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Thread: please explain the math

  1. #1
    Super Member grma33's Avatar
    Join Date
    May 2008
    Southern Ontario Canada
    I just love maryquilts.com free patterns but confusing.
    On the spiderweb she says she used 1.75{13/4}of 5 strips and came up with a 6.5 block.How is this possible?
    Also I`m doing the half log cabin ans she states on the pattern u have a 7.5 finished then block on point 4x5 and block size finished 10?
    Thanks Gale

  2. #2
    Power Poster
    Join Date
    Aug 2010
    Should be interesting to hear what other people say. If I did the math right the sqaure should come up to 6.75. Maybe she wants to to square it to 6.5. THis is just a guess, but I hope I am right.

  3. #3
    MTS is offline
    Join Date
    Nov 2010
    First part -

    I think her 6.5" refers to the unfinished striped HST blocks, even if it says her A and B blocks.

    You lose another 1/2" (actual 3/8" because of the angle cut). As long as you're consistent in all your blocks, you should be fine.

    The five strips sewn together will result in an unfinished 6.75" block.
    If you cut that in half diagonally, and sew it together with another equally sized striped triangle, the result will be a 6.5" unfinished block.

    The formula to make HST blocks-
    Desired FINISHED size plus 7/8" (1/2" for the seam allowances, and 3/8" for the angles).

    So a 6" finished HST block would require you start with 6 7/8" squares.
    She's fudging the 1/8". Again, as long as you're consistent, you should be fine.

    The next step in the pattern is when she combines the 4 HST blocks into one larger spiderweb block.
    She's squaring that to be 11.5", but according to all the other math, it should be 12" FINISHED.

    I would suggest you make a sample block with scraps so you can see how it works for you.

    Second part -
    Without seeing the actual directions and instructions, if you put a 7.5" UNFINISHED plain square on point, the diagonal measurement is 10.58", which will finish at 10".
    The formula is the size of the square x 1.41".
    Again, she's rounding. And again, consistency in the way YOU make the blocks is key.

    I know you wrote 7.5 finished but without the rest of the directions (is it a combo block or already combined?), it's hard to tell what she meant.

    eta: Ok, and went and looked at the Half Log Cabin block. Sorry, I don't get her math at all. A finished 7.5" block will be 10.5" on point.

    I've never done any of her patterns, and maybe there is a lot of "squaring up," but the math doesn't work for me.

  4. #4
    Super Member woody's Avatar
    Join Date
    Aug 2009
    Canberra, Australia
    Blog Entries
    I'm confused with the first one too, I get 6.75"?

    The second one says that you can vary the size of the block, so disregard that line but the rest of it seems to work out. You should end up with a quilt 4 blocks wide by 5 blocks long with a finished size of 10 inches

  5. #5
    Super Member
    Join Date
    Jan 2011
    Ocean Springs, MS
    I am lost too.

  6. #6
    Super Member grma33's Avatar
    Join Date
    May 2008
    Southern Ontario Canada
    ok thanks

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