Been quilting long enough to know how....but don't.
 

Ok..true confessions time. I have tried over and over when sewing blocks together, to have the back seams lay properly. I have ironed, I have used pins, I have held my finger over the seam until I was almost one with the machine and STILL, I'll have a seam that gets twisted in the sewing, so that when you turn it over, the first part of the seam allowance will point left and the end of the seam allowance will point right. It really bothers me, but not enough to rip every bloody block out and redo it.
What's the secret? Or, is it really that most quilters have this problem?

I am so watching this thread. My seams do the exact same thing-

I have that happen occasionally, but I can usually feel it as I am sewing. In other words, I can tell if a seam is twisting, but I keep going anyways. It usually irons flat, so I don't let it bother me. Most of my seams stay where they are supposed to.
Sue

It happens to me quite often and I don't care. As long as the front looks good and seams line up there I don't care if the occasional seam allowance gets flipped the wrong way. Hasn't caused a problem yet.

I know we have discussed the benefits of starch on this board quite abit. But I starch my fabrics , and that really helps the seams to behave . I starch my fabrics to force them to submit to my will. LOL. And torture the fabric a bit more by sticking it with pins and a hot iron. Some fabrics are more stubborn than others , but I can usually claim victory with starch and pins.

Try ironing the seam flat first before pressing to side. That seems to set the stitches and make seam flatter. I press to dark side of the fabric or alternate side I need to when joining seams. . Also when sewing put your top seam so that it pressed/lies to the left side and the bottom to the right . That allows the bottom seam to flow with the feed dogs and the top seam to be pushed/locked into the bottom. (make sense?). Also do not pin directly on the seam but rather on both sides of the seam after you have aligned up the seams by holding the pin straight. Pinniing directly on the seam will usually cause the seam to be off. Aslo I just heard at my LQS for their repair person to use you wider/regular sewing foot instead of you 1/4" foot when peicing. Just adjust you needle to make 1/4'seam. This allows the fabric to feed better/evenly thru the feeddogs .

ssshhhhh ***looking left, looking right****** no one can hear ......

I have that more often than I care to admit to ...... I just go with the flow :) I have set the seams, pins , look/feel the seams right before they go under the needle ... big sigh nothing seems to help ......

Happens to me on every quilt, but with time it is less and less.

Bigsister has an excellent point about the use of the feed dogs. I am using my 1/4" foot for all my piecing just to be sure I've got the accuracy, but my joining the pieces and blocks was easier, and straighter especially at beginning and end of the run, when I used a regular foot and moved the needle so that I could keep both feed dogs on the material. I don't quite get the top seam/bottom seam instructions but I will try it and figure it out. Anything but those lumps on the back of the quilt!