Updated: May 20, 2022
Curved piecing is scary. Somehow you're supposed to sew two curved edges together and end up with a flat piece. There's all this extra fabric and funny shapes. How on earth is this all supposed to work?!?
Breath, my quilty friend. This is a case of the imagination being much worse than reality. With a couple of easy guidelines, you'll be sewing curves like a pro in no time.
Trace then cut
Straight edge guided cut
Universal curve rulers
The general idea
Curved pieces will always have a concave arc and a matching convex arc. These will look similar to how they should look in the final block with one key difference. The curves will overlap by 1/2". That means, that the radius of curvature of these arcs (the size of the circle that fits against them) is different. They cannot and should not match in order to get flat pieces (sometimes you can fudge this a bit with improv piecing, but to get the flattest blocks, these curves should not match). This overlap is your seam allowance.
Seams are always sewn right sides together (that constant doesn't change), but due to the nature of the curve, you're going to have a lot of extra material from the outside curve. This is what makes curved piecing so scary: your piercing isn't flat anymore. That fact alone bothers a lot of quilters, myself included. It will take some active mental gymnastics to convince your brain that this is OK. Take a moment and suspend your instinctual judgment for just a little while; it will all make sense after you successfully sew your first curved block.
Cutting your pieces
Preparing curved pieces can be its own challenge. Almost all general quilting rulers only include straight edges and lines so it is far from immediately obvious how to even cut out your curved pieces. Because there are many more variations in curves than there are in straight-edged pieces, almost all curved quilt patterns will include a template. Sometimes there's a way around these templates, sometimes there's not. Here are the most common approaches.
Trace then cut - This is perhaps the most straightforward method. You will print out the pattern templates, cut them out, pin or weight them down on top of your fabric, then trace with a chalk pen or water-soluble pen, remove the templates (or leave them in place), and cut the traced line either freehand with a rotary cutter or with fabric scissors. This technique can be made easier by first gluing the paper template to a piece of cardboard or template plastic and cutting it out so you have a firmer edge to work with, but it still leaves a lot of room for error. If you're sloppy with your tracing or cutting, you can end up with imprecise pieces. However, the good news is that it is not nearly as critical to be precise in most curved patterns as it is in patterns where sharp points come together. Curves are more forgiving. If you choose this method, try spraying the paper template with hairspray or putting a loop of masking tape on the back of the template to keep them from moving around on the fabric as you trace or cut.
Straight edge guided cut - This approach requires the most finesse, but some people really like it. You will print and cut out your paper template as before. However, instead of tracing it, you will lay your quilting ruler on top of the template aligning the edge with the initial portion of the curve. You cut that initial portion leaving your rotary cutter stationary in the fabric while you pivot the ruler to be aligned with the next portion of the curve. Repeat until the whole curve has been cut. By cutting a bunch of short straight lines, you can approximate a curve nicely. The ruler is there to steady your hand, but you're still cutting mostly freehand.
Universal curve rulers - While I hate purchasing specialized rulers, this is one area where I think it's worth the investment. However, choose wisely because some rulers can do a lot more than others. My favorite is the Creative Grids Circle Savvy ruler. It's a bit pricey, but it can do everything! quarter, half, and whole circle pieces in any dimension, as well as a variety of orange peel cuts if you're OK with doing some fancy alignment. There are some other options out there, but I haven't found one nearly as versatile. With almost all of these rulers, you will first prepare a square of fabric using traditional methods, then align the square to the markings on the ruler and make a cut against the slot or template much like you would a straight quilting ruler, it just happens to be in a curve. Easy peasy. It's worth the investment in my opinion because, with a little finagling, you can use it for almost every curved piecing project you come across. A multitasker for sure!
With all these methods, I recommend purchasing a 28 mm rotary cutter (the baby one!). You can use the standard size (42 mm) for gently curved pieces no problem, but the tighter the curve gets, the more helpful the smaller size is. It's also immensely helpful when cutting curves freehand because the smaller size is much easier to control and therefore safer.
If you've never used this kind of rotary cutter, they are intended to be positioned vertically, rather than horizontally, like a standard rotary cutter. This makes the cut much more accurate and smoother, especially when using a slotted ruler.
Aligning your pieces
Now that your pieces are cut, it's time to align them and pin them (if you're into that) so that you can sew that treacherous curved seam. Here's my roadmap for success:
1. Start by marking the center of your curve. Most of the time, your templates will have a center mark that you can transfer to the fabric with a chalk pen or pin, but I find it easiest to find the center by creasing. Just fold each piece in half (providing it is symmetric) and give the edge a quick finger press or iron press. Only the edge nearest the seam actually needs to be pressed. Do this for both the concave and convex pieces.
2. Align the center points of the curve right sides together and affix with a pin or a clip, or glue (more on that later); whatever your preference is. Things are going to look funky at this stage, just bear with me. I find it easies to put the concave (outer) piece on top of the convex (inner) piece. That way, all the excess material will be on top and visible as you're sewing. It helps to press the convex piece wrong sides together and the concave piece right sides together so the creases lock together ensuring accurate alignment.
