I have the 6600 also. If you're using the accufeed 1/4" foot, are you engaging the accufeed in the uppermost position (extra high), locking it in and then dropping the foot when fully engaged? I use this foot for all my piecing. I find it gives me much more accurate seams. I know all our machines are a little different, but for a scant 1/4" I use the 5.9 setting. I still do a test piecing strip each time I start a quilt just to be sure. Different pressing techniques can also change the size of your blocks slightly.
You can also save your setting by using the memory buttons. Just push the blue "m" with the arrows at the top and the red "m" at the bottom and it will save it for the next time. Best of luck!
Originally Posted by
gigi712
JRedman, I have the 1/4" foot with flange and the accufeed will attach to it, however, I can't get my presser foot all the way down if that makes any sense.
Ok, everybody. I think I've hit my 'spot'. I know it sounds awful, but it's a good thang for me!!!! It's between 3.8 and 3.9, both work equally as well. Thanks everyone!!! Now to see if I can remember it next time I turn my machine on. Methinks I need a big marks a lot pen and write it down in big letters and post it in front of my machine. Will that work? Nah, but I can say I gave it a try. Thanks again, everyone. You've literally saved me from the looney bin today. Who knows about tomorrow? They keep a van on stand-by for me. 
r