Cut Triangle Squares Apart & Press
- Use scissors or rotary cutting equipment to cut through both layers of the square on the marked line.
- Place the cut units on your ironing board, darkest triangle up. Press a medium hot iron directly onto the units to set the seams.
- Open up one unit and carefully move the iron into the diagonal that separates the dark half from the light half. Repeat to press the second unit.
Now you have two identical half square triangle units. The straight grain of each triangle lies along its outer edges.
Use rotary cutting equipment to trim away the seam allowance nubs. Measure the units. If they are too small, make sure they were pressed adequately. If squares are still slightly small, try sewing the next squares together with seams that are slightly less than 1/4" from the marked center line.
Once you know your seams are accurate, speed up assembly time by chain piecing the squares.
Cut Large, then Trim Back
It adds an extra step, but I nearly always cut my squares a little larger than the size required. After units are sewn and pressed I align them under a rotary ruler and trim them back to the exact unfinished size my pattern calls for. It's especially helpful when making miniature quilts, since tiny differences can impact little blocks.The bias square and similar rulers have a diagonal rule that aligns with the diagonal in the triangle square and makes it simple to trim.