3. Next, match the beginning and end of the curved seam and affix with your preferred anchor (pin, wonder clip, glue). If your pieces are cut correctly (and your pattern author drew the templates correctly), the corner of the curved pieces on both sides of the curve should perfectly match. I call this the horseshoe crab stage.
I find it helpful to place two pins at the beginning of the curve; one vertical and one horizontal. This is to ensure that those edges don't shift as I place my pieces under my presser foot.
This final step is optional. If you've never sewn a curve before, I would encourage you to try this step. However, as you get more comfortable sewing curves, you may find it easier to just sew with the 3 landmark pins from Step 3. This is how I find it easier to sew curves, but you must be very careful not to stretch the concave (outer curve) as you sew.
4. Pin, clip, or glue the region between the corners and the center pin easing the curves together so that the edges are perfectly matched. The concave (outer) arc is going to have to bunch up a lot in order to accommodate this since there is so much more material than there is on the convex (inner) arc. That's perfectly OK as long as there aren't folds or pleats in the actual seam area.
Now you're ready to sew.
If you don't like pins, a glue stick is a great alternative. There are special basting glue sticks available. Your good-old washable craft glue stick is also a great option. If you have trouble getting these things to stick, you can use your iron to set the glue. All of this stuff comes out in the wash, so you don't have to worry about any after-effects. The benefit of glue is that nothing will be sliding around as you sew after you've removed the pins. It's great to use as training wheels when you're first learning, but you will probably find that pins or clips are easier once you've become more comfortable. Some folks also use Elmer's glue to baste seams. I'm not a huge fan of this method because it tends to go everywhere for me, but feel free to give it a try if you aren't thrilled with what you're currently using.
About those pins. I know a lot of quilters don't like using pins at all and are particularly opposed to them for piecing curves. Some people just find it easier to just match the leading edge of the curve and sew without pre-pinning everything matching the edges as you go. I strongly caution against this. While it does make it fairly easy to sew the seam, it also makes you very prone to stretching the curved edge as you go. You may not even realize you're doing it, but it really adds up over the whole length of the curve. At a minimum, this results in your pieces getting distorted, At worst, it can result in a very rippled seam and a block that won't lie flat. By matching the center and the edges before distributing the rest of the fabric, you minimize the amount of stretching that can occur and ensure that blocks will sew together as intended instead of getting shifted against one another. If you don't want to pin the whole curve, I would at least still pin the middle and end.
Sewing the seam
Sewing the seam that you've so carefully matched is comparatively straightforward. All the same quilting rules apply to curved sewing as they do for straight seam sewing. you just have a few added things to think about. Slow down and take your time using a stiletto to make sure that the edges of both pieces remain aligned as they go under your needle. A stiletto is critical; I can't sew curves well without one. (This is the one I use. You can read more about the purpose of a stiletto and what makes a good one here.)
As you sew, keep the edge of your fabric in contact with the edge of your 1/4" foot allowing the piece to pivot smoothly as you sew so that the edge you are currently sewing is always aligned. If you notice an excess fabric developing as you sew, try to absorb that before you get to your next checkpoint (middle pin or end pin). Small amounts can usually be shifted until they are gone, large amounts may need to be seam ripped.
I find it easiest to let the rest of the piece flop over while I get the leading edge under my needle. I'll take a couple of stitches then fix the rest of the piece and start aligning the edges.
I'll work my way around the first part of the curve using my hand between the two layers of fabric to adjust the alignment until I get to the middle pin. I don't pay attention to making sure anything is aligned, or even right side up, on the second half of the curve until I get to the middle pin. At the middle pin, I stop, make any adjustments, then remove the pin and continue in the same way until I get to the end. I use my stiletto to manhandle the corner to get everything aligned and then finish the curve.
This all sounds much more complicated than it is. You will get the hang of it after just a couple of curves. Just concentrate on the area just in front of your needle and treat it like any other piecing project. The more you worry about what's going on with the bulk piece, the more overwhelming it feels.
As you sew, you may notice some pleats developing in the excess fabric of the outer curve. That's fine! You just want to make sure there are no tucks or pleats developing in the seam itself. Those generally only occur when you have stretched the fabric somewhere along the line.
Pressing curved seams can feel a bit weird. The important thing to remember is that you are the boss, not the seam. You can press curved seams inward, outward, or open, just apply a little steam with your iron to soften things up. If you are sewing relatively tight curves, sometimes the seam will struggle to lie flat. In these cases, you can make shallow clips into the seam allowance to help alleviate the tension that is preventing the seams from lying flat. These are SHALLOW cuts, no more than 1/8" of an inch. Do not cut the seam you have just sewn! 3-4 cuts evenly spaced throughout the curve is usually more than enough to help everything relax.
I seam roll, press, and apply a tailors clapper just like I would any straight quilting seam. But in addition to that, I also like to press from the front after pressing from the back. I find this is especially helpful to make everything flat and crisp for curved blocks. Steam is your friend!
That's it! You've sewn your first curved seam. It's really not that bad when you're armed with a few key guidelines. It may feel like a lot of steps at first, but so did straight seam quilting when you were first getting started. In no time, these steps will feel as comfortable as straight seam sewing and you'll have a whole new world of patterns and design options available to you. Dive in and give it a try!