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math in quilting

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    math in quilting

    I know math is a hard one for some and especially for me but...it is necessary when cutting and piecing. Somewhere I read info on figuring out the size of a block if you are going to cut it on the diagonal once or twice. You take the size of the desired finished block and add so many inches to the block you are cutting to allow for the diagonal cut and the resewing of the pieces. Does anyone know this formula?

    #2
    Re: math in quilting

    The Pythagorean formula works for a square. The diagonal is the hypotenuse, and the sides are the legs. If you go to ask.com, they can explain how to do it. In math ideas - it is quickly referred to a squared plus b squared equals c squared. (a and b are legs and c is the hypotenuse. If I knew how to draw on the computer, it would be much easier to show. No wonder everyone is confused.

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      #3
      Re: math in quilting

      I add one inch.

      If I want a 3" finished half-square triangle block, I cut 2 four inch squares and draw a diagonal line on the back of one of them and put right sides together and sew 1/4" from the line on either side and cut apart on the line and then press to the dark side and trim.

      Some people who are really good add 7/8" to the finished size so if they wanted 3" finished, they would cut squares at 3 7/8's inches and not have to trim. Mine always turn out wonky using this method. I would rather cut large and trim.

      I forget what it is for a quarter square triangle. I'm thinking 1 1/4 but it might be 1 1/2" larger than finished size.
      Vonnie

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        #4
        Re: math in quilting

        Vonnie's method is probably the easiest to do, it's what I do.. Even with the extra work of squaring up the resulting blocks at least you know they will be correct.
        That alone will save you loads of time & frustration.
        Good luck.
        May the road rise up to meet you...
        May the wind be always at your back...
        May you be in Heaven a half hour before the Devil knows you're dead...
        Patt :icon_wave:

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          #5
          Re: math in quilting

          Have you seen today's thread about setting on point? It has a great Fons and Porter ruler and another post with a chart. Is this something that you're looking for? It looks like it saves on the math figuring.

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            #6
            Re: math in quilting

            Is this what you're looking for?

            Math for On-Point Quilts

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