I like this block a lot-putting it on my bucket list

That's a really interesting problem. Even though you have enough area with the two 10" squares, it's hard to figure out. If you cut each into 4 squares that are 5" each, you still wouldn't have enough for a nine patch. You'd only have eight squares.

If you cut each into thirds, you'd have 18 squares that are about 3 1/3" square. From 15 of those you could sew a block that's 5 x 5, which would turn out to be about 11 1/3" square. I think you'd have to cut them so that you could use the maximum number of the squares that you cut.

Very interesting...

I practiced using 11 1/2 block to start with and it was "almost" right for 12.5 but not quite so I looked thru my patterns and found one that used 4 1/2" blocks, 3 rows to make a 12.5 and had the 2 1/2" x 4 1/2" rectangles so instead of making an hourglass and then cutting it I just made it using a combination of patterns.... I also made one but I think the darker and white is much better than the lighter and white. Thanks for all the suggestions! I will definitely make the disappearing hour glass using the 10" blocks like in the video some day! Not sure what size it turns out but if its ALL the same size it wont matter :)

I made the disappearing pinwheel block from Jenny's tutorial. The finished block measured 12 1/2" using a 10" print and a 10" white sq.

The reason you can start with a 10" and end up with a 12.5" block is because you are starting with TWO 10" blocks one on top of the other. After sewing them together and cutting you open them up which gives you the full size of both of the blocks minus your seam allowances. In reality you're starting out with the equivalent of a piece of fabric that is 10"x20" and shrinking it down through cutting and seam allowances to a 12.5" square.

This is just too clever ! I can't wait to try the disappearing hour glass ! I'm glad I have a laptop to sit on my cutting board and walk me thru step by step. I'd love to see pics of the fabrics used by ones that make this.

If you're having problems with your bias edges and you know it's not your pressing habits, try easing off your pressure foot tension a little bit and use a walking foot

I don't remember where I found the chart. It's free to share as far as I know.

boone, I sure didn't get my 2-10" squares cut and come out 12 1/2. Im going to have to try that one again! LOL
Thanks for all the hints!

Seems logical to me if I sewed two 10" squares together I would have 20" to work with.