Math help  half square triangles
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I'm working on a pattern where the center of the block (see 1st picture) looks like that. Each piece gets cut at 3 7/8" square to finish at 3", making that whole piece 6" when it's completely finished.
But, I want the center piece to be a single piece of fabric (see 2nd picture), so rather than doing 4 sets of small HST units (especially since each outside wing will be a different color), I want to make the center into 1 big block. My plan is to do a big square and then cut the little wings into squares, sew them on top, and flip them up (rather than cutting the center center to exactly its size and working with it as a diamond ... I'd rather have a little bit of waste). So my thinking is that the center square should be cut to 6.5". Does that seem right? Then each wing still gets cut to 3 7/8"... or would it be 3.5"? I think it would be 3.5.... help! Thanks 
sounds right. to make certain, make one just to see how it works for you. that way, after only one, you can cut the rest according to exactly what you need to get the effect you want.

Your center block needs to be smaller than 6 1/2"
Draw this on a piece of paper, measure the distance from the top point to the bottom one. You will notice that this measurement is significantly longer than the side measurements of the inner square :) :) :) Start out with a 6 1/2" square, draw your square on point in the center, cut it apart and then add your seam allowances :) 
I'm thinking you winged pieces would be cut at 3 7/8". Cut 2 @ 3 7/8"; cut once on the diagonal; match up your centers and if you've got a 1/4" overhang then you know it's right.

I'm confuzzled... wouldn't the distance from the top point to bottom be 6 1/2" (or maybe 6, without the seam allowance?) If I'm doing a big square and adding squares to the sides for the triangles (a la snowball method), wouldn't I need it 6 1/2"? I know the finished sides will be 6 / sqrt (2), but I don't plan to cut it as a diamond.
Originally Posted by amma
(Post 4794718)
Your center block needs to be smaller than 6 1/2"
Draw this on a piece of paper, measure the distance from the top point to the bottom one. You will notice that this measurement is significantly longer than the side measurements of the inner square :) :) :) Start out with a 6 1/2" square, draw your square on point in the center, cut it apart and then add your seam allowances :) 
Originally Posted by joyce888
(Post 4794753)
I'm thinking you winged pieces would be cut at 3 7/8". Cut 2 @ 3 7/8"; cut once on the diagonal; match up your centers and if you've got a 1/4" overhang then you know it's right.

Originally Posted by LucyInTheSky
(Post 4794643)
I'm working on a pattern where the center of the block (see 1st picture) looks like that. Each piece gets cut at 3 7/8" square to finish at 3", making that whole piece 6" when it's completely finished.
But, I want the center piece to be a single piece of fabric (see 2nd picture), so rather than doing 4 sets of small HST units (especially since each outside wing will be a different color), I want to make the center into 1 big block. My plan is to do a big square and then cut the little wings into squares, sew them on top, and flip them up (rather than cutting the center center to exactly its size and working with it as a diamond ... I'd rather have a little bit of waste). So my thinking is that the center square should be cut to 6.5". Does that seem right? Then each wing still gets cut to 3 7/8"... or would it be 3.5"? I think it would be 3.5.... help! Thanks 
Originally Posted by LucyInTheSky
(Post 4794888)
I'm confuzzled... wouldn't the distance from the top point to bottom be 6 1/2" (or maybe 6, without the seam allowance?) If I'm doing a big square and adding squares to the sides for the triangles (a la snowball method), wouldn't I need it 6 1/2"? I know the finished sides will be 6 / sqrt (2), but I don't plan to cut it as a diamond.
The square in your diagram is ON POINT  so the DIAGONAL of the square (point to point) is what would be be 6" FINISHED, not the sides of the square  they would need to be smaller. How much smaller? The relationship is 1.414. For example, a 6" FINISHED block ON POINT will measure ~8.5" across FINISHED. 6" x 1.414 = 8.5" For your block, you need to work backwards: 6" FINISHED block divided by 1.414 = a 4.25" SQUARE plus .5" SEAM ALLOWANCE = 4.75" starting square for the center of the block. And if each side of the square is 4.25" FINISHED when it's on the DIAGONAL, then you'd need a 3" FINISHED square (3.5" UNFINISHED) square to use as the snowball. 4.25" divided by 1.414 = 3" FINISHED + .5" SEAM ALLOWANCE = 3.5" STARTING SNOWBALL Square. Since you're going to be sewing ON the diagonal, you don't need the extra 3/8" for the seam allowance like you do for HST blocks (as there aren't 2 equal seam allowances to worry about). There is a slight bit of rounding in the above calculations. Too convoluted? Try this other option  nowaste SquareinaSquare method: http://www.hgtv.com/video/superfast...deo/index.html I'd test one out first, starting with 4.75" squares. If you aren't married to the 6" FINISHED  meaning you're not combining this block with different blocks  then you could start with ANY size you wanted. Charm packs of 5" squares would render a slightly larger FINISHED block, but not much at all. And that method makes the sewing a BREEZE! 
Originally Posted by MTS
(Post 4794987)
Please allow me to add to your confuzzilation.:p
The square in your diagram is ON POINT  so the DIAGONAL of the square (point to point) is what would be be 6" FINISHED, not the sides of the square  they would need to be smaller. 
And as an update  finished the block. The big square needed to be 6.5". The little guys were 3.5" if they were sewn on as squares, but I ended up sewing them on as cut HST because of the fabric I had (BOM), so they were 3 7/8".

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