Prism99

It's hard to describe. It's an industrial sewing technique that evens out how two pieces feed (when the sewing machine is not doing a good job of it.)

One thing you can do is lift up both strips in your hand so you are feeding into the presser foot at about 90 degree angle. Basically what this is doing is putting more stress on the lower strip and less strip on the upper strip. This corrects a tendency on some machines to feed the bottom strip faster than the top strip.

Test your machine by taking two strips of the same length (say, two strips width-of-fabric). Start the strips so the ends are exactly together. After sewing them the entire length, see if one strip is shorter than the other strip. If it is, chances are it is the bottom strip that is shorter. The above technique will help correct that tendency.

You can also sew by holding just the top strip higher and just holding down the bottom strip a bit with your thumb, but I find that more difficult to do. Sort of like trying to pat your head and rub your tummy at the same time.

If you do the test and the top strip is shorter than the bottom strip, then your presser foot is probably too tight. On a lot of machines you can lighten the presser foot pressure.

Also, using a walking foot to piece will even out how the two strips feed. However, I find using a walking foot annoying when I am piecing.