The January Lucky Quilt Challenge was all about using bias tape as a design element, and I learned a lot doing it. Here are some specific pearls to save you from having to make the same experiments.
I started with a Clover bias tape maker. It was an older one, so the marking was in milllimeters rather than inches: 9mm. This is 0.354 inches or a little less than 3/8″. It appeared from the websites I looked at that the width of fabric should be approximately twice the width of the final binding. Twice 9 mm is 18, of course, which is about 0.704 inches or slightly less than 3/4 of an inch. I wasn’t sure about using 3/4″, so I decided to experiment with 1/2″, 5/8″ and 3/4″.
I wanted to include a seam on each bias strip trial- since the seams usually seem to occur at the most inconvenient places, design-wise.
Sewing these seams with very very tiny stitches permits you to trim these seams very closely, minimizing the volume of extra fabric so there is less bulk in the resulting bias tape. (bottom untrimmed, top trimmed).
The 1/2″ attempted bias tape is shown in the top photo of the set below. There is not quite enough fabric for reliable folds. The second photo is the 3/4″ strip, with a bit too much folded fabric. The final photo of the group below is the 5/8″ strip- see how it coils around easily without excess bulk, even at the top of the curl where there is a seam. Yes, Goldilocks, 5/8″ is definitely the best width of fabric strip to make 9mm bias tape.
What about attaching the tape to the surface of the quilt? Three options pop to mind: (1) separate top stitching on each side of the tape (2) wide zig-zag to tack down the whole tape at once, or a twin needle to tack both sides down at once. It turns out that an edge-stitching foot is the key to option #1.
Butting the tape edge against the guide bar makes a consistent top stitch that is easy to sew.
And here is what it looks like using a twin needle:
Finally, here is a close-up of all three stitching option. The top is the edge-stitching, the middle is the zigzag stitch, and the bottom was attached with twin needles.
In general I prefer the top version, the individually top-stitched edges. In some design setting, the second zig-zag option might be a good stylistic choice, with either blending or high-contrast thread. With a smaller stitch setting, the twin needle option could be useful if you needed to get a lot done in a hurry- turning corners neatly could be tricky though.
Takeaway: Experiment to determine the best fabric strip width for your chosen bias tape maker. And remember the various stitching options for reinforcing your design intentions!