D, concave shape.

    By simply cutting a tapered shape, as you suggest, the material is still flat and won't conform to the compound curve of your body as well. Those darts curve, or cup, the material so it more closely matches your body shape.

    The smoother and closer it fits your body, the warmer and more efficient it will be.


    Jerry
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  4. #4
    Senior Member Str1der's Avatar
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    Quote Originally Posted by JerryW View Post
    The darts do one very important thing - they give the shell a 3D, concave shape.

    By simply cutting a tapered shape, as you suggest, the material is still flat and won't conform to the compound curve of your body as well. Jerry
    Hmmm. I understand that the darts provide the differential cut and why that's important. I guess I don't understand why the tapered shape wouldn't yield the same thing. I agree the math gets trickier, but I'm an engineer and feel up to it. I guess if the darts are esier though I will probably just use them.
    "The Road goes ever on and on,
    Down from the door where it began.
    Now far ahead the Road has gone,
    And I must follow, if I can.
    Pursuing it with eager feet
    Until it joins some larger way
    Where many paths and errands meet.
    And whither then? I cannot say."
    ~Bilbo Baggins - LotR

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    Senior Member JerryW's Avatar
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    Quote Originally Posted by Wakozacho View Post
    Hmmm. I understand that the darts provide the differential cut and why that's important. I guess I don't understand why the tapered shape wouldn't yield the same thing. I agree the math gets trickier, but I'm an engineer and feel up to it. I guess if the darts are esier though I will probably just use them.
    Here's an easy way to see the difference - take two sheets of paper. With one of them, cut the tapered shape. With the other sheet, cut the darts and tape the edges back together.

    The first one will still lay flat on the table. The darted one will look like a bowl. Which one will better conform to the shape of your body when you are laying in the hammock?

    The trick to using darts is to get them the correct size.
    The "Search" function is your friend!

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    Senior Member JerryW's Avatar
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    Quote Originally Posted by Wakozacho View Post
    Hmmm. I understand that the darts provide the differential cut and why that's important.
    Actually, the darts don't provide the differential. The differential comes from the outer shell being larger than the inner shell.

    The darts provide shape.
    The "Search" function is your friend!

  7. #7
    Senior Member Str1der's Avatar
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    I guess I should be more clear. I'm planning 3 DIY projects (my firsts). All will be made with 800FP down and 1.1 ripstop or Momentum.

    1) Summer UQ - 3/4 length, 2" loft, 1.5" baffles, 52"L x 50"W (at head) x 40"W (at foot).
    2) Summer TQ - 2" loft, sewn-thru design, drawcord footbox 75"L x 52"W (at head) x 40"W (at foot).
    3) 3-Season TQ - 3" loft, 2.5" baffles, sewn-up footbox 75"L x 52"W (at head) x 40"W (at foot).

    I plan to use a differential cut (outside shells larger than inner liners) for all 3, but the concept of darting has me "baffled" . If I provide a differential cut, why do I still need darts? Are darts used for down projects? Are they used for a sewn-thru design like my summer tq?
    Last edited by Str1der; 07-01-2011 at 10:24.
    "The Road goes ever on and on,
    Down from the door where it began.
    Now far ahead the Road has gone,
    And I must follow, if I can.
    Pursuing it with eager feet
    Until it joins some larger way
    Where many paths and errands meet.
    And whither then? I cannot say."
    ~Bilbo Baggins - LotR

  8. #8
    silentorpheus's Avatar
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    Differential cut, with the outside layer larger than the inside, has less to do with the fit of the quilt (I'm sure it helps some, which is why I say 'less' and not 'nothing') but it allows the insulation to not be compressed and in the case of an UQ hang more freely when the inner layer is pulled snug against the body.

    Like Jerry said, the darts allow for the inner layer to actually fit your body shape. It's probably not as necessary for a top quilt, and even a simple under quilt will work without darts. You don't NEED them. But by using them, you can enhance the way it fits, and give it a more 3D shape.

    Think of a pair of pants. If you have flat front pants, with no pleats, you need to make sure you get your size correct. If you get a size that's a little too big, and use a belt to cinch them up, the waist band is going to pucker and fold over on itself in places, as the excess fabric has nowhere else to go. This means that the shape of the crotch and seat area of the pants is extra important, and if its, for lack of a better term, tight around your butt, and you get the next size up to give you more room, then the waist band area is going to be too big, and you have to cinch it up, thus creating that puckering effect.

    Now consider pleated front pants - in this case the pleats can be viewed as darts, in a way. This allows you to have a roomier pant, while still having a smaller waistband, by pinching off the extra fabric puckers you'd get in a flat front pant, and tacking them down in a visually pleasing way, in order to give you a better shape. Can you achieve the same effect by cutting the pants in a custom shape, that allows for a roomy butt area tapering to a slimmer waistband? Yes, you can. That's where darts come in. Instead of cutting some wierd wacko shape right off the bat, you start with the shape you want, then pinch in a little here, a little there, till it's shaped the way you like. Then to pleat you'd tack those pinched in parts down, in darts you remove them.

    In some ways darts are a visual thing, like pleats on a pair of pants. They take the extra folds of fabric created when you cinch something up and strategically remove them (where as pleats just tack them down) in a specific way so as to look good and not just pucker out anywhere. In pants this puckering simply looks bad, and can be a bit uncomfortable. In a quilt you're not as worried about the look, but those 'puckers' and folds can introduce air gaps that let cold air in. Can you fix it by custom cutting a tapered shape to your body? Mostly, yes. But it will never be as good as using darts to create a 3D shape that matches your body better.

    Another visual image to perhaps help - take a soccer or basketball, and think of a circle of paper or fabric cut out with the same diameter of the ball. if you try to wrap that circle around the ball, it will never really fit flat and conformed to the ball. But if you fold little darts into the outside edge of the paper, it allows the inside of the circle to stay the same size but the outside edge of the circle to fit more snug around the ball.

  9. #9
    Senior Member beep's Avatar
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    Quote Originally Posted by JerryW View Post
    Here's an easy way to see the difference - take two sheets of paper. With one of them, cut the tapered shape. With the other sheet, cut the darts and tape the edges back together.

    The first one will still lay flat on the table. The darted one will look like a bowl. Which one will better conform to the shape of your body when you are laying in the hammock?

    The trick to using darts is to get them the correct size.
    What he said!!! (Well said, Jerry!)
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    Senior Member Ramblinrev's Avatar
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    All this is well taken. I was thinking sewn through, not baffled. My bad.
    I may be slow... But I sure am gimpy.

    "Bless you child, when you set out to thread a needle don't hold the thread still and fetch the needle up to it; hold the needle still and poke the thread at it; that's the way a woman most always does, but a man always does t'other way."
    Mrs. Loftus to Huck Finn

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