I need help enlarging a block - PLEASE
 

The block below is from quilterscache and I'm trying to enlarge it to a 12 1/2" unfinished block. Can anyone help with the triangle in a triangle with a center square part? I've got the opposite side figured out.


http://www.quilterscache.com/T/TriangleChainBlock.html

The big turquoise triangle is 3" on the straight sides, in your 9" block. When you re-do for a 12" block, it becomes 4" on straight sides (w/o seam allowance). The little tri is 1.5" on str. sides; in 12" block it becomes 2". The turq. square is also 2" on sides. The beige strips will be 2x4.
This block is tricky because is partly 9-patch and partly 4-patch. The turq. sub-patches in the original are based on 1.5" so when you move to a 12" block, they now are based on 2". (Of course add seam allowance, and the extra bit if you're doing the half-sq triangle 2-at-one-time.)
9 is to 12 as 1.5 is to 2. Draw on graph paper to convince yourself. :) Hope this helps... Nancy
(PM if you want)

Great explanation nanibi. Thanks for the link joyce888!

Gulp, that is a challenge, indeed. I can figure out how to make simple blocks bigger but this one.... I was looking at the two larger triangles that are cut from a square. Can you start out with a a square that is 6.5 inches and cut it diagonally? Once the center seam of the block is done, the block should come to 12.5 unfinshed. And then figure out the rest of the measurements from there. For example I was eyeballing the two small squares. One square could be 1/3 of the measurement of the straight side of the largest triangle. Better yet, find someone who has the program for designing your own blocks....think it is called E7?

Marcia Hohn claims that as an original design.
she is, by all accounts and evidence a very generous person.

why not send her an email?
i'm sure she'd be happy to help. :)

Thanks for the responses everyone. I'm going to try nanibi's directions. And if all else fails I will contact the designer. Also good idea of drawing it out on graph paper.