Hi,
I have a 17.5 inch star block. I would like to use it as the center square in a quilt. No pattern for this. I want to set it on point using HST's to form light/dark dianomds around the star block. Anyone know what size my HST's should be. There must be a formula to figure this out.
TIA
True4uca

I did a search engine for the formula you need for setting triangles and also corner triangles. You can find your formula here
http://www.quiltbug.com/Articles/on-point.htm
I hope this helps
Peggy

I think it would be 12 7/8 square cut on the diagonal

a squared + b squared = c squared
if c is 17.5
then a and b would be 12 3/8
plus 1/2" seam allowance on each end
= 12 7/8

hey ! I was right!!!
thanks I bookmarked that site

is the 17.5 finished or unfinished block size?

If 17.5 inch is the finished side length of the block, then

The 12-3/8 inches for the finished short leg length of the block is right.

The usual "formula" for cutting the squares for HST is finished size plus 7/8 inch.

Then cut the squares 13-1/4 inches - need to allow that extra 3/8 inch for the points of the triangles.

Michele , what I want will be similar to your avatar pic. the star block is pre-printed panel (for pillow) it has two 1 inch borders printed after the star. I might cut those off if that will help get rid of that half inch. Just neasured it and it will always have the half inch.

Just visited the site Peggy listed. I think I've figured it out. I'll make the end (points) a little bigger. Opps that won't work.

that site agrees with the 12 7/8 that I came up with.
your block measures 17.5 but after sewing will finish 17
so the chart says 17 finished cut the square 12 7/8"
then cut on the diagonal
trust me!

IF the finished size is 17 inches, your number for the square size is correct.

I'm back ,had to visit local A/C dinner, it is hot. Ok I'm willing to take a leap of faith, really don't understand 12 7/8 square. I'm thinking 3-4 inch HST's to circle (diamond) my 17.5 inch block. I'm thinking 12 7/8 for the corner after I finish my HST's. I'm trying to figure out how big my HST's should be. I'm thinking each round of HST's might need to be bigger