Clipping vs notching curved seams: which one where

Clip an inward (concave) curve and notch an outward (convex) curve. Clipping is a straight snip into the seam allowance that lets it spread open when a neckline, armhole or waist curve is turned to the right side; notching is a small wedge cut out of the allowance so it can shrink without bunching when a collar, a patch pocket or a rounded hem is turned. Both stop 2 to 3 mm (1/8 in) short of the stitching, and on a tight curve they sit 1 cm (3/8 in) apart.

Why do curved seams need clipping or notching at all?

A seam allowance is a strip of fabric lying alongside the stitching. On a straight seam it is the same length as the seam. On a curve it is not: the raw edge of an inward curve is shorter than the stitching line, and the raw edge of an outward curve is longer. When you turn the seam and press it, the allowance has to lie flat against a curve of a different length, and it cannot.

Turn a neckline facing without clipping and the allowance pulls the neckline edge into a drawn, puckered line. Turn a collar point without notching and the extra fabric bunches into lumps you can feel through the top layer. The cuts release the allowance so it can follow the curve.

How do you tell an inward curve from an outward one?

Look at the garment piece, not the allowance. If the seam curves into the piece, like the edge of a bowl seen from above, it is inward (concave) and needs clipping: necklines, armholes, the waist of a skirt, the crotch curve of trousers, the lower edge of a yoke that dips. If the seam curves outward, like the outside of a ball, it is outward (convex) and needs notching: the round end of a collar, the curved bottom of a patch pocket, a rounded hem on a shirt, the bust curve on the center panel of a princess seam.

Many seams have both. A princess seam joins a convex center panel to a concave side panel, so one allowance is notched and the other clipped. A scalloped hem is a row of outward curves (notch) joined at points that are inward (clip once, deep).

How do you clip a curved seam step by step?

1. Sew the seam and press it flat as sewn. Pressing first settles the stitches; cut allowances fray if handled before pressing.
2. Trim the allowance to about 6 mm (1/4 in) on a faced or enclosed edge. Less fabric has less to fight the curve. Sewly's patterns come with 1.5 cm (5/8 in) allowances on wovens by default, which is comfortable for sewing and then trimmed here.
3. Grade if there are several layers: trim the facing's allowance narrower than the garment's, so the edges step down and do not print through. Grading seams is the term.
4. Clip with the points of small scissors, straight toward the stitching, stopping 2 to 3 mm (1/8 in) short. Hold the scissors so the blades are at right angles to the stitching line, not angled, so each clip is as short as it can be.
5. Space the clips 1 cm (3/8 in) apart on a tight curve such as the front of a round neckline, 2 to 3 cm (3/4 to 1 1/4 in) apart where the curve is gentle, and none at all on the straight parts.
6. Turn, understitch if it is a facing, and press over a tailor's ham so the curve is supported while it cools.

How do you notch a curved seam step by step?

1. Sew, press flat and trim as for clipping. On a collar or pocket that will be turned, trim to 6 mm (1/4 in) and grade the layers.
2. Cut small wedges out of the allowance with the points of the scissors: two angled snips that meet 2 to 3 mm (1/8 in) from the stitching, removing a triangle about 3 to 4 mm (1/8 to 3/16 in) wide at the raw edge. Pinking shears along a gently rounded edge remove a row of tiny wedges in one pass.
3. Space the notches 1 to 1.5 cm (3/8 to 5/8 in) apart on a tight curve and further apart as it straightens. Where two notches would nearly meet at the stitching, you have gone too tight: widen the spacing.
4. Turn right side out, push the curve out with a point turner or a blunt knitting needle, never scissors, and roll the seam to the edge between your fingers.
5. Press over the ham. The notches should close up under the pressed seam, with no overlap and no gap.

What are the most common mistakes?

• Cutting through the stitching. Fixed only by resewing that section inside the first line. Stop short and, on a 6 mm (1/4 in) allowance, stop earlier than you think.
• Clipping an outward curve. The flaps of allowance overlap when turned and make ridges. Notch instead.
• Notching when a clip would do. Removed fabric cannot be put back, and a notched inward curve can show light through the seam on fine fabric.
• Clipping before pressing and trimming. The frayed, full-width allowance will not lie flat however many clips you add.
• Too many clips. The allowance turns into fringe, loses strength and lets the seam stretch. Add clips gradually and test by turning.
• Clipping a seam that will be pressed open instead of turned. A princess seam pressed open needs only a few clips on the tightest section; a neckline facing turned to the inside needs the full treatment.

When should you grade or trim instead of clipping or notching?

On a gentle curve with a narrow allowance, trimming to 6 mm (1/4 in) and grading is often enough, and the seam stays stronger. On knits, which stretch, you can usually skip the cuts altogether. On very loosely woven or fraying fabric, substitute a narrow trim and a bias-bound edge for deep clips. Where the curve is enclosed by a bias binding rather than a facing, the binding is cut on the bias and bends by itself, so the garment edge is trimmed and only lightly clipped.

Sleeve caps are a special case: an eased sleeve head is not clipped, because the allowance is turned up into the sleeve and its fullness supports the cap. The pressing guide covers the ham and how to set a clipped curve so it stays curved.

Which should you choose?

• Neckline, armhole or waist curve with a facing: trim to 6 mm (1/4 in), grade, clip every 1 cm (3/8 in) on the tight part, understitch.
• Collar, cuff corner, patch pocket or rounded hem: trim, grade, notch every 1 to 1.5 cm (3/8 to 5/8 in), turn with a point turner.
• Princess seam pressed open: clip the concave side panel on the bust curve only; notch the convex center panel only if it refuses to lie flat.
• Crotch curve on trousers: clip the tightest part of the curve a few times after sewing it twice for strength; leave the rest.
• Knit fabric or a bias-bound edge: trim and skip the cuts, or clip only where the curve is tightest.
• Loosely woven or fraying fabric: fewer, shallower clips, a narrow zigzag along the allowance edge, or a bound edge instead. The facing guide shows how clipping and understitching work together on a neckline.