Make your triangle-squares larger than needed, then trim them down to size. Cut the initial squares 1/8" larger than specified. Using your preferred assembly method, make triangle-squares. Square each one up by lining up the 45° line on your ruler with the seam line and trimming the unit to the designated size. While this takes extra time, the precision is worth it for a lot of quilters, including many of our designers (and they're the pros!).
Use a scant seam allowance. When making triangle-squares, the distance you sew away from the marked diagonal lines should be just a little narrower than 1/4". This scant 1/4" seam allowance will give you the extra few threads you need to get precise triangle-squares. We recommend you still check the size and, if necessary, square up the block.
Draw the stitching lines. If you’re not sure if you’re sewing ¼” away from a center drawn line, try drawing your sewing lines instead. (This is especially helpful if you’re struggling with accuracy.
Pressing matters: Set the seam by pressing on top of the stitching lines. This helps the stitching sink into the fabric, so when you press the triangle-square open, you have a clean, straight line diagonally through the square.
Cut off the trianglular dog-ears that result when piecing triangle-squares. This will allow you to add the triangle-squares to other pieces with more precision.
Start with a leader/ender strip or use the straight stitch plate to avoid problems when you’re sewing multiple triangle-squares together, which can have a lot of bulk and stall your machine.