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  1. #1
    Senior Member nacra533's Avatar
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    Making a Stuff Sack to an Exact Size Tutorial

    Making a stuff sack to a specific size can be a challenge. It’s pretty easy if you make a round bottom stuff sack, but can be confusing if making a square/rectangular bottom one. It’s also difficult to determine the size of a square bottom sack you can make with a piece of scrap material.

    In this tutorial, I will hopefully demonstrate how to make a square/rectangular bottom stuff sack to a specific size. I typically make square bottom stuff sacks, but will show a rectangular version in an effort to make the example less confusing. I am assuming that you already know how to sew a square bottom stuff sack and you have a preferred method of installing the drawstring channel. Whatever method you use, just account for it in the CSA (channel seam allowance). This method use the following process which is similar to the one on thru-hiker.net:
    -Fold the fabric in half length wise.
    -Stitch the sides together (plan for your preferred drawstring channel). The fold becomes the bottom of the sack. The stitch lines are the sides.
    -Sew the drawstring channel.
    -Form and stitch the square/rectangular bottom, by pulling out the “corners”

    Let’s assume we want a 200 cubic inch stuff sack. Its finished size will be 10” tall with a 5”x4” rectangular bottom. It will have a draw string channel to close the bag.

    To calculate the blank of material you need to start with, I use this formula.

    Height of Fabric Blank = 2*H + y + 2*CSA
    Width of Fabric Blank = x + y + 2*SA


    In this example:
    H=10” (height of bag)
    x=5” (bottom)
    y=4” (bottom)
    SA = ˝” (side seam allowance)
    CSA = 1-1/2” (draw string channel seam allowance) (I should have used larger, but didn’t want to redraw the picture)

    Blank should be 27” tall x 10” wide

    For a square bottom sack, x = y





    What if I just have a scrap piece and want to know if it's big enough?

    If you already have a scrap of fabric and you want to know what size you can make, solve it backwards and make it a square bottom. For example, a 24x9” piece.

    Again, for a square bottom
    Max width (x) = (Fabric width - 2*SA) / 2.
    Sack height (H) = (height of fabric blank – y – 2*CSA) / 2
    x = y = 4" for a square bottom.
    Sack height (H) = 8.5"
    Also, if you always use 1/2" seam allowance, x = (Fabric width - 1") / 2

    assuming
    height of blank is 24”
    width of blank is 9”
    CSA = 1.5”

    So you can make an 8.5” stuff sack with a 4x4 bottom

    I like a 4x4 square bottom for things like hammocks, tarps, etc.. For larger items, figure out the rectangular bottom size you need.


    A discussion on a confusing part.

    Why is the bottom height (y) included in the sack width? (y = 4 for the example)
    Because it’s folded on the center, you have 2” on each side of the centerline fold. When you pull out the corners to form the bottom, it forms a 45 degree triangle. From geometry of a 45 degree triangle. Base = Height. Hypotenuse doesn’t matter. I know the triangle height is half of the y dimension, so the base is also ˝ of the y dimension.



    Clear as mud?

  2. #2
    Senior Member BurningCedar's Avatar
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    Thanks! This is really helpful as I've struggled with sewing stuff sacks to fit a specific application.

    I've bookmarked this page for future reference.
    David

    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 weary feet, Until it joins some larger way, Where many paths and errands meet. And whither then? I cannot say.
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  3. #3
    Senior Member Poppabear's Avatar
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    Very nice tutorial thanks for taking the time to post it. I've got it bookmarked for future reference.
    Terry

  4. #4
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    Thanks for this! I'm heading to Colombia in a month and want to bring a backpack small enough to satisfy the carry-on diminsions the airline enforces. My other bags are either too big for the carry-on, or too small to carry my stuff...so I'll just make a backpack to the perfect size!

    This math will help me figure out the measurements for the body of my pack, the rest will be easy!

  5. #5

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    Nacra-- This is awesome.
    The formulas and the very well labeled pictures makes this a snap to visualize and understand. Thanks a ton for posting this. Now if we can just get it formatted into a poster/page all will be well in the world.
    thanks again,
    jason

  6. #6
    Senior Member Lost_Biker's Avatar
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    Great info - thanks a bunch. All us noobs need all the help we can get.

  7. #7
    Senior Member thegreatjesse's Avatar
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    I barely passed Math 110 with a D... but I understand this! Thanks!

  8. #8
    I used this to make stuff sacks for 2 hammocks on Friday. They came out great if you overlook the sewing. Thanks for posting it Nacra533.

  9. #9
    TZBrown's Avatar
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    This is good, Thanks for sharing
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    But rather to skid in sideways, totally worn out, shouting,
    Woo Hoo!....What a Ride!

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  10. #10
    Member flying_bobo's Avatar
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    Nice, I will be using this!
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