tip #28, using sew-and-flip triangles and making hatchet units

Sew-and-flip triangles techniques are good to use in some units, but they are more complicated than they look. (There is some waste in making them, but the cut-aways can be saved for another use when making larger units than I am making here. With these, I threw away the cuttings.)
The ones I am showing use a 3 1/2 inch cut large square and a 2 inch cut top square that becomes a triangle.
There are several methods and I think I've tried them all--drawing the diagonal, using a plastic sole plate guide, drawing a line on my machine. That last method I used for many years. I put a piece of clear tape over the line to prevent it from wearing off.

My newest method seems to be more accurate for me. I press the smaller squares in half.
Place it carefully on the base fabric, then, sewing about a needle's width away to the right of the pressed line.
My #37 foot on my Bernina has an edge right by the needle that if I line it up with the fold, gives me just the distance I need.

I then press to the smaller squares, assess for accuracy, resew if needed, and clip out the bottom two layers.
This method has been very accurate. I had to re-sew only about 8 of the 200 dark squares on my latest project.

Such accuracy isn't necessary with many layouts and uses of the sew-and-flip method, but is needed when the hatchet units need to meet.
I re-press seams to allow them to nest together.