If you want to sew S-curves or even more complicated curves, you probably need more precision than you can get from the just-sew-it approach described in the last blog post. Instead you need to establish a seamline and cut seam allowances on either side.
You don't need to go all quilt-police-traditional and make templates to accomplish this, but you do need a way to make a copy of the curve that will become your seamline. Why not do templates? Because you would lose the spontaneity of the freehand curve and change the character of your improvisational composition, and also because exact templates are so fiddly and time-consuming.
Instead, here are two methods of making your curves fit together perfectly while keeping the freedom of the immediate free-cut line. I call them semi-templates. You don't need to cut templates to accomplish this, but you do need some way to "remember" your curve so you can add seam allowances as you cut.
The first method uses a template, but it's a free-cut template with a minimum of tedious fuss. Start with some pattern material that's big enough to draw your entire curve, and a cutting mat big enough to let you do it with one swoop of the rotary cutter. The pattern material can be freezer paper, newspaper, interfacing or tissue paper. Lay it out on your cutting board. Take your rotary cutter and slice a gorgeous curve through the pattern. If you want, you can stop there, or you can cut more curves as long as they don't cross any of your previous cuts.
(In the photos below I've made four cuts, the start of a large "striped" panel that can keep on going as long as I want. After these pieces are sewed together, I'll have to retrieve the template paper with the curved edge of 5, then make more cuts for more pieces.)
Don’t separate the two halves of the cut yet – first take a pencil and mark across both pieces every six inches or so, and/or at critical points on the curve. And mark across both pieces at the exact top and bottom of the curve.
Pick up one piece of the pattern and lay it on your fabric, making sure you keep track of whether this is going to be the right-hand piece or the left-hand piece. Now visualize how wide you want your seam allowance to be, and free-hand cut that distance away from the template.
It doesn’t have to be a perfect quarter-inch – no need to fuss with rulers, just eyeball it. There’s enough give in the fabric that you will not have problems. Finally, pin the two pieces together at the marked points, and sew. The seam will press perfectly flat.
Look at that beautiful curved seam! Now put template #1 aside, get templates #2 and #3 and repeat the process for the next curve.
Note that I do not suggest you cut out all the pieces at once. It's way too easy to lose your place and try to sew the wrong pieces together (ask me how I know). Instead cut two pieces (one curve), sew and press, then move on.
With this method you can make curve after curve, as in this quilt of mine. With some practice you can use this method to make winding-road seams with multiple changes of direction, as long as you mark and pin the seams carefully.
Instead of using the rotary cutter to make your curve, you use the marking wheel, which works exactly like the rotary cutter, with the same arm motion that gives you those nice, loose, artistic swoopy lines.
The creased lines don't show up all that well in the photos but they do in real life, at least long enough for you to cut and sew as needed.
As you did with the paper templates in the first method, put one or two marks across the seams and pin them so you match the curves before stitching. The more complicated the curve, the more places you should mark and pin.
In the next post I'm going to tell you to press your seam allowances toward the outside of a curve. That's great with a C-curve, but how about an S-curve? The "outside" may be toward the left as you start, but then the curve changes direction and "outside" is toward the right. I can't give you a hard-and-fast rule for these situations. If one leg of the curve is more gentle than the other, press that one toward the "inside" so it will become the "outside" when the going gets tough. If all else fails, flip the direction of the seam where the curve changes direction. Use your best judgment, and plenty of moisture and elbow grease at the ironing board.