No More Slipped Pieces
Foundation piecing is easy and fun, but even experienced foundation piecers find that keeping the fabric pieces properly aligned on the underside of the foundation can be a bit tricky at times. Try these simple ways to keep those little pieces of fabric under control:
"How do you sew multiple units together without slipping when they're still backed with paper?" you ask. "I've placed the two pieces together and carefully aligned the end points of the seam with a pin stabbed through each end, and pinned along the entire edge. But I still have problems getting the seam sewn accurately!"
First, finish sewing the individual unit properly. After stitching the entire foundation pieced unit (or block), press it well from the wrong side -- lots of pressure, no steam, and no back and forth movement. (Use a press cloth if the iron's heat reacts with the foundation's ink.)
Stitch around the unit or block about 1/8" into the seam allowance. This holds those edge pieces in place until the unit or block is sewn to other units or blocks. (I use a basting stitch which I unpick when removing the papers; others prefer to use a regular FPP stitch length instead -- choose whichever is easiest for you.) Trim the outside seam allowance to 1/4". Press the unit again from the back to make it as flat as possible.
Then try the tips below -- you may prefer one method in one situation (such as joining two small half-square triangle units) and maybe a combination of methods for another situation (such as joining two oddly shaped units with lots of seams to sew over).