Techniques · Piecing
How to sew curved seams
A curved seam joins an edge that bulges out to one that curves in. Here’s how to cut, pin and ease them, with a Drunkard’s Path unit sewn step by step.
The short answer
Mark the middle of each curve, put the inward curve on top, and pin the middles, then the ends, then between. Sew a ¼″ seam slowly, stopping with the needle down to ease the edges together, and press toward the outward curve.
The two pieces of a curve
A curved seam joins two pieces whose edges bend opposite ways. One bulges out (convex), like a slice of pie. The other curves in (concave), like the frame it sits in. The Drunkard’s Path unit is the classic pair: a quarter circle set into a square.
The two curves are different lengths on the cut edge, even though they sew to the same line. That’s why the inward edge looks too short when you pin it. It isn’t: it stretches a little along the bias as you sew, and that’s what makes the seam lie flat.
A ready-made 3″ Drunkard’s Path template or die cuts the same pieces, if its quarter circle is 2″ like these. Check before you buy: makers size them differently.
Cutting curved pieces
- Use a template with the seam allowance included, or an acrylic template or die cutter. A small (28 mm) rotary cutter turns tight curves cleanly.
- Mark the notches. Each template has a notch at the middle of the curve. Snip a tiny V in the seam allowance there, or fold the piece in half and finger-press a crease.
- Cut the straight edges on the grain, so the block’s outside edges don’t stretch. The curve itself will be on the bias, which is what you want.
Sewing a curve, step by step
Here is one Drunkard’s Path unit: A is the quarter circle, B the frame.
Then square the unit up if it needs it: it should measure 3½″ (3″ finished). Sew the sixteen units into rows, turning each as the block shows, and the rows into the block.
Gentle curves and tight ones
The bigger the circle, the easier the seam. A curve with a radius of 1″ or more sews easily; this one’s is 2″. A curve with a radius under ½″ is easier to appliqué on top than to piece. A long curve, over 4″ along its seam like the arcs of a Double Wedding Ring, gets three notches, numbered from the same end on both pieces, so you can match them in order.
If the inward curve pulls after sewing, clip its seam allowance: snips almost to the stitching, a few along the curve. Never clip the outward piece.
Common mistakes
- Pleats in the seam. Too much fabric eased in one place. Ease a little at a time, and stop to adjust often.
- Stretched edges. Pulling the top piece around the curve. Let it lie, and lift the foot to turn instead.
- Units that are too small. The seam drifted wider than ¼″ around the curve. Watch the edge at the needle, not the fabric ahead.
- Pressing toward the inward piece. It fights the curve and puckers. Press toward the outward curve.
In Quarter Inch: draw a curve in any block and it prints the templates with their notches, says which piece goes on top, and how to sew each seam. See Curved blocks with the Arc tool.
Questions
Short answers.
Something else? A real person replies.
hello@quarterinch.app
Which piece goes on top when sewing a curve?
The inward (concave) curve, the frame. It’s the one that has to ease around, and you can see it under the foot.
Why does my curved seam pucker?
Too much fabric eased in at one spot, or the top piece was pulled. Pin at the middle and ends, ease a little at a time, and press toward the outward curve.
Do I need to clip curved seams?
Only if the inward curve pulls after sewing. Snip its seam allowance almost to the stitching in a few places. Don’t clip the outward piece.
Can I sew curves without pins?
Yes, once you’re used to them: match the middles, hold the edges together right at the needle, and ease as you go. Pins make the first few much easier.