You can cut fabric for binding either on the grain or on the bias (at a 45-degree angle to the grain). Bias-cut strips are much more flexible than on-grain strips, so they are necessary for doing binding around curves, such as scallops or rounded corners. They will also work on straight areas. Striped fabric looks great cut on the bias for bindings. On-grain strips are fine if your quilt has only straight sides and square corners. (However, you should still join the strips with diagonal seams in order to distribute the bulk of the seam.)
Sometimes I combine both on-grain and bias-cut strips. Often this has to do with getting the most out of the fabric I have available. Or, I might have a narrow strip of cloth and I need a few bias strips but I want to make the rest of the strips as long as possible. Sometimes it’s because I’m doing rounded corners (I’ve done them on a lot of quilts lately).
Here’s how I cut for combined bias and on-grain strips. Keep in mind that this works best on non-directional fabrics such as solids or all-over prints.
First cut the bias strips at a 45-degree angle across one end of your fabric. I want about a 12″ length bias strip for each rounded corner of my quilt, so depending on the width of the fabric I may cut from 1 to 4 strips (you can cut longer strips down to the length you need, obviously). If I have a width-of-fabric 1/4 yard (which is 9″ high x 40″ wide), a diagonal strip will be right around 12″ long.
(Here’s a quick calculation to keep in mind: the diagonal length is just a little less than 1-1/2 times the length of the short side. So, for a quarter yard of fabric: 9″ x 1.5 = 13 minus a little = 12″)
After cutting off the bias strips, cut the rest of the fabric on-grain across the width. And a little bonus: one end of the strips is already cut on the bias, ready for its joining seam!
Now, before joining the strips lay them out around the perimeter of your quilt. Lay the bias strips on the curved areas (corners in this diagram, marked in blue). Fill in the straight spaces between with the on-grain strips (sides in this diagram, marked in red). Pin the strips together, adjusting the length as needed. Mark the starting point on the quilt and the starting end on the pinned strips.
Sew together the strips, then pin them to the quilt in the order you originally placed them. Sew your binding on and you’re finished!
For a PDF of my illustrated step-by-step instructions for binding, go to https://spiromaniacs.files.wordpress.com/2008/09/binding-a-quilt.pdf
Happy quilting! ~ RaNae 🙂