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  1. #1
    Member Meteor's Avatar
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    DIY Underquilt Calculations

    As I was putting together a google spreadsheet to calculate fabric lengths, radial baffle spacing for longitudinal baffles and down fill volume for a DIY underquilt, I thought, why not share it with HF? Thus, I present:

    DIY Underquilt Calculations

    The radial baffles are calculated using MAD777's method of calculation discussed in another thread, using 170 degrees to approximate the arc of the UQ as it wraps under the hammock.

    Anyone with the link can view - and yes, modify the spreadsheet. This will allow you to plug your own values into the cells that do not have a yellow background (yellow cells are calculated by the sheet). While this means that someone could go in and change the formulas, I'm hoping that won't happen (unless it is to correct or improve them.) Google spreadsheets won't allow you to protect only a part of a sheet (i.e. to protect the calculations), so we'll see how this goes. I have a back up.

    While I'm a software engineer, my math gene is a bit stunted so I implore the uber-math geeks (I can say geek because I is one) on this forum to please check my math!

    Hopefully you will find this useful. And hopefully it is correct (or will be corrected!)

  2. #2
    MAD777's Avatar
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    Nice work!

    Check the formula in cell B20. I think you meant to add the baffle height twice, once for each end of the quilt.

    Also, in cell B22, why not simply divide the inner shell width (44") by the number of baffles (8)? Check the outer baffle spacing as well.

    I'm not sure why the seam allowance is getting added to the baffle spacing in cells B24-27?

    I like this neat format. I wish my calcs were this neat.
    Mike
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  3. #3
    Member Meteor's Avatar
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    Quote Originally Posted by MAD777 View Post
    Nice work!
    Thanks! And thank you for the formula!

    Check the formula in cell B20. I think you meant to add the baffle height twice, once for each end of the quilt.
    You are correct - I changed it so that it multiplies all seam allowances by 2 to correct for the fact that (duh) you have seams on both ends.

    Also, in cell B22, why not simply divide the inner shell width (44") by the number of baffles (8)? Check the outer baffle spacing as well.
    Not sure why I didn't just divide the inner shell in that way, but I've changed it. I think I either misinterpreted something the other thread or it may have been a copy/paste error on my part. Corrected.

    I'm not sure why the seam allowance is getting added to the baffle spacing in cells B24-27?
    I added the seam allowances to the outside baffle chambers thinking that people may want to mark a line up to their seam allowance inside the long edges of the fabric for the outside chambers. However, since there is no baffle divider (nothing to divide) and the edges of the fabric are simply sewn together maybe it doesn't make sense?

  4. #4
    Needs more Hang time Catavarie's Avatar
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    While not a math geek, I would to applaud your efforts in putting this together.

    So I'm guessing this is for a paralellogram UQ and not a trapezoidal shaped?
    *Heaven best have trees, because I plan to lounge for eternity.

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  5. #5
    Member Meteor's Avatar
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    Yes, I would say that is accurate. However it should be of some use to those building trapezoidal UQs in that the derivations for the trapezoid could be calculated afterward, or could be added to the sheet.

  6. #6
    Senior Member normis1's Avatar
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    Hey Meteor - on the spreadsheet, does "Baffle Height" equate to loft, or is that actually intended to be the "finished" height of the baffle?

    Thanks for posting this, by the way. Very useful.
    - Norm

  7. #7
    Needs more Hang time Catavarie's Avatar
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    Quote Originally Posted by normis1 View Post
    Hey Meteor - on the spreadsheet, does "Baffle Height" equate to loft, or is that actually intended to be the "finished" height of the baffle?

    Thanks for posting this, by the way. Very useful.
    It is the hieght of the sewed baffle, not neccessarily the loft as the amount of fill can vary that. I beleive most people figure the baffles to be around an inch shorter than the final loft with around 20% overfill.
    *Heaven best have trees, because I plan to lounge for eternity.

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  8. #8
    Senior Member normis1's Avatar
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    Got it - thanks Cat.
    - Norm

  9. #9
    Member gt7599a's Avatar
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    @Meteor, thanks for the venue to share calculations. I've taken the liberty of adding a second sheet with formulas for a trapezoidal under quilt for bridge hammocks.

    -Ed
    Last edited by gt7599a; 11-06-2011 at 22:45. Reason: correct unclear wording for better clarity

  10. #10
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    Thank you Meteor and gt7599a for the calculations. Thanks for putting it together and making it easy.
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