When you're just starting out with quilting and brand new to rotary cutting and chain piecing, it can be very easy to disregard something as small an insignificant as your fabric grain.
What does it really matter, you may ask yourself, that your fabric be perfectly square?
I know this is what you're thinking because I used to think so too! I also used to wonder why my blocks never turned out quite the way that I wanted them to.
So here's a little primer on grainline and squaring:
Look at your fabric. Look really closely and you'll see little lines of thread interwoven together. The lines of thread should run perpendicular to one another so that when they meet they form a perfect 90 degree angle.
When you cut a square block out of a piece of fabric and the lengthwise and widthwise threads are running parallel with the cut edges of the block, then that block is cut "on grain." This means that the edges of the block will have less stretch and be therefore easier to handle and piece.
When a block is cut "off grain" the edges of that block will want to stretch and skew very unevenly. One edge might want to stretch for more than 1/2", while another edge will only stretch 1/4". When piecing a patchwork quilt, you typically don't want any stretch in your fabric at all, so the need to cut on grain is very necessary.
There is only one time that I can think of that quilters want their fabric to stretch and that is for Bias Binding. In order to cut on the bias, you position your ruler to cut at a 45 degree angle across the lengthwise and widthwise grain.
Any block or strip cut on the bias will have an intense amount of stretch. This is very useful when needing curved binding or other decorative additions to your quilt.
So in order to get your fabric square so you can cut your pieces on grain, you first need to prewash your fabric, iron, starch it, and then give it a little wiggle to get it perfectly square.
Watch this video to see just what kind of wiggle I'm talking about:
Click here if video does not appear.
This information and video was taken from "Stitch it Up a Notch: How to Piece Perfect Quilts"
Learn how to prepare your fabric, cut strips and pieces accurately, and piece your quilts perfectly!