Now that I've made about twenty nine-patch blocks I'm turning them on point like this. I need two 5 1/8" squares for each block, and I'm using a few different fabrics to keep it interesting.
I cut the squares once on the diagonal..
And then I trim the points off at about 4 3/4".
This allows me to centre the triangle on the ninepatch easily, but you can also just crease the centre of the block and the triangle and match them up if you don't want to do this step.

Lay the triangle on the block and make sure there is the same size little triangular piece showing at each end, this means it's centred.Sew triangles on opposite sides, press,then add the remaining two triangles.
You can see that trimming the points earlier makes lining up the last two triangles very easy, and there's nothing to trim afterwards either.

The nine patch is 6" and the blocks finish at 8 1/2", so they mount up pretty quickly.

Once I've finished these I'm going to play with the setting because I don't know how big I'm going to make it yet. One thing at a time, I'm having fun with these really simple blocks.