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Thread: Block size? Check my math please?

  1. #1
    Senior Member Millstream Mom's Avatar
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    I want to make a 9 patch block. If my finished block will be 12" then I should make my blocks all 4.5"? I will have 1/4" seams which would end up with 3 x 4" per row?


    OK... now I want to set the blocks on point so they will be set in as diamonds instead of running with the seams horizontally. I want to set 6 diamonds (which are my 9 patch blocks) running down a column. My question is about the half-square I will need to put between each 'diamond', as well as the small triangle at the top of each strip
    My block is 12.5" (12"finished size plus 1/4" seam allowance on each side. Do I cut a block 12.5" then cut into 2 large triangles, to make the pieces I need to set in? For some reason I'm thinking that will make it too short on one side?? And what about that little triangle I need to cut for the top corners? UGH!! Right now I'm suffering from "Paralysis by Analysis"
    :roll: Please.... I need your input!
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  2. #2
    Super Member feffertim's Avatar
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    Can't wait to see the answer to this. I struggle with this issue too. I know there is a formula for this.

  3. #3
    Super Member Lisa_wanna_b_quilter's Avatar
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    http://www.karencombs.com/setting_triang.htm

    This chart will help with the setting triangles.

    As for the 9 patch blocks, each square needs to be 4.5 inches. With your seam allowance you should end up with a 12.5 unfinished block or a 12 inch finished block.

  4. #4
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    For the ? triangle, you'll want to use a 1/2 square triangle (i.e. a square cut in half diagonally. For the others, you want to use 1/4" square tirangles (i.e. a square cut across both diagonals). This will give you the correct non-bias edges.

  5. #5
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    Yes.. the squares for the 9 patch should be 4.5" each.. the solid triangles should be 12 5/8" squares cut in 1/2 from corner to corner for the side blocks. I don't have the corner triangles figured yet. will let you know about those. I'm thinking you would cut a 13" block then cut corner to corner both directions to make those.. but I need to "prove" that out.

  6. #6
    Super Member feffertim's Avatar
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    Wow, thank you Lisa, this chart is exactly what I needed. Tells me everything

  7. #7
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    Yep.. just cut out paper "blocks" and my previous measurements work.

  8. #8
    Super Member hobo2000's Avatar
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    12" finished block cut a block 18.25 cut both diag for side setting tri's, cut a block 9 3/8 cut on diag. for corners.

  9. #9
    Senior Member Millstream Mom's Avatar
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    Lisa - Thank you for that chart! It's going right into my reference binder!

    MyTwoPals - I hadn't even taken bias into consideration!

    Tippy- I hadn't thought of cutting paper templates....oh... I need a coffee so bad! So a 13" block cut in half from corner to corner will give me the big "what size?" triangle that I had drawn? - I am such a "visual" learner! Show me and I get it - tell me and I'll misunderstand you in 20 ways.... drives my family bonkers!

    I'm glad I was able to calculate the small blocks for the 9Patch correctly! LOL! Did you ever have one of those days when you weren't just 100% confident in your skills? Today definitely qualifies! :)

  10. #10
    Senior Member Millstream Mom's Avatar
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    Uhoh.... I was replying at the same time as you were typing ToniMarie.

    So if I cut a block 18+1/4" and then cut it corner-to-corner twice.... then I get FOUR triangles that would fit in? NOW I understand that chart a little better!!! HAHA! OMG.... I'm going for a chocolate break - I think 2 days of dieting is affecting my concentration!

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