Open seam allowances need to be finished in some way, so they don’t fray.
Seam finishing may seem to be a hassle extra step, but it’s essential to do this if you want the garment to last.
Some people dislike doing this so much they only sew fabrics which don’t fray, like fleece and knits !

It’s easiest to finish the fabric edges when the fabric is flat, before sewing the seams. But this is only possible if you know you aren’t going to make any fitting alterations.

Many people use a serger/ overlocker to do the seam finishing.
But not to worry if you haven’t got one.
The easiest way of finishing seam edges using a conventional sewing machine is to use a zigzag stitch. Available on domestic sewing machines from about the mid-20c.

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Zigzag stitch

One thing I had difficulty getting my head round is that the ‘length’ of a zigzag stitch is :
– the length of one zig, not the length of the whole zigzag, and
– the distance the fabric moves, not the length of the diagonal stitch.
”zigzaglw”
Can be confusing – on my new machine, with some stitches you control the length of a zig-zag, with some you control the length of a zig. . .

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Zigzag stitch seam finish

There are many on-line tutorials on finishing seams using a zig-zag stitch.
Here’s a written photo tutorial from Tilly and the Buttons.
And here’s a video tutorial from Awl-Nighter.

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Getting a good result

The trouble with many zigzag tutorials is they don’t mention that it often doesn’t work very well – the fabric ‘tunnels’/ curls up inside the zigzag stitching. Especially with light fabrics (demos often cheat by using stiff fabric so the result looks good).
On my machine the zigzag works well on doubled fabric, but not on a single layer of lighter fabric.

Several possible solutions to this. Best to make samples until you find a method that works well for your fabric.

1. Loosen the top thread tension.

2. Use a narrower (and/or shorter) stitch.
A good zigzag option is 2mm long and 3mm wide. The largest your machine can do will probably ‘tunnel’ the stitching.

3. Use an overcast-overedge presser foot.

These have some sort of prong or flange which holds the thread so it can’t pull taught while the stitch is being made.

Most machines have some sort of foot like this. Here’s one from Singer.
”singer-overcast”
Check by stitching slowly ‘by hand’ (turning the wheel manually) that the stitch-foot combination work together without the needle hitting the foot.

4. Use a 3-step zigzag stitch instead.
”three-step-zigzag”
Available on most machines which have stitches beyond straight and zigzag. Pulls less because the stitches are shorter. Again, on most machines, stitch length is the length of 1 stitch, not the length of the complete zigzag.
On my machine a (0.5 length, 3.5 width) 3-step zigzag gives the least crumpled result I can get on one layer of lighter fabric.

Here’s a video tutorial from Sew In Brighton about using a 3-step zigzag.

5. Explore other stitches on your machine.
Many machines have several stitches specifically for overcasting.

Here’s a video of one of these Pfaff stitches (they do make life easy for themselves in the demo by sewing on a stiff fabric !).

The stitch that I like for edge finishing on wovens is actually supposed to be used for blind hemming on knit fabrics. I made a sampler of all the possible edge finishing stitches, and this gives the prettiest and flattest result.
”closed-overlock”
Not as quick as using a serger/ overlocker, but just as effective.

6. Stitch away from the edge
Most demos show the machine stitching so one side of the zigzag goes over the edge of the fabric. But you may only be able to get a good result if you stitch down the middle of the seam allowance. Then trim off the spare seam-allowance outside the zigzag, taking care not to cut off any of the zigzag points.
zigzag open seam
(source Grainline Studio seam finishes)
(You may be able to spot that the example cheats (like many) by stitching the sample on a tough fabric which it’s unlikely anything could distort.)

This takes more time, but the stitching is flatter. It doesn’t entirely prevent the edge from unravelling, but it does prevent much loosening of threads.

As a last resort (this solution is much more work but may be needed on light fabric) :
7. Add stabiliser under the zigzag stitching area
(washable fabric) Use a 1 inch/ 2 cm wide strip of water soluble embroidery stabiliser between the fabric and the feed dogs. If you really need to control things, you could put stabiliser on both sides of the fabric.

(dry cleaned fabric) Use a strip of tear-away embroidery stabiliser. Sew to the wrong side of the fabric, so what is left in the stitches after cutting away the stabiliser should be hidden by the seam allowance.

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Other open seam finishes

There are several more techniques for finishing open seams. Bulkier than zigzag, but look very good if anyone will see your seams (such as when you take off an unlined jacket or coat).

Turned and stitched
Here’s a tutorial from Tasia at Sewaholic.

Bias binding, Hong Kong finish
Hong-kong finish and bias bound seams, from Closet Core Files.

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Enclosed seams
This post has been about finishing open seams.
There are also many seam types which enclose the seam allowances, so there’s no need to worry about the edges fraying.

The easiest enclosed seam is the french seam. Here’s my post on the french seam and mock french seam.
This is especially valuable on fabrics that fray very easily, and on see-through fabrics. Also for delicate fabrics which you can’t manage to get any of your overlocking stitches to give a good seam finish result on. On my machine these can be a much quicker way of finishing a seam than using an overlocking stitch.

No shortage of techniques which give desirable seam finishes in special situations 😀

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First published January 2014, links checked October 2021

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