I did the shirring on the old Singer 611g eclectic, the Pfaff wasn't playing nicely. I wound the shirring elastic loosely on the machine, upped the tension a bit, and used a long stitch to sew the rows. I used the foot width as a marker, but the foot on the Singer is quite narrow and I should have made the rows a little wider. I always stretch the fabric out as I'm sewing, but the magic happens when you blast the steam over the shirring and it tightens up!
Magic!
Jessie