The key to foundation piecing is perfect trimming. And the key to perfect trimming is a postcard and the acrylic Add-a-Quarter ruler, which has a 1⁄4" raised lip along one long edge. To make a similar tool, build up layers of 1⁄4"-wide masking tape along one edge of any acrylic ruler.
1. In this example, fabrics for positions 1, 2, and 3 have been stitched to a foundation paper. The next step is to trim the left-hand edge of the joined pieces to create a straight edge for adding fabric for position 4.
2. Flip the unit over so the foundation paper is on top and the joined fabric pieces are on the bottom. (The edge to trim is now on the right.) Place a postcard or piece of cardstock on the next stitching line (between positions 1/2/3 and 4).
3. Fold the foundation paper back over the edge of the postcard. With the raised lip down, place the Add-a-Quarter ruler over the folded edge so the ruler abuts the paper-covered postcard edge. (If you’ve stitched a few stitches past the beginning and ending of the stitching line, tug the paper back a little to tear it free from the stitching.)
4. Rotary-cut along the edge of the ruler.
5. Remove the ruler, unfold the foundation paper, and turn the unit over so the trimmed fabric pieces are on top. The fabric pieces should extend exactly 1/4" into position 4.
6. Align an edge of the position 4 fabric piece with the newly trimmed edge, pin, and stitch. If you have more pieces to add, continue in same manner, trimming each edge before positioning the next piece.